msnbc.com news services
updated 4/5/2006 12:31:26 PM ET 2006-04-05T16:31:26

People living in areas where bird flu has been found in poultry or wild birds should keep their cats indoors, say scientists who believe the potential role of felines in spreading the virus is being overlooked.

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Cats have been known to become infected with the H5N1 virus and lab experiments show they can give it to other cats, although nobody knows whether they can transmit it to people or poultry, the researchers say in Thursday’s issue of the journal Nature.

Scientists know so little about H5N1 in cats that it’s difficult to assess the risk they pose when infected, wrote virologist Albert Osterhaus and colleagues at the Erasmus Medical Center in Rotterdam, The Netherlands, along with Peter Roeder of the Food and Agriculture Organization of the United Nations.

Still, “we believe that the potential role of cats should be considered in official guidelines for controlling the spread of H5N1 virus infection,” they wrote.

Osterhaus also warned that as well as passing H5N1 to other species, cats may help the virus to adapt into a more highly infectious strain in humans which could spark a pandemic.

“We have to take a number of precautionary measures,” said Osterhaus, a virologist and veterinarian.

“We need to keep in mind that mammals can be infected and that they can spread the disease, in principle.”

Animals such as dogs, foxes, ferrets and seals may also be vulnerable to infection, the researchers said in a commentary in the journal Nature.

In areas where H5N1 has been found in poultry or wild birds, cats should be kept away from infected birds or their droppings, and cats suspected of such contacts or showing symptoms of infection should be quarantined and tested, they wrote. Cats may need to be kept indoors and if animals or other carnivores show signs of illness they should be tested for H5N1.

“Perhaps there is a case for developing a vaccine for cats as well,” Osterhaus told Reuters.

Where possible, cats could be kept indoors to prevent contact, they wrote.

The European Center for Disease Prevention and Control, an agency of the European Union, has also recommended keeping cats indoors if they live within about six miles of a verified H5N1 infection in birds.

Official guidelines
Cats can also act as an early warning signal for the virus.

“When wild birds are infected we have seen that cats are quite effective in catching them and catching the disease. In this way they could be sentinels,” Osterhaus said.

Deaths from H5N1, which has infected 191 people and killed 108, have been reported in cats in countries in Asia and in Iraq and Germany. Tigers and leopards in zoos in Thailand have also died after eating fresh chicken carcasses.

“The potential role of cats should be considered in official guidelines for controlling the spread of H5N1 virus,” said Osterhaus, Thijs Kuiken of Erasmus University and Peter Roeder, an animal health officer at the Food and Agriculture Organization of the United Nations in Rome, in the journal.

Studies at Erasmus University have shown that cats can be infected through the respiratory tract, in a similar way to humans, but that the more likely route is through the gut by eating infected birds.

The animals develop serious or fatal disease and can transmit the virus to other cats.

“We have shown that cat-to-cat transmission is possible,” Osterhaus said. “That is important because it would predispose the virus to adapt to mammals. We cannot exclude that. How big the problem is we don’t know.”

It has also been shown that the amount of virus excreted by cats through the respiratory tract or in feces is lower than the levels from chickens.

The scientists do not know how long cats can excrete the virus, the minimal amount of virus needed to cause infection in cats or whether virus transmission from cats to poultry, humans and other species is possible.

“But given the potential contribution of these carnivore hosts to both virus transmission and its adaptation to mammals, we believe the time for increased surveillance and precaution is here,” they added in the journal.

Some bird flu experts said they found it premature to suggest keeping cats indoors. Scientists need to learn more about what role, if any, cats have in spreading H5N1 before making such blanket recommendations, said Dr. Arnold S. Monto of the University of Michigan School of Public Health.

Osterhaus, discussing his recommendations in a telephone interview, said that “people in the United States should realize the disease is not there, so there is no reason at this moment to be concerned at all.”

The Associated Press and Reuters contributed to this report

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