Bangladesh's Silent Threat: Persistence and Reassortment of Avian Influenza in A Poultry-Dense Ecosystem-A Comprehensive Review of Knowledge Gaps and Future Perspectives.

Avian influenza in Bangladesh presents a continuous and challenging threat due to the sustained co-circulation of highly pathogenic H5N1 and low pathogenic H9N2 avian influenza viruses within a densely populated poultry ecosystem. This study analyses the persistence and genetic reassortment dynamics of these viruses, emphasizing the significance of genetic exchange in sustaining viral virulence and adaptability. The research highlights high-pathogenicity H5N1 strains possessing the H9N2-PB1 gene, illustrating that genetic reassortment promotes the virus's persistence and evolution. It reinforces the enzootic character of LPAI H9N2, present in 55.8% of chickens, and reveals defects in the culling compensatory mechanism. Despite extensive control efforts over the decades, systemic challenges, like insufficient culling strategies, vaccine inconsistencies and the shedding of critical virus reservoirs, such as domestic ducks and backyard poultry, have impeded successful management. The work explores the difficulties presented by the endemicity of LPAI H9N2, its function as a genetic donor for H5N1, and the consequent "silent threat" that hinders surveillance and control efforts. Proposed future options include improved surveillance via whole genome sequencing, the extension of immunization initiatives, and the implementation of sustainable financial support schemes for farmers. The government and poultry industry should emphasize the necessity for a coordinated, multifaceted strategy to limit the risks of avian influenza in Bangladesh.