Infectious center assay of intracellular virus and infective virus titer for equine mononuclear cells infected in vivo and in vitro with equine herpesviruses.

A novel, simple method of infectious center assay was developed to detect and quantitate the intracellular existence of equine herpesvirus 1 and equine herpesvirus 2 in peripheral blood mononuclear cells infected in vivo and in vitro with the viruses by cocultivation of these cells with a permissive equine cell culture. The infectious center titers were correlated with the infectious virus titers. In vivo equine herpesvirus 1-infected mononuclear cells obtained from ponies experimentally infected with the virus and equine herpesvirus 2-infected mononuclear cells obtained from selected naturally infected ponies with the virus gave by infectious center assay a mean value of 67 infectious center/2 x 10(6) cells as a peak titer on day 4 postinfection and 26 infectious center/2 x 10(6) cells for equine herpesvirus 1 and equine herpesvirus 2 respectively. The mononuclear cells, in both cases, did not contain detectable infectious virus, but the infectious virus was detected from the respective cells when they were cultured in the presence of mitogen. The equine herpesvirus 1 infected mononuclear cells in culture gave a mean count of 8.05 x 10(2) infectious center/2 x 10(6) cells/mL and contained 1.08 x 10(4) plague assay/mL of infectious virus. Similarly the equine herpesvirus 2 infected mononuclear cells in culture gave a mean count of 7.1 x 10(1) infectious center/2 x 10(6) cells/mL and contained <10(1) tissue culture infective dose(50)/mL of infectious virus. Mononuclear cells infected in vitro with equine herpesvirus 1 gave a mean count of 9.3 x 10(4) infectious center/2 x 10(6) cells/mL and contained 5.75 x 10(3) plaque assay/mL of infectius virus. Culturing these cells in the presence of mitogen gave a mean count of 5.5 x 10(3) infectious center/2 x 10(6) cells/mL and contained 9 x 10(3) plague assay/mL of infectious virus. A correlation between infectious center assay and infectious virus assay is discussed.