Identification of seven isolants of infectious bronchitis virus by interference with the B-1 isolant of Newcastle disease virus.

Seven isolants of infectious bronchitis virus (IBV) interfered with the development of hemagglutinins (HA) by the B-1 isolant of Newcaslte disease virus (NDV) in eggs previously inoculated with these IBV isolants. The I50 [defined as the minimum amount of IBV needed to produce, upon inoculation in embryonating chicken eggs (ECE), HA interference in 50% of these ECE reioculated 10 hr later with 10(2,41 EID50 (HA) of the B-1 strain of NDV] was less than 1 EID50. The interference was considered specific for IBV because if could be eliminated by addition of homologous anti-IBV serum. Furthermore, three other common poultry viruses (laryngotracheitis, fowlpox, and CELO viruses) did not interfere with NDV. In view of its sensitivity, specificity, and simplicity of performance, the IBV-NDV interference test appears to have considerable potential as a diagnostic test for IBV under field conditions.