Approximately 1-4% of pigs that get swine flu will 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 2009 outbreak of swine flu that has infected humans is of the H1N1 type - this type is not as dangerous as some others.
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Fast facts on swine flu
Here are some key points about swine flu. More detail and supporting information is in the main article.
- Swine flu is extremely contagious between pigs
- Up to 4% of pigs who contract swine flu die
- Swine flu is normally of the H1N1 influenza subtype
- When viruses mix their genetic information it is referred to as a reassortment virus
- The most common way for a human to catch swine flu is through contact with a pig
- It is still entirely safe to eat properly cooked pork products
- There is currently no human vaccine for swine flu
- Symptoms of swine flu include coughs, chills and aches, similar to seasonal flu
- There are some effective medical treatments for swine flu
Avian influenza (bird flu) can also infect pigs
Sometimes viruses can jump between species, as with swine flu.
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 swine flu infecting humansSince 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 flu?
- 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 70°C (160°F) kills the virus. So the answer is "yes", pork meat and pork food products are safe to eat.
Where have pigs been infected with swine flu?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.
On the next page, we answer some more common questions about swine flu.