Berlin ? A weasel-like animal called a stone marten was infected with the deadly bird flu virus, marking the disease’s spread to another mammal species, a German laboratory said Thursday.

The sickly animal was found on the north German island of Ruegen, where three cats and dozens of wild birds have been infected with the disease, the agriculture ministry of the state of Mecklenburg-Western Pomerania said.

A little less than 2 feet in length, stone martens have long bushy tails and prey on squirrels, birds and eggs. They have brown fur with a patch of white on their chest.

A veterinarian put down the sickly marten and sent its corpse for further testing.

Visitors feed doves at a park Thursday March 9, 2006, in Shanghai, China. A 9-year-old girl has become China's tenth human fatality from the virulent H5N1 strain of bird flu, the government said Wednesday. The girl died Monday in the southeast coastal province of Zhejiang, the Health Ministry said.

The rapid spread of the virus in birds throughout Europe, the Middle East, Africa and Asia has been accompanied by fears it will mutate into a form easily transmissible between humans and cause a worldwide flu pandemic.

Scientists noted that cats and martens eat similar prey. Wild cats in Asia have tested positive for the disease, and cats in Austria have as well.

“The presence of an H5N1 infection in a second mammalian species is not surprising,” said Till Backhaus, the regional minister for agriculture.

Cats are believed to have caught the virus by eating infected birds. Given the species’ similar eating habits, Ulrich Arnold, a scientist at the University of Marburg’s Institute for Medical Microbiology, said the discovery was “no new situation for Germany.”

In Washington, Homeland Security Secretary Michael Chertoff said the deadly strain of bird flu could appear in the United States in the next few months as wild birds migrate from infected nations.

A stone marten is seen in the Zoological Garden in Dresden, Germany, Thursday, March 9, 2006. The H5N1 bird flu virus has been found in a stone marten, a German laboratory said Thursday, indicating the disease has spread to another species of mammal. The weasel-like animal was found on the island of Ruegen in north Germany on March 2.

Chertoff said “there will be a reasonable possibility of a domestic fowl outbreak” as migrating birds mix with ducks, chickens and other birds in the U.S. But he cautioned against panic, noting the Agriculture Department has dealt with other strains of bird flu for years.

If a bird flu case is confirmed in the United States, Chertoff said the Homeland Security Department would have specific plans to deal with it, including watching to see if it developed human health characteristics.