Highly pathogenic avian influenza (HPAI) H5N1 virus incursions from migrating birds have occurred multiple times in Romania since 2005. Beginning in September 2008 through April 2013, seasonal sentinel surveillance for avian influenza A viruses (AIVs) using domestic geese (Anser cygnoides) and ducks (Anas platyrhynchos) in the Danube Delta was established by placing 15 geese and 5 ducks at seven sites. Tracheal and cloacal swabs, and sera collections (starting in 2009) were taken monthly. We studied a total of 580 domestic birds and collected 5,520 cloacal and tracheal swabs from each and 2,760 sera samples. All swabs were studied with real-time reverse transcription polymerase chain reaction (rRT-PCR) for evidence of AIV. Serological samples were studied with hemagglutination inhibition assays against avian H5, H7, and H9 influenza viruses. From 2009 to 2013, 47 swab specimens from Cot Candura, Enisala, and Saon screened positive for AIV; further subtyping demonstrated that 14 ducks and 20 geese had cloacal evidence of H5N3 carriage. Correspondingly, 4 to 12 weeks after these molecular detections, sentinel bird sera revealed elevated HI titers against H5 virus antigens. We posit that domestic bird surveillance is an effective method to conduct AIV surveillance among migrating birds in delta areas. 1. Introduction Asian-lineage highly pathogenic avian influenza (HPAI) H5N1 virus has infected poultry in many countries of the world and is thought to be highly endemic in certain delta areas due to frequent viral incursions from large populations of migrating birds [1, 2]. As of 2011, the Food and Animal Organization (FAO) considered HPAI H5N1 to be enzootic among aquatic birds in Bangladesh, China, Egypt, India, Indonesia, and Vietnam [3]. The latest report from the World Organization for Animal Health revealed outbreaks of HPAI H5N1 that have occurred in Bangladesh, Bhutan, Cambodia, China, India, Korea, Nepal, and Vietnam in 2013 and in China, Nepal, and Vietnam during early 2014 [4]. Large populations of aquatic migratory birds frequent delta areas in Romania and evidence to date strongly suggests that they have introduced HPAI strains into Romania’s poultry. The first Romanian HPAI H5N1 incursions were detected in backyard poultry farms in October 2005 [5, 6]. The virus rapidly spread throughout the country until aggressive control measures were taken; the epizootic halted in July 2006 [7]. Laboratory studies demonstrated that the epidemic virus was similar to H5N1 viruses previously detected in Southeast Asia and Turkey and that migrating birds were
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