A dead pig is put into a quarantined pit in Hanoi to stop the spread of African swine fever MANAN VATSYAYANA/AFP via Getty Images

A quarter of the world’s domestic pigs have died this year as a virus rampages across Eurasia, and that may be just the start. Half the pigs in China – which last year numbered 440 million, some 50 per cent of the world’s pigs – have either died of African swine fever (ASF) or been killed to stamp out the virus.

ASF comes from East Africa. In 2007, it reached Georgia in the Caucasus in contaminated meat, and in infected wild boar. Now, it is all over Russia and eastern Europe and infected wild boar have turned up as far west as Belgium. It is also spreading in east Asia, killing many pigs in Vietnam and elsewhere.

ASF was spotted in China in August 2018. It is now in every province. The virus is also raging in North Korea, and infected wild pigs have entered South Korea.


At the end of September, according to the UN Food and Agriculture Organization in Rome, China’s Ministry of Agriculture and Rural Affairs estimated that there had been a 39 per cent decrease in the number of live pigs in China between August 2018 and August 2019, after a full year of ASF infections.

Some infected herds were culled in efforts to prevent further spread. But with a fatality rate in pigs of nearly 100 per cent, the virus may have done most of the killing.

Official figures are thought to be an underestimate, however. In October, Rabobank, a Dutch bank specialising in food and agriculture which works with sources in the industry, reported that the herd had fallen by half just in the first eight months of 2019, and that this will reach 55 per cent by year’s end. They say losses will continue, though they are expected to slow, as sanitary controls kick in.

The only way to get rid of ASF is to kill infected herds. But while pigs on farms can be destroyed and replaced, the disease persists in wild boar and feral hogs, as well as in meat, which is increasingly sold abroad. “I predict ASF virus will remain endemic for some time in east Asia and eastern Europe, with constant introductions around the world,” says Dirk Pfeiffer of City University in Hong Kong. “Currently nobody on this planet has the solution to the problem.”

Despite years of warnings from virologists, there is no vaccine. Most vaccines against viruses stimulate the body to make antibodies against viral structural proteins, such as those in the virus coating. These then stop the virus from entering cells, for example. But ASF, says Linda Dixon of The Pirbright Institute in Surrey, UK, is a large, complex virus, with two coatings and several ways of entering cells. Antibodies to various bits of it have never been enough to stop it.

We will now be able to look for better antibody targets, says Dixon, as scientists in China and Spain published the first detailed images of the virus last month (Journal of Biological Chemistry, doi.org/ddqz).

Experimental vaccines made of live, weakened ASF have worked better, says Dixon. These prompt specialised blood cells to recognise a range of viral proteins, but there are several hurdles to developing such vaccines for use. Meanwhile, she fears, ASF “could go global”.

This article was updated on 08.11.19 to provide more detail on the data on China’s pig deaths this year.