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8/5/13

A Fair-Weather Outbreak: Officials Prepare for Another Season of Influenza

Combination of People, Pigs at Fairs Increases Transmission Risk

COLUMBUS, Ohio – ’Tis the season for flu at state and county fairs, where the combination of masses of fairgoers, livestock exhibitors and hundreds of exhibition pigs creates an atmosphere ripe for influenza transmission from animals to humans – and in the opposite direction as well.

Last year, more than 300 U.S. human swine influenza cases were linked to 37 fairs in at least 10 states, and 16 people were hospitalized. In Ohio, 107 human cases were traced to 14 county fairs, and one person died.

People most at risk for complications if they are infected with influenza are children under 5 or adults over age 65, pregnant women in their last trimester and anyone with a compromised immune system. Avoiding or minimizing time spent in the pig barns at fairs is the safest bet for these at-risk populations, said Andrew Bowman, assistant professor of veterinary preventive medicine at The Ohio State University.

Bowman has been leading an influenza surveillance project at Ohio county fairs since 2009, and was the lead author on a study published last fall that confirmed flu transmission had occurred between pigs and people.

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"At this point in time we have to consider that flu could show up at any fair."


Because humans can also infect swine with influenza, Bowman recommends that people with flu-like illnesses stay away from pigs until they’ve been fever-free for 24 hours without medicine.

Symptoms are similar for both species: lethargy, fever, coughing, nasal discharge and poor appetite.

For those who do visit livestock on display, the Centers for Disease Control and Prevention recommends standard good hygiene practices: Wash hands, avoid touching the eyes and nose, and avoid eating or drinking in the barn.

In a study published last fall, Bowman and colleagues compared the genomic sequences of influenza A viruses recovered in July 2012 from swine and humans. The analysis, showing a greater than 99 percent genetic identity among the viral isolates, means pigs and humans were infected with the same virus.

“We’ve got people moving, and we’ve got pigs moving,” Bowman said. “Pointing fingers at the pigs isn’t going to solve all the problems.”

Bowman led a second study last year noting that predicting pig illness is not as simple as looking at the pigs for clinical signs of disease. According to that research, more than 80 percent of pigs that tested positive for influenza A virus at Ohio agricultural fairs between 2009 and 2011 showed no signs of illness. The researchers found at least one flu-positive pig at 12 fairs – almost a quarter of fairs tested.

The influenza strains identified in pigs during the study included H1N2 and H3N2 viruses – strains that have been circulating in pigs since 1998. In 2011, all of the flu isolates Bowman and colleagues found in pigs at the fairs contained a gene from the 2009 pandemic strain of H1N1, which is similar to the variant flu strain that caused human illness in 2011.

Though this finding alone is no cause for panic, it does show how quickly influenza viruses can change, Bowman said.

The big-picture concern among scientists monitoring these infections: The more often that flu viruses are transmitted between species, the better their chances are of evolving into a strain to which humans are not immune.

In 2012, fair-related variant influenza cases were first reported in northwest Indiana and were then subsequently identified in nine other states, Bowman said.

“At this point in time we have to consider that flu could show up at any fair,” he said.

About 150 million people attend fairs in North America every year, and most don’t have routine exposure to swine, Bowman said. At the same time, the close human-animal contact in the barns eases the way for influenza transmission between species.

Influenza A virus usually infects the respiratory tract, and pigs can “shed” the virus into the air, meaning flu-positive swine areas are potentially under a “cloud” of flu particles that would be difficult to avoid.

Fair officials are trying a variety of transmission-prevention strategies this year, including rigorous inspection of animals for flu-like symptoms and taking pigs’ temperature upon arrival at the fair barns. Though nothing has proven fail-safe, shortening the exhibition time for pigs at fairs to three or four days appears to be the most effective way of lowering flu cases in animals and people, Bowman said.

While animal vaccination has also been suggested, vaccines for pigs are just like those for humans – they need to be updated for contemporary strains. However, manufacture of swine influenza vaccines is not updated frequently and the medicines are sold in bulk amounts, making vaccination unaffordable or impractical for small pig farms.

Pigs that do catch the flu do not pose a food-safety risk, Bowman said. As long as pork is handled and cooked properly, it is safe to eat.

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Contact: Andrew Bowman, (614) 292-6923; Bowman.214@osu.edu

Written by Emily Caldwell, (614) 292-8310; Caldwell.151@osu.edu

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