Eliminating murine norovirus by cross-fostering

Murine norovirus (MNV) is a newly discovered and extremely prevalent pathogen of laboratory mouse colonies. MNV causes severe disease in some immunocompromised mouse strains and can cause persistent infections even in immunocompetent mice. Despite the fact that immunocompetent mice are generally asymptomatic, the possibility that MNV infection might alter immune responses makes its eradication a potentially useful goal for many facilities. Initial attempts by others to use a strategy of testing and culling were unsuccessful, whereas complete depopulation and facility decontamination was successful. However, these measures may be impractical, and finding less drastic approaches seemed prudent. Based on a report that cross-fostering of pups from MNV-positive mothers to MNV-negative ones could be successful in experimental MNV infection, we undertook a comprehensive fostering program using Swiss Webster mothers, careful sanitary measures, and fecal PCR testing to eradicate the virus from a mouse colony recently infected with MNV. We successfully decontaminated 17 of 18 (94%) litters and managed to prevent spread when a new MNV-infected mouse strain entered quarantine at our facility. These results suggest that cross-fostering, when performed in a setting of excellent sanitary procedures, may be practical for the large number of mouse facilities in which MNV is endemic.