Diseases of Marine Mammals

22 March 1999

Robert B. Moeller, Jr. D.V.M.

California Veterinary Diagnostic Laboratory

University of California

Tulare, California 93274

rmoeller@cvdls.ucdavis.edu

559-688-7543

The author of this lecture wishes to thank Drs. Migaki, Sweeney, Keyes, Walker, Montali, Magee, Albert, Stroud, McNeil, Hammond, Barr, Gage, Wilson, Britt, Domingo, Haines, Garner, Gulland, Wada, and Martineau for supplying photographs of the various diseases of marine mammals to the Registry of Veterinary Pathology.

Viral Diseases

1. Pox Virus

This disease is also known as "tattoo." Clinically, this disease is characterized by prominent well-delineated lines of hyperpigmentation of the epidermis with various design patterns. These design patterns have been described as targets, circles, and pinhole lesions. The lesions are usually smooth and flat, but may be raised. They are primarily located on the dorsal body, flippers, dorsal fins, and fluke. Although this virus does not appear to cause serious illness in cetaceans, the development of these lesions usually coincides with periods of poor health and stress.

Histologically, the lesion consists of ballooning (hydropic) degeneration of the deep layers of the stratum intermedium. Irregularly shaped or round variably size intracytoplasmic inclusions are present in the cells undergoing ballooning degeneration. The stratum externum may become thickened. Minimal inflammation is observed; this maybe the reason for persistence of the lesion. The cause of the hyperpigmentation is unknown, but there are various theories on this process. One theory is that stimulation of the dermal melanocytes by the viral infection causes hyperpigmentation of the dermis and epidermis. Another theory postulates that damage to the stratum externum and intermedium leads to filling in of these defects with debris and bacteria which then causes the discoloration of the epidermis.

This is an unusual pox lesion since it is not a proliferative lesion. The virus persists for long periods of time in the epidermis and slowly spreads in the affected animal. Animals appear not to develop antibodies to the virus; however, once antibodies develop to the pox virus, the lesion regresses with the affected skin becoming raised and bleached. The effected skin then undergoes necrosis and sloughing. Scraping the lesion has been known to cause regression. If lesions are biopsied, the pox lesion may regress in a zonal pattern around the biopsy site.

B. Seal Pox

Seal pox is a parapoxvirus that is known to affect numerous species of pinnipeds. (An orthopox has also been isolated from a grey seal, (Halichoerus grypus). The disease is most prevalent in California sea lions, South American sea lions and harbor seals. Cutaneous spread of this disease is mostly by head and neck rubbing, a common social behavior of sea lions and other pinniped. This viral disease is rarely fatal, but can cause a high morbidity. The clinical course of the disease may run about 15 weeks.

Seal pox is a proliferative lesion characterized by the formation of numerous 2 to 3 cm cutaneous nodules. These nodules eventually ulcerate and are slow to heal. Areas of alopecia develop over the healed areas. The lesions are most numerous over the head and neck but can occur anywhere on the body.

Microscopically, the lesion is characterized by ballooning degeneration of the stratum spinosum with pustule formation. Affected cells have one or two eosinophilic intracytoplasmic inclusions 2 to 15 u in diameter. Usually the affected epidermis has marked acanthosis with variable orthokeratotic and parakeratotic hyperkeratosis. Inflammation can be prominent, especially during regression of the lesion.

The histologic features of pox virus in South American sea lions has demonstrated a unique feature of downward proliferation of the epidermis with ulceration and pustule formation. In affected epithelial cells, only one large eosinophilic or basophilic intracytoplasmic inclusion body is observed. These inclusions are usually surrounded by a thin halo and the nucleus is compressed. These lesions can occasionally resemble the human disease molluscum contagiosum.

2. San Miguel Sea Lion Virus

San Miguel sea lion virus (SMSV) is caused by a calicivirus. This calicivirus is believed to be the viral agent responsible for vesicular exanthema of swine. Most viral strains of San Miguel sea lion virus are antigenically related to vesicular exanthema of swine. The disease occurs in sea lions and seals. It is characterized by the formation of vesicles on the flippers. These vesicles usually rupture and form prominent slow healing ulcers. This virus has also been implicated in causing ulcerative lesions on the lips, nose, chin, and gums. Microscopically, the lesion consists of spongiosis of the stratum spinosum, which later progresses to subcorneal vesicle formation. Intracytoplasmic or intranuclear inclusions are not present.

Several serotypes of San Miguel sea lion virus have been isolated from aborting sea lions and aborted fetuses. These serotypes of San Miguel sea lion virus are indistinguishable from serotypes of vesicular exanthema virus that cause abortions in swine. The relationship of San Miguel sea lion virus infection and abortions in affected marine mammals is suspected but not proven. The virus has been isolated from the opal-eye fish (Girella nigricans) which is believed to function as a reservoir for the spread of this disease. This fish is known to develop an active infection with viral replication in the spleen. The fish remains infected for about 31 days. Clinical disease has not been observed in infected fish.

A similar calicivirus has been isolated from Atlantic bottle-nosed dolphins. These animals are presented with vesicular skin lesions that eroded and leave shallow ulcers. It was felt that this virus is infective for both sea lions and dolphins.

3. Sea Lion Hepatitis Virus

Sea lion hepatitis virus is caused by an adenovirus. This virus is not highly virulent. Only a few animals demonstrate clinical disease, however, serological surveys demonstrate that large numbers of animals are exposed to the virus. Sea lions, seriously affected by this agent, usually die acutely with little clinical evidence of infection. At necropsy these animals are usually presented with icterus, splenomegaly, mesenteric lymphadenopathy, and discoloration of the liver. Microscopically, the liver lesion consists of random areas of coagulative and lytic necrosis of hepatocytes. In many cases, the necrosis is most severe in the centrolobular region of hepatic lobules. Large pale eosinophilic to dark basophilic intranuclear inclusions are present in hepatocytes and occasionally in Kupffer cells. The inflammatory response is usually minimal, with a few macrophages, lymphocytes, and neutrophils at the periphery of the necrotic lesion.

4. Influenza Virus

The influenza virus observed in seals has been identified as an influenza A virus (Type A/Seal/MA/1/80, Type A/Seal/MA/133/82, Type A/Seal/MA/3807/91, Type A/Seal/MA/3810/91, Type A/seal/M/3911/92). These viruses have been identified as an H3 influenza viruses. This subtype of virus is most frequently detected in birds, pigs, horses, and humans. It is felt that the viruses infecting seals are most closely related to H3 avian influenza viruses. Some feel that seals, like swine, may play a role in genetic reassortment of these influenza viruses, thus causing a potential for interspecies transmission.

These viruses have been associated with high mortality in harbor seals. This virus causes serious respiratory distress in affected seals. Affected animals are usually presented weak and have serious respiratory difficulties. A white mucinous to bloody discharge is observed in the trachea and bronchi. Pulmonary, mediastinal, and subcutaneous emphysema is commonly observed. Microscopically, there is a severe interstitial and hemorrhagic bronchopneumonia with hemorrhage in alveoli and prominent necrosis of bronchioles and bronchi. Mycoplasma (Mycoplasma phocidae) and other bacteria have been isolated from affected animals. It is felt that there is a synergic effect between the virus and bacterial agents since seals experimentally challenged with only the virus develop a mild respiratory disease.

5. Phocine morbillivirus (Phocine distemper virus, PDV-1, PDV-2)

Several disease outbreaks that killed thousands of seals in Northern Europe and Lake Biakal in Siberia have been attributed to a morbillivirus. The morbillivirus affecting harbor seals (Phoca vitulina) and grey seals (Halichoerus grypus) in Northern Europe and North America is caused by a morbillivirus, phocine distemper virus-1 (PDV-1), similar to, yet antigenically distinct, from canine distemper virus. Differences in DNA sequencing between PDV-1 and canine distemper are of such great magnitude that they need to be considered separate species. Serologic studies have demonstrated that harbor seals (Phoca groelandica), hooded seals (Cystophora cristata) and ringed seals (Phoca hispida) have an immune response by viral neutralization to PDV-1. The morbillivirus, phocid distemper virus-2 (PDV-2), isolated from Siberian seals (Phoca siberica) in Lake Baikal is closely related to a field strain of canine distemper virus found in Germany. Clinically, affected seals are very weak and have severe respiratory distress. A mucopurulent to serous oculonasal discharge is often observed. Many animals developed subcutaneous emphysema primarily around the neck and thorax. On necropsy, these animals have edematous lungs with sharply demarcated areas of red consolidation. Emphysema involving the interlobular septa and pleura of the caudal lung lobes is present. Many animals developed emphysema of the mediastinum, neck, fascia, and subcutis. Congestion and a thick mucopurulent exudate is observed in the upper respiratory tract. Pulmonary lymph nodes are edematous. Hydropericardium, hydrothorax, and hepatic congestion are common. Histologically, the lung lesion consists of a bronchointerstitial pneumonia with syncytial cells and type II pneumocyte proliferation. Eosinophilic intracytoplasmic inclusions are present in bronchial epithelium and syncytial cells. The brain has a nonsuppurative encephalitis characterized by necrosis of neurons (primarily in the cerebral cortex), nonsuppurative perivascular cuffs, and gliosis. Many affected neurons contain intranuclear and intracytoplasmic inclusions. Demyelination of the subepidermal white matter is also observed. Prominent depletion and necrosis of lymphocytes in lymphoid tissue is present. Some seals develop a necrotizing nonsuppurative myocarditis. Like canine distemper, intranuclear and intracytoplasmic inclusions are observed in the gastric mucosa and transitional epithelium of the urinary bladder and renal pelvis.

