Chicken infectious anemia virus helps fowl adenovirus break the protection of maternal antibody and cause inclusion body hepatitis-hydropericardium syndrome in layers after using co-contaminated Newcastle disease virus-attenuated vaccine.

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Inclusion body hepatitis-hydropericardium syndrome (IBH-HPS) caused by fowl adenovirus type 4 (FAdV-4) has caused huge economic losses for China in the past five years. At present, this disease is controlled in many flocks with the inactivated FAdV vaccine, but the offspring chicks of a layer breeding flock that were vaccinated with this vaccine still became infected and developed IBH-HPS with a 20% mortality rate. Analysis revealed that the NDV-attenuated vaccine in use from the above-mentioned poultry farm was simultaneously contaminated with FAdV-4 and chicken infectious anemia virus (CIAV). The FAdV and CIAV isolated from the vaccine were purified for the artificial preparation of an NDV-attenuated vaccine singly contaminated with FAdV or CIAV, or simultaneously contaminated with both of them. Seven-day-old layers with maternal FAdV antibody were inoculated with the artificially prepared, contaminated vaccines and assessed for corresponding indices. The experiments showed that no obvious symptoms occurred after using the NDV-attenuated vaccine singly contaminated with FAdV or CIAV; however, common IBH and occasional HPS-related death was found in birds after administering the NDV-attenuated vaccine co-contaminated with FAdV and CIAV. In conclusion, this study illustrated that CIAV could assist FAdV in breaking maternal FAdV antibody protection, which then caused the IBH-HPS after vaccination with the co-contaminated NDV vaccine.