The International Herald Tribune reports:

Authorities have culled more than half a million domestic birds on a farm in southern Russia hit by the H5N1 strain of bird flu, officials said Tuesday. More than 600,000 chickens on the Gulyai-Borisovskaya farm in the Rostov-on-Don region have been destroyed to prevent the virus from spreading, said Oleg Ugnivenko, a spokesman for the regional branch of Russia's Emergency Situations Ministry. The virus also sickened birds in the neighboring Tselinsky district, and authorities have taken steps to stop it from spreading, Ugnivenko said.

In September, authorities reported an H5N1 outbreak at a poultry farm in the neighboring Krasnodar region, and early in the year the strain was confirmed in several other regions across Russia.

No human cases of bird flu have been reported in Russia, which had its first reported cases of H5N1 in Siberia in 2005. World health authorities are tracking the H5N1 strain out of concern that it could mutate into a form more easily transmitted among people, sparking a global flu pandemic.