6. Morbillivirus in Cetaceans

A morbillivirus causing similar lesions to those observed in the phocine morbillivirus has also been observed in cetaceans. This viral infection was first identified in harbor porpoises (Phocoena phocoena) from the Irish Sea during the 1988 European phocine morbillivirus outbreak. In 1990 this virus killed numerous striped dolphins (Stenella coeruleoalba) along the Spanish Mediterranean coast and has been identified in outbreaks affecting bottlenosed dolphins along the Eastern Atlantic and Gulf Coast of the United States. Pilot whales (Globicephala sp.) are also infected with this or a similar morbillivirus. Morbilliviral infection has also been noted in the lymph nodes of a stranded fin whale (Balaenoptera physalus). (Syncytial cells in the lymph node which stain positive for morbillivirus and electron microscopy identification of viral nucleocapsid material compatible with morbillivirus.) The viruses affecting harbor porpoises and striped dolphins are closely related but antigenically distinct. These viruses are antigenically distinct from phocine morbillivirus and other mammalian morbilliviruses. However, the cetacean morbilliviruses appear to be related to the ruminant morbillivirus peste-des-petits ruminants. Serologic evidence of morbillivirus infection has been identified in numerous odontocete cetaceans in the western Atlantic and may have a potential impact on these species. Affected cetaceans develop similar pulmonary and central nervous system lesions that are observed in affected seals. Grossly, these animals develop a severe pneumonia with multiple foci of atelectasis and consolidation. Lung associated lymph nodes are often enlarged and edematous. Histologically, there is a bronchointerstitial pneumonia characterized by necrosis of bronchial and bronchiolar epithelium with a prominent mucopurulent exudate. Acidophilic intracytoplasmic inclusions are observed frequently (occasionally intranuclear inclusions are also observed). Type II pneumocyte hyperplasia and prominent mononuclear inflammation is observed in alveoli. Syncytia are observed in both the alveoli and bronchiolar epithelium. A non-suppurative meningoencephalitis is observed in most affected animals. This involves primarily the cerebral grey matter with occasional eosinophilic intranuclear inclusions present. Necrosis of the bile duct epithelium and transitional epithelium of the urinary bladder with occasional eosinophilic intracytoplasmic inclusions is also observed. The lymph nodes have prominent lymphoid depletion with scattered multinucleated syncytial cells present throughout the lymph node. Multinucleated syncytial cells and inflammation have been observed in the mammary gland. All affected areas demonstrate intense immunohistochemical staining for morbillivirus. Many affected dolphins also have serious secondary systemic infections of toxoplasmosis, aspergillosis and other fungi.

It is interesting to note that the Florida manatee (Trichechus manatus latirostris) has seroconverted by virus neutralization to dolphin morbillivirus. To date no clinical disease has been reported in these animals.

7. Seal Herpesvirus

Several herpes viruses have been isolated from harbor seals and a California sea lion. Two distinct types have been isolated from affected animals, these have been identified as phocid herpesvirus type 1 and type 2 (PHV-1and PHV-2). PHV-1 is characterized as a member of the alpha-herpesvirus subfamily. PHV-2 has been classified as a gamma-herpesvirus. Numerous pinniped species have antibodies to PHV-1 and PHV-2 (Ringed seals, spotted seals, harbor seals, bearded seals, ribbon seals, Steller sea lions, Northern fur seals and walrus). Most animals with seroconversion to these viruses do not demonstrate clinical disease.

PHV-1 which affects mostly young harbor seals has been shown to cause a serious systemic infection. Affected animals demonstrated an acute pneumonia, necrotizing hepatitis and necrotizing adrenalitis. Occasionally a non-suppurative encephalitis is observed with rare neuronal necrosis. The pneumonia is characterized as a diffuse interstitial pneumonia with multifocal fibrinous exudation and emphysema. Within the liver and adrenal gland, there is multifocal necrosis of the hepatic and adrenocortical parenchyma with a minimal mononuclear cell infiltrate. Acidophilic intranuclear inclusion bodies are observed in the areas of necrosis. Electron microscopy demonstrates unenveloped hexagonal viral particles 90 to 100 nm with a central dense core and cytoplasmic enveloped particles 150-160 nm in diameter. The nature of this virus and its potential to cause disease in wild and captive populations of seals is still unknown. This virus has been inoculated in young seals with only minimal upper respiratory signs (nasal discharge). Phocine herpesvirus most likely act similar to the other mammalian herpesviruses with the infections most often fatal in the young and seriously stressed animal. Most sick animals also have concurrent bacterial or protozoal infections that may mask the herpes viral infection. Like most herpes viruses, this herpes virus probably expresses itself in times of stress, as either subclinical oral or genital lesions.

The phocine herpesvirus-2 was isolated from a California sea lion with a severe bacterial pneumonia, free ranging harbor seals and from seals with abortions during the early epizootic of morbillivirus infection in Northern Europe. The importance of this virus in the pathogenesis of this pneumonia is unknown. (A non-oncogenic retrovirus was also isolated from the skin of this affected sea lion). This virus is highly cell associated and causes little or no disease in pinnipeds.

A gamma herpesvirus has been identified in a metastatic carcinoma of the lower genital tract from California sea lions. This virus is associated with the neoplastic cells. The association of the virus and the development of neoplasia of the vagina and cervix is unknown.

8. Herpesvirus in Beluga Whales (Delphinapterus leucas)

A herpesvirus has been observed to cause a focal dermatitis in beluga whales. These epidermal lesions consisted of random variably sized multiple discrete raised pale grey areas which eventually ulcerate and are slow to heal. Histologically the epithelial lesion involved the superficial epidermis with the epithelial cells undergoing intercellular edema, necrosis and microvesicle formation. The infected epithelial cells contained prominent eosinophilic intranuclear inclusion bodies.

9. Herpesvirus of Sea Otters (Enhydra lutris)

A herpesvirus has been implicated in causing extensive oral lesions in sea otters. Clinically these lesions consist of variably sized irregular white plaques and/or deep often bilaterally symmetrical ulcers. These lesions are commonly found mostly on the gingiva and under the tongue. In severely affected animals, the ulcers tend to coalesce to cover extensive areas of the buccal, labial, gingival and glossal mucosa. Infected animals rarely show a reluctance to eat, even with extensive oral lesions. Histologically, the lesions reveal extensive chronic ulcers with associated mixed bacterial colonies and separate foci of epithelial necrosis and intracellular edema. Numerous eosinophilic intranuclear inclusion bodies are observed in the degenerating and necrotic cells.

10. Herpesvirus of bottle nosed dolphins

A disseminated herpes viral infection was identified in an immature female bottle nosed dolphin. On necropsy, the animal had an enlarged thymus, pericardial hemorrhage and hydrothorax. Histologically there was a necrotizing interstitial pneumonia, lymphocytic myocarditis, splenic and lymphoid necrosis, and a necrotizing adrenalitis. Intranuclear inclusions are observed in numerous cells of the thymus, spleen, adrenal gland, heart, lungs, and glomeruli. Sequencing of DNA products indicates this virus is an alpha herpesvirus.

11. Hepatitis B-Like Infection in Dolphins

A hepatitis B-like infection has been identified in a Pacific white-sided dolphin (Lagenorhynchus obliquidens). This animal developed cyclic periods of inactivity, anorexia, and icterus. Blood values demonstrated a leukocytosis with neutrophilia, lymphopenia, and eosinopenia. Biochemical values showed markedly elevated alanine transaminase (ALT), aspartate transaminase (AST), gamma glutamyltransferase (GGT), lactic acid dehydrogenase, total bilirubin, direct bilirubin and indirect bilirubin. These findings suggested a chronic active hepatitis. Supportive measures were instituted and the dolphin eventually recovered. Serum from the animal was found to be positive for antihepatitis B virus core (anti-HBc) activity, hepatitis B virus DNA (HBV-DNA) and hepatitis B surface antibodies (Anti-HBs). Other cetaceans and humans who had contact with this animal were examined for hepatitis B antigens. One killer whale was positive while all other cetaceans and humans were negative.

12. Papillomas in cetaceans

Papillomas have been reported on the skin, penis, tongue, pharynx, and first gastric compartment of cetaceans. Although a papillomavirus has not always been implicated as the cause of these lesions, they should be suspected. In the beluga whale , the gastric papillomas identified in the first gastric compartment are white (like the surrounding normal mucosa), well defined, exophytic masses with a central wart like core composed of small filamentous papillae. Histologically, the papilloma develop into an exophytic cup shaped mass with marked epithelial proliferation supported by a thin fibrovascular proliferation forming numerous arborizing projections from the submucosa. The proliferating epithelium consists of a flattened basal cell layer 3 to 15 cells thick with a mature epithelium overlying the basal cells. Scattered amongst the hyperplastic epithelium, individual and small groups of epithelial cells undergo hydropic degeneration (cells become swollen and globular with a pale granular cytoplasm). Ultrastructurally, the cells undergoing hydropic degeneration with aggregates of small 40 nm hexagonal viral particles observed in the cytoplasm. These viral particles are consistent with papillomavirus. It is unclear if any of these papillomas cause physical problems with the affected animals. Papillomas on the penis are usually raised plaques on the mucosal surface. Like man, papillomavirus may infected the cervical mucosa and might cause neoplasia from this region.

