Transmission probabilities of mouse parvovirus 1 to sentinel mice chronically exposed to serial dilutions of contaminated bedding.

Intermittent serodetection of mouse parvovirus (MPV) infections in animal facilities occurs frequently when soiled bedding sentinel mouse monitoring systems are used. We evaluated induction of seroconversion in naïve single-caged weanling ICR mice (n = 10 per group) maintained on 5-fold serially diluted contaminated bedding obtained from SCID mice persistently shedding MPV1e. Soiled bedding from the infected SCID mice was collected, diluted, and redistributed weekly to cages housing ICR mice to represent chronic exposure to MPV at varying prevalence in a research colony. Sera was collected every other week for 12 wk and evaluated for reactivity to MPV nonstructural and capsid antigens by multiplex fluorescent immunoassay. Mice were euthanized after seroconversion, and DNA extracted from lymph node and spleen was evaluated by quantitative PCR. Cumulative incidence of MPV infection for each of the 7 soiled bedding dilution groups (range, 1:5 to 1:78125 [v/v]) was 100%, 100%, 90%, 20%, 70%, 60%, and 20%, respectively. Most seropositive mice (78%) converted within the first 2 to 3 wk of soiled bedding exposure, correlating to viral exposure when mice were 4 to 7 wk of age. Viral DNA was detected in lymphoid tissues collected from all mice that were seropositive to VP2 capsid antigen, whereas viral DNA was not detected in lymphoid tissue of seronegative mice. These data indicate seroconversion occurs consistently in young mice exposed to high doses of virus equivalent to fecal MPV loads observed in acutely infected mice, whereas seroconversion is inconsistent in mice chronically exposed to lower doses of virus.