15.09.2011

Avian influenza was detected in 9% of ducks in northwestern Minnesota in July through October 2007 and in 18% of ducks in the same period in 2008, according to a study published in PLoS One.
Using cloacal swabbing, US researchers detected avian influenza in 222 of 2,441 ducks (9.1%) in 2007 and in 438 of 2,452 (17.9%) ducks in 2008, with a peak incidence in late summer of both years. Almost two thirds of birds sampled were mallards. The researchers detected 27 avian influenza subtypes during 2007 and 31 during 2008. Ten of the 16 hemagglutinin (HA) subtypes were detected each year (H1, 3-8, and 10-12 during 2007; H1-8, 10, and 11 during 2008), and all neuraminidase (NA) subtypes were detected both years. Subtype diversity each year increased in prevalence into September. Predominant subtypes during 2007 (comprising ≥5% of subtype diversity) included H1N1, H3N6, H3N8, H4N6, H7N3, H10N7, and H11N9. Predominant subtypes during 2008 included H3N6, H3N8, H4N6, H4N8, H6N1, and H10N7. Additionally, within each HA subtype, the same predominant HA/NA subtype combinations were detected each year and included H1N1, H3N8, H4N6, H5N2, H6N1, H7N3, H8N4, H10N7, and H11N9. The H2N3 and H12N5 viruses also predominated within the H2 and H12 subtypes, respectively, but only were detected during a single year (H2 and H12 viruses were not detected during 2007 and 2008, respectively). Mallards were the predominant species sampled (63.7% of the total), and 531 Avian influenza virus were isolated from this species (80.5% of the total isolates). The study found that mallards had the highest prevalence of avian influenza, and that testing only juvenile mallards would suffice for surveillance purposes.