JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

November 2022

I-V14

 

Signalment (JPC Accession# 1497357):  California sea lion (Zalophus californianus)

 

HISTORY:  This sea lion presented with multiple vesicular and ulcerated skin lesions over various parts of the body. 

 

HISTOPATHOLOGIC DESCRIPTION: Haired skin: There are multifocal intracorneal vesicopustules, up to 3 mm in diameter, filled with degenerate and non-degenerate neutrophils, cellular and karyorrhectic necrotic debris, fibrin, and granular to amorphous, eosinophilic proteinaceous fluid. The epidermis is hyperplastic characterized by acanthosis, prominent rete ridges, and orthokeratotic hyperkeratosis; there is pigment in all layers (hyperpigmentation), and prominent intercellular bridging (spongiosis). Within the superficial dermis, there are low numbers of perivascular lymphocytes, plasma cells, and macrophages. Lymphatics are mildly dilated (edema), and the endothelium of superficial small vessels is prominent (reactive).

 

HISTOPATHOLOGIC DESCRIPTION:  Haired skin, pinna: There is a focally extensive 1.5 cm diameter area of ulceration and erosion bounded by remaining ends of a ruptured vesicle. The ulcerated and eroded epithelium is replaced and overlain by a serocellular crust composed of fibrin, necrotic debris, degenerate neutrophils, macrophages, lymphocytes, and plasma cells. The epithelium adjacent to the ulcer is hyperplastic with rete ridges and moderate orthokeratotic hyperkeratosis as well as prominent intercellular bridging (spongiosis). The underlying dermis contains low numbers of previously described inflammatory cells, granulation tissue characterized by numerous small caliber vessels oriented perpendicular to the ulcer, and edema characterized by ectatic lymphatics and increased clear space between dermal collagen fibers. 

 

MORPHOLOGIC DIAGNOSIS:  1. Haired skin: Epidermitis, vesiculopustular, subacute, multifocal, mild, with orthokeratotic hyperkeratosis and mild superficial perivascular lymphohistiocytic dermatitis, California sea lion (Zalophus califonianus), pinniped.  

2. Haired skin, pinna: Dermatitis, ulcerative, subacute, focally extensive, moderate, with orthokeratotic hyperkeratosis.

 

ETIOLOGY:  San Miguel sea lion virus (SMSV) (calicivirus)

 

ETIOLOGIC DIAGNOSIS:  Caliciviral dermatitis

 

GENERAL:  

• The Caliciviridae, a family of nonenveloped RNA viruses, is divided into five genera:  Vesivirus, Lagovirus, Sapovirus, Nebovirus, Norovirus; the first two contain most of the animal caliciviruses
• SMSV and vesicular exanthema of swine virus (VESV) are considered a single species/genotype of calicivirus with many serotypes
• SMSV belongs to the genus Vesivirus, and is endemic in pinnipeds and some cetaceans
• Overcrowding of pinnipeds (rookery/breeding site) produces the ideal environment for direct contact spread of the virus or viral contamination of the water
• Potentially zoonotic (vesicular dermatitis and flu-like symptoms)

            

PATHOGENESIS:  

• Biophysically and morphologically similar to VESV; damaged skin allows entry of the virus, followed by local viral replication in epidermal cells and viremia
• Vesicles form due to viral replication in epidermal cells leading to cell lysis, inflammatory cell infiltration, and separation of the epidermal layers by fluid transudate

 

TYPICAL CLINICAL FINDINGS:  

• There are vesicles up to 3 cm in diameter on the nonhaired skin of flippers and in the oral cavity; vesicles may rupture leading to erosion/ulceration
• Disease can be self limiting, with a rapid recovery

 

TYPICAL GROSS FINDINGS:  

• Vesicles, ulcers, or plaque-like lesions on the flippers or oral cavity
• Ulcerative stomatitis and nodular dermatitis of the lips, nasal planum, and chin reported
• Abortion and premature birth reported, but causation not proven

 

TYPICAL MICROSCOPIC FINDINGS:  

• Spongiosis of the stratum spinosum leading to subcorneal vesicles 
• Viral inclusions are not seen

 

ULTRASTRUCTURE:  

 

ADDITIONAL DIAGNOSTIC TESTS:  

 

DIFFERENTIAL DIAGNOSIS:

 

COMPARATIVE PATHOLOGY: 

 

Other Caliciviridae viruses: 

• Feline- Feline calicivirus (Vesivirus):  Causes feline respiratory disease with oral vesicles that ulcerate; conjunctivitis, stomatitis, gingivitis, rhinitis, tracheitis and pneumonia
• Lagomorph- Rabbit hemorrhagic disease (RHD), Viral hemorrhagic disease, or Rabbit calicivirus disease (RHD virus):  Causes necrotizing hepatitis, pulmonary edema, fibrin thrombi, and lymphoid necrosis; similar to the calicivirus that causes European brown hare syndrome (EBHS)
• Porcine- VESV (Vesivirus, Caliciviridae): Biophysically and morphologically similar to SMSV; thought to have originated from the feeding of uncooked contaminated (sea food) garbage; disease of historical significance only, eradicated from the US swine population in 1959; microvesicles to vesiculopustules to healing erosions with a marked perivascular inflammation in the underlying dermis of the snout, mouth, and nonhaired skin and feet; difficult to distinguish gross lesions from foot and mouth disease; reportable disease
• Avian- chicken calicivirus:  Stunting and high mortality in chicks
• Non-human primate- primate calicivirus:  Produces vesicles and persistent infections
• Mouse- murine norovirus: Hepatic inflammation and necrosis, also variable lesions in lung, gastrointestinal tract, mesenteric lymph nodes, brain, spleen

 

REFERENCES:  

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Wiley Blackwell; 2016: 264-6. 
2. Cheville NF. Cytopathology of viral diseases. In: Cheville NF, ed. Ultrastructural Pathology: The Comparative Cellular Basis of Disease. 2nd ed.  Ames, IA: Wiley-Blackwell; 2009: 399-401.
3. Colegrove KM, Burek-Huntington KA, Roe W, Siebert U. Pinnipediae In: Terio KA, McAloose D, Leger JS. Pathology of Wildlife and Zoo Animals. London, United Kingdom: Elsevier; 2018: 579.
4. Knowles, NJ, Reuter G. Diseases of the skin. In: Straw BE, D'Allaire S, Zimmerman JJ, D’Allaire S, Taylor DJ, eds.  Diseases of Swine. 10th ed. Ames, IA: John Wiley and Sons Ltd; 2012: 493-495.
5. MacLachlan NJ, Dubovi EJ, Barthold SW, Swayne DE, Winton JR. Caliciviridae. In: Veterinary Virology. 5th ed. San Diego, CA: Academic Press; 2017:503-506. 
6. Owen H, Flint M, de Wit M. Sirenia. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals, San Diego, CA: Elsevier 2018: 600.
7. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals.  Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016: 121.

 

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