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The pandemic virus does not yet appear to be spreading quickly among animals, according to the World Health Organisation. GENEVA, Nov 6 (Reuters) - Some pigs, turkeys and household pets have become infected with the H1N1 flu, but the pandemic virus does not yet appear to be spreading quickly among animals, the World Health Organisation said on Friday.

WHO spokesman Gregory Hartl said it was not clear how the isolated animals had contracted the flu virus that is spreading quickly among humans in the northern hemisphere, particularly in Eastern Europe. A novel flu virus -- looking like a mix of human and swine genes -- has been detected in some mink farms in Denmark, and seems to have infected only the animals and not the farm workers in proximity to them.

"There were no human cases associated with the minks, but we don't know in some cases," Hartl said.

In a statement on its website, the United Nations health agency said the mink case "demonstrates the constantly evolving ecology of influenza viruses, the potential for surprising changes, and the need for constant vigilance, also in animals."

"These recent findings further suggest that influenza A viruses in animals and humans increasingly behave like a pool of genes circulating among multiple hosts, and that the potential exists for novel influenza viruses to be generated in animals other than swine," the WHO said.

The Geneva-based agency recommends that farm workers be monitored for signs of respiratory illness and is calling for close collaboration between public health and veterinary authorities in countries were outbreaks are rife.

According to the WHO's latest official toll, which is thought to underestimate the total spread of the virus, more than 5, 700 people worldwide have died from H1N1 infection since its discovery earlier this year in North America.

Most patients experiencing serious effects have been younger than 65, differentiating the virus from seasonal influenza, which traditionally strikes the elderly.

GlaxoSmithKline and Sanofi-Aventis are among some 25 companies producing pandemic vaccine and other drugmakers including Switzerland's Roche Holding are making antiviral therapies for use as a frontline H1N1 drug.