The World Health Organization (search) said Friday that people hit by the bird flu (search) outbreak sweeping Asia should be quarantined to avoid contact with sufferers of regular influenza, because a combination of the two viruses may accelerate the spread of the disease.

However, a senior official at the U.N. agency said he saw no need for the kind of travel warnings WHO issued during the last year's SARS (search) epidemic.

Bird flu has swept through Cambodia, Taiwan, Japan, South Korea, Thailand and Vietnam, infecting millions of chickens. In Vietnam, the virus has killed at least five people. Two boys are sick with the disease in Thailand, where an elderly man who died Friday is also a suspected victim.

Scientists believe people get the disease through contact with sick birds. So far, there has been no evidence of person-to-person transmission. Governments have started mass culls of chickens as they scramble to contain the outbreak.

Scientists have reached no firm conclusions on why the flu is so contagious, but a leading theory is its adaptability. Experts from the U.N. health agency fear the bird flu could leap the species barrier and combine with a human flu to create a dangerous mutant form.

Meanwhile, Dr. Klaus Stohr, head of the WHO influenza program, said the organization has no plans for the kind of travel warnings issued last year when Asia and Canada were hit by the SARS epidemic. The U.N. agency advised against nonessential travel to affected areas during the outbreak of severe acute respiratory syndrome -- also a flu-like disease, which killed nearly 800 people worldwide -- but sees the H5N1 outbreak differently.

"This virus is not transmitted from human to human, so there is no deliberation at this stage on the usefulness or non-usefulness of travel recommendations," said Stohr.

"We have to put things into perspective. There is a chance that something can go wrong but it looks if we act decisively now then there still is a window of opportunity here to control the disease before it takes on global proportions."

Culling chickens in affected countries is "the key to the solution of the whole problem," Stohr added. "We do not have a problem of international spread by infected humans. We may have a problem of international spread by birds."

Still, he said, people who have gotten bird flu should be kept isolated to avoid the risk of contact with people suffering from more common forms of flu. Otherwise the two viruses might combine, creating a deadlier strain.

Hong Kong temporarily suspended live bird and poultry imports from Thailand on Friday. Japan, Hong Kong, Singapore and the Philippines have done likewise.

The European Union and non-EU Switzerland also have suspended imports. The ban includes all meat from chicken and other birds and derived products including raw material for pet food.

The biggest concern is the trade in live poultry, because the bird flu -- or H5N1 -- could decimate farm flocks in other countries, said Dr. Jorgen Schlundt, head of the WHO food safety program, dismissing any risk to humans from eating chicken.

"There's been no case where someone has eaten H5N1 in a frozen chicken and then gotten the disease," Schlundt said.

In its general guidelines, WHO recommends that consumers cook chicken thoroughly, to at least 158 degrees, to avoid salmonella and other health risks.