DNAViruses

Several different types of DNA-viruses may infect rodents and rabbits, the major problem in rodents of today being parvoviruses. Except for the poxviruses, most DNA-viruses do not produce overt disease, but they may often have essential impact on research. As a rule of thumb, DNA-viruses cause persistent infection.

Parvoviruses

Parvovirus infections in rats have traditionally been known to be caused especially by two viruses, Kilham rat virus (KRV) and Toolan's H1 virus (H1),100 while in mice, they have been caused by minute virus of mice (MVM).101 Antibodies are mostly detected by serology. Several antigenic types of parvoviruses are known, but KRV and H1 strains share common antigens and therefore cross-react in solid-phase serological assays. Orphan parvoviruses, a group of rodent parvoviruses distinct from MVM, KRV, and H1, were first discovered by the fact that antibodies to known rodent parvoviruses were detected by the immunofluorescence assay (IFA) but not by hemagglutination inhibition assay (HAI) in commercial breeding colonies of rats and mice.102 Today, OPVs have been isolated from mice, rats, and hamsters, and they have further been divided into mouse parvovirus (MPV), rat parvovirus (RPV), and hamster parvovirus (HPV). RPV is assumed to be a variant of KRV,103 while MPV resembles MVM in genome size, replication intermediates, and nonstructural proteins.104 Cross-infection between species-specific strains does not seem to occur.103 Horizontal transmission by fecal-oral contact is the most common. Vertical transmission is reported for some serotypes105 but normally is not seen after the infection has balanced in the colony and the female breeders have developed protective immunity. Intrauterine infections may be observed in rare cases. The prevalence among adult animals is normally high, 50 to 80%, but lowers (sometimes even to zero) after a period of infection. MVM, H1, MPV, RPV, and HPV are not known to cause any clinical disease, while some KRV-serotypes have been reported to cause jaundice and ataxia in rats less than 10 days of age. Parvoviruses require a protein produced by the host cell during the S phase and, therefore, only replicate in rapidly dividing cells. In rats infected prior to the fourth day of life, intranuclear inclusions are present in the actively mitotic cells composing the external germinal layer of the cerebellum. This leads to necrosis, thereby preventing the normal development of the cerebellum and resulting in granuloprival cerebellar hypoplasia. Also, hepatitis with intranuclear inclusions in the hepatocytes has been reported. Parvovirus infections in rats were previously fairly common in Europe,106 while it is far less common in mice. Results from Japan suggest that parvovirus infection in rats is most often caused by RPV.107

Rabbits may also harbor a parvovirus. Clinical signs in neonatal rabbits consist of anorexia and listlessness, while pathological signs are mostly located in the small intestines.108,109,110

Table 11.2 Virus Infections Observed in Mice (M), Rats (R), Guinea Pigs (GP), Syrian or Chinese Hamsters (H), and Rabbits (RB)

DNA-viruses

Table 11.2 Virus Infections Observed in Mice (M), Rats (R), Guinea Pigs (GP), Syrian or Chinese Hamsters (H), and Rabbits (RB)

Adenoviridae

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