JPC SYSTEMIC PATHOLOGY
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 with acanthosis, prominent rete ridges, orthokeratotic hyperkeratosis, pigment in all layers (hyperpigmentation), and moderate spongiosis (intercellular edema). 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 reactive.
HISTOPATHOLOGIC DESCRIPTION: Haired skin, pinna: There is a focally extensive 1.5 cm diameter ruptured, ulcerated vesicle with replacement of the epidermis by a serocellular crust of fibrin, necrotic debris, degenerate neutrophils, macrophages, lymphocytes, and plasma cells. The epithelium adjacent to the ulcer is hyperplastic with spongiosis and moderate orthokeratotic hyperkeratosis, and is undermined forming 2 overhanging flaps. The underlying dermis contains low numbers of previously described inflammatory cells, granulation tissue (characterized by numerous small caliber vessels that are oriented perpendicular to the ulcer) and edema (characterized by clear space between dermal collagen and ectatic lymphatics).
MORPHOLOGIC DIAGNOSIS: 1. Haired skin: Dermatitis, vesiculopustular, subacute, multifocal, mild, with orthokeratotic hyperkeratosis, California sea lion (Zalophus califonianus), pinniped.
- Haired skin, pinna: Dermatitis, ulcerative, subacute, focally extensive, mild, with orthokeratotic hyperkeratosis.
ETIOLOGY: San Miguel sea lion virus (SMSV) (calicivirus)
ETIOLOGIC DIAGNOSIS: Caliciviral dermatitis
- The Caliciviridae, a family of nonenveloped RNA viruses, is divided into four genera: Vesivirus, Lagovirus, Sapovirus, 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
- 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
TYPICAL MICROSCOPIC FINDINGS:
- Spongiosis of the stratum spinosum leading to subcorneal vesicles
- Viral inclusions are not seen
- Lymphocytolysis in regional lymph nodes
- Caliciviruses are nonenveloped, single stranded RNA, 35-39 nm in diameter with “cuplike cavities” (indentations) on the surface of the virion
ADDITIONAL DIAGNOSTIC TESTS:
- Viral isolation, electron microscopy, serology, DNA probes, indirect fluorescent antibody staining (IFA)
- Sealpoxvirus: Verrucous, self-limiting dermal nodules of skin and oral mucosa; histologic findings include acanthosis, ballooning degeneration, and eosinophilic intracytoplasmic viral inclusion bodies
- Caliciviruses in the SMSV group have been identified in many species of sea lions, seals, dolphins, whales, and terrestrial animals (feral swine, feral donkeys, gray foxes, domestic ruminants, and mink). SMSV serotype 7 isolated from opaleye fish
- 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
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