The Ministry of Agriculture and Rural Development said the disease has spread to 155 communes in Hanoi and 19 provinces, and the risk of it spreading on a large scale is very high.

The ministry blamed the recurrence on some small farmers buying breeding pigs of unknown origin, pig farms failing to ensure sanitation and lack of biosecurity measures.

Besides, some farmers did not inform veterinary officials when their pigs showed signs of infection, instead selling them for consumption. A shortage of veterinary staff has also been blamed for the failure to surveil and detect in time, the ministry said.

African swine fever was first detected in Vietnam in February 2019, and it spread to all 63 cities and provinces within seven months, forcing authorities to kill around six million pigs, or 20 percent of the country’s total number.

After adopting tough preventive measures, several provinces like Hoa Binh, Bac Kan, Lam Dong, Ha Giang, Hung Yen, Hai Duong, Thai Binh, and Nam Dinh announced the end of the disease.

This could be done if no pig death is reported for 30 days.

The African swine fever virus spreads through bodily secretions. Pigs can thus get infected by contact with infected sources, mainly other infected pigs, pork and other pig-derived products, but also other contaminated objects, according to the Food and Agriculture Organization.

Vietnam has the world’s seventh largest number of pigs and is the sixth largest pork producer, according to the Ministry of Industry and Trade.

Pork makes up 70 percent of the average Vietnamese diet.

The Ministry of Agriculture and Rural Development is discussing collaboration with its U.S. counterpart to develop a vaccine against the disease.

African swine fever has spread to some 50 countries and territories.