How African swine fever travels the world

One of the key precautions against an outbreak of African swine fever (ASF) is not to feed pigs leftover food. Any leftover pork from travelers on board an airplane or a ship that departed from a country with a reported case of the animal disease should be all brought back to the country or properly disposed of through heat treatment. This is a sobering lesson that the countries learned when the virus, which had originated in Africa, spread to Europe.

ASF was first described in 1921 when the virus in a wild boar in Kenya spread to pigs at a farm. Even at that time, it was thought to be a kind of an endemic disease that only emerges in Africa.

In 1957, however, products made of pork infected with ASF accidently arrived in Europe and spread the deadly virus with the fatality rate of 100 percent to a number of countries. Experts are divided on whether the infected food first traveled via an airplane or a vessel. Yet, it is clear that leftover food, which had been taken from Angola to Lisbon, was fed to pigs again. This led to a series of ASF outbreaks across Western Europe.

For 30 years since then, the animal disease has been a constant trouble for pig farms in Western Europe. Cases were reported in many countries including Spain in 1960, France in 1964, and Italy in 1967. To prevent a spread, tougher measures were put in place such as a blanket ban on feeding pigs leftover food without heat treatment and the installation of fences to prevent wild boars from crossing. Thanks to such efforts, Portugal and Spain could declare an end to ASF in 1993 and 1995, respectively.

Still, the ASF virus with a different genotype spread to Eastern Europe in 2007, apparently through infected leftover food from a cruise ship that departed Africa and anchored at a port in Georgia. The food was fed to pigs at a farm in Georgia, and the pigs started to fall. The disease then reached neighboring countries including Russia.

According to the European Food Safety Authority (EFSA)in 2013, 38 percent of the ASF cases was due to an infection through transportation, shipment, and movement. In other words, the virus is the most likely to be spread when an infected animal or food are moved to another place. Thirty-five percent of cases occurred by pigs that were fed leftover food. Countries with a large population of wild boars often build long fences near the border.

The outbreak of ASF in Shenyang, China in August 2018 was the first reported case of the fatal disease in Asia. As a result of the gene test, the virus was confirmed to have exactly the same genotype as the one found in Russia. As Shenyang, the largest city of Liaoning Province, is where trade is active with Eastern European countries, it is highly likely that the virus was brought into the country through livestock products. The disease then spread to Mongolia, North Korea, and Laos. The first confirmed case of ASF in South Korea was reported at a pig farm in Paju, Gyeonggi Province, on Sept. 17.


Hye-Ryung Choi herstory@donga.com