Evaluation of serological, histological and immunocytochemical methods forthe detection of infectious bursal disease virus infection in broiler flocks in New Zealand

Aims. To study and compare three diagnostic methods for the detection of in fectious bursal disease virus (IBDV) infection. Methods. Samples of sera and bursae were collected from two necks from each of two broiler farms (Farms A and B) in which IBD had occurred or was susp ected to have occurred. Sera were tested in ELISA and agar gel precipitatio n tests for the presence of IBD antibodies. Bursae were examined histologic ally for evidence of IBD lesions. An immunocytochemical test was developed to detect IBDV antigens in sections of bursa. Results. Bursae from serologically negative, 45-day-old birds from Farm A, Flock 1 and from serologically positive 49-day-old birds from Farm B, Flock I had histological and immunocytochemical evidence of IBDV infection. Bird s from Farm A, Flock 2, sampled 12 months after the sampling of Flock 1, an d specific-pathogen-free birds, showed no evidence of IBDV infection by any of the three diagnostic methods. Birds from Farm B, Flock 2, sampled on fo ur occasions, were positive for IBD at 20 days of age by histology and immu nocytochemistry but did not seroconvert until 42 days of age. Conclusions. Serological testing is not a reliable method for the detection of IBDV infection in New Zealand broiler necks because antibodies may not have developed to detectable levels by the time of slaughter. Histological examination of bursae allowed the demonstration of IBD-like lesions, but th ese need to be differentiated from those caused by other agents. The immuno cytochemistry test was able to detect early IBDV infection. It provided a r apid, definitive diagnosis and may be useful in control programmes. The res ults from Farm A demonstrate that strict biosecurity measures can be succes sful in the eradication of IBDV.