Health experts in Serbia have confirmed its first case of the lethal strain of the bird flu virus.

A wild swan was found dead last week near the border with Croatia.  Officials say tests run on the bird show it tested positive for the H5N1 strain of the virus.

Other birds that have been found dead in a handful of risk zones are being tested for the disease.  Officials have ordered all domestic birds in Serbia to be kept inside.

In Germany, health officials say a stone marten, a weasel-like mammal, has been detected with the H5N1 strain of the virus.

Bird flu has spread from Asia to Europe, Africa and the Middle East over the past several months.  It has killed more than 90 people since 2003, mostly in Asia.

The top United Nations bird flu expert has declared a regional crisis in West Africa, where Niger and Nigeria are struggling to contain the virus.

Dr. David Nabarro said Wednesday the spread of the deadly H5N1 strain has reached disturbing proportions in parts of West Africa and said the entire region is at risk.

Dr. Nabarro also said he expects bird flu to arrive in North America by the end of the year.

Some information for this report was provided by AFP, AP and Reuters.