Swine flu is an infection caused by a virus. It's named for a virus that pigs can get. People do not normally get swine flu, but human infections can and do happen. In 2009 a strain of swine flu called H1N1 infected many people around the world.

The virus is contagious and can spread from human to human. Symptoms of swine flu in people are similar to the symptoms of regular human flu and include fever, cough, sore throat, body aches, headache, chills and fatigue.

There are antiviral medicines you can take to prevent or treat swine flu. There is a vaccine available to protect against swine flu. You can help prevent the spread of germs that cause respiratory illnesses like influenza by

• Covering your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
• Washing your hands often with soap and water, especially after you cough or sneeze. You can also use alcohol-based hand cleaners.
• Avoiding touching your eyes, nose or mouth. Germs spread this way.
• Trying to avoid close contact with sick people.
• Staying home from work or school if you are sick.

What is Swine Influenza?

Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza virus that regularly causes outbreaks of influenza in pigs. Swine flu viruses do not usually infect humans, but rare human infections have occurred. Swine flu viruses can cause high levels of illness in pig herds, but cause few deaths in pigs. Swine influenza viruses can circulate among swine throughout the year, but most outbreaks occur during the late fall and winter months similar to outbreaks in humans.

How many swine flu viruses are there?

Like influenza viruses in humans and other animals, swine flu viruses change constantly. Pigs can be infected by avian influenza and human influenza viruses as well as swine influenza viruses. When influenza viruses from different species infect pigs, the viruses can reassort (i.e. swap genes) and new viruses that are a mix of swine, human and/or avian influenza viruses can emerge. Over the years, different variations of swine flu viruses have emerged. At this time, there are three main influenza A virus subtypes that have been isolated in pigs in the United States: H1N1, H1N2, and H3N2.

How does swine flu spread among pigs?

Swine flu viruses are thought to be spread among pigs mostly through close contact and possibly from contaminated objects moving between infected and uninfected pigs. Infected swine herds, including those vaccinated against swine flu, may have sporadic disease, or may show only mild or no symptoms of infection.

What are signs of swine flu in pigs?

Signs of swine flu in pigs can include fever, depression, coughing (barking), discharge from the nose or eyes, sneezing, breathing difficulties, eye redness or inflammation, and going off feed. Some pigs infected with influenza, however, may show no signs of illness at all.

How common is swine flu among pigs?

H1N1 and H3N2 swine flu viruses are endemic among pig populations in the United States and something that the industry deals with routinely. Outbreaks among pigs normally occur in colder weather months (late fall and winter), but can occur year round. While H1N1 swine viruses have been known to circulate among pig populations since at least 1930, H3N2 influenza viruses did not begin circulating among pigs in the United States until about 1998. The H3N2 viruses initially were introduced into the pig population from humans. However, since then the H3N2 viruses circulating in pigs have changed. The H3N2 viruses circulating in pigs now are very different from the seasonal H3N2 viruses that circulate in humans.

Is there a vaccine for swine flu?

Just as there are influenza vaccines for people, there are specific swine influenza vaccines available for pigs.

What is a variant influenza virus?

When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus.” For example, if a swine origin influenza A H3N2 virus is detected in a person, that virus will be called an “H3N2 variant” virus or “H3N2v” virus.

Can humans be infected with swine influenza viruses?

Yes. Swine flu viruses do not normally infect humans, however, sporadic human infections with influenza viruses that normally infect swine have occurred. When this happens, these viruses are called “variant viruses.” Most commonly, human infections with variant viruses have occurred in people exposed to infected pigs (e.g., children near pigs at a fair or workers in the swine industry). In addition, there have been documented cases of multiple persons becoming sick after exposure to one or more sick pigs. Also, cases of limited person-to-person spread of variant viruses have occurred.

How common is it for humans to be infected with influenza viruses that normally infect swine?

In the past, CDC received reports of approximately one human infected with influenza viruses that usually are found in swine every one to two years, but beginning in 2012, there was a jump in the number of these cases. The increased detection and reporting of these cases could be occurring for a number of reasons, including one or more of the following factors: first, pandemic preparedness efforts have improved state level surveillance and laboratory capacity to detect novel viruses in the United States; second, in 2005, novel influenza virus infections were made internationally reportable; and in 2007 they were made domestically reportable. And third, it’s also possible that there is a true increase in the number of these cases, possibly occurring from exposure to infected swine or through subsequent, limited human-to-human transmission.

Why are human infections with variant viruses of concern?

Influenza viruses that infect pigs may be different from human influenza viruses. Thus, influenza vaccines made against human influenza viruses are generally not expected to protect people from influenza viruses that normally circulate in pigs. In addition, because pigs are susceptible to avian, human and swine influenza viruses, they potentially may be infected with influenza viruses from different species (e.g., ducks and humans) at the same time. If this happens, it is possible for the genes of these viruses to mix and create a new virus. This type of major change in the influenza A viruses is known as antigenic shift. If this new virus causes illness in people and can be transmitted easily from person-to-person, an influenza pandemic can occur. This is what happened in 2009 when an influenza A H1N1 virus with swine, avian and human genes emerged in the spring of 2009 and caused the first pandemic in more than 40 years.

What symptoms do people have when they are infected with variant viruses?

People who have been infected with variant viruses have had symptoms similar to the symptoms of regular human seasonal influenza. These include fever, lethargy, lack of appetite and coughing. Some people also have reported runny nose, sore throat, eye irritation, nausea, vomiting and diarrhea.

