Bird flu was confirmed in four Asian nations and Denmark Thursday and may have killed turkeys in Israel, and scientists outlined the genetic changes needed to turn the virus into a human pandemic.
Afghanistan, India and Myanmar said tests had confirmed H5N1 caused recent outbreaks in birds, while Malaysia reported new cases in a wild bird and dead chickens.
Denmark, the latest European country affected, said tests showed a wild buzzard found south of Copenhagen had H5N1.
Israel suspects bird flu killed turkeys on two farms, although there were no test results yet, Agricultural Minister Zeev Boim said. Israel has so far been spared the virus.
In India, veterinary workers began throttling more than 70,000 birds to try to control the latest outbreak there. Hundreds of people were also tested for fever.
"There is no time for niceties. The birds have to be killed as fast as possible," said Bijay Kumar, animal husbandry commissioner of the state of Maharashtra, where bird flu resurfaced this week in backyard poultry.
Bird flu has spread with alarming speed in recent weeks across Europe, Africa and parts of Asia, leaving impoverished nations such as Afghanistan and Myanmar appealing for protective clothing and other basic equipment.
Bird flu is hard to catch, but people can contract it after coming into contact with infected birds.
U.S. scientists reported Thursday that they had found two small mutations that the virus would need to make to evolve into a human pandemic form, and said field tests could be used to monitor for the changes.
The more bird flu spreads, the greater the fear the virus will evolve into a form that could easily pass between people, triggering a pandemic in which millions could die.
Three young women who died in recent weeks in Azerbaijan, on the crossroads between Europe and Asia, tested positive for H5N1 infection. If the World Health Organization confirms that, their deaths would take the human toll to more than 100.
In Serbia, a teenager from a bird flu-stricken area was put in isolation after developing a high fever.
"The boy is from the family where we found a rooster with clinical symptoms of bird flu," Syria's chief epidemiologist Predrag Kon told Reuters. He said the youth would be kept in isolation for 72 hours or until the possibility of bird flu had been ruled out.
U.S. market regulators said they were confident that a pandemic would not disrupt trading, if one comes.
"We really believe that with proper planning, the markets can stay open, even with the most severe pandemic," said Alton Harvey, who heads contingency planning for the Securities and Exchange Commission.
"We think this is doable," he told a conference organized by the Center for Strategic and International Studies. "Because we have to -- we have no choice -- we will work it out. The markets will trade."
Swiss drug maker Roche AG said it was boosting output of its flu drug Tamiflu by one-third. Known generically as oseltamivir, it is one of the most effective treatments for people infected with H5N1, but in short supply.
Roche announced deals with external producers to boost capacity by 100 million treatments to a total of 400 million by the end of the year.
Dutch authorities launched a vaccination campaign for poultry. The Netherlands is one of the European Union's leading poultry producers.
So far the confirmed cases in Europe have been in wild birds, except for poultry in France, but producers worry that the virus could begin affecting flocks. Poultry prices have plunged in some countries.