People can catch the virus through contact with infected pigs and humans.

What are the symptoms of H1N1 in humans?

Symptoms are similar to those of human strains of the seasonal influenza virus, including fever, cough, sore throat and body aches.

But the symptoms can also include severe pneumonia that can result in death, the WHO says.

Where do outbreaks occur?

H1N1 is considered endemic in the United States, though outbreaks in pigs have also been reported elsewhere in North America, South America, Europe, Africa, and in parts of eastern Asia.

Is it safe to eat pork products?

Properly handled and prepared pork products are safe to eat, according to the WHO. The swine flu virus is killed when cooked at temperatures of 160 F/70 C or higher.

Does a vaccine exist?

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Q&A: What is H1N1?

Swine flu typically infects pigs, but the virus can cross the species barrier and infect humans [AFP] H1N1 pandemic flu has spread to some 160 countries and killed about 800 people. At this point, further spread of the pandemic, within affected countries and to new countries, is considered inevitable, acording to the World Health Organisation (WHO). The pandemic has spread internationally with unprecedented speed. In past pandemics, influenza viruses have needed more than six months to spread as widely as the new H1N1 virus has spread in less than six weeks. Here are some facts about H1N1: What is H1N1? The World Health organisation says H1N1, or "swine flu" is a highly contagious acute respiratory disease typically found in pigs. It spreads through tiny particles in the air or by direct contact. The virus tends to infect large numbers of a given pig population, killing between one and four per cent of those affected, the WHO says. Not every animal infected displays symptoms. How do humans contract the virus? Swine flu normally only infects pigs, but the virus can cross the species barrier and infect humans, the WHO says.

If H1N1 establishes efficient human-to-human contact, it can cause a pandemic [AFP]

There are no vaccines to protect humans from the current H1N1 virus.

The flu virus evolves quickly, meaning that vaccines are soon obsolete.

Health officials say there is no evidence to suggest that the vaccine prepared for seasonal flu will protect against H1N1.

Are there any other treatments?

The H1N1 virus detected in Mexico and the United States appears to respond to treatment with oseltamivir (Tamiflu) and zanamivir (Relenza). 

Gregory Hartl, a WHO spokesman said the first vaccine doses for the disease should be ready in the northern hemisphere in early autumn.

The WHO so far has promises of 150 million doses from two manufacturers for developing countries and is negotiating with other producers for further doses which will be earmarked for the least developed countries, he said.

What can be done to stop the spread of the disease?

Most of the cases have been detected by chance through seasonal influenza surveillance.

Health officials say maintaining good hygiene, including regular hand-washing and staying a safe distance from those infected, may help in preventing the spread of the virus.