JPC SYSTEMIC PATHOLOGY
SIGNALMENT: A 7-day-old CD rat.
HISTOPATHOLOGIC DESCRIPTION: Small intestine: Diffusely up to 80% of the villi are mildly to moderately blunted, atrophic and fused, and lined by attenuated to cuboidal epithelial cells. Epithelial cells at the tips of the villi are often swollen/hypertrophied and contain abundant, pale eosinophilic, vacuolated cytoplasm. Multifocally, villous tip enterocytes form syncytia with abudant pale flocculant cytoplasm, and containing up to 15 nuclei. Enterocytes are multifocally necrotic, characterized by shrunken, eosinophilic cytoplasm, pyknotic nuclei and replacement by karyorrhectic debris. The lamina propria is mildly expanded by low numbers of lymphocytes, plasma cells, neutrophils and eosinophils.
MORPHOLOGIC DIAGNOSIS: Small intestine: Villar blunting, atrophy and fusion, diffuse, moderate, with multifocal epithelial vacuolar degeneration and viral syncytia, CD rat, rodent.
ETIOLOGIC DIAGNOSIS: Rotaviral enteritis
CAUSE: Type B (atypical) rotavirus
CONDITION: Infectious Diarrhea of Infant Rats (IDIR)
- Type B (atypical) rotavirus is a non-enveloped, icosahedral, double-stranded RNA virus that causes diarrhea in rats less than two weeks of age; older animals (over two weeks of age) are susceptible to infection, but do not show clinical signs of disease; susceptible to clinical disease up to 12 days of age
- Family Reoviridae, genus Rotavirus, group B
- Atypical viruses (group B-G) are morphologically identical to typical and most common rotaviruses (group A) but do not share common capsid antigens
- Group A rotavirus is ubiquitous; very host specific
- Heat, pH, and desiccation stable; inactivated by disinfectants
- Initial target sites are villi tips and goblet cells of top one half to two thirds of small intestine villi
- Oral ingestion > uptake of virus by mature enterocytes > direct penetration of cell membrane or receptor-mediated endocytosis > replication in cytoplasm > released by cell lysis > villar atrophy (determines severity of disease) > diarrhea
- Pathogenic effects result from three causes (1) malabsorption (2) villus ischemia (3) secretory exotoxin, NSP4
- Viral antigens are present in affected enterocytes; syncytia and viral antigen are present only in the first 18-24 hours; then rapidly decrease in number
- High morbidity, low mortality
- Maternal IgG is protective during the first week of life
TYPICAL CLINICAL FINDINGS:
- Diarrhea 24-36 hours post infection; watery diarrhea for 5-6 days followed by full recovery
- Anorexia, poor growth (runts), weight loss, erythema, cracking and bleeding of the perianal skin
- Rats resistant after 2 weeks of age
TYPICAL GROSS FINDINGS:
- Stomach is usually filled with milk
- Distal small intestine and large intestine contain yellow brown to green fluid, poorly formed fecal pellets, gas and occasionally mucinous material
- Other organs are not remarkable
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Affects distal small intestine (jejunum and ileum) with ileum having most significant lesions
- Villus attenuation, villus epithelial necrosis (luminal one-third of the villi)
- Pathognomonic epithelial syncytia with up to 15 nuclei (from 18-24 hours only); +/- eosinophilic intracytoplasmic inclusions possible in syncytia
- Characteristic “wagon wheel” appearance of cytoplasmic virions
ADDITIONAL DIAGNOSTIC TESTS:
- Characteristic gross and microscopic findings and demonstration of rotaviral particles in tissue sections or intestinal contents
- Electron microscopy of epithelial syncytial cells and negatively stained feces or intestinal contents
- Indirect immunofluorescent staining
- PCR has been developed for bovine group B & F rotaviruses
Causes of diarrhea in rats:
- Bacteria: Clostridium piliforme, Salmonella, E. coli, Streptococcus Group D, Campylobacter sp.
- Parasites: Giardia muris, Spironucleus muris, Syphacia obvelata, muris, Aspicularis tetraptera
- Group A rotaviruses are far more common and infect humans (mostly infants), laboratory animals, wildlife, and domestic animals:
- Mice: Cause of epizootic diarrhea of infant mice (EDIM); like IDIR, infection possible at all ages with clinical disease apparent only in animals <2 weeks old; highly contagious; effects are transient
- Rabbits: diarrhea in suckling and weanling animals; often seen in co-infection with enteropathogenic coli or coccidian
- Cattle: Important cause of diarrhea in beef and dairy neonatal calves >5 days old up to 2-3 weeks old; disease is mild and transient but can be severe when co-infected with coli or coronavirus
- Pigs: May cause “3-week” or “white” scours in postweaning piglets 2-8 weeks of age; also affects older pigs that are susceptible; clinical signs are similar to but less severe than transmissible gastroenteritis
- Lambs: Diarrhea in neonatal lambs alone or in combination with coli or Cryptosporidium sp.; virus may infect the colon unlike in other species
- Foals: Diarrhea in foals <3-4 months of age; rare mortality; but, co-infection common with Salmonella and Cryptosporidium spp.
- Dogs and cats: Rare but can cause diarrhea in puppies and kittens <2 weeks of age
- Poultry: Subclinical infection or diarrhea in poults and chicks
- Almeida PR, Lorenzetti E, Cruz RS, et al. Diarrhea caused by rotavirus A, B, and C in suckling piglets from southern Brazil: molecular detection and histologic and immunohistochemical characterization. J Vet Diagn Invest. 2018 May;30(3):370-376.
- Balasuriya UBR, Stott JL. Reoviridae. In: Hirsh DC, MacLachlan NJ, Walker RL, eds. Veterinary Microbiology. 2nd ed. Ames, IA: Blackwell Publishing; 2004: 404-406.
- Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016:37-38, 267-268.
- Beserra LA, Gregori F. Description of rotavirus F in broilers from Brazilian poultry farms. Avian Dis. 2014 Sep;58(3):458-61.
- Conner ME, Ramig RF. Viral enteric diseases. In: Nathanson N, ed. Viral Pathogenesis. Philadelphia, PA: Lippincott-Raven Publishers; 1997: 720-743.
- Day JM. Rotavirus Infection. In: Swayne DE, ed. Diseases of Poultry. 13th ed., Ames, IA: Iowa State University Press;2013:281-291.
- Frederick J, Giguere S, Sanchez LC. Infectious agents detected in the feces of diarrheic foals: a retrospective study of 233 cases (2003-2008). J Vet Intern Med. 2009;23:1254-1260.
- Gelberg HB. Alimentary System and the Peritoneum, Omentum, Mesentery, and Peritoneal Cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:374-375.
- Huber AC, Yolken RH, Mader LC, Strandberg JD, Vonderfecht SL. Pathology of infectious diarrhea of infant rats (IDIR) induced by an antigenically distinct rotavirus. Vet Pathol. 1989; 26:376-85.
- Uzal FA, Platter 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: 112;115-117;151-153.
- Zachary JF. Mechanisms of Microbial Infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:200.