Given a paucity of data on the occurrence of avian influenza viruses (AIVs) in wild passerines and other small terrestrial species in Southeast Asia and the importance of highly pathogenic Asian-strain H5N1 outbreaks in humans and domestic poultry in these areas, we focused on surveillance for influenza A viral nucleic acids and antibodies for AIVs in wildcaught birds in northern Vietnam. Four of 197 serum samples collected in 2007 from Black-crested Bulbul (Pycnonotus melanicterus), Crow-billed Drongo (Dicrurus annectans), Buff-breasted Babbler (Pellorneum tickelli), and Black-browed Fulvetta (Alcippe grotei) were antibody positive for the H5 subtype. Fourteen of 193 samples collected in 2008 were positive for the influenza A viral M gene by real-time reverse transcriptase-polymerase chain reaction. These included samples from 10 Japanese White-eyes (Zosterops japonicus), two Puff-throated Bulbuls (Alophoixus pallidus), one White-tailed Robin (Cinclidium leucurum), and one Striped Titbabbler (Macronous gularis). Almost all positive samples were from bird species that forage in flocks, including Japanese White-eyes with an unusually high prevalence of 14.9%. We collected samples from birds from three habitat types but detected no strong pattern in prevalence. Our results suggest that attention should be given to terrestrial species, particularly flocking passerines, in AIV surveillance and monitoring programs.

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