A novel virus containing genes from the human swine flu virus and other swine influenza viruses has been identified in a surveillance program carried out by the University of Hong Kong (HKU). Researchers called the changes a genetic reassortment.

Though the new videos poses no immediate threat to humans, the findings highlight the fact that the human swine flu virus may change in unpredictable ways in pigs and thus trigger a new round of outbreaks.

The Influenza Research Team of HKU, in collaboration with the Food and Environmental Hygiene Department, has been watching flu viruses in pigs for the past 12 years, said Guan Yi, a professor of Department of Microbiology at the University of Hong Kong Li Ka Shing Faculty of Medicine.

The team took samples from 250 pigs in the Sheung Shui slaughter house twice a month and examined the DNA sequence of the viruses.

The H1N1 virus that caused the 2009 human swine flu pandemic was not detected in pigs prior to October 2009. Between October 2009 and January 2010, however, the virus was detected in pigs on four occasions, indicating the repeated transmission of the virus from humans to pigs. Similar findings were reported in other countries including Canada, the US and Singapore.

In January 2010, a hybrid virus that had acquired gene segments from the North American Triple reassortant swine virus, Eurasian swine viruses and the 2009 pandemic H1N1 virus was found, meaning the pandemic virus had genetically re-sorted with influenza viruses in pigs.

The researchers experimentally infected pigs with the hybrid virus. The infected pigs showed no apparent illness but were capable of transmitting the virus to other pigs.

The findings have been published in the prestigious international scientific journal Science.

The HKU researchers believed that the genetic reassortment very likely occurred in other parts of the world as well. The appearance of the altered virus in Hong Kong is not believed to be a unique event. Researchers believe it was detected here because there's a systematic surveillance program.

On the other hand, it is not the first time researchers have detected genetic reassortment of human flu virus in pigs, said Guan.

The hybrid virus identified in January did not appear virulent and it has not been transmitted to humans, he said.

There is no cause for people to stop eating pork because of the novel virus, said Malik Peipris, also a HKU microbiology professor.

"The Food and Agriculture Organization and the World Health Organization have clearly stated that, provided good hygiene measures are maintained and pork is well cooked, pigs and pork products do not pose an influenza threat to humans. Our findings do not provide reason to change this advice," he said.

The detection of the novel virus has heightened global surveillance of flu viruses in pigs, which have become a vehicle for genetic assortment of human, swine and avian influenza viruses.

"Our findings do emphasize the need for animal and public health authorities to work closely together to maintain surveillance of influenza viruses in pigs so that any unexpected changes in these viruses are rapidly detected and their significance rapidly evaluated," he said.

Thomas Tsang, controller of Center for Health Protection, said that the center has been informed of the HKU findings and will closely monitor the situation.

The genetic reassortment of human swine flu is a global issue. "A new pandemic may take place if genetic reassortment creates a novel virus that can be transmitted from human to human," he said.

Gabriel Leung, under secretary for Food and Health, said that since February the HKU researchers have found no recurrence of the H1N1 virus that caused the 2009 pandemic.

But the risk of genetic reassortment may increase again with another peak of human swine flu infection at the end of July.

China Daily

(HK Edition 06/19/2010 page1)