Swine flu (swine influenza) is a disease of pigs. It is a highly contagious respiratory disease caused by one of many Influenza A viruses. Approximately 1% to 4% of pigs that get swine flu die from it. It is spread among pigs by direct and indirect contact, aerosols, and from pigs that are infected but do not have symptoms. In many parts of the world pigs are vaccinated against swine flu.
Most commonly, swine flu is of the H1N1 influenza subtype. However, they can sometimes come from the other types, such as H1N2, H3N1, and H3N2.
The current outbreak of swine flu that has infected humans is of the H1N1 type - this type is not as dangerous as some others.
Avian Influenza (Bird Flu) can also infect pigs
Avian flu and human seasonal flu viruses can infect pigs, as well as swine influenza. The H3N2 influenza virus subtype, a virulent one, is thought to have come from pigs - it went on to infect humans.
It is possible for pigs to be infected with more than one flu virus subtype simultaneously. When this happens the genes of the viruses have the opportunity to mingle. When different flu subtypes mix they can create a new virus which contains the genes from several sources - a reassortant virus.
Although swine influenza tends to just infect pigs, they can, and sometimes do, jump the species barrier and infect humans.
What is the risk for human health?
Outbreaks of human infection from a virus which came from pigs (swine influenza) do happen and are sometimes reported. Symptoms will generally be similar to seasonal human influenzas - this can range from mild or no symptoms at all, to severe and possibly fatal pneumonia.
As swine flu symptoms are similar to typical human seasonal flu symptoms, and other upper respiratory tract infections, detection of swine flu in humans often does not happen, and when it does it is usually purely by chance through seasonal influenza surveillance. If symptoms are mild it is extremely unlikely that any connection to swine influenza is found - even if it is there. In other words, unless the doctors and experts are specifically looking for swine flu, it is rarely detected. Because of this, we really do not know what the true human infection rate is.
Examples of known swine flu infecting humans
Since the World Health Organization's (WHO's) implementation of IHR (2005) in 2007, they have been notified of swine influenza cases from the USA and Spain.
In March/April 2009 human cases of influenza A swine fever (H1N1) were first reported in California and Texas. Later other states also reported cases. A significant number of human cases during the same period have also been reported in Mexico - starting just in Mexico City, but now throughout various parts of the country. More cases are being reported in Canada, Europe, and New Zealand - mainly from people who have been in Mexico.
How does a human catch swine influenza?
- From contact with infected pigs (most common way)
- From contact with infected humans (much less common way)
Can I eat pork meat and pork products?
If the pork meat and pork food products have been handled properly transmission of swine influenza to humans is not possible. Cooking pork meats to a temperature of 70C (160F) kills the virus. So the answer is YES, pork meat and pork food products are safe to eat.
Where have pigs been infected?
As swine influenza infection among pigs is not an internationally notifiable disease we cannot be completely sure. Swine influenza infection among pigs is known to be endemic in the USA. Outbreaks have also occurred in other parts of North America, South American, Europe, Africa, China, Japan, and other parts of Asia.
Is there a pandemic risk?
People who are not in close contact with pigs generally have no immunity to the swine influenza viruses - they are less likely to be able to prevent a virus infection. If the virus infects enough people in a given area, the risk of an influenza pandemic is significantly greater. Experts say it is very hard to predict what impact a flu pandemic caused by a swine influenza virus would have on the global human population. This would depend on how virulent the virus is, what existing immunity among humans there already is, plus several other factors.
Do we have a specific swine flu vaccine?
No - not for humans.
Will current human flu vaccines help protect people from swine influenza infection?
We really don't know. Influenza viruses are adapting and changing all the time. If a vaccine was made, it would have to be specifically for a current strain that is circulating for it to be effective. The WHO says it needs access to as many viruses as possible so that it can isolate the most appropriate candidate vaccine.
What are the signs and symptoms of swine influenza in humans?
They are similar to those of regular flu, and include:
- Body aches
- Diarrhea (less common)
- Sore throat
- Temperature (fever)
- Tiredness (fatigue)
- Vomiting (less common)
There are some drugs around that can effectively treat swine flu infection in humans - and many types of flu infections in humans. There are two main types:
- adamantanes (amantadine and remantadine)
- inhibitors of influenza neuraminidase (oseltamivir and zanamivir)
What can I do to protect myself?
- Wash your hands regularly with soap
- Try to stay healthy
- Get plenty of sleep
- Do plenty of exercise
- Try to manage your stress
- Drink plenty of liquids
- Eat a well balanced diet
- Refrain from touching surfaces which may have the virus
- Do not get close to people who are sick
- Stay away from crowded areas if there is a swine flu outbreak in your area
- Limit your contact with other people
- Do not go to work or school
- When you cough or sneeze cover your mouth with a tissue. If you do not have a tissue, cover your mouth and nose.
- Put your used tissues in a waste basket
- Wash your hands and face regularly
- Keep all surfaces you have touched clean
- Follow your doctor's instructions
In Mexico City, where a sizeable number of people have become infected with H1N1 swine flu, authorities are urging people with flu symptoms to go straight to their doctors or a local hospital. They insist that the flu is completely treatable if the patient comes in straight away.
What is Swine Flu - Video
The Centers for Disease Control and Prevention (CDC) Influenza Division has produced a video all about swine flu.
This video includes information on the signs and symptoms of swine flu, how swine flu is transmitted, what medicines are available to treat it and steps that people can take to help protect themselves from it. There are also some tips on what to do if you become ill with swine flu.
Video by Centers for Disease Control and Prevention (CDC)