Swine Flu Virus Infections in Pigs

Swine influenza is a respiratory disease of pigs caused by type A influenza viruses and has a major economic impact on the swine industry in the United States. Flu outbreaks in pigs are common, especially during winter months. Swine flu can result in high rates of illness in herds.

Signs of swine flu in pigs may include:

  • coughing (“barking”)
  • discharge from the nose
  • sneezing
  • breathing difficulties
  • going off feed

High fevers in infected pigs are common, and can result in reduced fertility or elevated abortion rates among sows.
- Studies have shown that 30% to 50% of commercial U.S. swine have been infected with swine flu.
- Pigs most commonly get infected with flu viruses from other pigs (swine flu), but also can get infected with flu viruses from birds (avian flu), and from people (human flu). This cross-species spread of flu viruses can lead to new types of flu viruses.
- The number of subtypes and strains of flu virus circulating among U.S. herds has complicated swine flu vaccine programs and resulted in increased economic loss from illness in pigs.

How does swine flu spread among pigs?
Swine flu viruses are thought to spread mostly through close contact among pigs and possibly from contaminated objects moving between infected and uninfected pigs. Herds with continuous swine flu infections and herds that are vaccinated against swine flu might have sporadic disease, or may show only mild or no signs
of infection.

Can swine flu infections be prevented in pigs?
Swine flu infections can be potentially prevented by:
- Vaccinating herds
- Using good biosecurity measures
- Encouraging good hygiene practices among workers
- Using proper ventilation systems

What about flu vaccines for pigs?
Flu vaccines for pigs can help, but are not 100% effective. One reason is that several different strains of flu can infect pigs and vaccines might not protect against all strains.

How can veterinarians help?
Veterinarians can help to develop management strategies to reduce the spread of flu among herds and to prevent the spread of flu viruses between pigs, people, and birds.

Can people catch swine flu from eating pork?
There is no evidence to show that swine influenza can be transmitted through food. Eating properly handled and cooked pork and pork products is safe. Cooking pork to an internal temperature of 160°F kills bacteria and viruses.

What You Can Do
First, wash your hands frequently after exposure to animals and avoid contact with ill appearing animals. If you or your family becomes ill with flu-like symptoms, let your doctor know if you have been around pigs that could have the flu. A nose or throat swab is needed to determine if you might be infected with a swine flu virus.

Most cases of influenza in humans are caused by human flu viruses. However, in the unusual event that you are infected with a swine flu virus, the health department will want to talk with you about your illness and make sure that other people you live and work with are not sick with swine flu. Influenza medications are available to treat swine flu illness in people. These medicines should be started in the first 2 days of being ill to be most effective.

Flu Can Spread from Pigs to People and from People to Pigs
- Swine flu viruses can infect humans, but this is not common.
- Human and swine flu viruses are different. People who get vaccinated for human flu can still get sick from swine flu. Pigs that have been vaccinated for swine flu can still get sick from human flu.
- Symptoms of swine flu in people are no different from symptoms that people get when they are infected with human flu viruses.
- People infected with flu typically have fever (often high), cough, body aches, headaches, fatigue and runny or stuffy nose. Vomiting and diarrhea may also occur.
- Recent studies have shown that 15% to 25% of swine farmers might have been infected with swine flu viruses, as well as about 10% of veterinarians.
- Cases of swine flu have most commonly occurred in people with direct exposure to pigs, but some cases of human-to-human transmission have been reported.

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