Swine influenza virus remains a common enemy within pork operations and continues to give producers fits. Chances are from time to time you have seen the signs of SIV in your herd, including loss of appetite, listlessness, weight loss, labored breathing and coughing.
According to the Centers for Disease Control and Prevention, “H1N1 and H3N2 swine flu viruses are endemic among pig populations in the United States and something that the industry deals with routinely.”
Many operations have been affected by the virus and struggle to control the disease. CDC estimates that 51 percent of pigs in the north-central United States have been exposed to H1N1 influenza. The virus is commonly spread to new areas and farms due to moving infected pigs, transport vehicles or people. In fact, the current swine flu H3N2 viruses are closely related to human H3N2 viruses and were introduced into the pig population by people.
While SIV is often considered a late-fall and winter issue, the virus is increasingly present throughout the year. Virus is usually spread via aerosol transmission and can be shed for several days after infection.
Since lack of appetite affects performance, the principal economic loss occurs from stunted growth and delays in pigs reaching market weight. By itself, SIV usually runs its course and rarely causes death loss. However, you can expect that to change if SIV is complicated by infections such as Pasteurella multocida or Strep. suis.
Effective SIV vaccines are available, but sometimes that’s not enough to prevent infection. The reason, at least in part, lies with the virus’ unique abilities to change quickly, hampering your efforts to control it.
“The swine influenza virus is constantly changing and evolving,” says Marie Gramer, diagnostician at the University of Minnesota veterinary diagnostic laboratory. “Controlling SIV will continue to be a challenge because of the virus’ rapid evolution and ability to create new strains.”
Until 1998, the H1N1 virus was the only known cause of swine influenza. Gramer explains that in the late 1990s the H3N2 strain entered the U.S. swine herd, resulting in new virus strains. “The viruses causing swine influenza are quite capable of genetic re-assortment,” she adds. “We need to deal with the disease differently going forward because the disease profile has changed.”
To complicate matters further, any of the strains may be the culprit in an outbreak. “Farms may encounter any one of these virus strains from any of the different groups,” Gramer notes. “Plus, now we have human-like influenza viruses mixed in with swine influenza viruses, which are evolving as a separate group.”
New Threats, New Tools
In 2007, USDA approved a regulation to allow expedited updating of currently licensed SIV vaccines. The intention is to give vaccine manufacturers the ability to improve a vaccine’s protection level by updating it with new virus strains as they surface in the field.
“Vaccination works best when the virus in the vaccine matches the virus on the farm,” Gramer says. “Several strains can infect a farm at one time so the vaccines need to be updated regularly.”
“The virus is a moving target due to the variants that have emerged, so disease control has become a complicated issue,” says Michael Kuhn, senior swine veterinarian at Pfizer Animal Health. For example, to increase vaccination success against newly emerging virus threats, the company’s updated vaccine now contains two H1N1 strains, including a human-like strain and one new Group-IV H3N2 strain.
Continuous-flow production systems may face more challenge with SIV than more controlled pig flows. “The virus finds spots to linger and there’s usually a certain population that harbors the virus and passes it along to the next group,” Kuhn says. “Multi-site operations have helped break the cycle.”
SIV-immune status and disease history of surrounding farms can play important roles in determining vaccination regimens. Of course, you need to discuss a vaccination strategy with your veterinarian.
A common place to start is to vaccinate breeding animals. The resulting maternal antibodies that the sow passes along can help build piglets’ SIV-immune status. However, the amount of colostrum that each piglet receives can vary, which in turn affects the maternal antibody level delivered.
Timing vaccination of young pigs is difficult because of the maternal antibody variability from pig to pig. Until the maternal antibodies are depleted, they may interfere with vaccination success.
Due to the importance and challenges of matching the vaccine and the on-farm virus, some producers are using autogenous or custom-made vaccines. These are manufactured using isolates from the herd and are sometimes referred to as prescription vaccines.
“The flu vaccine portion of our business is growing steadily,” says Mark Titus, DVM, director of regulatory affairs for Newport Laboratories. The company produces autogenous vaccines.
“Our experience is that the protection we get from autogenous vaccines is more specific than what we get from a commercial vaccine off the shelf,” says Keith Wilson, DVM, director of production and veterinary services at Pro Pig. The company works with 28 grow/finish systems in central and northwest Iowa and southwest Minnesota.
SIV Biosecurity Review
Preventing the occurrence and spread of SIV can play an important role in fighting this virus on your farm. For example, measures such as biological filters to guard against porcine reproductive and respiratory syndrome virus are being used with success on some farms and may be part of the SIV solution.
The National Pork Board recommends that all pork production personnel be vaccinated each year before the flu season begins. “Producers and swine farm workers can reduce the risk of getting sick and bringing the flu to the farm or workplace by getting vaccinated,” says Liz Wagstrom, assistant vice president of science and technology for NPB.
Wagstrom recommends other practices to reduce infection spread such as having workers stay away from the farm if they are suffering from acute respiratory infections. “Virus shedding peaks when the clinical illness is most severe, but people may transmit the virus as long as the symptoms last — from three to seven days,” she notes.
Proper building ventilation and hygiene also will reduce virus transmission. Birds, particularly waterfowl, carry and spread the virus. Supplying pigs with water from ponds or reservoirs that hold migratory waterfowl can spell trouble.
Wagstrom suggests chlorinating water used on the farm if it is surface or pond water. “Chlorination helps, but only when there’s not a high level of organic matter,” Gramer adds. Be sure to bird-proof buildings to prevent access to pigs, facilities and feed.
Enforce other biosecurity practices such as using farm-specific clothing and footwear. “Swine influenza virus transmission often occurs between pigs and swine facility workers,” Gramer warns. The No. 1 way to decrease that transmission is for people to wear gloves and masks or some other type of respiratory protection.
At the very least, get workers to wash their hands with soap and hot water thoroughly and often. Also, don’t touch your face with your hands, and handle sneezing and coughing around pigs just as you would around people.
Is SIV control possible? “Yes, I think it is,” Gramer says. The researcher points to the need for collaboration among producers, veterinary research, diagnostic laboratories and vaccine makers to ensure that progress continues.
Certainly SIV’s rapidly changing nature makes control difficult and may cause setbacks. However, a comprehensive herd-health program, including an effective vaccination regimen and biosecurity measures, can help protect your herd from this quick change artist.