- Swine flu is a respiratory disease caused by influenza viruses that infect the respiratory tract of pigs and result in a barking cough, decreased appetite, nasal secretions, and listless behavior; the virus can be transmitted to humans.
- Swine flu viruses may mutate (change) so that they are easily transmissible among humans.
- The 2009 swine flu outbreak (pandemic) was due to infection with the H1N1 virus and was first observed in Mexico.
- Symptoms of swine flu in humans are similar to most influenza infections: fever (100 F or greater), cough, nasal secretions, fatigue, and headache.
- Vaccination is the best way to prevent or reduce the chances of becoming infected with influenza viruses.
- Two antiviral agents, zanamivir (Relenza) and oseltamivir (Tamiflu), have been reported to help prevent or reduce the effects of swine flu if taken within 48 hours of the onset of symptoms.
- There are various methods listed in this article to help individuals from getting the flu.
- The most serious complication of the flu is pneumonia.
Swine flu (swine influenza) is a respiratory disease caused by viruses (influenza viruses) that infect the respiratory tract of pigs, resulting in nasal secretions, a barking cough, decreased appetite, and listless behavior. Swine flu produces most of the same symptoms in pigs as human flu produces in people. Swine flu can last about one to two weeks in pigs that survive. Swine influenza virus was first isolated from pigs in 1930 in the U.S. and has been recognized by pork producers and veterinarians to cause infections in pigs worldwide. In a number of instances, people have developed the swine flu infection when they are closely associated with pigs (for example, farmers, pork processors), and likewise, pig populations have occasionally been infected with the human flu infection. In most instances, the cross-species infections (swine virus to man; human flu virus to pigs) have remained in local areas and have not caused national or worldwide infections in either pigs or humans.
Unfortunately, this cross-species situation with influenza viruses has had the potential to change. Investigators decided the 2009 so-called "swine flu" strain, first seen in Mexico, should be termed novel H1N1 flu since it was mainly found infecting people and exhibits two main surface antigens, H1 (hemagglutinin type 1) and N1 (neuraminidase type1). The eight RNA strands from novel H1N1 flu have one strand derived from human flu strains, two from avian (bird) strains, and five from swine strains.
Swine flu is transmitted from person to person by inhalation or ingestion of droplets containing virus from people sneezing or coughing; it is not transmitted by eating cooked pork products. The newest swine flu virus that has caused swine flu is influenza A H3N2v (commonly termed H3N2v) that began as an outbreak in 2011. The "v" in the name means the virus is a variant that normally infects only pigs but has begun to infect humans. There have been small outbreaks of H1N1 since the pandemic; a recent one is in India where at least three people have died.
Causes of Swine Flu
Swine flu is contagious, and it spreads in the same way as the seasonal flu. When people who have it cough or sneeze, they spray tiny drops of the virus into the air. If you come in contact with these drops or touch a surface (such as a doorknob or sink) that an infected person has recently touched, you can catch H1N1 swine flu.
Despite the name, you can't catch swine flu from eating bacon, ham, or any other pork product.
Swine Flu Symptoms
People who have swine flu can be contagious one day before they have any symptoms, and as many as 7 days after they get sick. Kids can be contagious for as long as 10 days.
Most symptoms are the same as seasonal flu. They can include:
- cough
- fever
- sore throat
- stuffy or runny nose
- body aches
- headache
- chills
- fatigue
Like seasonal flu, swine flu can lead to more serious complications, including pneumonia and respiratory failure. And it can make conditions like diabetes or asthma worse. If you have symptoms like shortness of breath, severe vomiting, abdominal pain, dizziness, or confusion, call your doctor or 911 right away.
Tests for Swine Flu
It's hard to tell whether you have swine flu or seasonal flu, because most symptoms are the same. People with swine flu may be more likely to feel nauseous and throw up than people who have seasonal flu. But a lab test is the only way to know for sure. Even a rapid flu test you can get in your doctor's office won't tell you for sure.
To test for swine flu, your doctor takes a sample from your nose or throat. You may not need to be tested. The CDC says the people who need to be tested are those in the hospital or those at high risk for getting life-threatening problems from the flu, such as:
- Children under 5 years old
- People 65 or older
- Children and teens (under age 18) who are getting long-term aspirin therapy, and who might be at risk for Reye's syndrome after being infected with swine flu. Reye's syndrome is a life-threatening illness linked to aspirin use in children.
- Pregnant women
- Adults and children who have chronic lung, heart, liver, blood, nervous system, neuromuscular, or metabolic problems
- Adults and children who have suppressed immune systems (including those who take medications to suppress their immune systems or who have HIV)
- People in nursing homes and other long-term care facilities
How Is Swine Flu Treated?
