D. J. Hulse-PostK. M. Sturm-RamirezJ. HumberdP. SeilerE. A. GovorkovaS. KraussC. ScholtissekP. PuthavathanaC. BuranathaiT. D. NguyenH. T. LongT. S P NaiposposH. ChenT. M. EllisY. GuanJ. S M PeirisR. G. WebsterSt. Jude Children Research HospitalMahidol UniversityThailand National Institute of Animal HealthNational Institute of Veterinary Research HanoiNational Institute of Hygiene and Epidemiology HanoiMinistry of Agriculture, IndonesiaChinese Academy of Agricultural SciencesFisheriesShantou University, Medical College (SUMC)The University of Hong Kong2018-06-212018-06-212005-07-26Proceedings of the National Academy of Sciences of the United States of America. Vol.102, No.30 (2005), 10682-10687002784242-s2.0-23044502533https://repository.li.mahidol.ac.th/handle/20.500.14594/16313Wild waterfowl, including ducks, are natural hosts of influenza A viruses. These viruses rarely caused disease in ducks until 2002, when some H5N1 strains became highly pathogenic. Here we show that these H5N1 viruses are reverting to nonpathogenicity in ducks. Ducks experimentally infected with viruses isolated between 2003 and 2004 shed virus for an extended time (up to 17 days), during which variant viruses with low pathogenicity were selected. These results suggest that the duck has become the "Trojan horse" of Asian H5N1 influenza viruses. The ducks that are unaffected by infection with these viruses continue to circulate these viruses, presenting a pandemic threat. © 2005 by The National Academy of Sciences of the USA.Mahidol UniversityBiochemistry, Genetics and Molecular BiologyMultidisciplinaryArticleSCOPUS10.1073/pnas.0504662102