Use of a constant-virus diluting-serum microneutralization technique for the detection and quantification of...

A constant-virus diluting-serum microneutralization test (CVMNT) for avian infectious bronchits virus (IBV) was evaluated for both reliability and repeatability. The virus used in the assay was a chick kidney (CK) cell-adapted strain, the Beaudette strain (IBV 42). Sera tested were from 24-week-old broiler-breeder chickens that had been vaccinated 3 times from a combination vaccine of Newcastle disease virus (NDV) and IBV. Test results were not repeatable or comparable when the same sera were tested on different days, but test results were repeatable and comparable when the sera were tested on the same day. Differences in virus titer at the different times that tests were performed appeared to cause the variation in test results. A comparison was made between the CVMNT and a constant-serum diluting-virus microneutralization test (CSMNT). The CVMNT was able to detect differences in flock antibody titers that the CSMNT could not.