Nearly 22,000 pigs have been culled since the outbreak was first confirmed last week in the border towns of Paju and Yeoncheon, but officials have yet to identify the infection route.
South Korea on Wednesday said it was intensifying efforts to clean farms around the country as it scrambles to contain the spread of the highly contagious African swine fever that has ravaged farms near its border with North Korea.
Lab tests Tuesday night confirmed the country's fifth case since last week from a farm in Ganghwa, an island county near its border with North Korea, raising fears that the country is losing a battle to halt the spread of the illness that wiped out pig populations across Asia.
Officials on Wednesday were investigating another suspected case at a different farm in Ganghwa where two pigs died and another had a miscarriage.
South Korea's Ministry of Agriculture, Food and Rural Affairs said hundreds of officials have been deployed to inspect disinfection efforts at pig farms, slaughterhouses and feed mills nationwide, which came under a government-imposed 48-hour standstill as of noon Tuesday.
African swine fever is harmless to people, but having it spread from farms to densely populated areas would make it harder to contain. The illness is highly contagious and fatal for pigs, with no known cure.
In South Korea, where diets rely heavily on pork, there is a concern the outbreak could spread and hurt an industry with 6,300 farms raising more than 11 million pigs. The disease decimated pig herds in China and other Asian countries before reaching the Koreas.
Government workers dressed in lab coats and masks guarded roadblocks near farms in border areas, where excavators have been used to dig huge pits used for killing and burying thousands of pigs.
The gates, entrances and grounds of many farms were covered in snowy layers of calcium oxide, a disinfectant.
"During the standstill, we will conduct extensive disinfection operations on farms and other related facilities and thoroughly examine the results to strictly maintain quarantine," Kim Hyun-soo, the country's agriculture minister, said in a news briefing on Wednesday.
Possible cooperation with North Korea?
Nearly 22,000 pigs have been culled since the outbreak was first confirmed last week in the border towns of Paju and Yeoncheon, but officials have yet to identify the infection route. The disease may have crossed from North Korea, which reported an outbreak near its border with China in late May.
Officials earlier this week confirmed the country's third and fourth cases from Gimpo, which is on the southern side of a river that separates the border region and the populous metropolitan area surrounding capital Seoul, and another farm in Paju.
North Korea in recent months has virtually scrapped all diplomatic activity and cooperation with South Korea amid a standstill in nuclear negotiations with the United States, which has complicated efforts to prevent the disease from reaching regions near the inter-Korean border.
In a closed-door briefing to lawmakers, South Korean National Intelligence Service Director Suh Hoon said North Korea had new cases after July despite culling pigs, disinfecting farms and restricting the distribution of pork products, according to lawmakers who attended the session.
Lee Hye-hoon, chairwoman of the National Assembly's intelligence committee, said Suh used charts to explain how the disease has apparently spread to nearly all parts of North Korea. According to Lee, Suh said the agency has heard from unspecified civilian sources that pig herds in North Pyongan province — a region north of capital Pyongyang — have supposedly been "annihilated."
Lee said Suh said his agency was struggling to obtain more information because the North has been rejecting repeated South Korean calls for joint quarantine efforts.
"It was difficult to gauge (from Suh's briefing) whether quarantine measures in North Korea have been thorough and sufficient," Lee told The Associated Press.