Transmission of mouse parvovirus to neonatal mice

To investigate the infection of newborn mice with mouse parvovirus (MPV), a single MPV-infected mouse was added to each of 15 cages, each of which housed an uninfected breeding pair of Swiss Webster mice just before parturition. Seven litters were left with their parents, and the remaining 8 litters were fostered at postpartum day 1. All dams were shedding MPV at 1 and 2 wk after exposure. Soiled-bedding transmission did not differ between cages with and without litters. Half the foster dams but none of the fostered pups seroconverted to MPV. None of the pups left with their birth mothers had MPV DNA in their feces at 3 or 6 wk after exposure, but pups in 6 of 7 litters were MPV seropositive at 6 wk. To investigate MPV infection of older neonatal mice, 9 dams with 7-d-old litters and 9 dams with 14-d-old litters each were exposed to an MPV-infected mouse. At weaning, pups exposed to MPV at 7 or 14 d of age were shedding MPV and were seronegative but became seropositive by 6 wk of age and transmitted the infection to sentinels. In conclusion, fostering of pups had no benefit and may spread infection because the pups may act as fomites, infecting the foster dam. Infection of 7- or 14-d-old mice likely occurred because maternal antibodies had not been transferred to the progeny before they began to ingest MPV-laden feces.