By Vissuta Pothong
BANGKOK/WASHINGTON (Reuters) - Bird flu has spread to a new species in Asia, scientists said on Friday, reporting that two house cats in Thailand died of the same strain that has killed 22 people across the continent.
China also confirmed two more suspected outbreaks and U.S. officials reported a milder strain of the virus in a fourth state.
With the virus spreading at an unprecedented rate in poultry, researchers warned it poses a substantial threat to human health and urged development of a human vaccine. Scientists fear the disease can spread as easily between species as it has between countries.
"It is a pandemic threat constantly simmering," Dr Marion Koopmans, of the National Institute of Public Health and the Environment in the Netherlands, told Reuters in London.
China confirmed two more suspected outbreaks of the influenza H5N1 virus in two provinces and Thai officials said the virus had reappeared in two provinces that had been declared under control.
In the United States, the Texas Animal Health Commission said a flock of chickens had tested positive for the milder H5N2 strain of avian influenza. It said the strain posed no health threat to humans and caused relatively low mortality in chickens.
Texas became the fourth U.S. state affected by the disease this year, after Delaware, New Jersey and Pennsylvania. But Texas state veterinarian Bob Hillman said it did not appear the bird flu had spread from the east coast states.
Canada announced the discovery of its first case of a milder strain of the virus on Thursday.
In two reports in the Lancet medical journal, Koopmans and Professor Malik Peiris of the University of Hong Kong, who both dealt with previous cases of animal-to-human transmission of flu, described why the current avian outbreak is so dangerous.
Koopmans said it is possible the virus may not be completely controlled in poultry because it is so widespread, which supported the case for making a vaccine a top priority.
An Australian government research lab said a locally developed drug, Relenza, used for treating human influenza, had proven effective against bird flu in laboratory tests.
In Bangkok scientists confirmed the deaths of two house cats from bird flu, the first domesticated mammals known to have contracted the disease in this outbreak.
"We found H5N1 in two of the three cats," said Teerapol Sirinaruemit, a veterinarian at Kasetsart University's animal hospital, who conducted autopsies on three animals.
"They might have caught the virus from eating chicken carcasses or from live chickens that had bird flu," he said.
The three were among 15 cats living in a house near an infected chicken farm 40 miles west of Bangkok, Teerapol said. Fourteen cats died, but it was unclear if all had been infected with the H5N1 virus.
The Rome-based Food and Agriculture Organization said the cats' deaths required more careful analysis. "We also need to know what specific diagnostic tests were performed and how the testing was carried out," the group said in a statement.
NOT NECESSARILY MORE RISK
In Geneva, the World Health Organization said confirmation that the disease had killed the two house cats in Thailand would not necessarily signify an increased risk to humans.
Teerapol said two exotic cats at a zoo near Bangkok also had been confirmed to have bird flu. A rare Thai leopard, which was fed raw infected chicken, died of the H5N1 virus last month. The other, a white tiger, had recovered.
The Canadian Food Inspection Agency was still conducting laboratory tests, but officials said they had identified the H7 strain of avian influenza in British Columbia -- the same type found recently in Delaware in the United States.
Japan immediately said it was halting all imports of poultry from Canada.
Thai Prime Minister Thaksin Shinawatra, cautioned Thais not to feed their pets uncooked chicken meat. "Please don't panic," he told reporters in Bangkok, adding: "If animals eat raw infected chicken, they will have no immunity."
Health experts say well-cooked chicken and eggs pose no danger.