HANOI, March 13 (Xinhua) -- Vietnam's northern Son La province has become the latest locality in the country stricken by African swine fever (ASF), Vietnam News Agency reported on Wednesday.

After an ASF outbreak was detected in Thuan Chau district on Monday, all over 100 infected pigs have been culled to prevent the animal disease from spreading.

Earlier, Vietnam's Department of Animal Health said the animal epidemic has been reported in 12 Vietnamese localities - the capital Hanoi, Hai Phong city, Hung Yen, Hai Duong, Thai Binh, Ha Nam, Thanh Hoa, Hoa Binh, Dien Bien, Thai Nguyen, Quang Ninh and Ninh Binh provinces, leading to culling of 11,500 pigs.

ASF has affected 21 countries so far, and there is no approved vaccine against the disease, according to the World Organization for Animal Health.

ASF is a severe viral disease affecting domestic and wild pigs which can be spread by live or dead pig and pork products, the organization said, noting that the ASF virus is harmless to humans, but causes hemorrhagic fever in pigs and wild boars that is almost fatal.