Comparison of different computational methods for measuring antibodies to avian infectious bronchitis virus in single...

Twenty-eight one-day-old chickens with infectious bronchitis virus (IBV) maternal antibodies were immunized with strain H120 (Bronchovac-I, Phylaxia) in spray form. The chickens were kept in an isolator. On day 42 and 56 the chickens were immunized with IBV strain M41 (10(3.0)EID50/0.1 ml). Serum antibody titres were measured by both serial dilution and single dilution ELISA on day 42, 56 and 76. "Twice negative average" (TNA), "sample to positive" (SP) and "subtraction method" (SM) titres were calculated from the serially diluted sera, and SP and SM titres were calculated from the single dilution. Titres obtained by the different methods showed a good correlation for sera of low, medium and high antibody levels. The authors recommend the use of the single dilution method.