Some of the same antiviral drugs that are used to treat seasonal flu also work against H1N1 swine flu. Oseltamivir (Tamiflu) and zanamivir (Relenza) seem to work best, although some kinds of swine flu are resistant to Tamiflu.
These drugs can help you get over swine flu faster. They can also help keep it from being too severe. They work best when taken within 48 hours of the first flu symptoms, but they can help when taken later.
Antibiotics won't help, because flu is caused by a virus, not bacteria.
Over-the-counter pain remedies and cold and flu medications can help relieve aches, pains, and fever. Don't give aspirin to children under age 18 because of the risk for Reye’s syndrome. Check to make sure that over-the-counter cold medications do not have aspirin before giving them to children.
Vaccine for Swine Flu
The same flu vaccine that protects against seasonal flu also protects against the H1N1 swine flu strain. You can get it as a shot or as a nasal spray. Either way, it "teaches" your immune system to attack the real virus.
Besides a flu shot, there are other things you can do to stay healthy:
- Wash your hands throughout the day with soap and water. Sing the "Happy Birthday" song twice to make sure you've washed long enough. Or use an alcohol-based hand sanitizer.
- Don't touch your eyes, nose, or mouth.
- Avoid people who are sick.
Why is swine flu now infecting humans?
Many researchers now consider that two main series of events can lead to swine flu (and also avian or bird flu) becoming a major cause for influenza illness in humans.
First, the influenza viruses (types A, B, C) are enveloped RNA viruses with a segmented genome; this means the viral RNA genetic code is not a single strand of RNA but exists as eight different RNA segments in the influenza viruses. A human (or bird) influenza virus can infect a pig respiratory cell at the same time as a swine influenza virus; some of the replicating RNA strands from the human virus can get mistakenly enclosed inside the enveloped swine influenza virus. For example, one cell could contain eight swine flu and eight human flu RNA segments. The total number of RNA types in one cell would be 16; four swine and four human flu RNA segments could be incorporated into one particle, making a viable eight RNA-segmented flu virus from the 16 available segment types. Various combinations of RNA segments can result in a new subtype of virus (this process is known as antigenic shift) that may have the ability to preferentially infect humans but still show characteristics unique to the swine influenza virus.
It is even possible to include RNA strands from birds, swine, and human influenza viruses into one virus if a single cell becomes infected with all three types of influenza (for example, two bird flu, three swine flu, and three human flu RNA segments to produce a viable eight-segment new type of flu viral genome). Formation of a new viral type is considered to be antigenic shift; small changes within an individual RNA segment in flu viruses are termed antigenic drift and result in minor changes in the virus. However, these small genetic changes can accumulate over time to produce enough minor changes that cumulatively alter the virus' makeup over time (usually years).
Second, pigs can play a unique role as an intermediary host to new flu types because pig respiratory cells can be infected directly with bird, human, and other mammalian flu viruses. Consequently, pig respiratory cells are able to be infected with many types of flu and can function as a "mixing pot" for flu RNA segments (see figure 1). Bird flu viruses, which usually infect the gastrointestinal cells of many bird species, are shed in bird feces. Pigs can pick these viruses up from the environment, and this seems to be the major way that bird flu virus RNA segments enter the mammalian flu virus population. Figure 1 shows this process in H1N1, but the figure represents the genetic process for all flu viruses, including human, swine, and avian strains.
What is the prognosis (outlook) and complications for patients who get swine flu?
In general, the majority (about 90%-95%) of people who get the disease feel terrible (see symptoms) but recover with no problems, as seen in patients in Mexico, the U.S., and many other countries.
People with suppressed immune systems historically have worse outcomes than uncompromised individuals; investigators suspect that as swine flu spreads, the mortality rates may rise and be high in this population. Current data suggest that pregnant individuals, children under 2 years of age, young adults, and individuals with any immune compromise or debilitation are likely to have a worse prognosis. Complications of swine flu may resemble severe viral pneumonia or the SARS (severe acute respiratory syndrome caused by a coronavirus strain) outbreak in 2002-2003 in which the disease spread to about 10 countries with over 7,000 cases, caused over 700 deaths, and had a 10% mortality rate. At the beginning of the pandemic, the numbers of people with flu-like illness were higher than usual and the illness initially affected a much younger population than the conventional flu.
As the pandemic progressed, more young children became infected than usual, but the mortality statistics became more similar to the conventional flu mortality rate, with an older population (especially ages 50-64) having the highest death rate. Pneumonia (viral and secondary bacterial pneumonia), is the most serious complication of the flu as it can cause death. Other complications include sinus and ear infections, asthma exacerbations, and/or bronchitis.
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