Long-Term Dynamics of Different Avian Influenza Viruses in Mallard (Anas platyrhynchos) Population in Moscow City and Moscow Oblast: Dependence on the Migration Activity

The purpose of this study was the research of the avian influenza virus diversity at Moscow waterbodies and comparison of the virology changing pattern to the mallard’s migratory features and wintering capacities at Moscow waterbodies, as well as an attempt to explain shifting in the virus composition and diversity. Mallard droppings were collected in the autumn of 2008–2023 from shores of Moscow and Moscow oblast waterbodies. Avian influenza viruses were extracted from the feces using a standard extraction process with the virus breeding on the chicken embryos. After the breeding the extracted viruses were subtyped by PCR with specific primaries to give type A virus sequences. In 2008–2013 European strains of the virus were prevalent in the mallard samples, whereas in 2014–2019 the prevalence shifted to Asian strains. Correlation of these observations with the changes in mallard migration allowed the assumption that European strains were entered into the Moscow oblast mainly from the southern Europe. The Asian strains were entered from the Western Europe. During 2008–2019 in the mallard feces from the Moscow waterbodies we observed a reduction of the virus strains. The frequency and the diversity of the extracted viruses decreased sharply after 2014. There could be several causes for the decline in the strain diversity, in particular, changes in the ratio of ducks hunted during spring and autumn hunting, increased mallard numbers at winter grounds within the breeding range, as well as reduced numbers of black-headed gulls that are also carriers of the avian influenza viruses.