Patterns of Avian Influenza A (H5) and A (H9) virus infection in backyard, commercial broiler and layer chicken farms in Bangladesh

In order to control Highly Pathogenic Avian Influenza (HPAI) H5N1 and Low Pathogenic Avian Influenza (LPAI) H9N2 virus spread in endemically infected countries, a detailed understanding of infection patterns is required. We conducted cross-sectional studies in Bangladesh in 2016 and 2017, on 144 backyard, 106 broiler and 113 layer chicken farms. Although all sampled birds were negative for H5 virus by RT-PCR, H5 antibodies were detected in unvaccinated birds on all three farming systems. Higher H5 antibody prevalence was observed in ducks raised on backyard farms, 14.2% (95% CI: 10.0%-19.8%), compared to in-contact backyard chickens, 4.2% (95% CI: 2.8%-6.1%). The H5 antibody prevalence was lower in broiler chickens, 1.5% (95% CI: 0.9%-2.5%), compared to layer chickens, 7.8% (95% CI: 6.1%-9.8%). H9 viruses were detected by RT-PCR in 0.5% (95% CI: 0.2%-1.3%) and 0.6% (95% CI: 0.3%-1.5%) of broilers and layers, respectively, and in 0.2% (95% CI: 0.0%-1.2%) of backyard chickens. Backyard chickens and ducks showed similar H9 antibody prevalence, 16.0% (95% CI: 13.2%-19.2%) and 15.7% (95% CI: 11.3%-21.4%), which was higher compared to layers, 5.8% (95% CI: 4.3%-7.6%), and broilers, 1.5% (95% CI: 0.9%-2.5%). Over the course of a production cycle, H5 and H9 antibody prevalence increased with the age of backyard and layer chickens. Usually, multiple ducks within a flock were H5 antibody positive, in contrast to backyard chickens, broilers and layers where only individual birds within flocks developed H5 antibodies. Our findings highlight low virus circulation in healthy chickens of all production systems in Bangladesh, which is in contrast to high virus circulation reported from live bird markets. Data generated in this project can be used to adopt risk-based surveillance approaches in different chicken production systems in Bangladesh and to inform mathematical models exploring HPAI infection dynamics in poultry from the source of production.