Farmers, veterinarians and meat processors who routinely come into contact with pigs in their jobs have a markedly increased risk of infection with flu viruses that infect pigs, according to a study funded in part by the National Institute of Allergy and Infectious Diseases (NIAID).
While the findings are not entirely unexpected, the strikingly higher risk of infection coupled with the fact that pigs can be infected by swine viruses, bird (avian) viruses as well as human flu viruses--thereby acting as a virtual virus "mixing bowl," especially on farms where pigs, chickens and people coexist--is a potential public health concern, the study authors assert. The paper appears online this week in Clinical Infectious Diseases.
"Pigs play a role in transmitting influenza virus to humans," says NIAID Director Anthony S. Fauci, M.D. "The worry is that if a pig were to become simultaneously infected with both a human and an avian influenza virus, genes from these viruses could reassemble into a new virus that could be transmitted to and cause disease in people."
The study results strongly suggest that occupational exposure to pigs significantly increases the risk of developing swine influenza infection. Agricultural workers should, therefore, be considered in developing flu pandemic surveillance plans and antiviral and immunization strategies, according to the study's co-investigator, Gregory C. Gray, M.D., director of the University of Iowa Center for Emerging Infectious Diseases.
"If migratory birds introduce the H5N1 bird flu virus into swine or poultry populations in this country, agricultural workers may be at a much greater risk of developing a variant H5N1 and passing it along to non-agricultural workers," Gray says. "Not protecting agricultural workers could amplify influenza transmission among humans and domestic animals during a pandemic and cause considerable damage to the swine and poultry industries, as well as the U.S. economy." While swine in other countries have been infected by the H5N1 virus, to date, the virus has not become readily transmissible between swine.
Swine influenza infections generally produce mild or no symptoms in both pigs and humans. However, exposure to swine flu virus at a 1988 Wisconsin county fair resulted in serious illness for 50 swine exhibitors and three of their family members; one previously healthy woman who became infected died.