Etiology: Parvoviruses are single stranded nonenveloped DNA viruses. Multiple species of parvoviruses in rats include Rat Virus (RV or Kilham rat virus), H-1 (Toolan’s H-1 virus), Rat Minute Virus (RMV 1a, 1b and 1c) and Rat Parvovirus 1 and 2 (RPV-1, RPV-2). Of these, RV is the only virus species reported to cause clinical disease in rats. The other parvoviruses are antigenically distinct from RV, and have not been associated with naturally-occurring disease.
Incidence: Incidence of infection is low.
Transmission: Transmission occurs primarily by direct contact or contact with fomites.
Clinical Signs: Parvovirus infections are usually subclinical. Clinical disease from RV has been reported when virus was introduced to a naive population. In newly infected breeding colonies, RV may cause decreased fertility, fetal resorption, small litters, and runting of pups. RV infection in juvenile and young adult male rats may result in lethal disease from hemorrhage and necrosis of brain and gonads.
Pathology: RV infects actively replicating cells and causes cytolysis. Lesions associated with RV infection include cerebellar hypoplasia (A., 10X and B., 40X), hemorrhagic infarction, thrombosis of multiple organ systems, focal necrosis, hypertrophy, and vacuolar degeneration of hepatocytes. No pathology has been associated with other parvovirus infections.
Diagnosis: Serologic assays (MFI, IFA) are used for virus identification. PCR assays of feces and mesenteric lymph node tissue can be used to identify and speciate parvovirus infection in rats.