Two domestic cats in Thailand have died of the same bird flu that has killed at least 22 people in Asia, a veterinarian said on Friday, a day after Canada announced its first case of a different strain of the virus.
The discoveries have alarmed scientists, who now fear the disease can spread as easily between species as it has between countries.
They said on Friday developing human vaccines must be a priority to prevent a flu pandemic like the one in 1918 that killed up to 50 million people world-wide.
"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 on Friday, and Thai officials said the virus had reappeared in two provinces that had been declared under control.
With the virus spreading at an unprecedented rate through poultry, and with 22 people dead in Asia, researchers warned it poses a substantial threat to human health.
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.
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.
The virus has also crossed the species barrier to domestic animals, and in Bangkok on Friday scientists confirmed the deaths of two house cats.
JAPAN BANS CANADIAN POULTRY: Meanwhile, 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 reacted immediately, saying it was halting all imports of poultry from Canada.