Swine flu is an infection in humans that is caused by strains of influenza virus that infect and cause outbreaks in pigs (swine).
Most people who have been infected with swine flu have had close contact with an infected pig.
People may have human flu-like symptoms such as fever, cough, and headache.
To diagnose swine flu, doctors test samples of secretions taken from the person's nose and throat.
Resting, drinking plenty of fluids, and avoiding exertion can help people recover, as can taking pain relievers, decongestants, and sometimes antiviral medications.
Swine flu is caused by several strains of influenza A virus that normally are transmitted between pigs (pigs usually have symptoms including fever, coughing, sneezing, and red eyes). These strains can infect other animals too, such as birds (chickens, turkeys, ducks, pet and zoo birds), dogs, horses, whales, and seals. The strains can then spread from animals to people if the genetic material of the virus changes (mutates), enabling it to attach to cells in the human respiratory tract.
Infections that can be transmitted between animals and people are called zoonotic diseases, or zoonoses (see Introduction to Diseases Spread Between Animals and People (Zoonoses)). See also Avian Influenza (Bird Flu), Equine Influenza, and Canine Influenza (Flu).
Swine flu is considered a variation of influenza (flu) in humans. People who are at high risk of swine flu are those who have direct or indirect contact with infected pigs, such as pig farmers and other people who work in the pig industry and children at agricultural exhibitions. Pig-to-human transmission (spread) of the virus is rare. Infected pigs have the virus in their nasal secretions and can spread it to humans in the same way seasonal influenza viruses spread among people. Once infected, humans can spread swine flu to each other (person-to-person transmission), but this is rare. Swine flu does not develop in people who eat infected pork.
All recognized influenza virus strains are named. For example, strains of influenza A virus are named based on the properties of the 2 proteins that are present on the surface of the virus. The proteins are hemagglutinin (H) and neuraminidase (NA). To date, 18 subtypes of H and 11 subtypes of NA have been identified in influenza viruses. Subtypes are numbered, so, for example, a virus with subtype 1 of hemagglutinin and subtype 1 of neuraminidase is named H1N1. The H1N1 strain caused the swine flu pandemic in 2009–2010. Other variants that cause swine flu are H1N2 and H3N2.
This illustration shows a generic influenza A virus. Covering the surface of the virus are the proteins hemagglutinin (H; light blue) and neuraminidase (NA; red), which determine the strain of virus.
CDC/Illustrator: Dan Higgins
Swine flu pandemic
A pandemic is a sudden, unexpected outbreak of a disease that spreads rapidly across a large region, typically across continents and sometimes even worldwide.
The H1N1 swine flu pandemic occurred in 2009–2010. This strain had a combination of genes from pig (swine), bird, and human influenza viruses. Because the first reports focused on the swine component, it was referred to publicly as "swine flu," even though it was not acquired directly from pigs. People acquired this H1N1 strain from other infected people like they would ordinary flu.
The 2009 swine flu pandemic spread to more than 70 countries and throughout the United States. It was fatal for some people, and most of the deaths occurred in Mexico. Since 2009, this H1N1 strain has circulated as a seasonal influenza strain.
Symptoms of Swine Flu
Symptoms of swine flu usually start 1 to 4 days after a person is infected but can take 7 days to appear. The illness lasts about 3 to 5 days.
Common symptoms in people of any age include fever, cough, sore throat, runny nose, muscle aches, and headache.
In children, swine flu can cause vomiting and diarrhea. Children may not develop a fever, and the whites of their eyes may become bloodshot.
Diagnosis of Swine Flu
A doctor's examination
Sometimes tests on samples of secretions taken from the nose and throat
People who have flu-like symptoms (fever, cough, and headache) and who have had contact with pigs in an area where pigs are known to be infected with swine flu or who have had contact with a person infected with swine flu should see a doctor.
When doctors suspect a person has swine flu, they test samples of secretions taken from the nose and throat to identify the virus. Such tests are done mainly when people appear very ill and have been admitted to the hospital or when a doctor suspects another cause for the symptoms. Some tests can be done in the doctor's office.
Treatment of Swine Flu
Rest and plenty of fluids
Sometimes antiviral medications
The main treatment for swine flu is to rest, drink plenty of fluids, and avoid exertion. People may resume their normal activities 24 to 48 hours after the fever is gone, but most people take several more days to recover.
People may treat fever and aches with acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen. Because of the risk of Reye syndrome (a rare but life-threatening disorder in children that causes inflammation and swelling of the brain and impairment and loss of function of the liver), people 18 years old and under should not be given aspirin. Acetaminophen and ibuprofen can be used in children if needed. Other measures used to relieve symptoms of the common cold, such as nasal decongestants, may help relieve symptoms of swine flu. Decongestants should not be given to children under 4 years old. (See also table .)
People who have moderate difficulty breathing may need to be hospitalized and given oxygen. Those with severe difficulty breathing may need mechanical ventilation to help them breathe. People who develop complications also require appropriate treatment, such as dialysis for kidney injury and medications that increase blood pressure for shock.
The antiviral medications oseltamivir, zanamivir, baloxavir marboxil, and peramivir are helpful in treating people who have swine flu. However, these medications work only if taken within the first day or two after symptoms begin. Antiviral medications reduce the severity of symptoms and shorten the duration of fever and the time it takes a person to return to their normal activities.
Doctors give antiviral medications to the following:
People who are hospitalized
People whose illness is severe, complicated, or worsening
People at high risk of complications
Oseltamivir, zanamivir, baloxavir marboxil, and peramivir can relieve symptoms caused by variant influenza type A viruses, including the strain that causes swine flu.
Oseltamivir is taken as a pill or a liquid. It can be taken by people 2 weeks old and older.
Zanamivir is a powder that is inhaled with an inhaler. It can be taken by people age 7 years old and older.
Baloxavir marboxil is taken as a pill. It can be taken by people age 5 years old and older.
Peramivir is given as a single injection into a vein (intravenously). It can be given to people 6 months old and older who cannot tolerate medications taken by mouth or by inhaler.
If a bacterial infection develops, doctors prescribe antibiotics.
Prevention of Swine Flu
People who handle or care for pigs can reduce their chances of catching swine flu by doing the following:
Washing hands frequently with soap and running water before and after exposure to animals (or using alcohol-based hand sanitizer if soap is unavailable)
Avoiding close contact with animals that look or act ill and during outbreaks, when possible
Avoiding contact with pigs when experiencing human flu-like symptoms
People who cannot avoid contact with pigs when sick or cannot avoid contact with pigs known or suspected to be infected, should wear appropriate protective clothing and gear (for example, gloves, masks that cover their mouth and nose, and other personal protective equipment).
Doctors do not usually give antiviral medications to people who have swine flu. However, doctors sometimes give them to certain people who are at high risk of complications.
There is no swine flu vaccine available for people. Seasonal flu vaccines are not designed to protect people from swine flu, but people should still get a flu shot each year to protect themselves from influenza and to reduce the risk of transmitting influenza A viruses to other people and to pigs. There are swine flu vaccines available for pigs. See CDC: What People Who Raise Pigs Need To Know About Influenza (Flu).
Drug Information for the Topic
