The $$P_{24}^{37}$$ Modification of The Infectious Bovine Rhinotracheitis Virus-Serum Neutralization Test

The applicability of a modified infectious bovine rhino-tracheitis constant-virus/varying-serum neutralization test, with preincubation of virus-serum mixtures at 37°C for 24 hrs. ( $$P_{24}^{37}$$ test) as against 1 hr. in the conventional ( $$P_{1}^{37}$$ ) test, was elucidated by examination of about 5000 bovine sera. The sensitivity of the test was studied mainly in parallel $${{P_{24}^{37}} \mathord{\left/ {\vphantom {{P_{24}^{37}} {P_1^{37}}}} \right. } {P_1^{37}}}$$ testings of sera from animals in two infected herds and of sera taken from a bullock during one month following nasal infection. In agreement with conclusions in previous papers, the $$P_{1}^{37}$$ test appeared to be inadequately sensitive, and the $$P_{24}^{37}$$ test regularly gave titers that were about 4 in logs higher than the $$P_{1}^{37}$$ titers, which means that the $$P_{24}^{37}$$ test is about 16 times as sensitive as the conventional test. From examinations of 4902 sera from four different groups of cattle it was concluded that with the technique described and with the use of undiluted serum, the specificity of the $$P_{24}^{37}$$ test would be as good as 0.999. The observed high sensitivity and specificity of the $$P_{24}^{37}$$ test give high diagnostic values of both negative and positive reactions.