Abstract
Rural farming communities in northern Vietnam do not routinely practice vaccination for influenza A viruses (IAV) for either humans or poultry, which enables us to study transmission intensity via seroepidemiology. Using samples from a longitudinal cohort of farming households, we determined the number of symptomatic and asymptomatic human infections for seasonal IAV and avian A/H9 over 2 years. As expected, we detected virologically confirmed acute cases of seasonal IAV in humans, as well as large numbers of subclinical seroconversions to A/H1pdm [55/265 (21 %)], A/H3 [95/265 (36 %)] and A/H9 [24/265 (9 %)]. Five of the A/H9 human seroconverters likely represented true infections rather than heterosubtypic immunity, because the individuals seroconverted solely to A/H9. Among co-located poultry, we found significantly higher seroprevalance for A/H5 compared to A/H9 in both chickens and ducks [for northern study sites overall, 337/1105 (30.5 %) seropositive for A/H5 and 123/1105 (11.1 %) seropositive for A/H9].
Highlights
Rural farming communities in northern Vietnam do not routinely practice vaccination for influenza A viruses (IAV) for either humans or poultry, which enables us to study transmission intensity via seroepidemiology
Pathogenic avian influenza (HPAI) A/H5 viruses have been endemic in Vietnamese poultry ever since the first major epizootic waves in 2005, which caused losses of >20 % of the standing poultry population at the time (45 million dead or destroyed) [4]
It has been suggested that vaccination against seasonal IAVs among individuals at high risk for animal IAVs constitutes a fundamental tool for reducing the risk of co-infections, thereby reducing the potential evolution of novel IAVs by reassortment [6]
Summary
Rural farming communities in northern Vietnam do not routinely practice vaccination for influenza A viruses (IAV) for either humans or poultry, which enables us to study transmission intensity via seroepidemiology. We present a seroepidemiological study concerning low-pathogenic avian influenza (LPAI) A/H9 viruses among unvaccinated human and poultry populations in the backyard smallholder farms of Vietnam.
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