Use of polymerase chain reaction to diagnose a natural outbreak of mouse hepatitis virus infection in nude mice.

The enormous cost of eliminating mouse hepatitis virus (MHV) from a mouse colony demands that a confirmed etiologic diagnosis be made to justify the necessary remedial action. We describe an outbreak of MHV in nude mice in which histopathologic findings provided a presumptive diagnosis, but results of serologic testing of affected nude mice and immunocompetent sentinels were negative. Results of transmission electron microscopy of liver specimens from affected mice were equivocal. Confirmation of the etiopathogenesis was eventually provided by reverse transcriptase-polymerase chain reaction (RT-PCR), using primers with nested sequences directed to two separate but highly conserved regions of the MHV genome. This procedure detected MHV in the liver of an affected nude mouse and in a sentinel, although in the latter a positive result was obtained only because of the increased sensitivity of nested primers used in a second round of amplification. Virus was not detected in cell lines that had been injected into the mice, and the source of the outbreak was not found. These results indicate the applicability of RT-PCR for detecting MHV in a field situation while also illustrating that conventional, complementary techniques still have an essential role in reaching a diagnosis. It is recommended that specimens should be taken for histologic examination and serologic testing, as well as for molecular studies when MHV infection is suspected.