An international team of researchers said Friday that the new H1N1 virus must have been circulating undetected for years, likely in pigs, according to a report by Reuters. The most complete analysis to date points to pigs as a potential source.

"The results of the study show the global need for more systematic surveillance of influenza viruses in pigs," Dr. Nancy Cox, chief of the influenza division at the U.S. Centers for Disease Control and Prevention, told reporters.

The report by Cox and an international team of researchers in the journal Science said the virus "might have been circulating undetected among swine herds somewhere in the world." They said pigs are clearly a potential source of human pandemics.

The researchers confirmed the mixture of human, pig and bird genes in the new virus, which has infected more than 11,000 people in 42 countries, and killed 86. The World Health Organization is considering declaring a full pandemic of the virus, which causes mostly mild disease in people.

The researchers have sequenced the genetic codes of 70 different samples of the new virus from the United States and Mexico. They said other virus mixtures are infecting pigs but simply have not yet been seen.

"We can actually determine where each of the genes ... originated," Cox said. The new virus is a mixture of mixtures -- it includes part of a so-called triple reassortant virus that contains elements of human, bird and swine strains. However, they still do not know how the new virus arose.

Read more on the genetic study of the new H1N1 virus.

For more information about the H1N1 outbreak, visit Pork's H1N1 Special Section.

Source: Reuters