Influenza-A Viruses in Ducks in Northwestern Minnesota: Fine Scale Spatial and Temporal Variation in Prevalence and Subtype Diversity

Waterfowl from northwestern Minnesota were sampled by cloacal swabbing for Avian Influenza Virus (AIV) from July – October in 2007 and 2008. AIV was detected in 222 (9.1%) of 2,441 ducks in 2007 and in 438 (17.9%) of 2,452 ducks in 2008. Prevalence of AIV peaked in late summer. We detected 27 AIV subtypes during 2007 and 31 during 2008. Ten hemagglutinin (HA) subtypes were detected each year (i.e., H1, 3–8, and 10–12 during 2007; H1-8, 10 and 11 during 2008). All neuraminidase (NA) subtypes were detected during each year of the study. Subtype diversity varied between years and increased with 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 AIV were isolated from this species (80.5% of the total isolates). Mallard data collected during both years adequately described the observed temporal and spatial prevalence from the total sample and also adequately represented subtype diversity. Juvenile mallards also were adequate in describing the temporal and spatial prevalence of AIV as well as subtype diversity.2007年7月至10月及2008年同期，研究人员通过泄殖腔拭子采样法，对明尼苏达州西北部的野生水禽开展禽流感病毒（Avian Influenza Virus, AIV）监测采样。2007年共检测2441只鸭只，其中222份样本呈AIV阳性，阳性率为9.1%；2008年共检测2452只鸭只，检出438份阳性样本，阳性率达17.9%。AIV阳性率在夏末达到峰值。 2007年共检出27种AIV亚型，2008年则检出31种。两年均检测到10种血凝素（hemagglutinin, HA）亚型：2007年为H1、H3至H8、H10至H12；2008年为H1至H8、H10及H11。两年均检出全部神经氨酸酶（neuraminidase, NA）亚型。亚型多样性存在年际差异，且随阳性率升高于9月逐步增加。 2007年占亚型多样性比例≥5%的优势亚型包括H1N1、H3N6、H3N8、H4N6、H7N3、H10N7及H11N9；2008年的优势亚型则为H3N6、H3N8、H4N6、H4N8、H6N1及H10N7。此外，各HA亚型中，两年均检出相同的优势HA/NA组合，包括H1N1、H3N8、H4N6、H5N2、H6N1、H7N3、H8N4、H10N7及H11N9。其中H2N3和H12N5分别为H2和H12亚型内的优势毒株，但仅在单一年份检出（H2亚型毒株未在2008年检出，H12亚型毒株未在2007年检出）。 绿头鸭为本次采样的优势物种，占总样本量的63.7%，且从中分离得到531株AIV，占总分离株数的80.5%。两年收集的绿头鸭数据可充分反映总样本中观测到的时空分布阳性率，同时也能较好代表亚型多样性特征。幼龄绿头鸭的数据同样可充分表征AIV的时空分布阳性率及亚型多样性。