A nightmare is unfolding for animal health experts: African swine fever (ASF), a highly contagious, often fatal disease of domestic pigs and wild boars, has appeared in China, the world’s largest pork producer. As of today, ASF has been reported at sites in four provinces in China’s northeast, thousands of kilometers apart. Containing the disease in a population of more than 430 million hogs, many raised in smallholder farmyards with minimal biosecurity, could be a monumental challenge.
“The entry of ASF into China is really a very serious issue,” says Yang Hanchun, a swine viral disease scientist at China Agricultural University in Beijing. Given the scale of China's pork sector, the economic impact could be devastating, Yang says, and the outbreak puts a crucial protein source at risk. From China, the virus could also spread elsewhere; if it becomes endemic, “it will represent a major threat for the rest of the world, including the American continent,” says François Roger, an animal epidemiologist at the Agricultural Research Center for International Development in Montpellier, France, who warned that the spread of ASF to China would have “dramatic consequences” in a paper in Veterinary Record last year.
The virus that causes ASF does not harm humans, but it spreads rapidly among domestic pigs and wild boars through direct contact or exposure to farm workers’ contaminated shoes, clothing, and equipment. It can survive heat and cold and persists for weeks in carcasses, feces, and fresh and semicured pork products, such as sausages. Ticks can also spread it. Infection causes a high fever, internal bleeding, and, often, death. There is no ASF vaccine and no treatment for infected animals.
Endemic in most African countries, ASF jumped to the nation of Georgia in 2007 and later spread through Russia; it has also been reported in Poland and the Czech Republic, and scientists worry about a jump to major pork producers such as Germany and Denmark.
East Asia’s first confirmed outbreak occurred on 1 August in Shenyang, a city in Liaoning province, China’s Ministry of Agriculture says. Investigators have traced the disease back through sales of pigs and concluded the virus has been circulating in the area since at least March, says Wantanee Kalpravidh, a veterinarian at the Food and Agriculture Organization’s (FAO’s) Emergency Centre for Transboundary Animal Disease in Bangkok.
A genetic analysis suggests the virus is closely related to the strain circulating in Russia, scientists from the Institute of Military Veterinary Medicine in Changchun, and other Chinese institutions reported on 13 August in Transboundary and Emerging Diseases. “The increasing demand for pork has resulted in a great increase in the volume of live pigs and pork products imported to China,” heightening the risk of introduction, they wrote. The virus probably arrived in imported pork products, Kalpravidh says, which then infected pigs that were fed contaminated table and kitchen scraps.
A second outbreak occurred on 14 August at a slaughterhouse in Zhengzhou, the capital of Henan province; the afflicted pigs had been shipped from a market in Jiamusi, a town in Heilongjiang province, more than 2000 kilometers to the northeast. The virus struck again on 15 August at a farm in Lianyungang, in Jiangsu province. The Chinese government has responded by culling sick and exposed animals—nearly 9000 were killed in Shenyang alone—blockading outbreak areas; disinfecting farms, markets, and processing facilities; controlling the movement of live pigs and pork products; screening animals; and conducting epidemiological surveys.
But there are serious challenges to containing the virus. Pig producers in China range from massive, sophisticated operations to small backyard farms; tailoring a response to suit them all “is the biggest challenge for China to control ASF,” Yang says. The complexity of the production chain makes tracing paths of infection “an incredible effort to tackle,” says Juan Lubroth, chief veterinarian at FAO’s headquarters in Rome. Kalpravidh says China is trying to earn the cooperation of producers by immediately compensating them for culled animals, in hopes of stopping them from slaughtering sick pigs and selling their meat. But ticks and wild boar could also spread the disease, although their role is poorly understood.
So far, Lubroth says, China’s “very sophisticated and knowledgeable veterinary workforce” has operated aggressively, and the government has been transparent about ASF’s spread. But containing ASF “won’t happen overnight,” he warns.
With reporting by Bian Huihui.
*Update, 25 August 2018, 8:45 a.m.: This article was updated with a link to a relevant paper.