Fall 2009

An Update on Influenza A H1N1 Research in Pigs

H1N1 will not pose a food safety risk for consumers

By Beth Young, DVM, MU Extension Commercial Ag Program Swine Veterinarian

Novel influenza A H1N1 continues to circulate among the human population. As the winter flu season approaches, there is speculation that the number of human cases of influenza A H1N1 in the USA will increase.

This new influenza strain is not known to be circulating among pig populations in Missouri or anywhere else in the USA. To date, all 114 swine samples submitted to the National Animal Health Laboratory Network for novel H1N1 testing have been negative. However, if increased numbers of human cases of influenza should occur this winter, the risk of pig herds in the USA becoming infected with the novel influenza A H1N1 virus will also increase.

While the ease with which this particular strain of the virus is spread between people and pigs has yet to be determined, researchers have demonstrated that this new influenza strain can be transmitted relatively easily from pig-to-pig.

If the disease is inadvertently introduced into a swine herd, it is likely that it would quickly spread between animals and become established in the herd. Normal bio-security measures have been intensified as pork producers take extra steps to protect their herds and reduce exposure risks.

Fortunately, the clinical signs of influenza that have been reported in pigs experimentally infected with the novel influenza virus are similar to those seen in typical cases of swine influenza. Signs include fever, runny nose and eyes, coughing, decreased activity, and lack of appetite. The clinical signs produced by the new influenza strain appear to be no more severe than those produced by other strains of swine influenza virus. There are no reports of pigs dying from the disease.

Typical swine influenza viruses do not contaminate pork, nor are they transmitted to people through the consumption of pork products. Researchers with the Agricultural Research Service (ARS) recently confirmed this fact about the novel H1N1 virus.

Pigs were experimentally infected with the same strain of the new influenza virus that was isolated in people in California. Five days after being infected, samples were collected from various tissues of the pigs and tested for the presence of live influenza virus. Live influenza virus was only found in the respiratory tracts (nose and lung) of the infected pigs while none was found in their muscles or internal organs.

This experiment shows that this new strain of influenza behaves similarly to typical swine influenza strains and will not contaminate the meat of infected pigs. In the event that novel H1N1 influenza does become established in American pig herds, it will not pose a food safety risk for consumers.

Scientists with the ARS also examined whether the immunity produced in response to exposure to swine influenza viruses known to be circulating in American pigs would provide protection against the novel H1N1 strain in pigs. Their results suggested that pigs that have developed immunity through past exposure to typical swine influenza strains may not be protected against the novel H1N1 strain.

Results also suggested that commercial swine influenza vaccines currently available for use in pigs in the United States may not provide protection against the new influenza strain. To facilitate the development of new influenza vaccines for pigs that would provide protection against the new strain, the USDA has made a “master seed virus” available to veterinary vaccine manufacturers. This eliminates the need for each manufacturer to develop and test their own master seed virus and thus will decrease the time needed to create a new vaccine. However, a date for the release of a commercially available novel H1N1 influenza vaccine for pigs has not been set.

In the meantime, producers can reduce the influenza risk to their herds by maintaining strict biosecurity protocols. The number of visitors to the herd should be kept to a minimum. People entering the pig barn should shower and/or change out of their street clothes. Anyone working with pigs is encouraged to get a flu shot. Under all circumstances, anyone that has flu-like symptoms should not be allowed into the barn.

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