Trypsin-induced Hemagglutination Assay for the Detection of Infectious Bronchitis Virus

A trypsin-induced hemagglutination (THA) assay was standardized to detect infectious bronchitis virus (IBV) in allantoic fluid (AF) of embryonated eggs. The test was used in 20 samples, each collected from 5 different layer farms suspected for IBV. Allantoic fluid from inoculated embryos was harvested and treated with reagent grade trypsin at the percentages of 0.25, 0.50, 1.0 and 2.0 for 30 minutes to 3 hours at pH 7.2. The IBV in trypsinized AF was identified by clear and consistent agglutination of chicken red blood cells within 5 minutes of incubation at 37C. The results indicated that AF treated with equal volume of 1.0% reagent grade trypsin elicited the hemagglutinating (HA) activity in 3.0 hours whereas 2.0% reagent grade trypsin elicited the HA activity only after 30 minutes incubation at 37C. Sensitivity of THA was 92% as compared with 76% for agar gel precipitation test. Gross pathological lesions (curling and dwarfing) in chick embryo, intracereberal inoculation of un-weaned mice and pathogenicity test in one-day-old broiler chicks showed 79, 84 and 77% sensitivity, respectively.