Detection and persistence of infectious bursal disease virus in specific-pathogen-free and commercial broiler chickens

In an earlier study, specific-pathogen-free (SPF) chickens were inoculated with infectious bursal disease virus (IBDV) at 3 wk of age. Their bursas we re examined for virus at different intervals postinoculation (PI) by revers e transcriptase (RT)/polymerase chain reaction (PCR) and by virus isolation in chicken embryos up to 21 days Pl. The RT/PCR was positive, but attempts to isolate infectious virus from bursal homogenates failed. This prompted us to investigate the persistence of IBDV or its RNA in the bursa of Fabric ius (BF) of inoculated and vaccinated SPF chicks and of inoculated and vacc inated commercial broiler chicks that have maternally derived antibodies. Four trials were conducted in SPF and commercial broiler chickens. Infectio us virus was detected by embryo inoculation up to 7 days PI in the BF of SP F chickens inoculated at 2 or 3 wk of age and up to 21 days PI by RT/PCR, w hereas the viral RNA was detected by RT/PCR for up to 28 days PI. In SPF ch icks inoculated at I day of age, the bursa-derived virus or its RNA was det ected at 7 and 14 days PI when inoculated at a high dose (10(4) mean embryo infective dose [EID50]/bird) or at a low dose (10(25) EID50/bird). In comm ercial 1-day-old broiler chicks, the bursa-derived virus was detected at 7 and 14 days PI when inoculated at a high dose (10(4) EID50/bird), whereas t he virus was detected only at 14 days PI when inoculated at a low dose (10( 25) EID50/bird). In SPF and commercial chicks vaccinated with a modified li ve IBDV vaccine, the virus or its RNA was detected at 7 and 14 days postvac cination in SPF chicks, but neither the live vaccine virus nor its RNA was detected in commercial broilers vaccinated at 1 day or 2 wk of age.