Comparative sensitivity of infectivity assay and mouse antibody production (MAP) test for detection of mouse thymic virus (MTLV).

Mouse thymic virus (murid herpesvirus-3; MTLV) is a naturally occurring T lymphotropic herpesvirus of mice. We compared the sensitivity of infectivity assay, which tests for induction of thymic necrosis in newborn mice, and an enzyme immunoassay (ELISA)-based modified mouse antibody production (MAP) test. Infection in adult mice was verified by infectivity assay of salivary glands. Approximately ten times as much virus was required to infect adult mice as newborns. No adults became infected at the lowest dose (just below 1 ID50 by thymic necrosis in newborn mice); a dose tenfold higher resulted in both infection and seroconversion in three out of five mice. At higher doses tested (up to 8000 ID50), all mice became infected and seroconverted. Infected mice shed virus and remained seropositive for at least six months. False positives were observed in ELISA; these could be eliminated by adding control (uninfected) thymic homogenate (1/10 volume of a 10% homogenate) to the sample diluent. These data suggest that the MAP assay can be a reliable and sensitive indicator of infection in adult mice undergoing primary infection. Although slightly less sensitive than infectivity assay for detecting MTLV, the MAP test is likely to detect most samples containing virus. It is recommended that several mice be used for each sample and that all positive serum samples be retested with control thymic homogenate for increased reliability.