Bacterial Diseases

Bacterial diseases are the leading cause of death in marine mammals. These organisms are usually observed as opportunistic invaders in conjunction with parasitic, viral or traumatic injuries. The inhibition of bacteria in the marine mammal's environment is one of the most important factors in maintaining marine mammal health in captivity.

One must remember that these animals are mammals and therefore are affected by the same bacteria as their terrestrial counterparts. This discussion will focus only on bacteria that have gained notoriety as pathogens in the marine mammal.

1. Erysipelothrix rhusiopathiae

Erysipelothrix rhusiopathiae is a small pleomorphic gram positive rod. This bacteria causes two distinct forms of disease in dolphins: a dermatological disease and a septicemic disease. The dermatological disease is characterized by dermal infarction that results in sloughing of the epidermis. Occasionally micro-infarcts result in the characteristic rhomboid areas of cutaneous necrosis. If untreated, these animals will usually die. The septicemic disease is usually peracute, with the animal found moribund or dead. At necropsy, affected animals may demonstrate multifocal areas of necrosis and inflammation involving numerous organs. Culturing the agent (a small pleomorphic gram positive bacilli) from affected tissues and blood (lymph nodes, kidney, liver, heart, blood) is the only way of identifying this organism as the agent responsible for the septicemia. A killed bacterin is available for vaccination. This vaccine has had excellent results in controlling the disease. It is important to remember that Erysipelas is commonly found in fish; ingestion may be the route of infection in cetaceans.

2. Pseudomonas Infection

Various species of Pseudomonas (gram negative bacilli) have been incriminated in causing bacterial disease in both pinnipeds and cetaceans. It is felt that this organism is an opportunistic pathogen which colonizes wounds and can lead to septicemia. Pseudomonas aeruginosa has caused bronchopneumonia and multiple large cutaneous ulcers in Atlantic bottlenose dolphins. The bacteria are known to progress deep into the cutaneous tissue, causing serious damage to the animal. Many times pseudomonas septicemia causes a characteristic proliferation of gram negative bacilli into the wall of affected blood vessels. If affected animals develop a septicemia, cutaneous lesions similar to those observed with erysipelas may develop. Thus, culturing the lesions is the only method of determining which organism is responsible for the animals illness.

Pseudomonas pseudomallei is a pathogen found in Southeast Asia. The organism is a water contaminant and is thought to gain entrance into the animal through cutaneous wounds. A septicemia soon follows which may result in death. Animals often die peracutely with no clinical signs. Grossly and histologically, lesions are characterized by multifocal areas of necrosis and inflammation involving many organs (lungs, liver, spleen, kidneys, and lymph nodes). This agent is infectious to man and may be transmitted via cuts or abrasions as well as by aerosol transmission.

3. Edwardsiella

Edwardsiella species are gram negative bacilli that are common inhabitants of water. These bacteria are noted to cause bacterial septicemia in fish. This organism can be a pathogen in both pinnipeds and cetaceans. Animals present with a serious necrotizing enterocolitis and/or septicemia. Animals with septicemia can develop a severe embolic interstitial or bronchointerstitial pneumonia, a necrotizing hepatitis and a necrotizing splenitis. Animals with an intestinal lesion develop a necrotizing and hemorrhagic enteritis/colitis similar to that found in salmonella infections. Isolation of Edwardsiella from the lungs and liver are usually suggestive of a septicemia. Animals that develop this disease are usually debilitated or stressed and probably get these organisms from ingestion of contaminated fish.

4. Salmonella

Salmonella are gram negative, non-lactose fermenting bacilli. Salmonella infections have been observed in both cetaceans and pinnipeds. Salmonella typhimurium, S. enteritidis and S. newport are the most prevalent salmonella that cause disease. Other Salmonella species have been isolated from marine mammals without apparent disease. These bacteria are of particular concern for animals housed in rehabilitation centers. Thus, recently stranded animals should be quarantined and monitored for salmonella prior to placing with other animals. Salmonella infections usually occur in animals that are debilitated and/or stressed. Animals present with a hemorrhagic diarrhea and/or septicemia. Animals with the hemorrhagic diarrhea usually have a necrotizing enterocolitis. Culturing the feces is recommended for isolation of the organism. Animals that develop a septicemia can die acutely with no clinical signs. On necropsy, the animal may have a bronchopneumonia and/or a diffuse embolic interstitial pneumonia. A necrotizing hepatitis and splenitis are common; meningoencephalitis may occur. Isolation of the organism from the lungs and liver are usually consistent with a septicemia.

Leptospirosis, primarily caused by Leptospira pomona, (L. gryppo, L. icterohemorrhagiciae, and L. bratislava have been identified serologically, however, this may be due to antigen cross reactivity of L pomona with these leptospira.) is known to cause abortions and renal disease in California sea lions and Northern fur seals. This disease is believed to be endemic in rookeries in California and is most prevalent in the autumn affecting predominately subadult and young adult males. Animals affected are usually depressed, anoretic, pyrexic, and reluctant to move due to posterior limb paresis. Other lesions include icterus, oral ulcerations and excessive thirst. Clinically most animals have a leukocytosis and elevated creatinine, phosphorus and BUN levels, which indicate renal disease. Grossly, the kidneys are swollen. On cut surfaces the renal cortex and medulla are pale with loss of differentiation. Hemorrhage at the corticomedullary junction and subcapsular region is commonly observed in the kidney. In some animals the liver is swollen and friable. Histologically, a lymphoplasmacytic interstitial nephritis with tubular necrosis is present with the spirochete present in the renal tubular epithelium and free in the lumina. In newborn and aborted fetuses, the disease is characterized by subcutaneous hemorrhage and hemorrhage into the anterior chamber of the eye (The disease "Red Eye"). This disease may have zoonotic significance since affected sea lions have demonstrated that they may shed the bacteria in the urine for up to 154 days. In the live animal, rising titers or titers above 1:3200 are considered to be infected with leptospirosis.

5. Dermatophilus congolensis

Dermatophilus congolensis is a disfiguring cutaneous disease affecting pinnipeds (South American sea lion). This disease is characterized by a scruffy pustular or exudative dermatitis involving the entire body. These lesions are elevated above the skin, forming very prominent scabs. Mortality is low, but morbidity is high.

Histologic examination of the epidermis demonstrates the characteristic multiple layers of coagulative necrosis of the epidermis with a peripheral line of degenerating neutrophils separating each necrotic layer. Numerous gram positive cocci that form the characteristic parallel rows are observed in the necrotic debris.

6. Mycobacteriosis

Several species of Mycobacteria have been isolated from seals (M. tuberculosis complex (M. bovis), M. fortuitum, M. chelonei), a California sea lion (M. smegmatis), and several manatee (M. chelonei and M. marinum). These infections have been presented as either nonhealing chronic cutaneous lesions, generalized infections with caseonecrotic granulomas in various organs and lymph nodes or pulmonary infections with granulomas present. Numerous acid-fast bacteria are observed in the cutaneous lesions. Microorganisms may be more difficult to find in granulomas caused by M. tuberculosis complex (M. bovis). Since several of these species of Mycobacteria are found in the soil and water, persistent nonhealing cutaneous lesions should be cultured for Mycobacterium. All these organisms have a zoonotic potential, care should be taken when treating and handling these wounds.

7. Staphylococcus sp.

Staphylococcus aureus has been implicated as one of the cause of pneumonia in dolphins maintained in captivity. Staphylococcus has also been isolated from septicemia which have lead to embolic nephritis and cerebral abscesses as well as cutaneous lesions. S. aureus is a part of the normal flora of the blow hole of many normal dolphins. However, some investigators feel that if it is present in the upper respiratory tract, it should be considered a potential pathogen. Staphylococcus delphini has been isolated from a purulent dermatitis in dolphins. In seals, staphylococcus has been identified in animals with cutaneous abscesses or pneumonia.

8. Clostridial disease

Clostridium perfringens has been reported to cause enterotoxemia in young pinnipeds, gas producing myositis in dolphins and cutaneous abscesses in fur seals. The necrotizing myositis observed in dolphins and the subcutaneous abscesses in pinnipeds has been attributed to injection site contamination. Since Clostridium perfringens and other clostridial organisms are normal inhabitants of the gut and common in dead animals, it is best to do impression smears from the lesion (gut or muscle) on clean glass slides for bacterial evaluation.

9. Klebsiella

Klebsiella (Gram negative bacilli) has seen associated with pneumonia in marine mammals. As usual, bacterial cultures are necessary to differentiate this organism from other bacterial infections.

10 Nocardia

Nocardia asteroides has been isolated from numerous cetaceans. This organism has been associated with necrotizing and pyogranulomatous lymphadenitis, pleuritis, encephalitis and mastitis. The organism is a thin filamentous gram positive organism which can be acid fast.

11. Brucella

Brucella has been identified in several species of cetaceans (Atlantic white-sided dolphins, Lagenorhynchus acutus; striped dolphins, Stenella caeruleoalba; and bottlenosed dolphin, Tursiops truncatus), pinnipeds ( hooded seal, Cystophora cristata; grey seal, Halichoerus grypus, Pacific harbor seals, Phoca vitulina richardsi) and a European otter (Lutra lutra). These organisms have been identified from an aborted fetus (Tursiops truncatus) and subcutaneous lesions, lymph nodes, liver, and pneumonia. The placenta developed a necrotizing placentitis with gram negative coccobacilli within the trophoblast. Lesions in lymph nodes, liver and lungs are characterized by a multifocal granulomatous inflammation. Biotyping of the bacteria indicates that these bacteria are closely related to Brucella abortus or Brucella melitensis. However, it is felt that these may represent a new species of brucella. It is currently unclear as to what impact this organism has on marine mammals. Brucella organisms have been identifies in the lungworm Parafilaroides. Brucella organisms have been observed in the uterus and intestines of this lungworm. The importance of this lungworm in the transmission of brucella to animals is unknown. These parasites may represent an important transport host for the dissemination of this bacteria in the wild.

