A worker in a protective suit disinfects a pig farm on Tuesday in Incheon, South Korea. Photo: VCG

South Korea confirmed its fourth case of African swine fever on Tuesday, as Pyongyang was yet to respond to Seoul's request to make joint efforts to tackle the deadly animal disease.

The latest case was confirmed at a farm in Paju, a city near the inter-Korean border where the nation's first case was recorded, according to Seoul's agriculture ministry.

South Korea has culled around 15,000 pigs since the first case was reported on September 17. 

"We have carried out an immediate culling and are proceeding with an epidemiological investigation," the ministry said in a statement, adding that some 2,300 pigs were being raised at the affected farm.

The fourth case came a day after Seoul's unification ministry said it last week sent a request to North Korea to make collaborative efforts on the matter, although is yet to receive a reply from Pyongyang.

The virus is not harmful to humans but cases of haemorrhagic fever in pigs is almost always fatal. 

There is no antidote or vaccine and the only known way to prevent the disease from spreading is a mass cull of affected livestock.

The second and third cases in South Korea - confirmed on September 18 and 23, respectively - were also reported from cities in Gyeonggi Province, where Paju belongs and is adjacent to the inter-Korean border.

While Seoul authorities have never confirmed whether the outbreak stemmed from North Korea, Pyongyang in late May told the World Organization for Animal Health that dozens of pigs had died from the disease at a farm near the Chinese border.

In June, Seoul said the disease was "highly likely" to enter the country from North Korea and ordered fences to be erected at farms along the border to prevent possible contact between pigs and wild boar.

Kim Jun-young, a vet and a vice president of the Korean Veterinary Medical Association in South Korea, said it is possible that the outbreak has spread to all provinces in North Korea.

In North Korea, swine fever has killed all pigs in North Pyongan Province, the Yonhap News Agency reported, citing South Korea's intelligence agency.

There are around 6,700 pig farms across South Korea and pig farming accounts for 40 percent of the total livestock industry.

Seoul believes Pyongyang raises some 2.6 million pigs across 14 state-run farms. The outbreak could worsen food shortages in North Korea, where, according to the World Food Programme, its output last year hit the lowest level since 2008.

In May, the UN's Food and Agricultural Organization said pork prices had risen by up to 50 percent both in China and on the Chicago futures exchange as a result of the outbreak.

Last month, it said almost 5 million pigs in Asia had died or been culled because of the spread of the disease.

African swine fever, nearly 100 percent fatal to pigs though not harmful to humans, has spread throughout Asia - including to both Koreas and to Vietnam, Laos and the Philippines - since first being ­detected in China in mid-2018, resulting in large-scale culls and lower output of pork.