A cross-sectional study to quantify the prevalence of avian influenza viruses in poultry at intervention and non-intervention live bird markets in central Vietnam, 2014

Abstract

In Vietnam, live bird markets are found in most populated centres, providing the means by which fresh poultry can be purchased by consumers for immediate consumption. Live bird markets are aggregation points for large numbers of poultry, and therefore, it is common for a range of avian influenza viruses to be mixed within live bird markets as a result of different poultry types and species being brought together from different geographical locations. We conducted a cross-sectional study in seven live bird markets in four districts of Thua Thien Hue Province in August and December, 2014. The aims of this study were to (i) document the prevalence of avian influenza in live bird markets (as measured by virus isolation); and (ii) quantify individual bird-, seller- and market-level characteristics that rendered poultry more likely to be positive for avian influenza virus at the time of sale. A questionnaire soliciting details of knowledge, attitude and avian influenza practices was administered to poultry sellers in study markets. At the same time, swabs and faecal samples were collected from individual poultry and submitted for isolation of avian influenza virus. The final data set comprised samples from 1,629 birds from 83 sellers in the seven live bird markets. A total of 113 birds were positive for virus isolation; a prevalence of 6.9 (95% CI 5.8-8.3) avian influenza virus-positive birds per 100 birds submitted for sale. After adjusting for clustering at the market and individual seller levels, none of the explanatory variables solicited in the questionnaire were significantly associated with avian influenza virus isolation positivity. The proportions of variance at the individual market, seller and individual bird levels were 6%, 48% and 46%, respectively. We conclude that the emphasis of avian influenza control efforts in Vietnam should be at the individual seller level as opposed to the market level.

A systematic approach to illuminate a new hot spot of avian influenza virus circulation in South Vietnam, 2016–2017

“…LBMs in this study (14%) was higher than the AIV positivity prevalence of 6.9% among LBMs in the centre of Vietnam identified by Chu et al (2017), and 5.8% in the north of Vietnam identified by Thuy et al (2016). Assuming these differences in prevalence are real and not due to, for example, seasonal and yearly fluctuations in the incidence of AI, our results imply that LBMs in southern Vietnam play a more dominant role in maintaining AIV circulation in the poultry population compared to other areas of the country.…”

“…Although LBM closures break the viral amplification cycle, AIVs are often re-introduced once they are re-opened (Kung et al, 2003). A previous Vietnamese study investigating the effectiveness of virus control measures in LBMs showed no differences in AIV prevalence between LBMs with and without biosecurity interventions (Chu et al, 2017). One interpretation of these findings is that the introduction of AIV into LBMs occurs continuously.…”

“…Although the number of HPAI outbreaks in Vietnam due to infection with H5N1 subtype viruses has markedly decreased since 2004 (FAO Vietnam, 2017), substantial losses in the domestic poultry sector continue to occur. A number of studies have improved our understanding of the epidemiology of AI by identifying drivers of virus spread (Nomura et al, 2012;Okamatsu et al, 2013;Nguyen et al, 2014;Chu et al, 2016Chu et al, , 2017Nguyen et al, 2020). As part of their efforts to reduce AI virus (AIV) infection risk, the Vietnamese government has developed both active and passive surveillance programs.…”

A systematic study towards evolutionary and epidemiological dynamics of currently predominant H5 highly pathogenic avian influenza viruses in Vietnam

“…S1). Moreover, all H5 HPAIVs in our surveillance were isolated in LBMs and LBM-like locations, indicating that LBMs play important roles for virus persistence and dissemination 18,28 . These findings confirmed relatively constant epidemiology of H5 HPAIVs in regards that abundance of waterfowl species and live poultry trading activities facilitate H5 HPAIV persistence and these elements should be primary targets of the surveillance and control system.…”

The Presence of Poultry Influenza Strains in Two Live Bird Markets near the East-West Boundary of Vietnam

“…Therefore, LBMs are home to many poultry species and contain pathogens from various places. LBMs provide a very favorable environment for the avian influenza virus to exchange and disperse [6,7]. Previous studies have shown that the poultry markets in Vietnam have many different subtypes of influenza viruses such as H3, H4, H5, H6, H7, and H9 and N1, N2, N3, N6, and N8 [8, 9].…”