Study links poultry networks to H9N2 prevalence in Vietnam

Both subtypes affect poultry production and pose zoonotic risks directly and through their involvement in the generation of novel virus reassortments.

In Vietnam, the subtypes are frequently detected in live bird markets, and higher prevalence is associated with practices such as mixing poultry from multiple sources.

Figure 2. Time-scaled phylogenies of hemagglutinin sampled avian influenza virus A(H9N2) virus genomes in study of H9N2 virus prevalence across chicken production and distribution networks, Bac Giang, Hanoi, Hai Duong, and Quang Ninh Provinces, Vietnam, March 2021–March 2022. Tree tips are labeled by the unique sampled site identification; red text indicates sequences from 3 farms in the spatiotemporal cluster. Branches are colored by posterior support, and horizontal node bars represent 95% highest posterior density intervals of node ages. Heatmaps indicate province, site type, and chicken type of each sequence. C, chicken type; P, province; S, site type.

However, that finding should be interpreted cautiously because farms and the markets they supply have limited prevalence data, and the focus on markets has diverted attention from larger slaughter facilities despite those facilities playing a key role in poultry distribution, the researchers stated.

Together, those gaps constrain understanding of avian influenza virus (AIV) transmission risk along the production and distribution network (PDN) through which poultry are raised, traded, and consumed.

The researchers conducted a cross-sectional study in northern Vietnam to assess avian influenza A(H5N1) and A(H9N2) prevalence in chickens, determine how AIV prevalence varied between farms and the different distribution facility types, and examine how viral genetic diversity was structured along the PDN.

Figure 3. Time-scaled phylogenies of neuraminidase of sampled avian influenza virus A(H9N2) virus genomes in study of H9N2 virus prevalence across chicken production and distribution networks, Bac Giang, Hanoi, Hai Duong, and Quang Ninh Provinces, Vietnam, March 2021–March 2022. Tree tips are labeled by the unique sampled site identification; red text indicates sequences from 3 farms in the spatiotemporal cluster. Branches are colored by posterior support, and horizontal node bars represent 95% highest posterior density intervals of node ages. Heatmaps indicate province, site type, and chicken type of each sequence. C, chicken type; P, province; S site type.

Findings from the study

The researchers found that poultry production and distribution network configurations, including the origins of supplying farms, influence H9N2 virus prevalence and thus human exposure risk.

The pattern of viral circulation amplification along the PDN is consistent with studies in southern Vietnam and Bangladesh and probably reflects trading conditions.

For example, birds are mixed from multiple sources and experience lengthy, stressful transportation (for example: crowding and lack of sustenance), creating opportunities for virus exposure and transmission en route; that finding was supported by the improved model fit when they included supplying areas, suggesting that procurement and distribution practices influence viral prevalence at distribution facilities.

High viral prevalence in slaughter points and retail markets probably reflects sourcing involving multiple suppliers, including wholesale markets, indicating that chickens spent longer in the PDN before sampling. The lack of geographic structure in AIV genetic diversity further points to extensive viral mixing among poultry populations. Control and surveillance efforts should therefore address the entire poultry PDN.

The Vietnam Avian and Human Influenza Preparedness program has prioritized upgrading wholesale markets and industrial slaughterhouses and promoting their use. Although low prevalence in such facilities supports this focus, slaughterhouses remain underused, and informal slaughter points are still preferred. Surveillance and risk mitigation strategies must also target the numerous distribution facilities in Vietnam that are small and informal but widely used.

Read full paper of the study here.