Disease Dynamics and Bird Migration—Linking Mallards Anas platyrhynchos and Subtype Diversity of the Influenza A Virus in Time and Space

Abstract

The mallard Anas platyrhynchos is a reservoir species for influenza A virus in the northern hemisphere, with particularly high prevalence rates prior to as well as during its prolonged autumn migration. It has been proposed that the virus is brought from the breeding grounds and transmitted to conspecifics during subsequent staging during migration, and so a better understanding of the natal origin of staging ducks is vital to deciphering the dynamics of viral movement pathways. Ottenby is an important stopover site in southeast Sweden almost halfway downstream in the major Northwest European flyway, and is used by millions of waterfowl each year. Here, mallards were captured and sampled for influenza A virus infection, and positive samples were subtyped in order to study possible links to the natal area, which were determined by a novel approach combining banding recovery data and isotopic measurements (δ2H) of feathers grown on breeding grounds. Geographic assignments showed that the core natal areas of studied mallards were in Estonia, southern and central Finland, and northwestern Russia. This study demonstrates a clear temporal succession of latitudes of natal origin during the course of autumn migration. We also demonstrate a corresponding and concomitant shift in virus subtypes. Acknowledging that these two different patterns were based in part upon different data, a likely interpretation worth further testing is that the early arriving birds with more proximate origins have different influenza A subtypes than the more distantly originating late autumn birds. If true, this knowledge would allow novel insight into the origins and transmission of the influenza A virus among migratory hosts previously unavailable through conventional approaches.

Molecular Epidemiology of Outbreak-Associated and Wild-Waterfowl-Derived Newcastle Disease Virus Strains in Finland, Including a Novel Class I Genotype

“…Finland is located on the Western European flyway, and a big proportion of hatch-year dabbling ducks wintering in West and Central Europe have been found to originate in Southern Finland (16). Interestingly, while a clear phylogenetic separation can be seen between North American and Eurasian AIV strains, our wildwaterfowl-derived strains were closely related to strains that were isolated on the other side of the Atlantic Ocean.…”

“…In total, 715 birds were sampled (Table 4), most of which were wild waterfowl. The most prevalent species sampled for active surveillance were mallard (Anas platyrhynchos) (53%) and Eurasian teal (Anas crecca) (22%), as they are the most common bagged duck species and nest in high numbers in our study areas (16,22). The samples were derived from the whole country, except from the northernmost part of Finland.…”

“…The samples were collected by voluntary hunters and staff of the Finnish Game and Fisheries Research Institute, as part of an active surveillance program of AIV and NDV. Samples were collected from a total of 715 birds, from four main areas in Central and Southern Finland, where waterfowl nest in high numbers (16,22). In addition, positive samples derived as part of passive surveillance (dead and clinically affected birds) and from NDV outbreaks were included in our study.…”

Evolutionary Dynamics and Global Diversity of Influenza A Virus

“…Much of the observed subtype diversity can be linked to wild migratory birds, in particular, mallards, from which the greatest number of unique subtypes (n ϭ 94) of any bird species have been reported. Extensive breeding and wintering grounds found in temperate zones bring large numbers of migratory birds, often of mixed species, in close contact for large parts of the year, resulting in the maintenance of existing subtypes as well as the establishment of new subtypes through reassortment (32)(33)(34). A concerted effort to monitor the IAV subtypes circulating among wild birds in these temperate zones may help to identify emerging subtypes before they make their way into domestic birds.…”

Impact of Climate Change on the Geographic Scope of Diseases

“…During migratory movements, birds have the potential of carrying and dispersing pathogens that can be dangerous for both humans and of course other animals and birds [128][129][130]. This spread of pathogens occurs at multiple geographic scales, consequently influencing disease dynamics [131][132][133][134]. Many disease pathogens can be spread in this manner and these include; viruses (e.g., West Nile, Sindbis, Newcastle), bacteria (e.g., borrelia, mycobacteria, salmonellae), and protozoa (e.g., cryptosporidia) [128].…”