Bird flu has jumped species barrier to cats

The H5N1 strain of bird flu swept through 10 Asian countries early this year, resulting in the death or slaughter of over 100 million chickens and the deaths of more than 20 people.

Since mid-December 2003, Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand and Vietnam have reported outbreaks of the avian influenza strain H5N1. Vietnam and Thailand have reported influenza H5N1 infection in humans with 32 laboratory-confirmed cases and 22 deaths, a mortality rate of nearly 70 percent. More than 100 million domestic poultry have been killed to halt the epidemic and prevent transmission to humans.

Now the United Nations health agency is investigating reports that bird flu, which experts say could mutate into a potentially deadly human pandemic under certain conditions, has now jumped the species barrier to infect cats.

This follows recent WHO reports that pigs can be infected with both avian and human influenza A viruses. Human influenza H3N2 viruses have been detected in pigs in Asia, Europe and Africa.

This is an extraordinary finding because it was thought cats could not be infected with highly pathogenic avian influenza (H5N1), the strain that has already killed some two dozen people in Asia this year and resulted in the deaths or culling of more than 100 million birds, World Health Organization (WHO) official Dick Thompson told a news briefing in Geneva today.

To date, H5N1 is the only strain of the H5 subtype known to jump directly from infected poultry to cause illness in humans.

Two of the three criteria that characterized the influenza pandemic of 1918-1919 have already been fulfilled in the current epidemic of avian influenza: the ability of the virus to infect humans resulting in high mortality, and a global immunologically naive human population. The third criterion, efficient human-to-human transmission, has not been observed.

Researchers are concerned because influenza viruses mutate frequently, potentially allowing them to change the host receptor specificity from avian to human.

According to a report in Science magazine, the cats further went on to infect other cats. WHO will now study cats to see if they played any role in the human disease. There is no indication as of now that they did, but it is something that WHO will have to take a deeper look at, Mr. Thompson said.

Only last week WHO called for additional studies on bird flu and other influenza viruses in pigs. Pigs can be infected with both avian and human influenza. The agency has warned that the co-circulation of bird, human, and pig viruses could lead to a genetic exchange of material that could set off a human pandemic.