Comparison of a Tissue-Culture Virus-Neutralization Test and the Enzyme-Linked Immunosorbent Assay for Measurement of Antibodies to Infectious Bronchitis

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Abstract
Two serological tests, the virus-neutralization (VN) test in tissue culture using a tissue-cell-adapted virus and the enzyme-linked immunosorbent assay (ELISA), were compared to detect antibodies against Massachusetts [M] 41 and Connecticut [C] 46 strains of infectious bronchitis virus (IBV). The VN test was conducted in wells of microplates. The 2 strains of IBV were adapted after 20 serial passages to induce a cytopathic effect in 24 h in chicken embryo kidney cells (CEKC). The ELISA test was carried out using partially purified virus as antigen following ultracentrifugation of each strain of IBV. The ELISA test detected higher geometric mean antibody titers (GMT) against both strains of IBV than did the VN test. Serum samples (104) taken at 1, 3, 5, 9, 22, 24 and 26 wk of age from a flock of chickens vaccinated with the M strain 3 times and the C strain of IBV 2 times during the growing period showed higher antibody titer responses to the C 46 than to the M 41 strain. Maternal antibodies in chicks 1 wk of age were readily detected by the ELISA test; low or insignificant titers were found by the VN test. Sera of vaccinated chickens collected following challenge with M 41 or C 46 strain of IBV showed that the ELISA was more sensitive and showed higher titers than did the VN test. Although the VN test showed no rise in GMT in the same sera tested with the heterologous virus, the ELISA showed a slight increase or cross-reaction. The serum samples from the unchallenged control group showed no change in GMT with either test or IBV strain.