Routine surveillance has indicated the presence of H5 and N1 avian influenza subtypes in samples from two wild mute swans in Michigan, but testing has ruled out the possibility of this being the highly pathogenic H5N1 strain that has spread through birds in Asia, Europe and Africa, according to USDA and the Department of Interior. Test results thus far indicate this is low pathogenicity avian influenza, which poses no threat to human health.
The swans were sampled as part of the expanded avian influenza surveillance program. They were showing no signs of sickness, which suggests that this is low pathogenicity avian influenza. Additionally, genetic analysis of the virus conducted at USDA's National Veterinary Services laboratories in
It is possible that these birds were not infected with an H5N1 strain, but instead with two separate avian influenza viruses, one containing H5 and the other containing N1. The confirmatory testing underway at NVSL will clarify whether one or more strains of the virus are present, the specific subtype, as well as pathogenicity.
APHIS Director Ron DeHaven explains a second pathogenicity test injects the virus into eight baby chicks. If after 10 days six or more of the chicks show signs of disease or die, it is classified as a highly pathogenic virus. These results are expected within two weeks and will be made public when completed. It should be noted that wild birds are known to harbor many influenza viruses, and the finding of one or more of these viruses during routine testing is not unusual.
The swans were sampled August 8 at the Mouillee state game area located on the coast of
Initial screening tests on the swan samples were conducted by
Sue Haseltine, Department of Interior associate director for biology, explains over 8,000 tests have been conducted over the past two months by her department. Nearly 4,000 of those tests were done in
Low pathogenicity avian influenza commonly occurs in wild birds, where it typically causes only minor symptoms or no noticeable symptoms. These strains of the virus are not a human health concern. This includes LPAI H5N1, commonly referred to as the North American H5N1. This strain of low pathogenicity avian influenza is very different from the more severe HPAI H5N1 circulating overseas, which is commonly referred to as the Asian H5N1.
Evidence of LPAI H5N1 has been found on two occasions in wild birds in the