What People Who Raise Pigs Need To Know About Influenza (Flu)

FluView screen for Novel Influenza A Virus Infections

CDC data on the most current case counts for variant flu virus infections in humans reported in the United States.



As someone who raises pigs, whether for show (e.g., 4-H or National FFA Organization) or as part of a farming operation (i.e., commercial pork producer or swine farmer), you may have questions about flu in both pigs and people. This document addresses what is known about flu viruses in pigs and people and what people in contact with pigs can do to reduce the risk of getting sick or of getting their pigs sick.

Flu in Pigs and People

There are many causes of respiratory disease in pigs, including flu. Most of the flu type A viruses that spread in pigs are different from those that spread in people. When flu A viruses that normally spread in pigs are found in a person, they are called “variant” flu virus infections.
There are three main flu A viruses that spread in U.S. pigs: H1N1, H1N2 and H3N2. These viruses are genetically different from the flu A H1N1 and H3N2 viruses that commonly spread in people. People may have little to no immune protection against those flu A viruses that spread in pigs, and human flu vaccines do not protect against the flu A viruses that spread in pigs.
Flu A viruses that commonly infect pigs and pig herds can result in high rates of illness among pigs, but few deaths.
Signs of flu in pigs include:

  • Depression (not moving, “sick” appearance)
  • Loss of appetite (not eating)
  • Fever
  • Lying down
  • Coughing (“barking”)
  • Breathing trouble
  • Discharge from the nose (runny nose) or eyes

Pigs also can be infected with flu A viruses that usually spread in people and flu A viruses that normally spread in birds. This cross-species spread and possible mixing of flu A viruses in pigs can lead to new and very different flu A viruses that might gain the ability to spread easily between people and cause a pandemic.

Questions & Answers about Flu in Pigs

Q. How does flu spread among pigs?

A. Flu A viruses spread among pigs in the same way that human flu viruses spread among people. That is mainly through droplets containing flu A virus that spread through the air when infected pigs cough or sneeze. Flu A viruses also can spread through close contact between infected and uninfected pigs and from contact with an object contaminated by virus from an infected pig. Pigs also can be infected by flu A viruses from their human caretakers.

Q. Can flu virus infections be prevented in pigs?

A. It is possible to lessen the risk of flu A virus infections in pigs and/or severity of disease by following these management strategies:

  • Vaccinating herds (with swine flu vaccines)
  • Using good biosecurity measures
  • Using all-in and all-out husbandry procedures, and limiting pig movement between the pens, swine barns, and farms
  • Keeping swine barns, feeding, and water equipment, clean and sanitary
  • Vaccinating pig caretakers annually with the seasonal flu vaccine
  • Using proper ventilation systems in enclosed spaces, such as swine barns
  • If attending agricultural fairs, exhibitions, or terminal shows where many pigs are present, reducing the time that pigs are at the fair or exhibited can reduce transmission of flu among pigs and between pigs and people. More information is available at Key Facts for People Exhibiting Pigs at Fairs | CDC

Q. What about flu vaccines for pigs?

A. Flu vaccines for pigs can help reduce the risk of pigs getting flu but may not be 100% effective. Sometimes, flu vaccines used in pigs may not protect against the virus or viruses that are spreading in pigs, because the vaccine virus may not match the flu A virus that is circulating in the pigs. More information is available at influenza-vaccine-selection-for-pigs-producer-brochure (iastate.edu).

Q. How can veterinarians help?

A. You should work together with your veterinarian to develop herd management and vaccination strategies to reduce the spread of flu A among swine herds and to prevent the introduction and spread of flu viruses between pigs, people, and birds.

Q. Can people get flu A virus infection from a pig by eating pork?

A. Flu A viruses in pigs have not been shown to be transmissible to people through eating properly handled and prepared pork (cooked pig meat) or other products derived from pigs. For more information about the proper handling and preparation of pork, visit the USDA website fact sheet Fresh Pork from Farm to Table.

Q. What about the 2009 H1N1 virus?

A. The 2009 H1N1 flu A virus was first detected in people in the United States in April 2009. The virus was new to people and was able to spread easily from person-to-person, causing the first flu pandemic in more than 40 years. This virus had two genes from flu A viruses that normally spread in pigs in Europe and Asia, three genes from flu A viruses that normally spread in North American pigs, as well as genes from human and bird flu A viruses. This particular virus had not been detected in North American pigs before April 2009. The 2009 H1N1 flu A virus is now considered a human seasonal flu A virus.

In October 2009, the first 2009 H1N1 flu A virus infection in a pig in the United States was confirmed. Pigs in other countries also have been infected with the 2009 H1N1 flu A virus, including in Canada, Australia and Argentina. USDA and other researchers conducted studies in pigs that showed that the 2009 H1N1 virus caused illness in swine similar to those of other well-known, circulating swine flu A viruses.

Q. How common are variant flu virus infections in people?

A. There have been sporadic variant flu virus infections and small variant outbreaks, particularly among people exposed to pigs in the fair setting, in the past.

