Swine flu
Influenza is caused by infection with a virus. There are many types of flu virus and these are constantly changing, which makes it hard for the human immune system to deal with it. The particular type of influenza virus that causes swine flu is known as H1N1, which is a type of Influenza A (there are also influenza B and C viruses).
It is the same group of H1N1 viruses which cause the regular yearly flu outbreaks in humans, but swine flu is caused by different strains of H1N1. The current strain of swine flu has not previously been found in pigs or humans, and contains a mixture of genetic material from human, pig and bird flu. In other words it is a new variety of flu which people are therefore unlikely to have much immunity to.
Outbreaks of flu tend to follow certain patterns. Every year the number of flu cases rise during the winter months - this is seasonal flu. If a lot of people are affected it may be said to be an epidemic, and about one per cent of those affected are likely to die from it, usually due to complications such as a secondary bacterial infection of the lungs.
But every so often, with a major change in the flu virus, it spreads rapidly around the world causing a high number of deaths. This is pandemic flu. One of the factors that scientists look out for is when a new strain of flu arises among animals and spreads to humans, changing again to develop the ability to spread from human to human without any contact with the animals.
Initally all the confirmed cases of swine flu in the UK were in people who had visited Mexico where the outbreak was first reported, but recent cases have been confirmed as being the result of virus transmission within the UK.
In the early stages it can be difficult to predict how severe a pandemic will be. However, initial laboratory studies of the strain of H1N1 causing the Mexico outbreak suggest that it is a relatively mild strain and that further mutation of the virus would be needed to cause severe problems.
It is thought to be far less dangerous than the H5N1 strain of bird or avian flu which has caused so much worry in the past few years.
Although anyone can catch flu, seasonal flu tends to cause more problems among the elderly, the very young and the chronically ill. However pandemic flu tends to affect previously healthy adults - this has been the case in Mexico where young men and women have been the main victims of swine flu.
Initially in this outbreak of swine flu humans picked up the virus through contact with pigs but now it is being passed from human to human in some countries. This is probably occurring in the same way as seasonal flu, through coughing and sneezing which generates an aerosol of virus particles into the atmosphere that can spread for up to a metre, or through contact with contaminated surfaces such as door handles.
Those living in close proximity to someone with the infection are at greatest risk.
Swine flu is highly contagious. Symptoms begin within two days of exposure, at which point the person is most infectious. They are very similar to those produced by seasonal flu, including :
High fever (usually above 38 oC)
Cough
Sore throat
Headache
Aching muscles
Chills and shivers despite fever
Exhaustion or fatigue
It can be difficult to tell mild flu from a cold but it is usually more generalised (the symptoms of a cold tend to be limited to the head while the flu causes aching and fatigue all over) and more severe with higher fever.
If complications such as pneumonia develop there may be other symptoms such as difficulty breathing or diarrhoea, a symptom which appears to be a particular feature of the swine flu outbreak in Mexico.
The symptoms and signs in an affected person are usually enough to suggest that flu is to blame, but it can be confused with other viral illnesses. Laboratory tests are needed to confirm the diagnosis and, more specifically, identify exactly which strain of flu it is.
A number of tests can be done in the laboratory to identify flu, using swabs or washings from the nose or throat for example. These can give results within 15 minutes but may not identify the exact strains of flu involved, only that influenza type A or B is present.
These rapid tests are only 50-70 per cent sensitive for detecting flu and so may give a negative result when a person does in fact have flu.
More reliable tests, which also identify exactly which sub-type or strain of flu is present, may involve growing or culturing the virus in the laboratory, and can therefore take a couple of days to give a definite result. These tests may be needed to confirm a specific strain such as swine flu.
If you think you have developed flu-like symptoms, you should stay at home and avoid contact with other people. Call your doctor to discuss your symptoms - they may decide to come and take samples from you. It's important to tell them if you have recently been in contact with someone else with flu or if you have recently travelled abroad.
Treat symptoms as they arise. Try to keep well hydrated with plenty of clear fluids. Take paracetamol or ibuprofen (not for children because of the risk of Reyes syndrome) for aches and pains, and use simple remedies such as cough syrups and vapour rubs. Try to rest as much as possible.
