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 were examined for virus at different intervals postinoculation (PI) by reverse 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 Fabricius (BF) of inoculated and vaccinated SPF chicks and of inoculated and vaccinated commercial broiler chicks that have maternally derived antibodies. Four trials were conducted in SPF and commercial broiler chickens. Infectious virus was detected by embryo inoculation up to 7 days PI in the BF of SPF chickens inoculated at 2 or 3 wk of age and up to 21 days PI by RT/PCR, whereas the viral RNA was detected by RT/PCR for up to 28 days PI. In SPF chicks inoculated at I day of age, the bursa-derived virus or its RNA was detected 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 commercial 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 the 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 live IBDV vaccine, the virus or its RNA was detected at 7 and 14 days postvaccination 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.