Abstract
BackgroundWild aquatic birds constitute the natural reservoir for avian influenza viruses (AIVs). Separate Eurasian and American AIV gene pools exist. Here, the prevalence and diversity of AIVs in gulls and dabbling ducks in Norway were described. The influence of host species and temporal changes on AIV prevalence was examined. Five AIVs from Norway, including three from common gull (Larus canus), were analyzed along with 10 available AIV genomes from gulls in Eurasia to search for evidence of intracontinental and intercontinental reassortment of gene segments encoding the internal viral proteins.MethodsSwabs collected from 2417 dabbling ducks and gulls in the south-west of Norway during five ordinary hunting seasons (August-December) in the period 2005–2010 were analyzed for presence of AIV. Multivariate linear regression was used to identify associations between AIV prevalence, host species and sampling time. Five AIVs from mallard (Anas platyrhynchos) (H3N8, H9N2) and common gull (H6N8, H13N2, H16N3) were full-length characterized and phylogenetically analyzed together with GenBank reference sequences.ResultsLow pathogenic AIVs were detected in 15.5% (CI: 14.1–17.0) of the samples. The overall AIV prevalence was lower in December compared to that found in August to November (p = 0.003). AIV was detected in 18.7% (CI: 16.8–20.6) of the dabbling ducks. A high AIV prevalence of 7.8% (CI; 5.9–10.0) was found in gulls. A similar temporal pattern in AIV prevalence was found in both bird groups. Thirteen hemagglutinin and eight neuraminidase subtypes were detected. No evidence of intercontinental reassortment was found. Eurasian avian (non H13 and H16) PB2 or PA genes were identified in five reference Eurasian gull (H13 and H16) AIV genomes from GenBank. The NA gene from the Norwegian H13N2 gull isolate was of Eurasian avian origin.ConclusionsThe similar temporal pattern in AIV prevalence found in dabbling ducks and gulls, the relatively high virus prevalence detected in gulls and the evidence of intracontinental reassortment in AIVs from gulls indicate that gulls that interact with dabbling ducks are likely to be mixing vessels for AIVs from waterfowl and gulls. Our results support that intercontinental reassortment is rare in AIVs from gulls in Eurasia.
Highlights
Wild aquatic birds constitute the natural reservoir for avian influenza viruses (AIVs)
Comparison of Akaike information criteria (AIC) values for different multivariate logistic regression models showed that bird group, year of sampling and December as sampling month or not were the variables that best described the AIV status of each bird
Phylogenetic analysis Phylogenetic analysis of the five virus isolates sequenced in this study showed that all internal gene segments were of Eurasian origin, and neither these isolates nor the reference AIVs from Eurasian gulls contained evidence of genetic reassortment between Eurasian and American AIVs (Figure 4)
Summary
Wild aquatic birds constitute the natural reservoir for avian influenza viruses (AIVs). The prevalence and diversity of AIVs in gulls and dabbling ducks in Norway were described. The influence of host species and temporal changes on AIV prevalence was examined. The natural reservoir for 16 hemagglutinin (HA) (H1-H16) and 9 neuraminidase (NA) (N1-N9) subtypes of influenza A viruses is wild aquatic birds, primarily ducks, gulls and shorebirds [1,2]. Influenza A viruses that cause epidemics and pandemics in humans, mammals and domestic poultry evolve directly or indirectly from the natural reservoir of avian influenza viruses (AIVs) [1]. The AIV prevalence in dabbling ducks is high in the fall, whereas a lower prevalence is found in the spring [7]. The AIV prevalence is generally low [7,8,9], higher virus prevalence has occasionally been detected in gull colonies [10,11]
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