Antibody titers to infectious bursal disease virus in broiler chicks after vaccination at one day of age with infectious bursal disease virus and Marek's disease virus

The effect of day-of-age vaccination with infectious bursal disease virus (IBDV) alone or in combination with Marek's disease virus (MDV) in broiler chicks was investigated. One-day-old commercial broiler progeny obtained from IBDV-immunized breeder flocks were vaccinated subcutaneously according to the manufacturer's directions with live-attenuated commercially available vaccines as follows: IBDV alone, MDV alone, IBDV + MDV, and unvaccinated control. IBDV was not detected after vaccination by reverse transcriptase/polymerase chain reaction in any of the bursal, thymic, and splenic tissues tested. Serum IBDV antibody levels, as monitored by enzyme-linked immunosorbent assay (ELISA), showed similar rates of decline among the four groups, and, by day 28 postinoculation, serum antibody levels in all groups were below detectable limits. IBDV-specific neutralizing maternal antibody (MA) titers in the IBDV + MDV and control groups, as monitored by the virus neutralization assay (VN), remained higher and declined more slowly throughout the experiment as compared with VN titers in the IBDV- and the MDV-vaccinated groups. In a second experiment, groups of one-day-old broiler chicks were vaccinated as in Experiment 1. Serum IBDV antibody detected by ELISA and VN assay declined parallel to those observed in Experiment 1. Histopathologic lesions characteristic of IBDV were not observed in any of the groups. Vaccination with MDV alone was associated with increased rates of IBDV neutralizing MA decline similar to those caused by vaccination with IBDV alone, whereas concurrent vaccination with IBDV + MDV was not associated with increased rates of IBDV neutralizing MA decline over that of nonvaccinated controls. Results of these studies indicate that IBDV vaccination at 1 day of age does not cause accelerated IBDV-specific MA decline as detected by ELISA but does appear to cause an accelerated decline in neutralizing IBDV-specific MA. Furthermore, vaccination with IBDV at 1 day of age appeared to slow the accelerated rate of IBDV neutralizing antibody decline caused by MDV vaccination.