Issue 36, January 2009
About this Newsletter

Spotlight on Swine Influenza Virus

Every year in the United States, hundreds of thousands of people get influenza. Mild cases can cause significant discomfort and severe cases can be fatal; influenza kills about 36,000 people in the United States annually.

Catching the flu is something pigs and people have in common. Every year, pigs around the world are infected by the nasty, but rarely fatal, swine influenza virus (SIV), and they have been known to pass it to humans with whom they share close and frequent contact. Humans, in turn, have been known to pass influenza to pigs.

The United States doesn't have an established SIV surveillance system, but that may change soon, thanks to a collaborative effort involving the Agricultural Research Service's (ARS) National Animal Disease Center in Ames, Iowa. Scientists there are cooperating with the Centers for Disease Control and Prevention (CDC) and the Animal and Plant Health Inspection Service (APHIS) to develop a national SIV surveillance pilot program. ARS and APHIS are part of the U.S. Department of Agriculture (USDA).

Sick as a Hog: The Toll of SIV

SIV is a contagious respiratory disease that affects pigs around the world. Before 1998, most SIV cases reported in the United States were caused by one strain of flu virus, but over the past decade, new strains—containing genetic material from human and avian influenza strains—have appeared with growing frequency. Today, U.S. herds are affected by many SIV strains, a situation that complicates vaccination efforts.

Cells are observed for indications of swine influenza virus.

Pigs don't like being sick and producers don't like losing profits, so any research that will improve current prevention and treatment options, such as SIV vaccines, would be welcomed by the pork industry. Although it's seldom fatal, SIV is a major contributor to the porcine respiratory disease complex, arguably the swine industry's most costly infectious disease challenge.  

Increasing surveillance of SIV in swine could have benefits for humans as well. SIV can exchange genetic material with human and avian flu viruses, and it can be transmitted between humans and pigs. This means that the virus has the ability to foster a new—and potentially highly infectious—strain of human influenza.

"The more information we have, the more effectively we can design and implement programs to protect swine and humans from flu," says ARS veterinary medical officer Amy Vincent, a key player in initiating the collaborative effort.

In September 2008, the government agencies kicked off a two-year effort to design and establish a national surveillance system, which they envision as a possible precursor to a permanent USDA-funded program. When the program is set up, the agencies will encourage veterinary diagnostic laboratories across the nation to send SIV samples to APHIS. Scientists there and at ARS will test and characterize the samples. That information will be shared with ARS and CDC. In addition, the CDC will share human flu viruses with APHIS in cases where human illness with SIV is suspected.

At the Biosafety Level 2 laboratory in Ames, Vincent and her colleagues will sequence selective SIV genomes and study their effects on pigs. If the strains have the potential to impact human health, CDC scientists may use the samples to develop diagnostic tests or vaccines for humans.

Pigs and People in the Pink: Surveillance Benefits

Establishing routine surveillance procedures could have many benefits. Concerned agencies would obtain more information about the frequency, variability and location of SIV outbreaks. This, in turn, would provide the foundation for a better understanding of SIV's influence on livestock and human health. Ultimately, it could lead to improved diagnostic tests, preventative management, and vaccines for swine and humans.

This is particularly important because of the many documented instances in which human flu viruses have been transmitted to pigs, resulting in outbreaks among swine across the country. Improvements would bolster existing flu prevention methods, such as recommending seasonal vaccinations for people who work with pigs, and encouraging workers with flu symptoms to limit their contact with pig herds.

"Ideally, this surveillance system will make it possible to quickly identify significant changes in SIV in the future," Vincent says. This could be particularly useful if, for example, a new strain of SIV underwent genetic changes that made it easier to pass to humans.

Veterinarians or producers interested in participating in the surveillance system should contact their veterinary diagnostic laboratory or the APHIS Veterinary Services National Veterinary Service Laboratories.

For more information about ARS research on swine influenza, contact Cyril Gay, Leader of ARS National Program #103: Animal Health.