Millions of chickens in several Asian nations have been slaughtered in recent days because of an outbreak of a bird flu virus that in Vietnam has also spread to some humans and killed at least three. The outbreak has strained businesses that trade in poultry products, but has yet to have a major impact on the general economies.

While health officials try to contain the highly contagious bird flu virus and worry about its possible spread to the region's large human populations, businessmen in Southeast Asia worry about the economic impact of the disease if it is not contained soon.

Poultry sales have been banned in Vietnam, where several people have died after coming into contact with infected chickens in unsanitary conditions. The disease has spread to half of the country's provinces and several million chickens have been slaughtered. Vietnam produces some 200 million chickens per year.

Ponchai Thurhatum, the director of KFC restaurants in Vietnam, which specialize in U.S.-style fried chicken, says the chain's nine restaurants in Vietnam are still open. But he says they are using chicken purchased earlier from parts of the country that are free of the disease. Nevertheless, he says the epidemic has affected business.

"We have reduced the orders to keep up with the sales, which have dropped, dropped 40 to 50 percent so far," he said.

Mr. Ponchai says he has ordered imported chicken to use when current stocks are finished. In the meantime, he says the restaurants will sell seafood and other non-poultry products to maintain cash flow.

Chicken flocks are also being culled in Thailand, which for the past month has been battling an outbreak of what officials insist is chicken cholera, a less virulent disease than bird flu. Nevertheless, Thai newspapers have quoted chicken farmers as saying the disease is bird flu, more than half a million chickens have been killed, and Singapore has banned imports of Thai chicken.

Millions of chickens have also been culled in South Korea and Japan in recent days.

The Food and Agriculture chairman of Thailand's Board of Trade, Chatchai Boonyarat, predicts the setback to Thailand's poultry industry will be minor.

"In the short term, there will be a shortage of chicken meat, but the life cycle of the chicken is very short so it will not affect that much," he said.

Thailand exported a half million tons of chicken products last year worth more than $1 billion.

In both Vietnam and Thailand, however, chicken exports rank well below such foreign exchange earners as rice, coffee and tourism.

Experts note that Southeast Asian countries like Thailand have launched programs to raise food safety standards in order to satisfy safety-conscious markets in Europe and the Americas. As a result, new regional laboratories are being built to monitor livestock, and preventive measures, such as vaccination and improved sanitation, have been instituted at farms.

Still, they note that such measures are expensive, and therefore small, family-owned chicken farms are vulnerable to epidemics and their financial repercussions.