H3N2 influenza unlikely to spread between humans

Aug 11 2009

Seeing animals up close is an integral part of experiencing the state and county fairs that take place around the country each summer and fall. And with good hygiene, Kansas State University veterinary experts say fair visitors shouldn't worry about contracting diseases from animals.

"Be very attentive to good hygiene and wash your hands after contact with animals," said Gary Anderson, director of K-State's Veterinary Diagnostic Laboratory. "We encourage people to visit animal exhibits at fairs as long as they take appropriate precautions."

A case of H3N2 influenza was reported in Riley County after a child apparently had direct contact with pigs at a county fair. The Kansas Department of Health and Environment reported that the child completely recovered.

K-State experts said people shouldn't worry excessively about contracting H3N2 from pigs. For one thing, attention to hygiene and proper hand washing are a good defense, they said. Another reason is that this virus does not appear to be particularly virulent for humans.

Not all influenza viruses are like the pandemic H1N1, which has the ability to easily spread from human to human. The K-State researchers said that although H3N2 can pass from pigs to humans, it has not been shown to pass from humans to humans easily. However, there is the potential that it could pass from people back to pigs. This is one reason why workers in swine operations wear masks and other personal protective equipment when working with the animals.

Also, the researchers said it should be emphasized that pork is safe to eat, even when influenza viruses have been involved.

"This H3N2 is a virus that doesn't appear to be particularly virulent for humans," Anderson said. "You could say that the person infected was a dead-end host because it didn't like him too much. The virus didn't manage to survive and be passed on."

The H3N2 virus is different from the novel pandemic H1N1 virus that does spread among people. According to the literature, the majority of swine viruses that transfer to humans are H1N1 types, said Juergen Richt, Regents Distinguished Professor at K-State's College of Veterinary Medicine and a Kansas Bioscience Authority Eminent Scholar.

However, Richt said that the H3N2 virus introduced to North American pigs in the mid-1990s was a human-swine double reassortant virus.

"This scenario shows the need for and importance of studying zoonotic infectious diseases -- those that spread between humans and animals and vice versa -- and that's where we at K-State have expertise," Richt said. "Even if there is a disease problem, our faculty here at K-State can provide answers and solutions. We can diagnose diseases quickly and therefore can provide clear answers to pressing questions."

Anderson said that another K-State strength is having a strong partnership between diagnostics and research.

"It makes our research and diagnostic efforts that much better," he said.

Anderson said that the K-State Veterinary Diagnostic Lab and researchers in K-State's College of Veterinary Medicine welcome opportunities to work on infectious zoonotic diseases with state agencies like the Kansas Department of Health and Environment and the Kansas Animal Health Department, as well as federal researchers at the Centers for Disease Control and Prevention and the U.S. Department of Agriculture.

"At K-State, we're ready for the unknown," Anderson said.

A strong partnership between diagnostics and research has helped Richt and a fellow K-State researcher in dealing with an unknown flu strain while both were researchers at the U.S. Department of Agriculture's National Animal Disease Center in Ames, Iowa.

When diagnosticians from the University of Minnesota ran into difficulties determining exactly what type of flu was in a pig sample from two Missouri farms, they turned to Richt and Wenjun Ma, who is now a research assistant professor at K-State.

In two weeks, Ma said, they had sequenced the virus, which turned out to be H2N3 -- not to be confused with H3N2 that showed up in Riley County. This information helped Ma, Richt and U.S. Department of Agriculture colleagues develop a vaccine for it and create better diagnostic tools.

"When diagnostic labs get a sample, they now can use the diagnostic tools we developed," Richt said.

Their work was published in 2007 in the Proceedings of the National Academy of Sciences, a prestigious academic journal.

But how do influenza strains get their names anyway? H1N1, H1N2, H2N3, H3N1, H3N2, H5N1 look like a jumble of numbers and letters to most of us, but they actually tell scientists quite a bit about particular strains of influenza viruses.

Anderson and Richt explained that influenza subtypes get their names from the unique combination of proteins on the outer layer of the virus. The H stands for hemagglutinin, for which there are 16 types, and the N is for neuraminidase, for which there are nine types.

Richt said that in mammals -- humans, pigs, horses, dogs, marine mammals and the like -- only a few of these H's and N's can be consistently isolated, whereas all 16 H's and nine N's have been found in waterfowl and seabirds. He said that when mammalian virus strains meld, or "mate," with avian strains they may become virulent in other animals like humans and in pigs.

Because these proteins are on the outer layer of the virus, they make first contact with the receptors that line the animals' respiratory tracts and with their immune systems. That also means these are the genes most likely to be altered, resulting in new, mutated strains of flu, the researchers said.

Novel viruses often are a combination of two or three viruses, Richt said. So, a particularly virulent virus like the pandemic H1N1 flu virus contains genes from human, swine and avian strains.

Biographical information on Anderson and Richt is available at: http://www.k-state.edu/media/mediaguide/bios/andersonbio.html and http://www.k-state.edu/media/mediaguide/bios/richtbio.html