If your doctor is concerned they may prescribe anti-viral medication such as Tamiflu (Oseltamivir) or Relenza (Zanamivir). Swine flu seems to respond to these medicines in the same way as seasonal flu.
The treatments are not a cure but can reduce the risk of infection for those who have been exposed to the virus, reduce the ability of a person with the virus to pass it on, and shorten the course of the illness when someone has flu. Most importantly these drugs treatments reduce the risk of serious complications and death. For maximum effect, the drugs should be given as early as possible to someone who has the flu.
There is not yet a vaccine specifically for the strain of H1N1 swine influenza virus which has caused the 2009 Mexico outbreak, and it will take several months to develop one. It's not yet clear whether current flu vaccines may offer a degree of protection.
As with all infections, good hygiene is absolutely essential to reduce the risk of spread or contact with the virus:
Wash your hands regularly
Cover your mouth and nose when you cough or sneeze
Use tissues and dispose of them carefully
Clean hard surfaces regularly with a standard cleaning fluid
Avoid close contact with people who have fever and a cough
The effectiveness of wearing a face mask in preventing transmission of the flu virus isn't yet clear, although it may give some protection to those people such as health professionals who work closely with someone with symptoms of flu
Influenza is caused by infection with a virus. There are many types of flu virus and these are constantly changing, which makes it hard for the human immune system to deal with it. The particular type of influenza virus that causes swine flu is known as H1N1, which is a type of Influenza A (there are also influenza B and C viruses).
It is the same group of H1N1 viruses which cause the regular yearly flu outbreaks in humans, but swine flu is caused by different strains of H1N1. The current strain of swine flu has not previously been found in pigs or humans, and contains a mixture of genetic material from human, pig and bird flu. In other words it is a new variety of flu which people are therefore unlikely to have much immunity to.
Outbreaks of flu tend to follow certain patterns. Every year the number of flu cases rise during the winter months - this is seasonal flu. If a lot of people are affected it may be said to be an epidemic, and about one per cent of those affected are likely to die from it, usually due to complications such as a secondary bacterial infection of the lungs.
But every so often, with a major change in the flu virus, it spreads rapidly around the world causing a high number of deaths. This is pandemic flu. One of the factors that scientists look out for is when a new strain of flu arises among animals and spreads to humans, changing again to develop the ability to spread from human to human without any contact with the animals.
Initally all the confirmed cases of swine flu in the UK were in people who had visited Mexico where the outbreak was first reported, but recent cases have been confirmed as being the result of virus transmission within the UK.
In the early stages it can be difficult to predict how severe a pandemic will be. However, initial laboratory studies of the strain of H1N1 causing the Mexico outbreak suggest that it is a relatively mild strain and that further mutation of the virus would be needed to cause severe problems.
It is thought to be far less dangerous than the H5N1 strain of bird or avian flu which has caused so much worry in the past few years.
Although anyone can catch flu, seasonal flu tends to cause more problems among the elderly, the very young and the chronically ill. However pandemic flu tends to affect previously healthy adults - this has been the case in Mexico where young men and women have been the main victims of swine flu.
Initially in this outbreak of swine flu humans picked up the virus through contact with pigs but now it is being passed from human to human in some countries. This is probably occurring in the same way as seasonal flu, through coughing and sneezing which generates an aerosol of virus particles into the atmosphere that can spread for up to a metre, or through contact with contaminated surfaces such as door handles.
Those living in close proximity to someone with the infection are at greatest risk.
Swine flu is highly contagious. Symptoms begin within two days of exposure, at which point the person is most infectious. They are very similar to those produced by seasonal flu, including :
High fever (usually above 38 oC)
Cough
Sore throat
Headache
Aching muscles
Chills and shivers despite fever
Exhaustion or fatigue
It can be difficult to tell mild flu from a cold but it is usually more generalised (the symptoms of a cold tend to be limited to the head while the flu causes aching and fatigue all over) and more severe with higher fever.
If complications such as pneumonia develop there may be other symptoms such as difficulty breathing or diarrhoea, a symptom which appears to be a particular feature of the swine flu outbreak in Mexico.
The symptoms and signs in an affected person are usually enough to suggest that flu is to blame, but it can be confused with other viral illnesses. Laboratory tests are needed to confirm the diagnosis and, more specifically, identify exactly which strain of flu it is.