The effect of infectious bursal disease virus (IBDV) on Salmonella typhimurium (ST) infections in broilers was investigated in terms of Salmonella shedding and persistence, pathogenicity, and isotype specific humoral immune responses. Thirty-six, 1 day-old, straight-run commercial broiler chickens that were Salmonella negative by polymerase chain reaction (PCR) and culture were divided into two groups of 18 chicks each (ST and ST-IBDV). One group (ST-IBDV) of chicks received the E/Del strain of IBDV (105.0 median tissue culture infective dose [TCID50]/ml) through the ocular and cloacal routes divided into doses of 50 μl each at 2 days of age. Both groups were then inoculated with 108 colony-forming units (CFU)/ml nalidixic acid-resistant ST in the drinking water at 3 days of age. Environmental Salmonella counts were higher in the ST-IBDV group at 2 and 3 wk postinfection (PI) compared to the ST group. ST carriage in the cecal contents between the ST and ST-IBDV groups was not statistically different. The ST-IBDV group had a single mortality at 10 days postinfection compared to none in the ST group. The ST-IBDV group had significantly lower bursa to body weight ratios at 4 and 6 wk, as well as higher bursal lesion scores than the ST group at 2, 4, and 6 wk PI. The ST group had significant increase in serum IgG from 2 to 6 wk PI in comparison to the ST-IBDV group, which had no significant changes over time. Both IgA and IgM were significantly increased at 4 and 6 wk relative to 2-wk levels. There was an IBDV-induced failure of anti-Salmonella IgG seroconversion over time in ST-IBDV. Both groups continued to shed high levels of Salmonella up to the end of the study despite high antibody levels in the ST group and an unimpaired IgM and IgA production in the ST-IBDV group, indicating a limited influence of humoral immunity on Salmonella clearance.
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Vol. 48 • No. 2