SOFIA (Reuters) – Bulgarian veterinary authorities said on Tuesday they would cull 17,000 pigs after detecting an outbreak of African swine fever at a breeding farm in the northeast, the fourth industrial farm hit by the fast-spreading virus.

The outbreak was detected at a farm in the village of Popina, near the Danube town of Silistra. Some 87,000 pigs have been killed on another three farms in the past 10 days.

European Union-member Bulgaria has so far detected more than 20 outbreaks of African swine fever at industrial or backyard farms in the northern part of the country.

Agriculture Minister Desislava Taneva said on Monday 20-km sanitary zones were being set up around all 62 registered industrial pig farms in the Black Sea state with no small private pig farms and home-breeding of pigs without bio-security measures allowed in the zones.

Authorities have declared a state of emergency in four districts in northern Bulgaria, where there have been outbreaks among home-raised pigs.

Bulgaria has mobilised military and police forces to help combat the disease and protect its pig breeding industry.

African swine fever is a highly contagious disease that affects pigs and wild boar. It does not affect humans.

(Reporting by Angel Krasimirov; Editing by Janet Lawrence)