Seroconversion of 1-year-old Mice to Murine Norovirus.

Rodent sentinel screening for adventitious pathogens is an integral part of many biomedical research institutes and universities that use rodents in research. Typical screening programs involving live sentinel animals typically purchase youngSPF sentinel animals that are sampled and replaced quarterly. Previous reports suggest that mice as old as 6 mo are effectivesentinels for various agents. In efforts to reduce the number of animals used in our sentinel program, we wanted to investigatethe possibility of keeping sentinel animals inhouse for 12 mo at a time. We exposed mice (age, 40 to 48 wk) to murinenorovirus (MNV) to test whether they could reliably produce detectable levels of antibodies (similar to younger mice) tothis adventitious pathogen. Mice first exposed to MNV at 40 to 48 wk of age seroconverted to MNV after both direct inoculation(through gavage) and indirect exposure (from soiled-bedding transfer) at the same or greater frequency than mice firstexposed at 8 to 12 wk of age. These findings indicate that, at least for MNV, sentinel residence time can be extended from 3to 12 mo without compromising the reliability of seroconversion, thus ultimately reducing sentinel animal numbers. Thispractice, combined with nonanimal testing modalities (for example, exhaust duct sampling), can increase the sensitivity andspecificity of rodent surveillance programs and minimize the use of live animals.