Abstract
Background:Subtype H5N1 avian influenza viruses, both high pathogenicity and low pathogenicity, have been enzootic in Vietnam since 2001. The viruses are readily identified at live bird markets, but virus prevalence on smallholder poultry is typically zero or very low. If the true direction of the viral transmission chain is farm to market, it is unknown why farm prevalence should be low when market prevalence is moderate to high.Methods:We established a cohort of 50 smallholder poultry farms in Ca Mau province in the Mekong Delta region of Vietnam. From March 2016 to January 2017, we collected naso-pharyngeal and cloacal samples from 156 ducks and 96 chickens. In addition, 126 environmental samples were collected. Samples were assayed for H5 subtype influenza by real-time RT-PCR.Results/Discussion: None of the 378 collected samples were positive for H5 influenza. This is likely to mean that circulation of subtype H5 influenza viruses was low in Ca Mau in 2016. Detection of avian influenza on smallholder poultry farms is necessary to determine the directionality and association between farm prevalence and market prevalence of avian influenza viruses. Larger farm-level studies should be planned as these will be critical for determining the presence and strength of this association.
Highlights
We established a cohort of 50 smallholder poultry farms in Ca Mau province in the Mekong Delta region of Vietnam
Avian influenza viruses are endemic in poultry populations in South East Asia
Viral prevalence is occasionally detected at live poultry markets[2,3,4] but rarely on farms[4,5,6]
Summary
Avian influenza viruses are endemic in poultry populations in South East Asia. The prevalence of the virus varies substantially by region. Viral prevalence is occasionally detected at live poultry markets[2,3,4] but rarely on farms[4,5,6]. This is unexpected because poultry spend the first 6 to 8 weeks of their life on a farm and typically only the last 6-12 hours at a poultry market[20,21]. The viruses are readily identified at live bird markets, but virus prevalence on smallholder poultry is typically zero or very low. If the true direction of the viral transmission chain is farm to market, it is unknown why farm prevalence should be low when market prevalence is moderate to high
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