(ATTN: ADDS details on discovery of additional dead wild boars in 3rd para)
SEOUL, Oct. 13 (Yonhap) -- South Korea's quarantine authorities remained alert on Sunday over the potential nationwide spread of African swine fever (ASF) after wild boars were found dead with traces of the disease north of Seoul.
The quarantine authorities said Saturday two wild boars, found dead in Cheorwon, 90 kilometers north of Seoul and bordering North Korea, tested positive for the deadly animal disease, marking the first time traces of ASF had been found in Gangwon Province.
On Sunday, two more wild boars found dead in the area tested positive for the disease. Since the first such case was reported earlier this month from a town near the inter-Korean border, Sunday's discovery raised the number of dead wild boar with traces of the disease to five.
South Korea has confirmed 14 cases of ASF at local pig farms since mid-September, when the country experienced its first-ever outbreak of the highly contagious disease. Since October 9, there have been no additional confirmed ASF cases.
All of the cases were reported in areas in Gyeonggi Province and Incheon, adjacent to North Korea, which experienced its own outbreak earlier this year.
The disease is not harmful to people, but it is fatal for pigs, and there are no cures currently available.
How the virus traveled into South Korea remains unknown, although some suspect that it came from North Korea. The disease is spread through direct contact with animals carrying the virus or by contaminated feed.
Although it is unlikely the wild boars traveled into the country straight from the North, it is possible their infection came from there indirectly.
In May, North Korea reported its first outbreak of the disease -- at a farm near its border with China -- to the World Organization for Animal Health.
Since its outbreak in China in August last year, the disease has spread to neighboring countries including Mongolia and Vietnam.
Quarantine officials have been implementing all-out operations to tackle the virus, especially focusing their efforts on preventing the virus from traveling south.
The ministry, which earlier decided to slaughter all pigs within a 3-kilometer radius of infected farms, has culled more than 150,000 pigs since the outbreak started.
Additionally, the ministry is currently purchasing pigs from other farms outside of that range in selected towns -- Paju, Gimpo, and Yeoncheon -- to be slaughtered and inspected before their meat is released to the market. Pigs that are not purchased will also eventually be culled.
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