Swine flu: its origins and symptoms to look out for

Swine flu was declared a global pandemic by the World Health Organisation on June 11, 2009. The initial outbreak of the new strain of the swine flu, or H1N1, virus was in Mexico before spreading to the rest of the world. On July 21, the WHO reported the global death toll had reached more than 700; the agency has now stopped counting laboratory-confirmed cases as it is a waste of resources.

In Britain, Prof Nigel Dimmock, a virologist at Warwick University, has claimed that half the UK population could come down with swine flu this year. His worst case scenario is that 150,000 people could die in Britain.

WHAT IS SWINE FLU?
It is a flu virus that affects pigs, often hitting farms in autumn and winter. It rarely spreads to humans. But when it does, the outbreak begins with someone being in contact with an infected pig.

Flu viruses have the ability to mutate quickly, and pigs provide an excellent host for this. The new version has developed the ability to spread among humans, who then infect each other through coughing and sneezing. It cannot be spread by eating pork or pork products.

This outbreak has been caused by a version of the H1N1 strain of influenza type A. It is the same strain as causes flu outbreaks in humans, however the new version contains genetic material from strains of the virus that affect humans, birds and swine.

Fresh research from the University of Winsconsin suggests the new strain is related to the 'Spanish flu' virus of 1918 that killed millions. The study suggests it penetrates deeper into the respiratory tissues - making it more likely to cause pneumonia. Blood tests show that people who lived through the 1918 flu pandemic are immune to swine flu, but not to the seasonal flu that hits every year.

On the plus side, the H1N1 strain is far less dangerous than H5N1, or bird flu, and despite the similiarities it is not (yet) as severe as the 1918 version.

WHAT ARE THE SYMPTOMS?
The symptoms are the same as with normal seasonal flu: fever (a body temperature of over 38C or 100.4F), coughing, sore throat, aching muscles, limb or joint pain, runny nose, lack of appetite and nausea. Some patients have also reported diarrhoea and vomiting.

Several of those diagnosed with swine flu after trips to Mexico mistook the first signs as the effects of jetlag. Those who have died suffered from pneumonia and respiratory failure.

WHO IS CATCHING IT?
The illness has spread rapidly, with 'hotspots' developing in urban areas. In Britain, these are London, Glasgow and the West Midlands. In July the Government warned that cases could reach 100,000 a day in August.

Early fears that it was most lethal to people aged 25 to 45 have subsided. In the UK symptoms exhibited by victims have not been severe. People with long term health conditions are deemed most at risk by the NHS and so far there have been very few deaths among who did not have underlying health issues.

IS THERE A VACCINE?
Large quantities will be manufactured after human trials which began in Australia on July 20. The first batch of vaccine is not expected in Britain until August or September. Despite a claim by the Government that it could be 'fast-tracked', the WHO announced that trials taking several weeks would be necessary.

However, it is not plain sailing. Scientists have told the WHO that the 'seed strains' grown to produce the vaccine are giving poor yields of antigen. The yield is a quarter to a half of that vaccine makers typically get for seasonal flu vaccine production.

The good news is that Tamiflu and other antiviral drugs are also effective against swine flu viruses, although they may not work against new strains if they emerge.

HOW IS BRITAIN DEALING WITH THE OUTBREAK?
When the new vaccine arrives there are plans to vaccinate the entire population, with high risk groups and medical workers first on the list.

Because of the recent bird flu scare, Britain also has a stockpile of the antiviral drugs Tamiflu and Relenza, enough to treat half the population. These drugs do not completely cure swine flu, but they can reduce its severity and help limit its spread.

New cases are now being diagnosed by phone and sufferers being asked to quarantine themselves for up to two weeks.

On July 23, the Government is due to launch the National Pandemic Flu Service which will allow people to self-diagnose online or by phone and order Tamiflu without visiting doctors' surgeries.

SHOULD WE BE WEARING FACEMASKS?
It is unnecessary. The Department of Health advises that "available scientific evidence does not support the general wearing of facemasks by those who are not ill whilst going about their normal activities". However, the Department is making efforts to increase its stock of facemasks for use by hospital staff in the event of a pandemic being declared.