A Modified Direct Complement Fixation Test for the Detection of Antibodies in the Serum of Cattle Previously Infected with Vesicular Stomatitis Virus

Abstract

Summary A modified direct complement fixation method for the detection of antibodies in heat-inactivated sera of cattle infected with vesicular stomatitis virus is described. The addition of fresh unheated bovine serum to the diluted guinea pig complement constitutes the only modification. In its absence no fixation of complement is observed. The normal serum supplying the apparently essential heat-labile factor, is pretested for absence of nonspecific reactivity with test antigen. Sera of animals around 6 months of age show less nonspecific reactivity than sera of adult cattle. This method when applied in testing serial bleedings from cattle infected with either the New Jersey or Indiana type of vesicular stomatitis virus, detected the antibodies 9 to 10 days after intralingual infection. Antibodies were demonstrable at a diagnostic level for at least 90 days afterward. The test was shown to be sufficiently specific to indicate the type of virus in epithelial tongue tissue collected at the acute stage of infection and to reveal the type-specificity of the antibodies in serum of convalescent cattle. In indirect complement fixation tests, the inhibition titers of early convalescent sera were much lower than those recorded in the modified direct complement fixation test. The difference was negligible with hyperimmune sera.