11. Streptococcus

Streptococcus spp. have been isolated from seals with pneumonia and septicemia and cetaceans with septicemia, metritis, pneumonia and skin lesions. These are primarily beta-hemolytic streptococcal species (Gram positive diplococci). Most are normal inhabitants of the skin and upper respiratory tract. A beta-hemolytic streptococcus, Streptococcus phocae, was isolated from many of the seals that died of pneumonia during the phocine morbillivirus outbreak in the North Atlantic. Most animals present themselves clinically with dyspnea, coughing and a nasal discharge. Pathological examination demonstrated a severe pneumonia with areas of consolidation of the lungs, purulent exudate in the bronchi and bronchioles, interlobular edema and emphysema. Rarely do streptococcal organisms cause a primary infection. These organisms usually are associated with viral infections.

Mycotic Diseases

Numerous mycotic diseases have been reported in pinnipeds and cetaceans. Most have been single reportable cases; only several fungal organisms have been associated with outbreaks of disease.

Since fungal organisms are usually opportunistic or secondary invaders; these organisms pose a serious health risk to the animal that is immunocompromised. Animals that are malnourished, have preexisting viral or bacterial diseases, have undergone prolonged drug (antibiotic) therapy, or immunosuppressed due to stress are predisposed to get these infections.

1. Candidiasis

Candida albicans is the most common species of Candida to cause clinical disease in stressed pinnipeds and cetaceans. Infected animals usually develop cutaneous and/or intestinal infections with lesions occurring primarily at mucocutaneous junctions, blowhole and vagina. Disseminated candidiasis has been reported in the killer whale and other cetaceans. It is felt that most marine mammals can be infected by Candida. Infections are usually observed in animals that are severely stressed and/or under prolonged antibiotic therapy. These lesions appear as white or yellow creamy plaques. In internal organs, prominent focal areas of necrosis are visible. Histologically large colonies of septate hyphae, pseudohyphae (3 to 7 microns wide) and blastospores (3 to 5 microns diameter) are observed in the necrotic lesions. The finding of Candida in the esophagus or vagina is very common and may be identified histologically as an incidental finding. However, when the organism invades healthy tissue, the fungus is considered pathogenic.

2. Loboa loboi

Lobomycosis is a fungal disease that affects the skin of the Atlantic bottle-nosed dolphin and man. Grossly, these lesions are located anywhere on the animal's body (head, fin and flukes are the most common sites) and are white, multiple and nodular. These lesions have a cobble stone appearance on the skin. Histologically, there is a superficial granulomatous dermatitis involving the papillary dermis. This granulomatous dermatitis is composed almost entirely of macrophages and multinucleated giant cells containing numerous round yeast forms (5-10 microns in diameter) connected to each other and forming long chains. Some yeast forms contain a 1 to 2 micron central body. Larger yeast forms may have a rough and spiny surface. The epidermis over these areas of inflammation is acanthotic with downward growth of the rete pegs. Clinically the animals are not seriously affected by the growth of the organisms; however, if these become large, the animal may become debilitated and die (usually due to secondary bacterial infections). Treatment has not proven successful, however, removal of the affected area has shown positive results.

3. Fusarium

Outbreaks of Fusarium-induced dermatitis has been observed in a group of captive California sea lions, grey seals, harbor seals, Atlantic white sided dolphins and a pygmy sperm whale. The lesions consisted of papules and nodules on the face, trunk, flippers and the caudal portions of the body. Histologically, there is hyperplasia of the follicular and epidermal epithelium with associated chronic active inflammation and numerous fungal hyphae (Septate branching hyphae, 2 to 5 microns in width with parallel sides). In marine mammals, Fusarium spp. are most likely opportunistic invaders of the skin. Animals that are immunocompromised due to stress or illness may be most susceptible. Damage to the integument due to excessive chlorination of the water and high fluctuating pool temperatures may also play an important role in this disease. Treatment of the animals with ketoconazole caused the dermatitis to resolve in 3 to 4 weeks.

4. Aspergillus and Zygomycetes Infections:

Aspergillus and Zygomycetes infections cause serious disease in individual animals. As with infection with Candida, the affected animals are usually stressed and/or under prolonged antibiotic therapy. Infection can involve focal areas, usually the esophagus or lungs; however, systemic spread of the fungus is common. Lesions involving the esophagus and trachea usually appear as ulcers with yellow to cream colored plaques over the affected area. Systemic spread leads to necrosis of multiple tissues with liver and kidney commonly involved. Diagnosis is by observing the characteristic hypha (Aspergillus: long branched septated hyphae, 3 to 4 microns wide with parallel walls. Zygomycetes: long non-septate non-parallel walled hyphae with irregular branching).

5. Dermatophytosis: Microsporum and Trichophyton spp.

Cutaneous infections with Microsporum canis and Trichophyton spp. have been reported in both cetaceans and pinnipeds. Microsporum canis has been isolated from harbor seals and Trichophyton spp. in Northern fur seals (Callorhinus ursinus), Steller sea lions (Eumetopias jubatus) and bottlenosed dolphins (Turciops truncatus). Infections in the seals is characterized by round depilated areas, 2 to 3 cm in diameter on the face and back. These depilated areas spread over the entire body. Histologically there is epidermal hyperplasia with hyperkeratosis, parakeratosis, necrosis and microvesiculation and microabscess formation. Numerous neutrophils are present in the affected epidermis. Numerous branched septated hyphae 2 to 7 microns in diameter are observed in the parakeratotic and necrotic regions.

6. Coccidioides immitis

Coccidioides immitis has been identified as an endemic disease in the California sea lion (Zalophus californianus) and an isolated case in the California sea otter (Enhydra lutris) and bottlenosed dolphin (Tursiops truncatus gilli). This organism appears to be endemic in animals that inhabit the southern and central part of their range from Baja California, Mexico in the south to Monterey County, California in the north. Coccidioides immitis is an infectious agent to numerous animal species and is a serious health risk to man (Valley Fever) when living in endemic areas. Endemic areas are Arizona, Southern and Central California, Mexico, New Mexico, Nevada, Utah and Texas. This organism probably infects sea lions, like most animals, as a mild respiratory disease. Recovery usually occurs after a short illness. Some animals develop a serious disseminated disease. Sick animals usually beach and are presented ill. Gross necropsy findings are focal to disseminated granulomas involving the lungs, liver, pancreas, numerous lymph nodes (retropharengeal, submandibular, mesenteric, and tracheobronchial lymph nodes) and occasionally a purulent pleuritis and peritonitis. Histologically the affected organs develop pyogranulomatous inflammation with variable numbers of multinucleated giant cells and large round double contoured wall spherules, 10-70 micron in diameter. Filling the spherules are numerous small 2-5 micron endospores. Animals are most likely infected by the inhalation of spores. Coccidioides immitis is also known to survive in sea water for several weeks. It is unknown if sea water could be a means of infecting animals.

Protozoal Diseases

1. Sarcocystis sp.

Sarcocystis species have been reported in numerous pinnipeds and cetaceans. These species of sarcocystis are S. balaenopteralis in a whale (Balaenoptera borealis) and several unnamed species of Sarcocystis in a sperm whale (Physeter catodon), Northern fur seal (Callorhinus ursinus), striped dolphin (Stenella caeruleoalba) and ringed seals (Phoca hispida). These protozoal organisms appear to be incidental findings in these animals. Little is known about their life cycle. Recently a necrotizing hepatitis characterized by multifocal areas of necrosis has been observed in a captive sea lion. This organism appears to be similar to Sarcocystis canis; it is not known whether this organism is normally found in this animal.

2. Toxoplasma gondii

Toxoplasma gondii has been observed in several species of marine mammals including: the California sea lion, Northern fur seal, harbor seal, manatee, Atlantic bottlenosed dolphin (Tursiops truncatus), and Spinner dolphin. These animals have demonstrated a disseminated infection with necrosis of numerous organs containing toxoplasma tachyzoites. It is felt that these animals probably were immunocompromised.

3. Ciliated Protozoa of Dolphins

A ciliated protozoa is often found in necrotic cutaneous lesions in the Atlantic bottlenosed dolphin. These lesions are usually pyogranulomatous lesions with large ciliate protozoa scattered amongst the necrotic debris. These ciliated protozoa are large (up to 60 to 80 microns in diameter with a large 20 micron nucleus). These protozoa may be opportunistic invaders since these protozoa are commonly found around the blowhole of dolphins without any inflammation .

4. Giardiasis

Giardia sp. oocyst have been identified in fecal samples from ringed seals (Phoca hispida) in arctic and subartic regions of Canada. Infected animals have not demonstrated illness. The zoonotic potential of infected seals to act as reservors for human infection is unknown.

External Parasites

1. Lice

Lice are a common finding on pinnipeds. Only anapluran (sucking) lice have been found on these animals. Antarctophthirius microchir is a common louse noted on sea lion pups. These insects cause alopecia in infected animals. These organisms are believed to be the intermediate host for the filarid nematodes of pinnipeds; however, this has not been proven.

