Temporal, spatial and species patterns of avian influenza viruses among wild birds
Hanson, Britta Ann
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Recent direct transmissions of avian influenza viruses (AIV) to humans and the continued threat of AIV outbreaks within domestic birds and livestock emphasize the need for current data of AIV within wild bird populations. However, in North America, the majority of the information on subtype prevalence and diversity is more than 10 years old and these were collected from relatively few species. This study examined the distribution of AIV among wild birds migrating through or wintering in the Atlantic, Mississippi and Central flyways of the U.S during 1998-2002. During the fall seasons 1998-2000 in Minnesota, the predominant hemagglutinin (H) subtypes of AIV isolated from ducks were the H3, H4 and H6 subtypes. This is consistent with previous studies. However, unlike past surveys, more than 20% of the isolates were subtypes associated with human or poultry disease (H5, H7 and H9). In contrast, no H3, H4 or H6 viruses were detected in ducks sampled in Texas during February in 2001 and 2002. The 11-15% AIV prevalence in these wintering ducks was higher than expected and only the H2, H7 and H8 subtypes were isolated. During April - September, 2000, AIVs were detected in shorebirds at only two of five locations sampled and the prevalence among individual shorebird species varied. Most AIVs (67.5%) were isolated from ruddy turnstone (Arenaria interpres) in the Delaware Bay. Unlike a previous survey of shorebirds in the northeastern U.S. in which the H9 and H13 subtypes predominated, the H10 and H12 subtypes comprised >60% of all isolates and no H9 or H13 subtypes were detected. Given the unexpected predominance of the subtypes detected in this study, it appears that the subtypes most often associated with migrating waterfowl (H3, H4 and H6) and shorebirds (H9 and H13) are not necessarily predictable and may vary with time and location of sampling. Also, the 11-15% prevalence of AIV in wintering ducks in Texas suggests that assumptions regarding AIV as primarily a fall season event are not always accurate. It is likely that AIV ecology is not completely understood and the current results indicate that seasonal, species or site characteristics will greatly influence AIV subtype diversity and prevalence.