MHV or not MHV, that is the question!
Abstract for National AALAS Presentation
Late Breaking News Session, November 8, 1999
Submitted by The Jackson Laboratory Animal Health Staff James R. Fahey, PhD, DVM, dip ACVM (Head of Diagnostic Laboratory), Terrie Cunliffe-Beamer, DVM, MS, dip ACLAM (Head of Clinical Laboratory Animal Health), Peggy J. Danneman, VMD, MS, dip ACLAM (Acting Director of Laboratory Animal Health), John P. Sundberg, DVM, PhD, dip ACVP (Head of Pathology, Senior Staff Scientist)
Mouse Hepatitis Virus (MHV) is a term that refers to a spectrum of enveloped, positive sense ssRNA coronaviruses that vary greatly in their tropism for host tissues and pathogenicity. This variation in tissue tropism and pathogenicity are among the factors that can make detection of MHV in laboratory mouse colonies a diagnostic challenge. Currently, the available methods of MHV diagnosis include serologic assays (ELISA, IFA), electron microscopy, histopathology and molecular techniques (RT-PCR, etc). Assurance of an accurate diagnosis of MHV infection is greatest when a combination of the above-mentioned tests is used. In response to recent MHV outbreaks in lab animal facilities throughout the United States, The Jackson Laboratory (TJL) undertook extensive testing for MHV in our production colonies. The primary testing consisted of serologic screening by ELISA in all production colonies. Of more than 2400 ELISA tests performed more than 98% were negative. A few samples gave nonspecific tissue reactions that could not be interpreted as either positive or negative. As a result, nonspecific ELISA tests were generally followed-up by IFA testing. In addition to serology, we also performed RT-PCR on more than 370 mouse fecal RNA extracts using 1,2,or 3 primer sets, each of which recognizes a non-overlapping region of the MHV genome. One primer set gave weak - and inconsistent - positive results on several fecal samples. These weak positive results from fecal samples were never positive with the other two primer sets, nor could any viruses be found in fecal samples from these putatively positive mice by negative stain electron microscopy. In addition to the above testing, we performed necropsy and histopathology on DBA/2J sentinel mice that were housed in the cages of putatively infected mice. No histopathologic lesions consistent with MHV infection were found. The results of our study will be used to discuss the importance of using multiple testing methods to diagnose MHV infections of mice and also the pitfalls of accepting data from single tests as proof of an MHV outbreak.
