A Survey of Avian Influenza in Wild Birds and Domestic Ducks in Bangladesh

Background: Wild waterfowl are the natural reservoirs for avian influenza viruses and responsible for persistence of these viruses in the wild. Freshwater wetlands (haors) in northern Bangladesh provide habitat for resident and migratory wild birds and domestic ducks during the cold season from November to March. The Bay of Bengal’s coastal areas are also wintering grounds for migratory birds. We conducted a study of wild birds and domestic ducks in these areas to assess the presence of avian influenza viruses. Methods: We sampled wild birds from Hakaluki and Tanguar haors in two districts of northern Bangladesh and two coastal sandbars near Sonadia Island in southeastern Bangladesh. We used mist nets, noose traps and dazzling to capture these wild birds. We collected oropharyngeal and cloacal swabs from each bird in viral transport media (VTM). Cloacal swabs were also abtainedfrom domestic ducks (Anas platyrhynchos) from Hakaluki haor. Swab samples were tested by real time reverse transcriptase polymerase chain reaction (rRT-PCR) with specific primers to identify the influenza A Matrix (M) gene and the H5 subtype of hemagglutinin (HA) genes. Results: We sampled 472 wild birds of 67 species and 20 families from November 2010 to March 2011, of which 140 were resident and 332 were migratory. Among them, 275 were from Hakaluki haor, 130 from Tanguar haor, and 67 from coastal sandbars. We detected 12 (2.5%, CI 1.3 - 4.4%) wild birds positive to influenza A by rRT-PCR. The influenza A infected birds from Hakaluki haor included 11 migratory waterfowl: nine northern pintails (Anas acuta), one ferruginous pochard (Aythya nyroca), and one garganey (Anas querquedula). From the coastal area, one lesser sand plover (Charadrius mongolus), a migratory wader, tested positive for influenza A. Birds sampled from Tanguar haor tested negative for influenza A. Among the 400 domestic ducks 32 tested positive for influenza A (8%, CI 5.5 - 11.1%). All influenza A positive birds and ducks tested negative for H5. Conclusions: Migratory wild birds and domestic ducks share habitat in Bangladesh and both carry and shed influenza A virus. Sampling wild birds in these areas and genotyping the viruses will allow identification of influenza virus strains that may represent a risk both to domestic poultry and to humans