WHO Recommends: Watch Closely Animals for Flu

Household pets have become infected with the H1N1 flu, but the pandemic virus does not yet  spread quickly among animals, the World Health Organization 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.

According to the WHO's latest official toll more than 5,700 people worldwide have died from H1N1 infection since its discovery earlier this year in North America.