A serum neutralization test for infectious bovine rhinotracheitis based on colour reaction and cytopathic effects in cell culture.

A serum neutralization (SN) test based on a combination of indicator colour change in medium and cytopathic (CP) effect in cells has been devised for the detection of infectious bovine rhinotracheitis antibodies. Serum dilutions of 1:6, 1:18 and 1:54 are made in a medium containing phenol red and are mixed in equal quantities with a suspension of virus containing 100 cell culture infectious doses (CCID(50)) per volume of mixture. The serum-virus mixtures are held in small glass tubes and are covered with a layer of mineral oil. Following a two hour period of incubation at 37 degrees C a quantity of bovine fetal kidney cells is added to each tube to detect the presence of unneutralized virus. After four to six days incubation the results of the SN test may be read by microscopic examination for CP effect by means of an inverted microscope, or by observing the colour of the phenol red.