Wild Green-winged Teal ducks in central Illinois have tested positive for a low-pathogenic strain of avian influenza, the government said on Friday.

"Initial tests confirm that these wild duck samples do not contain the highly pathogenic H5N1 strain that has spread through birds in Asia, Europe and Africa," the Agriculture and Interior departments said in a statement.

Five of 11 samples taken from the ducks tested positive for the H5 virus subtype and one contained the H5 and N1 subtypes, they said. The samples were sent to a federal laboratory [National Veterinary Services Laboratory, NVSL] in Ames, Iowa, for further testing of virus strains.

The samples were collected on Sunday at the Rice Lake Conservation area in Fulton County, central Illinois. The ducks showed no signs of illness, which also indicates a low-risk strain of avian influenza.

As a precaution against the highly pathogenic H5N1 virus that has killed millions of fowl, the government has stepped up testing of wild birds. The Agriculture and Interior departments say they expect to find additional cases of common strains of avian influenza that pose no risk to humans.

Tests have found suspected bird flu in wild, migratory ducks in Illinois, but federal officials said Friday it's not likely to be the deadly Asian subtype they fear could reach North America.

Initial test results suggest the ducks had a strain of virus that poses no threat to human health, officials from the U.S. Department of Agriculture and Department of the Interior said.

The ducks showed no sign of being sick, which also suggests a common strain of bird influenza. Results from further testing are expected within several weeks and will be made public, officials said.

Other states have also had wild birds test positive recently for the low-grade strain of bird flu, including Pennsylvania, Maryland and Michigan.

The samples from green-winged teals were collected on 24 Sep 2006 in the Rice Lake Conservation Area of Fulton County in west central Illinois. The USDA and the Illinois Department of Natural Resources are cooperating to sample and test wild birds for the virus in a stepped-up monitoring program.

There is no known health risk to hunters or hunting dogs from the wild birds with the low-grade bird flu. Officials said hunters should always wash their hands when handling wildlife and cook foods thoroughly.

No birds in North America have tested positive for the Asian subtype of the bird flu virus known as H5N1, which has killed at least 148 people. The greatest number of deaths has been in Indonesia, according to the World Health Organization.

Wherever the disease has spread to humans, it has been through people's direct contact with the birds, mostly in Asia involving poultry. Experts fear the virus could mutate into a form that could be easily transmitted among humans, causing a worldwide pandemic that could kill millions of people.