Environmental samples, a sensitive and practical alternative to individual bird sampling in the surveillance of H9N2 vaccinated turkey flocks.

Surveillance for influenza A virus infections in vaccinated poultry flocks remains challenging due to animal welfare, logistical and financial constraints, particularly under current EU regulations governing high pathogenicity avian influenza (HPAI) vaccination. In this field study, we evaluated two environmental sampling (ES) methods - bedding boot swabs and drinker wipes - as alternatives to legally mandated individual bird testing, which involved monthly swabbing of 60 healthy birds (active surveillance, AS) and weekly swabbing of dead or sick birds (passive surveillance, PS). A total of 56 turkey flocks from 23 holdings in Lower Saxony, Germany, were monitored throughout the fattening period following single H9N2 vaccination at hatch. Semiquantitative reverse transcription polymerase chain reaction (RT-qPCR) revealed that, despite vaccination, H9N2 virus incursions occurred at least once in 76.8% (43/56) of flocks during the subsequent fattening period. Influenza A virus detection rate on the basis of individual samples was significantly higher by ES (24.1%) than through AS (10.65%;