Russian doctors fear that a new flu virus might appear as a result of reassortment between the swine flu and bird flu viruses, Russia's chief sanitary official said on Monday.

"We have been monitoring it very closely," Gennady Onishchenko told journalists.

The H1N1 swine flu virus, which has sickened about half a million people worldwide with about 7,800 fatalities, is believed to have originated as a result of reassortment between the viruses of human flu, swine flu and bird flu.

The combination of H5N1 bird flu and H1N1 viruses could become a monstrous hybrid - a virus that combines high mortality rate of the former and ability to transmit efficiently among people of the latter.

The announcement followed media reports that doctors have registered a swine flu mutation, resistant to Tamiflu, a drug commonly used to treat the disease. AFP reported that in some cases the mutated virus also had an increased ability to attack lung tissue.

MOSCOW, November 30 (RIA Novosti)