Prevalence of rat virus infection in progeny of acutely or persistently infected pregnant rats

Infant rats are susceptible to persistent rat virus (RV) infection, but risk of persistent infection after prenatal exposure to virus is unclear. We examined this aspect of RV infection in the progeny of dams inoculated with virus during or prior to pregnancy. Sprague-Dawley (SD) dams were infected during pregnancy (gestation day 9) by oronasal inoculation with 10(5) TCID50 of the UMass strain of RV. SD rats were infected prior to pregnancy by oronasal inoculation of two-day-old females with 10(2) TCID50 of RV-UMass, which induced persistent infection. They were mated to non-immune males after reaching sexual maturity. Rats were assessed for RV infection by virus isolation, in situ hybridization, contact transmission, or serologic testing. The progeny of dams inoculated with virus during gestation had high prevalence of infection through postpartum week 9 (9 of 12 rats were virus positive at week 3, and 7 of 10 were virus positive at week 9). Additionally, 2 of 10 rats were virus positive at least through postpartum week 15. The progeny from persistently infected, seropositive dams had no evidence of infection and did not transmit infection to contact sentinels. However, 12 dams were virus positive at necropsy and 9 had transmitted infection to their breeding partners. These results indicate that prenatal infection in non-immune dams can lead to RV persistence in their progeny. By contrast, the progeny of persistently infected dams are protected from infection, presumably by maternal antibody, although their dams can transmit infection to their breeding partners.