The ecology and age structure of a highly pathogenic avian influenza virus outbreak in wild mute swans

• Published in: Parasitology Vol. 139; no. 14; pp. 1914 - 1923
• Main Authors: PYBUS, O. G., PERRINS, C. M., CHOUDHURY, B., MANVELL, R. J., NUNEZ, A., SCHULENBURG, B., SHELDON, B. C., BROWN, I. H.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.12.2012
• Subjects: Age Distribution; age structure; Animals; Animals, Wild - virology; Anseriformes - virology; antibodies; Antibodies, Viral - blood; Aquatic birds; avian influenza; Disease Outbreaks - veterinary; Ecology; Epidemiology; epizootic diseases; Hemagglutinins, Viral - genetics; immigration; Influenza A virus; Influenza A Virus, H5N1 Subtype - classification; Influenza A Virus, H5N1 Subtype - genetics; Influenza in Birds - epidemiology; Influenza in Birds - immunology; Influenza in Birds - mortality; Influenza in Birds - virology; Molecular Sequence Data; Mortality; nucleoproteins; Outbreaks; Phylogeny; polymerase chain reaction; swans; Time Factors; United Kingdom; United Kingdom - epidemiology; viruses; water birds; wild birds; United Kingdom; Avian influenza virus; phylogenetics; molecular clock; age structure; swans; serology
• ISSN: 0031-1820; 1469-8161; 1469-8161
• DOI: 10.1017/S0031182012000261

The first UK epizootic of highly pathogenic (HP) H5N1 influenza in wild birds occurred in 2008, in a population of mute swans that had been the subject of ornithological study for decades. Here we use an innovative combination of ornithological, phylogenetic and immunological approaches to investigate the ecology and age structure of HP H5N1 in nature. We screened samples from swans and waterbirds using PCR and sequenced HP H5N1-positive samples. The outbreak's origin was investigated by linking bird count data with a molecular clock analysis of sampled virus sequences. We used ringing records to reconstruct the age-structure of outbreak mortality, and we estimated the age distribution of prior exposure to avian influenza. Outbreak mortality was low and all HP H5N1-positive mute swans in the affected population were <3 years old. Only the youngest age classes contained an appreciable number of individuals with no detectable antibody responses to viral nucleoprotein. Phylogenetic analysis indicated that the outbreak strain circulated locally for ∼1 month before detection and arrived when the immigration rate of migrant waterbirds was highest. Our data are consistent with the hypothesis that HP H5N1 epizootics in wild swans exhibit limited mortality due to immune protection arising from previous exposure. Our study population may represent a valuable resource for investigating the natural ecology and epidemiology of avian influenza.