Prevalence of Helicobacter hepaticus, murine norovirus, and Pneumocystis carinii and eradication efficacy of cross-fostering in genetically engineered mice.

We investigated the prevalence of Helicobacter hepaticus, murine norovirus (MNV), and Pneumocystis carinii and the efficacy of cross-fostering for their eradication in 49 genetically engineered mouse (GEM) strains at our institute. Prevalences of H. hepaticus, MNV, and P. carinii were 33.9, 36.5, and 8.6%, respectively, and immunodeficient strains showed relatively higher prevalence of the 3 pathogens than immunocompetent strains. Additionally, the same immune phenotype strains showed similar prevalences. Furthermore, it was found that NKT cells might play a role in H. hepaticus resistance. Interestingly, there was a high incidence of H. hepaticus and MNV multiple infection. Strains with single or multiple infections of H. hepaticus, MNV, and/or P. carinii were selected, and cross-fostering was conducted. Cross-fosterings were successful at eradicating P. carinii, but there were some failures for H. hepaticus and MNV, and the efficacy of eradication was relatively low compared with previous studies. We thought that this low efficacy might have been due to persistent infection and the high suscepibility to H. hepaticus and MNV of immunodeficient GEM strains. Therefore, cross-fostering may be appropriate for P. carinii eradication, but be inappropriate for repopulation of a new breeding colony with H. hepaticus or MNV infected GEM strains. Our findings provide basic data on maintenance, strain susceptibility, and successful rederivation, especially for GEMs.