Evaluating how infectious bursal disease virus influences influenza A virus transmission in chickens

Infectious bursal disease virus (IBDV) is a major cause of immunosuppression in chickens that has been shown to affect influenza A virus (AIV) pathogenicity and shedding patterns. In this study, we compared the shedding of a low passage duck origin AIV in two groups of specific- pathogen free chickens: one group that was IBDV-inoculated and one sham-inoculated group. At three weeks age, the birds were divided and intranasally given one of three doses (102, 103, 105) of A/mallard/OH/421/1987 (H7N8) low pathogenicity AIV. Although the bursae of the IBDV-infected chicks had higher lesion scores, the damage was minimal. We observed that this low IBDV exposure increased resistance to AIV challenge. There was no difference between the mean days of shedding between the two groups, although the IBDV inoculated group shed less virus (approximately 1 log10 less per bird). Uninoculated contacts co-housed with the treatment groups given 105 AIV became infected. Additionally, chicks shedding approximately 103-4 EID50/ml AIV (CT of 33 or less) transmitted virus to cage mates. These findings demonstrate that the impacts of immunosuppressive agents on AIV challenge may vary, based on a number of confounding factors.