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 (avian influenza 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 3 weeks of 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. 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.