Cetaceans are also known to harbor lice. Several species of lice have been isolated from the skin of these animals. Clinical disease has not been associated with these organisms.

2. Mites

Demodex zalophi has been observed in California sea lions. These animals develop alopecia and thickening of the skin over the genitalia, flippers and ventral body. The mites live in hair follicles and are diagnosed by skin scrapings.

Sea otters have also been observed to have demodex mites. These mites are observed in hair follicles around the face. No serious dermatologic conditions have been observed in these animals. Demodex mites only cause a mild follicular ectasia and minimal associated folliculitis.

3. Barnacles

Barnacles are common on certain cetaceans. These can be either sessile or pedunculated. They do not cause damage to the skin of affected animals.

Internal Parasites of Pinnipeds

(1) Lung mites:

Lung mites are common parasites of the nasal passages, trachea, bronchi, and bronchioles. Both seals and sea lions are affected. The most common mites observed are Orthohalarachne diminuata and Orthohalarachne attenuata. O. diminuata inhabits the airways of the lung, and O. attenuata are found in the nasopharynx. The nasal mite, Halarachne miroungae has been observed in sea otters. Grossly these mites are seen as small white specks on the mucosa of the respiratory tract (O. attenuata, .5 to 5 mm; O. diminuata, .6 to .8 mm). Clinically, these mites do not cause any serious problems, however, they might cause copious amounts of mucus in the upper respiratory tract and nose, nasal discharge, dyspnea, and coughing.

(2) Lungworms

(a) Parafilaroides decorus is the most common lungworm of young (1- to 2-year-old) California sea lions. The intermediate host for this metastrongylid is the opal eye fish (Girella nigricans). After ingestion of the fish and release of the larvae into the gastrointestinal tract, the larvae migrate to the lungs (alveoli), where maturation occurs. Females release larvae in the alveoli; larvae then migrate up the respiratory airways, are swallowed, and are then discharged with the feces. Histologically, uncomplicated infections result in goblet cell hyperplasia of the bronchiolar epithelium in which mucoid obstruction is observed. A suppurative or granulomatous bronchopneumonia is observed if a secondary bacterial infection occurs. Grossly, these lungs have a patchy, or mottled, appearance of red and grey hepatization. Other Parafilaroides species have been noted in the lungs of other species of pinnipeds. Parafilaroides lungworms have been identified with brucella bacteria present in their uterus and gut. These lungworms may cause brucellosis infection in pinnipeds.

(b) Otostrongylus circumlitus is another large Metastrongylid nematode that inhabits the primary and secondary bronchi of harbor seals and northern elephant seals. This parasite causes prominent bronchiectasis. Bronchiectatic abscesses containing these parasites are occasionally observed. Histologically, the bronchi and bronchioles have marked goblet cell hyperplasia of the peribronchiolar glands; mucus plugs fill the dilated bronchioles. As with most lungworms, a verminous pneumonia may develop as a result of secondary bacterial infection.

2) Digestive tract

(a) Stomach worms

Contracaecum and Anisakis are the most common nematode stomach worms of both pinnipeds and cetaceans. These parasites cause ulceration of the gastric mucosa and submucosa during migration. Occasionally Anisakine parasites may induce nodules in the gastric mucosa and submucosa. On histologic examination, parasites are found in the ulcerated regions. In cetaceans (odontocete), these parasites are located in the first and third chamber of the stomach. These parasites are usually incidental findings; however, they have been noted to cause hemorrhage and melena in both pinnipeds and porpoises. The life cycle is not fully understood; it is felt that a crustacean is the first intermediate host and a fish (many different species) is the second intermediate host. (The Pacific herring is the second intermediate host for Anisakis spp.)

(b) Hookworms (Uncinaria lucasi and Uncinaria hamiltoni)

Hookworms are common in sea lions and the Northern fur seal. Uncinaria lucasi is the most pathologic hookworm for Northern fur seal pups. Young fur seals and sea lions become infected during ingestion of the mother's milk. The parasites become adults within several weeks and cause severe hemorrhage into the intestines, which results in anemia. Surviving pups usually shed the parasites after three months. Surviving animals later become reinfected with the third-stage larvae by larval penetration of the skin or by ingestion of the larvae. These larvae migrate to the blubber of the ventral abdomen or mammary glands, where they remain dormant until they are shed in the females milk.

(C) Liver Flukes

Zalophotrema hepaticum is the liver fluke of sea lions. This fluke causes little damage and is found in the common bile duct, intrahepatic bile duct, and gallbladder. Occasionally these flukes will cause cystic cavitation in the hepatic parenchyma.

In sea otters, (also bearded seals) the gallbladder fluke, Orthosplanchnus fraterculus, causes cystic hyperplasia of the gallbladder mucosa. It also is believed to be responsible for causing a chronic fibrosing cholecystitis which is sometimes characterized by nodular thickening of the periductal and gallbladder connective tissue. This parasite does not appear to adversely affect the host.

These flukes are very small, 1-3mm in length. The eggs are the characteristic yellow color of fluke eggs and triangular in appearance.

(d) Acanthocephalids

Acanthocephalids are common intestinal parasites in pinnipeds and sea otters. These parasites are primarily of the genus Corynosoma. Acanthocephalids are observed usually as incidental findings in the colon and small intestine (ileum and jejunum). These parasites bury their heads deep into the mucosa and submucosa. In pinnipeds they rarely cause problems. However, in sea otters they are known to burrow through the intestinal wall and cause a life threatening peritonitis. Three other species of Acanthocephalids also occasionally infect sea otters, Falsifilicollis altmani, F. kenti, and F. major.

3. Cardiovascular system

Heartworm disease in pinnipeds is caused by both Dirofilaria immitis and Dipetalonema spirocauda. D. spirocauda is the most common heartworm found in most feral pinnipeds (primarily harbor seals). The life cycle is unknown, but the louse is suspected to be the intermediate host. These parasites are observed in the right ventricle and pulmonary arteries. Severe infection causes dilatation of the right ventricle and myocardial hypertrophy. Microscopically, the pulmonary arteries and arterioles have prominent intimal proliferation. Secondary chronic passive congestion may be observed in severely affected animals.

Dirofilaria immitis is occasionally observed in captive pinnipeds. These parasites live in the same location and cause the same problems as D. spirocauda. The identification of microfilaria is helpful in separating D. immitis from D. spirocauda. The microfilaria of D. immitis are usually larger (300 x 5 microns) than D. spirocauda (225 x 4 microns). However, microfilaria from D. spirocauda cannot be differentiated morphologically from the common nonpathogenic subcutaneous filariid Dipetalonema odendhali.

Dipetalonema odendhali is often found in the subcutaneous tissue, in the intermuscular fascia, beneath the parietal peritoneum, free in the abdominal and thoracic cavities, and in the pericardial sac.

Internal Parasites of Cetaceans

(1) Respiratory tract

(a) Nasitrema sp.

Nasitrema flukes are common flukes located in the head sinuses of many porpoises, dolphins, and toothed whales. These flukes range in size from 9 to 12 mm (Nasitrema stenosomum) to 28 to 35 mm (Nasitrema gondo). This parasite is normally found in the submucosal glands of these sinuses. Occasionally this fluke is observed in the middle ear. This parasite rarely causes problems; however, these flukes will occasionally migrate to the brain and cause serious central nervous system damage. Lesions caused by this fluke usually contain numerous small yellow triangulated fluke eggs (60 to 80 microns on the long axis with a single operculum). Numerous strandings have been associated with parasitic migration of this parasite into the brain. The life cycle is unknown.

(b) Hunterotrema caballeroi

This is a rather large fluke (up to 25 cm long) observed in the Amazon River dolphin. This parasite causes a mild to moderate mucoid exudate in the bronchi of these animals. However, it has been incriminated in bronchial obstruction, bronchiectasis, and atelectasis.

(c) Stenurus sp.

This is another common nematode (metastrongyle) located in the pulmonary parenchyma of the harbor porpoise and dall porpoise. These parasites usually cause subpleural nodules, which are filled with the parasites. This parasite has been known to migrate and fill the tympanic bullae. These parasites have been incriminated in dolphin strandings when the parasites have been observed in the tympanic bullae.

(d) Halocercus sp.

The nematode Halocercus is a lungworm (Metastrongyle) that affects dolphins and porpoises. These parasites inhabit the small bronchi and bronchioles. Heavily infected animals may develop a neutrophilic and eosinophilic bronchopneumonia. These parasites form granulomas within the bronchioles, which become encapsulated and calcify. The bronchopneumonia is often accompanied by hypertrophy of the smooth muscles of the terminal bronchioles. The life cycle of this lungworm is unknown, but believed to be direct. Infections of young dolphins with these parasites also suggests transplacental transmission of the parasite.

(e) Crassicaudia sp.

These nematodes are commonly found in the pterygoid air sinus and are associated with erosions of the pterygoid bone. Migration of this organism to the brain or tympanic bulla can lead to CNS lesions and strandings of affected animals. Crassicauda sp. have been found in the mammary gland, air sinuses, blubber and muscle.

2. Digestive Tract

(a) Braunina cordiformis

This fluke is usually observed in the second chamber of the stomach of Atlantic bottlenosed dolphins. It causes minimal damage and irritation to the gastric mucosa. The fluke, when attached to the gastric mucosa, has a characteristic urn shaped appearance (5 mm x 5mm) in the lumen of the stomach.

