Stockholm  - The current outbreak of swine flu which has caused alarm around the world is a variant of a disease first identified in 1930. "Classic" swine flu affects the respiratory tract in pigs and tends to strike in the autumn and winter. Experts say that it is highly infectious, but only occasionally kills.

At present, the virus is known to occur in four variants, identified as H1N1, H1N2, H3N1 and H3N2. The virus now attacking humans is a variant of the H1N1 strain, the most common.

Scientists say that it is not yet clear why the current outbreak in humans appears to have such a high death rate, and why it seems to have struck young people rather than the elderly.

While the virus is most often found in pigs, it has long been known to infect birds, horses and humans as well. Over the past 50 years, 17 cases of human infection with swine flu have been identified in Europe.

The world's most notorious outbreak came in 1976, when over 200 recruits at a US army training camp at Fort Dix, New Jersey, came down with the disease. Twelve people were hospitalized in the outbreak, and one died.

The symptoms of the disease in humans are similar to those of seasonal influenza: sudden fever, sneezing, breathing difficulties, and possibly diarrhoea.

The disease is also spread in the same way as human flu, via coughing, sneezing or touching an infected surface such as a door- knob. Experts stress that it cannot be caught by eating pork, but recommend cooking any pork products thoroughly as a precaution.

Drug companies are still working on a vaccine. In the mean time, the anti-viral drugs oseltamivir and zanamivir are reportedly effective in preventing or treating the disease.

Source: European Centre for Disease Prevention and Control, Stockholm.