Diagnosis of mouse hepatitis virus contamination in mouse population by using nude mice and RT-PCR.

Mouse hepatitis virus (MHV) infection in laboratory mouse populations is a serious problem, because the MHV infections are known to interfere with research results. Confirmation of indirect serological detection methods by viral isolation is difficult. Reverse transcription plus polymerase chain reaction (RT-PCR) was used to test 94 mouse tissue samples from suspected naturally MHV infected mice. Positive results were only obtained from two colon samples and one mixed sample with colon and liver. The low positive rate is probably due to the virus being rapidly cleared by the MHV antibodies produced in the mouse. However, RT-PCR detection of MHV in nude mice placed in the same cages with other non-nude mice or placed in cages with used dirty bedding, showed a very high positive rate: 10 out of 12 colon samples were positive (83%), and 5 out of 10 faecal samples were positive (50%). A single-tube, single step RT-PCR method and two procedures for isolation of the viral RNA for the RT-PCR assay were also included in this article.