(b) Pholeter gastrophilus

Pholeter gastrophilus is another fluke observed in the second chamber of the stomach of dolphins. This parasite buries deep in the submucosa, forming prominent small black cavitary nodules that can be identified on palpation. The mucosa usually remains intact over these parasitic nodules. The nodules have abundant fibrous connective tissue surrounding the parasite with a variable granulomatous and eosinophilic inflammatory reaction. These flukes have prominent cuticular spines on the tegument and yellow, single operculated eggs.

(c) Cyclorchis campula (Also Campula pilliata & C. oblonga)

This is a trematode that primarily inhabits the bile and pancreatic ducts of cetaceans. This parasite causes extensive irritation of the ducts, with hyperplasia of the ductal epithelium and fibroplasia developing around the ducts. This chronic irritation may progress to a chronic fibrosing hepatitis and pancreatitis. Numerous parasites are found in the large dilated pancreatic ducts; the smaller ducts are usually sclerotic. The fluke has numerous prominent tegumental spines. This parasite, like Nasatrema, have characteristic small yellow triangular eggs.

Miscellaneous Diseases

1. Freshwater and Cetaceans

Cetaceans that are not maintained in ocean sea water (3.4% salt) can develop skin and corneal lesions. These lesions usually develop in animals that have been maintained for a week or longer in water containing less than 1% salt. These lesions are characterized by areas of ulceration and necrosis of the epidermis and corneal opacity. Histologically, the lesion is characterized by ballooning degeneration of the stratum externum (parakeratotic layer). Later the entire thickness of the epidermis becomes necrotic and/or ulcerated. If these animals are placed back into normal sea water, recovery usually occurs.

2. Pinniped Hyponatremia

This is a problem observed primarily in seals. This disorder is characterized by a decline (either sudden or gradual) in blood sodium levels and is observed primarily in animals held in fresh water. It is brought on by various stresses or disease (i.e., Vitamin E deficiency). Clinically, affected animals demonstrate one or more of the following signs: lethargy, ataxia, head and body shaking, convulsions, and sudden death. Diagnosis is confirmed by finding blood sodium levels between 120 and 147 mEq/L (normal, 150 to 160 mEq/L). Salt administration is the treatment of choice in affected animals.

3. Thiamine Deficiency

Thiamine deficiency has been observed in both pinnipeds and cetaceans. This deficiency is associated with the ingestion of thiaminase-containing fish (herring, smelt, capelin). Clinically, these animals develop anorexia, irregular breathing, and unresponsiveness to touch, noise, and light stimulation. Untreated animals develop central nervous system signs (tremors and spasms, capable of leading to death). It does not appear that any consistent histologic lesions are associated with thiamine deficiency in these animals. It has been reported that affected sea lions had a dilated left ventricle and myelin sheath degeneration of the peripheral and vagus nerves. Treatment and prevention are by the use of thiamine supplements in the diet.

4. Vitamin E Deficiency

Vitamin E deficiency develops in marine mammals that are fed improperly stored fish that are high in unsaturated fatty acids. This deficiency is felt to cause both muscle degeneration and steatitis. Seals are the marine mammal most commonly affected. Affected animals are usually anorectic, reluctant to move, and have an arched posture. Histologically, the muscles are undergoing degeneration and necrosis. Steatitis has been observed in California sea lions and Amazon River dolphins. These animals developed a fatal condition characterized by weakness and generalized subcutaneous nodules of fat necrosis. Vitamin E supplements aid in the prevention of the disease and should be established on the basis of fat content of the fish, storage, and method of preparation and feeding. Since the viscera of fish contain more vitamin E than the flesh, it is preferable to feed whole fish instead of eviscerated fish. It is important to remember that pinnipeds suffering from vitamin E deficiency are more likely to develop hyponatremia. Treatment of choice for seals with hyponatremia is vitamin E supplementation and the addition of salt to the diet.

5. Capture Myopathy

Exertional rhabdomyolysis has been noted in captive marine mammals during capture, restraint, and transportation. These animals develop skeletal muscle degeneration and necrosis. It is felt that low or deficient levels of vitamin E may play an important role in the development of this condition.

6. Scombroid Poisoning

Scombroid poisoning is a condition in man and marine mammals associated with the ingestion of poorly preserved scombroid fish (tuna and mackerel). Clinically, affected animals develop nonspecific signs (inappetence, debilitation, irritable behavior, gastric ulcers, and pulmonary edema), which disappear on change of diet. Animals that have ingested this poorly preserved fish usually recover. One should always use caution when feeding scombroid fish. Ensure that these fish have been stored frozen for less than four months.

7. Microphthalmia and Freshwater Dolphins

Many species of freshwater dolphin (particularly the Ganges River dolphin) have microphthalmia and apparent blindness. This is a normal finding in these animals. Histologically, these eyes have a minimal slit-like opening between the eyelids and a microphthalmic eyeball. The eye is nonfunctional and has a thick cornea, iris, ciliary body, retina, and optic nerve.

8. Disaccharide Intolerance in Pinnipeds

Pinnipeds have no tolerance for dietary disaccharides, including both lactose and sucrose. If abandoned pups are fed formula high in sugars, diarrhea develops; as the intolerance progresses, a dermatitis develops and death follows. It appears that pinniped milk does not contain lactose or any other carbohydrate. These animals lack enzymes in the intestine to properly degrade these sugars. Formulas composed of fish or marine products containing a high fat content and only simple sugars should be used when feeding abandoned pups.

9. Cutaneous Gout

The Amazon dolphin (Inia geoffrensis) has higher serum uric acid levels than other cetaceans (10 mg/dl, which is approximately 10 times higher than that reported for other cetaceans). One Amazon dolphin developed near the base of the flippers an ulcerative dermatitis that was characterized by a granulomatous inflammatory reaction associated with numerous urate crystals in the tissue. The animal was treated with allopurinol over a six-month period. The treatment decreased the animal's serum uric acid concentration and healed the lesions.

10. Heat Prostration

Since cetaceans have a thick layer of blubber surrounding their body, dissipation of heat can be a serious problem in stranded animals. Stranded animals need to be kept shaded, cool and moist at all times. Ideally they should be kept out of the sun to prevent sunburn. Once an animal is stranded and left out of water in the sun, its body temperature greatly increases causing serious problems for the animal. Animals that die of heat prostration usually demonstrate diffuse edema and congestion of the lungs.

11. Sunburn in Cetaceans

Cetaceans need to have their skin protected from the direct affects of the sun. Animals that are either out of the water due to stranding or for physical examination need to be monitored to protect them from the sun. Sun screens (zinc oxide) can be useful in protecting these animals. Animals that are sunburned have ballooning degeneration of the epidermis which, in severe cases, can ultimately lead to necrosis of the epidermis.

12. Sea Otter Hemorrhagic Gastroenteritis

The cause of sea otter hemorrhagic gastroenteritis is unknown. This disease is usually observed in severely stressed or debilitated animals. Affected animals develop a severe bloody diarrhea and are usually depressed and anoretic. Most affected animals usually die.

At necropsy the only lesion observed is blood in the entire intestinal tract extending from the duodenum to the rectum. Histologically, there is little damage to the intestinal mucosa: prominent pooling of blood in the mucosa and submucosa is often observed. Isolation of bacteria from the lesion have failed to identify a specific bacterial agent. The pathogenesis of this lesion is unclear. It is felt that the gastrointestinal tract may act as a shock organ with pooling of blood into the intestinal mucosa and diapedesis of blood into the intestinal lumen.

13. Nephrolithiasis in Pinnipeds

The finding of kidney stones in seals is a common finding. These stones appear to be incidental findings in many seals and are considered of little pathologic significance.

14. Trauma

Trauma due to shark bites, whale bites, or man-made actions such as shooting or boat strikes can be observed in all marine mammals. Shark bites are often characterized by parallel rake or bite marks on the body.

15. Cardiomyopathy in Pygmy and Dwarf Sperm Whales

A cardiomyopathy involving the right ventricle has been observed in pygmy (Kogia breviceps) and dwarf (Kogia simus) sperm whales. This lesion has been observed primarily in adult animals. Grossly, the right ventricle is enlarged and flabby. Histologically there is moderate to focally extensive myocardial fibrosis involving the right ventricle and ventricular septa. Myofiber degeneration characterized by hyaline change and loss of striations is frequently associated with the fibrosis. Occasionally remaining myofibers demonstrate crisscrossing or whirling patterns, and myofiber hypertrophy with enlarged nuclei and nucleoli and sarcoplasmic lipofuscinosis. No changes were observed in the coronary arteries, endocardium, pericardium or aorta. Most livers have centrolobular hepatocellular loss and/or necrosis suggestive of right side heart failure. The cause of this lesion is unknown.

16. Vaginal calculi in Dolphins

Vaginal calculi have been observed in the common, Pacific white-sided and spotted dolphins. These calculi become very large, exhibit concentric crystallized layers and contain calcium phosphate compounds. These calculi are found associated with the cervix, pseudocervix, and vagina. Most calculi contain fetal bones which suggests that parts of the fetal skeleton become entrapped in this location and crystallize.

