JPC Systemic Pathology
Signalment (JPC #1171326): A guinea pig
HISTORY: Incidental finding
HISTOPATHOLOGIC DESCRIPTION: Salivary gland: Multifocally within periductal areas the interstitium is expanded by moderate numbers of lymphocytes and fewer plasma cells and macrophages, admixed with small amounts of necrotic cellular and karyorrhectic debris. Multifocally, rare acinar cells are enlarged up to ten times normal (cytomegaly), with abundant eosinophilic granular cytoplasm and one to two nuclei containing an 8-12 um diameter, deeply eosinophilic, round to oval intranuclear inclusion body which marginates the chromatin (“owl eye cells”). Multifocally, there is deeply basophilic mineral.
MORPHOLOGIC DIAGNOSIS: Salivary gland: Sialoadenitis, lymphoplasmacytic, multifocal, mild, with rare acinar eosinophilic inclusion bodies, breed unspecified, guinea pig (Cavia porcellus), rodent.
ETIOLOGIC DIAGNOSIS: Herpesviral sialoadenitis
CAUSE: Guinea pig cytomegalovirus (GPCMV); Caviid herpesvirus 2
- Common incidental finding in guinea pigs, affecting up to 70-80% of adults
- Animal model for human cytomegalovirus infection
- Cytomegaloviruses belong to the family Herpesviridae, subfamily betaherpesvirus; species-specific
- dsDNA virus with fibrous core, icosahedral capsid
- Replicates in host cell nucleus; acquires envelope by budding through the host nuclear membrane; fragile, does not survive in environment
- Transmission requires close contact with infected body secretions (e.g. coitus, nursing, closely confined populations)
- Latent phase, with relapses during periods of stress
- Transmission via exposure to infected saliva or urine or transplacentally
- Guinea pigs are used as an animal model because both humans and guinea pigs have hemochorial placentation with a single trophoblast layer; transplacental transmission and fetal infection occur in both species
- Maternal and fetal outcomes are dependent on many variables (timing and route of infection, strain of guinea pig, source of virus and maternal immunity); viral inoculation early in pregnancy tends to lead to pup resorption, whereas challenge in late pregnancy tends to lead to pup mortality; maternal immunity may reduce in utero transmission and improve fetal outcomes
- Salivary glands, kidney and liver are the primary target tissues for GPCMV in the guinea pig
TYPICAL CLINICAL FINDINGS: None
TYPICAL GROSS FINDINGS: None
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Lesions are primarily to the ductal epithelial cells of the salivary glands
- Karyomegaly with large eosinophilic intranuclear inclusion bodies that marginate chromatin (“owl eye cells”)
- Lymphoplasmacytic or neutrophilic inflammation
- Interstitial pneumonitis and multifocal necrosis within lymph nodes, spleen, liver, kidney, and lung may be present in acute systemic form of the disease
- Viral isolation from actively shedding animals
- Serology (ELISA)
- In situ hybridization
DIFFERENTIAL DIAGNOSIS: (For intranuclear inclusions)
- Guinea pig herpes-like virus (Caviid herpesvirus 1): Isolated from many strains of guinea pigs; no clinical signs; no gross or microscopic lesions; produces intranuclear inclusions in degenerating kidney cell cultures
- Guinea pig X virus (Caviid herpesvirus 3): Experimentally, Hartley guinea pigs develop focal hepatic necrosis and mortality; has not been shown to cause natural disease, but could be a complicating factor in laboratory animals
- Guinea pig adenovirus infection: Large basophilic intranuclear inclusions in respiratory epithelium; severe pneumonia
- Mouse CMV: uncommon in laboratory mice; inclusion body sialoadenitis a typical lesion; does not cross the placenta
- Swine (Suid herpesvirus-2) - inclusion body rhinitis: mild to severe nonsuppurative necrotizing rhinitis in pigs <4 weeks of age
- Non-human primates: Common asymptomatic infection in many species of NHP; rhesus CMV (macacine herpesvirus-3) can cause disease in immunosuppressed macaques including disseminated lesion in brain, lymph nodes, liver, spleen, kidney, small intestine and nervous system
- Chimpanzee: Disseminated CMV infection in captive chimpanzees; occasional intranuclear inclusions in myocardium, retina, brain, salivary gland, spleen, lymph node, stomach, tonsil, pancreas, intestine, arteries and adrenal gland
- Horses (Equid herpesvirus-2, EHV-2): found in normal horses and foals with respiratory disease
- Bovine (bovine herpesvirus-4, BoHV-4): important cause of abortion; classified as a gammaherpesvirus
- Human cytomegalovirus (HCMV): Most frequent congenital infection worldwide; leading cause of sensorineural hearing loss, developmental delay, and neurological deficits; transplacental transmission during maternal viremia
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