Studies with Rinderpest Virus ill Tissue Culture III. The Stability of Cultured Virus and its Use in Virus Neutralization Tests

Abstract

The stability of cultured rinderpest virus, in maintenance medium containing 5% normal ox serum, was studied at 4°, 37°, and 56° C. The half-life at these temperatures was calculated and the results compared with figures available for other strains of rinderpest virus in cattle tissues and for measles virus in tissue culture fluids. Data were also provided on the freezing of the same virus at _25° C and _70° C, with storage for periods of up to four months. The accuracy of replicate virus titrations, in primary or serially-cultivated calf-kidney cells, was determined. Details were given of tissue culture techniques for the detection and titration of neutralizing antibody to rinderpest virus in the sera of animal especially cattle. Box titrations of a standard ox immune serum showed that a 1 log increase in virus dose lowered the SN 50 titre of the serum by a mean 0.56 log units. The error in replicate titrations of two standard immune Hera, using different batches of calf-kidney cells as substrate, was determined. The effect of normal ox serum on rinderpest virus was investigated and the sera of over 3.000 experimental cattle were examined by a "screening" test for immunity. There were no false positives and only 0.25% of the serologically-negative cattle gave later evidence of resistance to challenge. Tissue culture techniques for the detection and titration of rinderpest neutralizing antibody are briefly compared with the methods hitherto available.