Although swine influenza viruses usually sicken only pigs, potentially one might also spark a pandemic in people, as occurred with the 2009 H1N1 influenza virus. Because few long-term studies have surveyed flu viruses in swine, however, gaps exist in what is known about the evolution of swine influenza viruses and the conditions that enable a swine virus to infect humans and cause disease. Increased transportation of live pigs appears to have driven an increase in the diversity of swine influenza viruses found in the animals in Hong Kong over the last three decades, according to a new study.
In the longest study of its kind, Duke-NUS Graduate Medical School researchers found that swine viruses crossed geographic borders and mixed with local viruses, increasing their diversity.
"The majority of reported human infections have been people with close contact to farm animals," said Vijaykrishna Dhanasekaran, Ph.D., an assistant professor at Duke-NUS, who works in the Laboratory of Virus Evolution.
"I think the risk of swine-to-human transmission has not increased greatly, but the diversity of swine viruses has increased as shown in our study," Vijaykrishna said. "This means that the repertoire of viruses that humans are in contact with everyday has increased and this may lead to a higher likelihood of swine-to-human transmission, although the risk remains unquantified."
The study was published online in the journal Nature on May 25.
"The geographic transport of swine viruses that we highlight in our study is likely through the transport of live pigs," Vijaykrishna said. "Most swine viruses that have been described to date have been isolated from farmed pigs in Asia, Europe and North America. Some viruses have been isolated from backyard pigs in southeast Asia. However, no information is available on status of influenza in naturally roaming wild or domestic pigs."