Can people catch swine flu/variant flu from eating pork?

Swine influenza has not been shown to be transmissible to people through eating properly handled and prepared pork (pig meat) or other products derived from pigs.

How are variant influenza viruses spread?

Influenza viruses can be directly transmitted from pigs to people and from people to pigs. These infections have most commonly been reported after close proximity to infected pigs, such as in pig barns and livestock exhibits housing pigs at fairs. Infected pig cough or sneeze and droplets with influenza virus in them can spread through the air. If these droplets land in your nose or mouth, or are inhaled, you can be infected. There also is some evidence that you might get infected by touching a surface with virus on it and then touching your mouth or nose. A third way to possibly get infected is to inhale droplets or dust containing influenza virus. Scientists aren’t really sure which of these ways of spread is the most common.

Human-to-human transmission of variant flu viruses also has occurred, though this method of spread has been limited. This kind of transmission is thought to occur in the same way that seasonal flu transmits in people, which is mainly through coughing or sneezing by people who are infected. People also may become infected by touching something with flu viruses on it and then touching their mouth or nose. It’s important to note that in most cases, variant flu viruses have not shown the ability to spread easily and sustainably from person to person.

How can human infections with variant influenza viruses be diagnosed?

To diagnose variant influenza A virus infection, a respiratory specimen would generally need to be collected within the first 4 to 5 days of illness (when an infected person is most likely to be shedding virus). However, some people, especially children, may shed virus longer. Since the 2009 H1N1 pandemic, state health departments have the ability to test for novel (non-human) influenza viruses. However, if a variant influenza virus is suspected, it is sent to CDC for further testing.

What medications are available to treat variant flu infections in humans?

There are three different antiviral drugs that are recommended for use in the United States for the treatment of influenza: oseltamivir, peramivir and zanamivir.

Influenza antiviral drugs can be used to treat influenza infections, including human infections with influenza viruses that normally circulate in swine (swine influenza). There are three different antiviral drugs that are recommended for use in the United States for the treatment of influenza: oseltamivir, peramivir and zanamivir.

What to do if you get sick

At this time, CDC recommends the following:

• If you go to a doctor for flu symptoms (see below) following direct or close contact with swine, tell your doctor about this exposure.
• If you have flu symptoms, follow CDC’s regular recommendations for seeking treatment for influenza.
• If you have symptoms of flu and are very sick or worried about your illness contact your health care provider.

Certain people are at greater risk of serious flu-related complications (including young children, elderly persons, pregnant women and people with certain long-term medical conditions) and this is true both for seasonal flu and novel flu virus infections.

Your doctor may prescribe antiviral drugs that can treat the flu, including H3N2v. These drugs work better for treatment the sooner they are started. If you are prescribed antiviral drugs by your doctor, you should finish all of the medication, according to your doctor’s instructions.

Also, whenever you have flu symptoms and are seeing a health care provider, always remember to tell them if you have asthma, diabetes, heart disease, neurological and neurodevelopmental conditions, are pregnant, or are older than 65 or younger than 5 years. These conditions and age factors put you at high risk of serious complications if you have the flu.

Flu signs and symptoms usually include fever and respiratory symptoms, such as cough and runny nose, and possibly other symptoms, such as body aches, nausea, vomiting, or diarrhea.

Health care providers will determine whether influenza testing and possible treatment are needed. There are influenza antiviral drugs that can be used to treat infection with H3N2v viruses as well as seasonal influenza viruses.

Pigs can be infected with their own influenza viruses (called swine influenza) that are usually different from human flu viruses. While rare, influenza can spread from pigs to people and from people to pigs. When people get swine flu viruses, it’s usually after contact with pigs. This has happened in different settings, including fairs. The Centers for Disease Control and Prevention (CDC) recommends people take the following actions to help prevent the spread of flu between pigs and people.

For People with High Risk Factors:

• Anyone who is at high risk of serious flu complications planning to attend a setting where pigs will be present should avoid pigs and swine barns.
• People who are at high risk of serious flu complications include children younger than 5 years, people 65 years and older, pregnant women, 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).

For People Not at High Risk:

• Don’t take food or drink into pig areas; don’t eat, drink or put anything in your mouth in pig areas.
• Don’t take toys, pacifiers, cups, baby bottles, strollers, or similar items into pig areas.
• Avoid close contact with pigs that look or act ill.
• Take protective measures if you must come in contact with pigs that are known or suspected to be sick. This includes minimizing contact with pigs and wearing personal protective equipment like protective clothing, gloves and masks that cover your mouth and nose when contact is required.
• 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.
• To further reduce the risk of infection, minimize contact with pigs in the pig barn and arenas.
• Watch your pig (if you have one) for illness. Call a veterinarian if you suspect illness.
• Avoid contact with pigs if you have flu symptoms. Wait to have contact with pigs until 7 days after your illness started or until you have been without fever for 24 hours without the use of fever-reducing medications, whichever is longer. If you must have contact with pigs while you are sick, take the protective actions listed above.

People with high risk factors who develop flu symptoms should call a health care provider. Tell them about your high risk factor and any exposure to pigs or swine barns you’ve had recently. Human seasonal flu vaccine will not protect against commonly circulating swine influenza viruses, but prescription influenza antiviral drugs can treat infections with these viruses in people.