AVIAN INFLUENZA TESTS COMPLETE ON WILD NORTHERN PINTAIL DUCKS IN MONTANA
WASHINGTON, Oct. 7, 2006 - The U.S. Departments of Agriculture and Interior today announced final test results, which confirm that a low pathogenic H5 avian influenza virus was found in samples collected last month from wild Northern pintail ducks in Montana. This type of avian influenza has been detected several times in wild birds in North America and poses no risk to human health.
The USDA National Veterinary Services Laboratories (NVSL) confirmed the presence of low pathogenic H5N3 avian influenza through virus isolation in two of the 16 samples collected from wild pintails in Cascade County, Montana. Initial screening results announced on Sept. 21 indicated that H5 and N1 subtypes might be present in the collected samples, but further testing was necessary to confirm the H and N subtypes as well as pathogenicity.
The initial rapid screening tests are highly sensitive and can detect active and inactive viruses in samples. Varieties of this test can screen for the presence of all strains of avian influenza virus. Because these rapid screening tests are highly sensitive, it is not uncommon to have positive results for a specific subtype on the initial screen test and yet not be able to isolate a virus of that subtype. This was the case for the N1 subtype in this sample which tested as a weak positive in the initial screen test. During confirmatory testing, an N1 subtype was not isolated but instead an N3 was found. As previously announced, genetic testing ruled out the possibility that the samples carried the highly pathogenic strain of H5N1 avian influenza that is circulating overseas.
Low pathogenic strains of avian influenza occur naturally in wild birds and typically cause only minor sickness or no noticeable signs of disease in birds. In most cases it causes no signs of infection or only minor symptoms in birds. These strains are common in the U.S. and around the world. Low pathogenic avian influenza viruses are very different from the more severe highly pathogenic H5N1 circulating in parts of Asia, Europe and Africa. Highly pathogenic strains of avian influenza spread rapidly and are often fatal to chickens and turkeys.
The Departments of Agriculture and Interior are working collaboratively with States and academic institutions to sample wild birds throughout the United States for the presence of highly pathogenic avian influenza.