African swine fever (ASF), the disease which has hit the world's top pork producer China hard, originated in Africa before spreading to Europe and Asia. It has been found in 50 countries, killing hundreds of million pigs, while reshaping global meat and feed markets.

"We are really facing a threat that is global," OIE Director General Monique Eloit told Reuters in an interview.

"The risk exists for all countries, whether they are geographically close or geographically distant because there is a multitude of potential sources of contamination."

African swine fever, which is not harmful to humans, can be transmitted by a tourist bringing back a ham or sausage sandwich from a contaminated country, throwing it away and the garbage being reused by farmers to feed their pigs, Eloit said.

There are additional risks from trading live animals and food products across borders and from small breeders using restaurant or train station waste to feed their stock.

The disease has spread rapidly to several countries in Southeast Asia including Vietnam, Cambodia, Laos, Korea and the Philippines and more countries are likely to be hit in the coming months.

"In the short term we are not going towards an improvement. We will continue to have more outbreaks in the infected countries. Neighbouring countries are at high risk and for some the question is when they will be infected," Eloit said, stressing that controls were difficult to implement.

The spread of African swine fever has not only ravaged the Asian pig population, but also sent international pork prices rocketing and hit animal feed markets such as corn and soybeans.

It has also weighed on results of agricultural commodity groups due to weaker feed demand for hog breeding.

China's hog herd was more than 40 percent smaller in September than a year earlier, its farm ministry said earlier this month. But several in the industry believe the losses are much greater.

Beijing issued a series of policies in September aimed at supporting national hog production and securing meat supplies.

Eloit said the measures were adequate but needed to be fully implemented.

"There is a difference between what is decided on paper - I do not think there is any concern here - and how we actually get to apply them on the ground especially in countries that are very large, which have a wide variety of production," she said

In Europe, the situation is different because outbreaks mainly concern wild boars, Eloit added.

African swine fever has been found on farms in eastern Europe but its spread had been mostly contained, due mainly to tight security measures implemented in some countries.