17. Northern Elephant Seal Skin Disease (NESSD)

Northern elephant seal skin disease (NESSD) is a skin condition of unknown etiology involving young seals less than 2 years of age. The skin lesions are characterized by variably sized areas of alopecia and hyperpigmentation with variably sized areas of epidermal ulceration and necrosis. Microscopically the lesions are characterized by an ulcerative dermatitis with marked hyperkeratosis of the epidermis and follicular epithelium, acanthosis and sebaceous gland metaplasia and atrophy. Some follicular dilatation with prominent amounts of keratin within the dilated follicle has also been observed. Secondary suppurative inflammation due to bacterial infections are common. Diseased seals have depressed thyroxine, triodothyroxine, retinol, serum iron, albumen, calcium and cholesterol levels. Alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, gamma glutamyl transpeptidase, BUN, and uric acid were elevated. Diseased seals are usually smaller in size (15% smaller) than non-affected animals. Affected animals have elevated serum polychlorinated biphenyl (PCB) and p,p’ dichloro-diphenyl-dichloroethane (p.p’DDE; a metabolite of DDT) levels. Lesions observed in affected animals are similar to those observed in PCB toxicosis.

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64) Scheiblauer H.: Pathogenicity of Influenza A/Seal/Mass/1/80 virus mutants for mammalian species. Arch Viol. 140(2):341-348, 1995.

65) Seal B.S.: Analysis of serologic relationship among SMSV and VESV isolates. Application of Western blot assays for detection of antibodies in swine sera to these virus types. J. Vet. Diagn. Invest. 7(2):190-195, 1995.

67) Smith A.W.: Calicivirus-induced vesicular disease in cetaceans and probably interspecies transmission. JAVMA. 183: 1223-1225, 1983.

73) Stack M.J.: Mixed parapox and calicivirus infections of grey seals(Halichoerus grypus) in Cornwall. Vet. Record. 132: 163-165, 1993.

75) Taubenberger J.K: Two morbilliviruses implicated in bottlenosed dolphins epizootics.

Emerging Infectious Diseases. 2(3): 213-216, 1996.

77) Wilson T.W.: Pox in young, captive harbor seals. JAVMA. 161: 611, 1972.

81) Van Bressen M.F.: Morbillivirus infection in Mediterranean Striped Dolphins.(Stenella

coernulwalba). Vet Record. 12: 471-472, 1991.

82) Visser I.K.G.: Characterization of morbilliviruses isolated from dolphins and porpoises in Europe. Journal of General Virology. 74: 631-641, 1993.

83) Visser I.K.G.: Continued presence of phocine distemper virus in the Dutch Wadden Sea seal population. Vet. Record. 133: 320-322, 1993.

84) Visser I.K.G.: Prevalence of morbilliviruses among pinniped and cetacean species.

Rev Sci Tech Off. Int. Epiz. 12(1):197-202, 1993.

85) Van Bressem M.F.: Morbillivirus infection in Mediterranean Striped Dolphins (Stenella

caeruleoalba). Vet Record. 129: 471-472, 1991.

86) Zarnke R.L.: Serologic survey for phocid herpesvirus-1 in marine mammals form Alaska and Russia. J. Wild. Dis. 33(3)459-465, 1997.

Bacterial Diseases

1) Baker J.R.: Pathology and bacteriology of adult male Antarctic fur seals, Arctocephelus gazella, dying at Bird Island, South Georgia. Br. Vet. J. 145:263-275, 1989.

2) Baker J.R.: Isolation of salmonellae from seals from U.K. waters. Vet. Record. 136: 471-472, 1995.

3) Boever W.: Mycobacterium chelonei infection in a Natterer Manatee. JAVMA. 169: 927-929,

1976.

5) Colgrove, G.S.: Cerebral abscess associated with stranding in a dolphin. J. Wildlife Disease.

12:271-274, 1976.

7) Cousin D.V.: Tuberculosis in captive seals: Bacteriological studies on an isolate belonging to the

Mycobacterium tuberculosis complex. Res. Vet. Sci. 48:196-200, 1990.

8) Cousin D.V.: Tuberculosis in wild seals and characterization of the seal bacillus. Aust. Vet. J. 7:92-97, 1993.

9) Diamond S.S.: Fatal bronchopneumonia and dermatitis caused by Pseudomonas aeruginosa in an Atlantic bottlenosed dolphin. JAVMA. 37(3):303-305, 1979.

11) Enalt D.R.: Characteristics of a Brucella species from a bottlenosed dolphin (Tursiops truncatus).

J. Vet Diagn Invest. 6:448-452 , 1994.

13) Foster G.: Isolation of Brucella species from cetaceans, seals and an otter. Vet Record.

138(24): 583-586, 1996.

14) Forshaw D.: Tuberculosis in a captive colony of pinnipeds. J. Wild. Dis. 27:288-295, 1991.

15) Garner M.M.: Evidence of Brucella infection in Parafilaroides lungworms in a Pacific harbor seal (Phoca vitulina richardsi). J. Vet. Diagn. Invest. 9:298-303,1997.

16) Greenwood A. G. Clostridial myositis in marine mammals. Vet Record. July 15 1978, p54-55.

19) Gulland F.M.D.: Leptospirosis in California sea lions (Zalophus californianus) stranded along the central California coast, 1981-1984. J. Wild. Dis. 32(4): 572-580, 1996.

22) Jahans K.L. The Characterization of Brucella strain isolated from marine mammals. Vet Micro 57:373-382, 1997.

23. Joseph B.E.: Valvular endocarditis in a Northern sea otter(Enhydra lutris). J. Zoo and Wild. Med. 21: 88-91, 1990.

24) Kettener P.S. Septic embolic nephritis in a dolphin caused by Staphylococcus aureus. Australian Vet. Journ. 50: 123, 1974.

26) Kinsel M. J. Fatal Ersipelothrix rhusiopathiae septicemia in a captive Pacific white-sided dolphin (Larenorhyncus obliquidens) J. Zoo and Wildlife Medicine: 28(4): 493-497, 1997.

28) Medway W.: Respiratory problem in captive small cetaceans. JAVMA. 163:571-573, 1973.

30). Pier A.C. Cetacean Nocardiosis. J Wildl disease 6: 112-118, 1970.

31) Ramano M.I.: Genetic characterization of Mycobacteria from South American wild seals. Vet. Micro. 57 (1-2): 89-98, 1995.

32) Rand C.S. Nodular suppurative cutaneous cellulitis in a Galapagos sea lion. Journal of wildlife diseases 11: 325-329, 1975.

33) Ross H.M.: Brucella species infection in sea mammals. Vet Record. 134 (14): 359, 1994.

34) Ross H.M.: Brucella species infection in North Sea seal and cetacean populations. Vet Record. 138 (26): 647-648, 1996.

35) Siebold H.R.: Erysipelothrix septicemia in the porpoise. JAVMA. June 1, 537-539, 1956.

37) Smith A.W.: A preliminary report on potentially pathogenic microbiological agents recently isolated from pinnipeds. J. Wildl. Disease 10:54-59, 1974.

40) Stroud R.K. Salmonella meningoencephalitis in a Northern fur seal (Callorhinus ursinus). Journal of wildlife Diseases 16: 15-18., 1980.

41) Sweeney J.C. Survey of Diseases in free-living California sea lions. Journal of Wildlife Disease 10: 370-376, 1974.

43) Sweeney J.C.: Common disease of small cetaceans. JAVMA. 167:533-540, 1975.

44) Stadlander C.T.: Characterization of cytopathogenicity of aquarium seal mycoplasmas and seal

Finger Mycoplasmas by light and scanning electron microscopy. Int J Med Microbiol Viral Parasital Infect Disease. 280 (4):458-467-1994.

45) Streitfeld M.M.: Staphylococcus aureaus infections of captive dolphins (Tursiops truncatus and oceanarium personnel. AJVR 37 (3): 303-305, 1976.

46) Stoskopf M.K.: Tuberculosis in pinnipeds. Proc. Anim. Meet An. Assoc. Zoo Vet. P. 393, 1987.

47) Trudgett A.: Analysis of a seal and a porpoise morbillivirus using monoclonal antibodies. Vet Record. 128:61, 1991.

48) Varaldo, P.E.: Staphylococcus aureus NOV., a Coagulase positive species Isolated from dolphins.

International Journal of Systemic Bacteriology. 38:436-439, 1988.

49) Vedros N.: Leptospirosis epizootic among California sea lions. Science 179: 1250-1251, 1971.

51) Woods, R.: Tuberculosis in a wild Australian fur seal (Arctocephalus pusillus dorifesus) from Tasmania. J. Wildl. Dis. 31(1): 83-86, 1995.

52) Van Pelt R.W.: Staphylococcal infection and toxoplasmosis in a young harbor seal. J. Wildl. Dis. 9: 258, 1973.

Mycotic Diseases

2. Cornell L.H. Coccidioidomycosis in a California sea otter (Enhydra lutris). J. Wild. Dis 15:373- 378, 1979.

3) Carrol J.M. Pulmonary aspergillosis of the bottlenosed dolphin (Tursiops truncatus). Veterinary Clinical Pathology 2:139-140, 1968.

4) Dilbone R.P.: Mycosis in a manatee. JAVMA 147: 1095, 1965.

6) Dunn J.L.: Candidiasis in captive cetacean. JAVMA. 181; 1316-1321, 1982.

7) Fauquier D.A. Coccidioidomycosis in free-living California sea lions (Zalophus californianus) in central California. J. Wild. Dis. 32(4): 707-710, 1996.

8) Farnsworth R.J. Dermatomycosis in a harbor seal causes by Mycosporum canis. Journal of Zoo Animal Medicine 6:26-27.

9) Frasco, S.: Mycotic dermatitis in an Atlantic white sided dolphin, a pigmy sperm whale and

two harbor seals. JAVMA. 208 (5) 727-729, 1996.

12) Migaki G.: Pulmonary cryptococcoses in an Atlantic bottlenosed dolphin (Tursiops truncatus). Lab Ani Sci. 28: 603-606, 1978.

