Swine fever infection vector remains mystery

A government helicopter releases disinfectants to prevent the spread of African swine fever in Gimpo, Gyeonggi Province, Tuesday. Yonhap

By Kim Hyun-bin

Quarantine authorities still do not know how African swine fever (ASF) has spread here, because no clear vectors for the disease's spread have been found in confirmed cases.

Not knowing the cause is making it more difficult to take preventive measures.

When ASF was confirmed in South Korea in mid-September, the authorities suspected a virus spread via wild boars from North Korea, where the deadly virus reportedly has been rampant.

But experts said boars would be unlikely to enter the South after breaking through barbed wire in the demilitarized zone (DMZ). Also, boars found in the south side of the DMZ tested negative for the virus.

Another suspicion was that the virus was transmitted via water in the Imjin River, which flows from the North to the South toward the Han River. The nine farms here where ASF was confirmed are close to the river.

But 20 water samples from the Imjin and Han rivers tested negative.

Some other vectors include using leftover food for pigs, or farm workers visiting countries where ASF is spread. But none of the confirmed cases had these factors.

Now some people suspect cats living in the wild could have spread the virus after coming in contact with infected animals or eating the remains of infected animals, and then following nearby rivers. All the contaminated pig farms are around two to three kilometers from rivers.

A confirmed ASF case at a pig farm on Seokmo Island in Ganghwa, Incheon, fuels the speculation that wildlife such as rats or cats could have spread the virus. Only one bridge connects the island with other regions, and the farm had only two pigs and no outside cars visited there, according to quarantine authorities

Many experts say the situation is similar to the avian influenza virus that swept through the country in 2016. The virus was spread to secluded areas including Yeongcheon, Gimpo and Ganghwa.

There was no proof that cats were involved in spreading the bird flu virus, but in December 2016, the remains of two stray cats discovered in Pocheon, Gyeonggi Province, were found to have the H5N6 virus.

Prime Minister Lee Nak-yon also said last week that there could be other unknown ways of spreading the virus.

“The current quarantine system could be missing something,” Lee said at a meeting with government officials. “For example, the virus could be spread through underground water, or via flies or small winged animals, and in such cases the current system cannot prevent the spread.”