WASHINGTON, (Reuters) – The new virus that has  killed as many as 177 people and spread globally is a mongrel  that appears to have mixed with another hybrid virus containing  swine, bird and human bits, U.S. researchers reported yesterday.

Raul Rabadan and colleagues at Columbia University in New  York analyzed the published genetic sequences from the H1N1  virus that has brought the world to the brink of a pandemic.

“The closest relatives to the virus we have found are swine  viruses,” Rabadan said in a telephone interview.
“Six segments of the virus are related to swine viruses  from North America and the other two from swine viruses  isolated in Europe/Asia,” they wrote in the online journal  Eurosurveillance.

The U.S. Centers for Disease Control and Prevention said  last week after discovering this virus in two U.S. children  that it had four virus types — two swine, an avian and a human  component.
It may be even more complex than that.

Influenza viruses mutate constantly and they also swap  genetic material with one another promiscuously, especially if  an animal or person is infected with two strains at once.

Rabadan’s team said this particular strain looked partly  like another hybrid, or what scientists call a reassortant,  virus.
“The North American ancestors are related to the multiple  reassortants, H1N2 and H3N2 swine viruses isolated in North  America since 1998,” they wrote.

“In particular, the swine H3N2 isolates from 1998 were a  triple reassortment of human, swine and avian origin.”
Scientists can study those genetics to try to track the  origin of the new virus. Mexican officials have denied it came  from pigs in Mexico and pork producers have been battling  rumors it could have come from pig farms there.
Rabadan said the findings did not show the virus came  directly from pigs. “We don’t know how long this virus has been  in humans,” he said.