13) Migaki G.: Sporotrichosis in a Pacific white-sided dolphin (Lagenorhynchus obliguidens). AJVR. 39:1916-1919, 1978.

15) Nakeeb S. Chronic cutaneous Candidiasis in bottle-nosed dolphins. JAVMA. 171:961-966, 1977.

16) Reed R.E.: Coccidioidomycosis in a California sea lion (Zalophus californianus). J Wild Dis. 12:372-375, 1976.

17) Reidarson T. H. Coccidioidomycoisis in a bottlenosed dolphin. J Wildlife Dis. 34(3)629-631.

19) Sweeney J.C.: Systemic mycosis in marine mammals. JAVMA. 169:946-948, 1976.

20) Tanaka E.: Dermatophytosis in a Steller sea lion (Eumetopias jubatus). J Vet Med Sci. 56(3):551- 553, 1994.

21) Williamson W.M.: North American blastomycosis in a Northern sea lion. JAVMA. Nov. 15, 1959: 513-515.

22) Wilson T.M.: Histoplasmosis in a harp seal. JAVMA. 165: 815-817, 1974.

Protozoal Diseases

1) Akao, S.: A new species of Sarcocystis parasitic in the whale (Balaenoptera borealis). J. Protozool. 7:290-294, 1970.

3) Brown R.J.: Sarcocystis in the Northern fur seal. J. Wildl. Dis. 10: 53, 1974.

4) Dailey, M.D.: Parasites and associated pathology observed in cetaceans stranded along the Oregon coast. J. Wildl. Disease. 14:503, 1978.

5) Hadwen S.: Cyst forming protozoa in reindeer and caribou and a Sarcosporidean parasite of the seal (Phoca richardi). JAVMA. 61: 374-382, 1922.

8) Howard E.B.: Pathology of Marine Mammal Disease. CRC press, Boca Raton, Fl., 1993.

9) Inskeep W.: Toxoplasmosis in Atlantic bottlenosed dolphins (Tursiops truncatus). J Wild Disease. 26: 377-382, 1990.

10 Mense G.M.: Acute hepatic necrosis associated with a Sarcocystis canis like protozoa in a sea lion. (Zalophus californianus). J. Vet Diagn Invest. In press.

11 ) Migaki G.: Fatal disseminated toxoplasmosis in a spinner dolphin (Stenella longirostris). Vet Path. 27: 463-464, 1990.

15) Olson M.E. Giardiasis in ringed seals from the Western Arctic. J. Wild. Dis. 33(3): 646-648, 1997.

Parasites

1) Abolla E. Long term recording of gastric ulcers in cetaceans stranded on the Galician (NW Spain) coast. Diseases of aquatic Organisms 32:71-73,1998.

4) Conlogue G.J.: Pediculosis and severe heartworm infection in a harbor seal. Vet Med. 75:1184- 1187, 1980.

5) Conlogue G.J.: Parasites of the Dall’s porpoise (Phocoenoides dalli). J. Wildl Dis. 21:160-166, 1985.

7) Dailey M.: Evidence of prenatal infection in the Bottlenosed dolphin (Tursiops truncatus) with the lungworm Halocercus lagenorhynchi. J Wildl Dis. 27:164-165, 1995.

9) Dailey M.D.: Disease of Mammalia: Cetacea. In Disease of Marine Mammals. Vol IV, Part 2. O. Kinne (ed.) Biologische Anstaff Helgoland, Hamburg, Germany. 1985, p805-847.

14) Garner M.M.: Evidence of Brucella infection in Parafilaroides lungworms in a Pacific harbor seal (Phoca vitulina richardsi). J. Vet. Diagn. Invest. 9:298-303,1997.

19) Koie M. The life cycle of Contracaecum osculatum senso stricto in view of experimental infections. Parasitology Res. 81(6):481-489,1995.

21) Lyons E.: Uncinariasis in Northern fur seals and California sea lion pups from California. J. Wild. Dis. 33(4): 848-852, 1997

27) Moser M.: The lungworm Halocercus spp. In cetaceans from California. J. Wildl, Dis. 29(3):507- 508, 1993.

29) O'Shea T.J.: Nasitrema associated encephalitis in striped dolphin (Stenella caeruleoalba) stranded in the Gulf of Mexico. J. Wild Dis. 27(4):706-709, 1991.

32) Ridgeway S.H.: Cerebral and cerebellar involvement of trematode parasites in dolphins and their possible role in strandings. J. Wild Dis. 8:33-43, 1972.

33) Rausch R.: Studies on the helminth fauna of Alaska. XIII. Diseases in the sea otter, with special reference to helminth parasites. Ecology. 34: 584-604, 1953.

34) Schryver H.F.: The stomach fluke Brauninia cordiformis in the Atlantic bottlenosed dolphin. JAVMA. 151: 884-886, 1967.

37) Wazura K.W.: Helminths of the beluga whale (Delphinapterus leucas) from the Mackenzie river delta, Northwest Territories. J Wild Dis. 22: 440-442.

Miscellaneous Disease

1) Alexander J.W.: Vertebral osteomyelitis and suspected disko-spondylitis in an Atlantic bottlenosed dolphin (Tursiops truncatus). J Wild Disease 25: 118-121, 1989.

2) Baker J.R.: Pollution associated uterine lesions in grey seals from the Liverpool Bay area of the Irish Sea. Vet Record. 125: 330, 1989.

3) Beckmen K.B.: Clinical and pathological characterization of Northern elephant seal skin disease. J. Wild. Dis. 33(3): 438-449, 1997.

4) Bossart G.D.: Invasive gingival squamous cell carcinoma in a California sea lion (Zalophus californianus). J Zoo and Wild Med. 21: 92-94, 1990

5) Bossart G.D.: Cardiomyopathy in stranded pygmy and dwarf sperm whales. JAVMA. 187: 11, 1137-1140, 1985.

7) De Guise S.: Tumors in St. Lawrence beluga whales (Delphinapterus leucas). Vet. Path. 31:444- 449, 1994.

8) De Guise S.: Non-neoplastic lesions in beluga whales and other marine mammals from the St. Lawrence estuary. J. Comp Path. 112: 257-271, 1995.

9) De Guise S.: Intestinal adenocarcinoma in two Beluga whales (Delphinapterus leucas). Can Vet J. 36(9): 563-565, 1995.

10) De Guise S.: Pathology and toxicology of Beluga whales from the St. Lawrence estuary, Quebec, Canada. Past, present and future. Sci. Total Environ. 154(2-3): 201-215, 1994.

11) De Guise S.: True hermaphroditism in a St. Lawrence Beluga whale (Delphinapterus leucas). J. Wildl. Dis. 32(3): 548-551, 1996.

13) Frasca S.: Acute gastric dilatation with volvulus in a Northern fur seal (Callorhinus ursinus). J. Wildl. Dis. 32(3): 548-551, 1996.

19) Geraci J.R.: Tumors in cetaceans: Analysis and new findings. Can J Fish Aquat Sci. 44: 1289- 1300, 1987.

20) Gulland F.M.: Metastatic carcinoma of probable transitional cell orgin in 66 free living California sea lions, 1979-1994. J. Wildl. Dis. 32(2): 250-258, 1996.

21) Gulland F.M.: Baseline coagulation assay values for Northern Elephant seals (Mirounga angustirostris) and disseminated intravascular coagulation in this species. J. Wildl. Dis. 32(3): 536-540, 1996.

22) Heidel J.R.: Intestinal volvulus in a Bowhead whale, Balaena mysticetus. J. Wildl. Dis. 30(1): 126-128, 1994.

23) Hirst L.W.: Pathologic findings in the anterior segment of thepinniped eye. JAVMA. 183: 1226-1231, 1983.

25) Martineau D.: Pathology of stranded Beluga whales (Delphinapterus leucas) from the St. Lawrence Estuary, Quebec, Canada. J Comp Path. 98: 287-311, 1988.

26) Martineau D.: Transitional cell carcinoma of the urinary bladder in a Beluga whale (Delphinapterus leucas). Can Vet J. 26: 297-302, 1985.

27) Martineau D.: Pathology and toxicology of beluga whales from the St. Lawrence estuary, Quebec, Canada, Past, present and future. Science of the Total Environment. 154: 201-215, 1994.

28) Migaki G.: Renal adenoma in an Atlantic bottlenosed dolphin. AJVR. 39: 1920-1921, 1978.

29) Miller G.J.: Ecotoxicology of petroleum hydrocarbons in the Marine environment. J Applied Tox. 2: 88-97, 1982.

30) Morimitsu T. Histopathology of eighth crainal nerve of mass stranding dolphins at Gato Island. Japan. J Wildl Dis. 28(4): 656-658, 1992.

31) Shlosberg A.: Lead toxicosis in a captive bottlenosed dolphin (Tursiops truncatus) consequent to ingestion of air gun pellets. J. Wild. Dis. 33(1):135-139, 1997.

32) Stoskopf M.K.: Ocular anterior segment disease in Northern fur seals. JAVMA. 187: 1141- 1145, 1985.

33) Stroud R.K.: Nephrolithiasis in a harbor seal. JAVMA. 175: 924-925, 1979.

35) White J.R.: Thiamine deficiency in an Atlantic bottle-nosed dolphin on a diet of raw fish. JAVMA. 157: 559, 1970.

36) Woodhouse C.D.: Observations of vaginal calculi in dolphins. J. Wildl. Dis. 27(3): 421-427, 1991.