WHO Urges More Studies on Bird Flu Infections in Cats

By Stephanie Nebehay

GENEVA — If cats turn out to carry H5N1 without showing symptoms, it could signal the bird flu virus is adapting to mammals, posing a potentially higher risk to humans, a World Health Organization (WHO) official said on Tuesday.

Michael Perdue, a scientist at WHO’s global influenza program, said more studies were needed on infections in cats, including how they shed the virus in their environment.

But the American expert reiterated that there was no evidence they were a silent reservoir or played a role in transmitting the deadly virus.

Austria’s health minister Maria Rauch-Kallat said on Monday that a cat in an animal sanctuary in the southern city of Graz had tested positive for H5N1 but had yet to show any symptoms of the disease.

However, the virus can take up to a week to strike and perhaps the cat in Austria could still develop clinical signs, according to Perdue.

"We have to follow-up with laboratory studies to see if it (the virus) changed genetically and is not causing clinical signs," Perdue told Reuters.

"If it is true, it would imply the virus has changed significantly," he said.

The virus has killed 95 people in East Asia and the Middle East since late 2003. Most of the victims contracted the disease directly from sick poultry, but experts fear the virus could mutate and spread easily among people, sparking a pandemic which could kill millions.

Animals carrying H5N1 without showing any signs of ill health could make it harder to detect and contain bird flu. The longer the virus remains dormant in a mammal, without it getting sick or dying, the greater the risk of it also mutating into a more dangerous form.

"The longer it stays in mammals one would assume it is more likely to be adapted to mammals, as opposed to staying in birds. If the virus obtains all the mutations needed to transmit easily between mammals it could imply higher risk to humans," Perdue said.

The Austrian cat was among 170 kept in cages next to birds including a swan that died of the disease and chicken and ducks found to have the virus after they were culled last month.

Germany last week reported the first European case of H5N1 bird flu in a domestic cat on the northern island of Ruegen, an area where several wild birds have died from the virus.

"There is still not any indication of cat to human transmission. That would change everything, or if the virus started circulating among cats it would be problematic," Perdue said.

If the virus circulated amongst cats, it could prove to be a "nightmare surveillance-wise," he added.

Perdue noted that flu viruses can jump species barriers.

U.S. experts, writing in the journal Science last September, reported that an influenza virus called H3N8 had made an unusual jump from horses to dogs and killed some racing greyhounds.

That virus can also infect dogs without making them sick, but there was no evidence it can infect people, they said.

"It was a different virus, but the horse virus jumped to dogs. We know there are species to species jumps," Perdue said.