Failure of productive infection of Mallards (Anas platyrhynchos) with H16 subtype of avian influenza viruses

BACKGROUND Mallard ducks and other waterfowl represent the most important reservoirs of low pathogenic avian influenza viruses (LPAIV). In addition, mallards are the most abundant duck species in Eurasia that migrate over long distances. Despite extended wild bird monitoring studies over the past decade in many Eurasian countries and investigating hundreds of thousands of wild bird samples, no mallard duck was found to be positive for avian influenza virus of subtype H16 in faecal, cloacal or oropharyngeal samples. Just three cases of H16 infections in Anseriformes species were described worldwide. In contrast, H16 viruses have been repeatedly isolated from birds of the Laridae family. OBJECTIVE Here, we tested the hypothesis that mallards are less permissive to infection with H16 viruses. METHODS Groups of mallard ducks of different age were inoculated via the oculo-nasal-oral route with different infectious doses of an H16N3 AIV. RESULTS The ducks did not show any clinical symptoms, and no virus shedding was evident from cloacal and respiratory routes after experimental infection as shown by negative RT-qPCR results. In addition, all serum samples taken on days 8, 21 and 24 post-inoculation were negative by competitive NP-ELISA. CONCLUSIONS This study provided evidence that mallards are resistant to infection with H16N3 LPAIV.