Flu Viruses Can Spread from Pigs to People and from People to Pigs

  • Human flu A viruses can infect pigs and can introduce new flu A viruses into the pig population.
  • Flu A viruses that normally spread in pigs can infect people, but this is uncommon. When this occurs, it is called a “variant” flu virus infection.
  • Reported infections with variant influenza viruses in the United States includes the most up to date information about infections with variant viruses that have been reported to CDC.
  • The flu A viruses that commonly spread in people are different from the ones that spread in pigs.
  • People who get an annual flu vaccine (to protect against human seasonal flu) can still get sick with flu A virus infections from pigs.
  • Pigs that have been vaccinated for swine flu can still get sick with some human flu A viruses.
  • When people are infected with variant flu viruses, the symptoms are basically the same as those caused by illness with human flu viruses and can include fever, cough, body aches, headaches, fatigue, and runny or stuffy nose. There may also be vomiting or diarrhea.
  • Most reported cases of human infection with variant flu viruses have occurred in people who have been near infected pigs in public settings, such as fairs or petting zoos, or who work directly with infected pigs.
  • Investigations of variant flu virus infections are routine. These investigations are designed to determine if the flu A virus in question is spreading from person to person. It is important to know if flu A viruses common among pigs are spreading among people so that cases in other people can be prevented.

Preventing the Spread of Flu Viruses Between People and Pigs

Like everyone else, animal caretakers caring for pigs should get annual seasonal flu vaccines. Although vaccination of people with seasonal flu vaccine probably will not protect against infection with variant flu viruses (because swine flu A viruses are substantially different from human flu A viruses), vaccination is important to reduce the risk of spreading human seasonal flu A viruses from ill people to other people and to pigs. Seasonal flu vaccination might also decrease the potential for people or pigs to become infected with human flu A viruses and flu A viruses from pigs at the same time. Such co-infections could result in the reassortment of two different influenza A viruses into a new flu A virus that has a different combination of genes, and which could pose a significant public or animal health concern.
Protective measures for animal caretakers at higher risk of serious flu complications

  • People at higher risk of serious flu complications from infection with human or swine flu A viruses include the following: children younger than 5 years, people 65 years and older, pregnant people, and people with certain long-term health conditions (like asthma and other lung disease, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions). More information is available at People at Higher Risk of Flu Complications | CDC.
  • Animal caretakers who are at higher risk of serious flu complications should avoid pigs and swine barns, if possible.
  • If animal caretakers at higher risk of serious flu complications cannot avoid exposure to pigs, they should wear a well-fitting mask that covers the nose and mouth (e.g., an N95 respirator or KN95 respirator if available, or if not available, a surgical mask) when around pigs to reduce the risk of exposure to flu A viruses from pigs. Animal caretakers at higher risk should also wash their hands with soap and running water before and after exposure to pigs or a swine barn. If soap and water are not available, use an alcohol-based hand rub.

Other routine measures to take:

  • Wash your hands often with soap and running water before and after exposure to pigs. If soap and water are not available, use an alcohol-based hand rub.
  • Avoid close contact with pigs that look or act ill, when possible.
  • Avoid contact with pigs if you are experiencing flu-like symptoms.
  • If you must come in contact with pigs while you are sick, or if you must come in contact with pigs (or their environment) that are known or suspected to be infected, you should take appropriate protective measures. For example, wear protective clothing, gloves, well-fitting masks that cover your nose and mouth (e.g., an N95 respirator or KN95 respirator if available, or if not available, a surgical mask), and other “personal protective equipment” or PPE and practice good respiratory and hand hygiene.

If you or your family members become sick with flu-like symptoms and need medical treatment, take the following actions:

  • Contact your health care provider and let them know about your symptoms and that you have been around pigs. Your doctor may prescribe treatment with flu antiviral medications and may want a nose and throat specimen collected from you for testing at your state health department. Antiviral treatment for flu works best when started soon after symptoms begin.
  • Stay home from work and school, avoid travel, and avoid or limit contact with other people and pigs as much as possible for 7 days after your symptoms begin or until you have been fever-free for 24 hours without the use of fever reducing medications, whichever is longer. This is to protect other people and healthy pigs from getting sick.
  • Practice good respiratory and hand hygiene. This includes covering your mouth and nose with a tissue when coughing or sneezing and putting used tissues in a waste basket. Always wash your hands after coughing or sneezing. This is to lower the risk of spreading whatever virus infection you have to others.

Almost all flu cases in people are caused by human flu viruses, not viruses from pigs. However, if you are infected with a flu A virus of animal origin, 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 the same virus. If you do get sick with variant flu, there are prescription antiviral medications that can treat your illness. Illnesses associated with variant flu virus infection have been mostly mild with symptoms similar to those of human seasonal flu. However, serious illness can occur, especially in people who are at higher risk of developing serious flu complications. It is important to contact your doctor right away and tell them if you develop flu symptoms and have had recent exposure to pigs or settings where pigs are kept.