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All subtypes of influenza Type A viruses infect wild birds, especially waterfowl and shorebirds, but rarely cause disease or mortality in these aquatic species. Aquatic birds are the natural reservoirs for low pathogenic avian influenza viruses (LPAI) that are distributed globally. However, some AI subtypes can be virulent in other animals and humans and some highly pathogenic AI viruses (HPAI) have caused major outbreaks in poultry and even pandemics in the human population. The emergence of a HPAI H5N1 subtype in southeast Asian poultry in 1997 subsequently involved migratory waterfowl in 2005 and has since spread westward throughout the Asian, European, and African continents. This rapid continental spread alarmed animal and human health agencies in North America and initiated the establishment of a National Strategy for Pandemic Influenza in the United States to increase and expand surveillance for the early detection of this virus, to improve and expand preventative measures, and to develop contingency responses to possible outbreaks. One of the methods of emergency surveillance developed and implemented was an interagency, early detection system for HPAI H5N1 avian influenza in wild migratory birds with the potential to bring in the virus from Asia or Europe and spread it throughout North America.
As part of this early detection system, the Wildlife Services National Wildlife Research Center developed testing methods, sampling protocols, guidelines, and analyzed 50,184 avian fecal samples collected by Wildlife Service biologists in 50 states and the U. S. territories. Samples were pooled in the laboratory (n = 10,541 pools) and analyzed using RT-PCR. AI viruses were detected in 4.0% of the 10,541 sample pools analyzed and H5/H7 subtypes were detected in 0.2% of the sample pools. Positive H5 and H7 subtypes were shipped to the National Veterinary Services Laboratory for further evaluation and confirmation. This monitoring effort was successful in detecting AI viruses in environmental samples and has proven to be a rapid and cost effective surveillance method.