"Bird flu outbreaks are not impossible in August in the Chelyabinsk Region. In 2005, three out of the seven registered bird flu outbreaks occurred in August," a spokesman said.
According to the World Health Organization (WHO), bird flu has killed 192 people around the world since late 2003.
Indonesia has been the worst hit by human bird flu cases, and has the highest mortality rate from infections with the deadly H5N1 viral strain, at about 80%. The virus has spread rapidly in the country, which has the world's fourth largest population.
The second hardest-hit country is Vietnam, where 95 human bird flu cases have been registered, with 42 deaths.