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Researchers are elucidating the relationship between swine flu — influenza A(H1N1) — and animals and humans.

Researchers from the Friedrich-Loeffler Institute in Germany found pigs can catch influenza A(H1N1) from humans and pass it on to each other. Writing in the Journal of General Virology last week (10 July) they said that if the virus passed from humans to pigs and back again it could mutate to become more dangerous.

Two studies published earlier this month (2 July) in Science have used ferrets — good animal models of influenza — to study the differences between seasonal flu and influenza A(H1N1). Both found that A(H1N1) was more severe and can cause gastrointestinal problems and vomiting.

They also found it replicated extensively in the respiratory tract while seasonal flu was more superficial and replicated in the animals' noses.

But the researchers in the Netherlands found that both types of flu were equally good at infecting people via respiratory droplets while the US team found it was tougher to pass on A(H1N1).

Researchers said in Nature yesterday (14 July) that influenza A(H1N1) causes more lung damage than seasonal flu and is similar to the 1918 pandemic virus. It does not appear to cause disease in pigs — perhaps explaining its undetected circulation in pigs — and people born before 1920 may have antibodies to A(H1N1).

A paper published in the Proceedings of the National Academy of Sciences yesterday (13 July) has provided insight into the complex history of influenza viruses. The researchers concluded that viruses of great flu pandemics were caused by crossbreeding in birds and mammals — and circulated for years before causing human pandemics.

The WHO yesterday (13 July) gave companies the go-ahead for full-scale influenza A(H1N1) vaccine production. Marie-Paule Kieny, director of the Initiative for Vaccine Research at WHO, told a press briefing the WHO Strategy Advisory Group of Experts had described the virus as "unstoppable" and recommended health workers be prioritised in vaccination campaigns.

Three cases of virus resistant to Tamiflu have been found so far — in Hong Kong, Japan and the Netherlands. They are still sensitive to the other effective drug, Relenza, and the mechanism behind the resistance is not yet clear. The WHO said it would continue to monitor all viruses for antiviral resistance.

The mixed picture in the spread of the virus across the globe was acknowledged in a WHO press briefing last week (7 July). The WHO's Keiji Fukuda said that in Chile 99 per cent of flu was A(H1N1) while in South Africa seasonal flu continued to dominate.

Fukuda also announced they would be calling the virus H1N1/09 to avoid stigmatisation of both the pork industry and location where the virus was discovered.

In the same press conference he said: "We have two new National Influenza Centres in Africa — one in Cameroon and one in Côte d'Ivoire … surveillance is definitely much better than it was three or four years ago. We will continue to try to build that capacity everywhere in the world where countries are requesting help."

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