In March 2017, an outbreak of a devastating disease of pigs called African swine fever was reported in a backyard farm in the Russian city of Irkutsk. The discovery of ASF in this remote Siberian city foreshadowed the recent appearance of the disease in China, home to almost half of the world’s population of domestic pigs. The outbreaks in China are potentially disastrous for pig farming and pork production in a country that has the highest per capita consumption of pork in the world. ASF now threatens neighbouring countries in Southeast Asia and the Korean Peninsula.
ASF is caused by a virus infection that affects only wild and domestic pigs. It is not a human disease, and human consumption of infected pork is harmless. In domestic pigs and wild boar, infection causes a skin rash, severe internal bleeding and the accumulation of fluid in the lungs. For most pigs, this is fatal. The virus is very hardy and can survive for months in chilled or frozen meat, cured hams and sausages –cooking inactivates the virus. It can also survive for long periods in the environment in pig excretions, such as faeces or urine, and in blood, which can contain very high amounts of virus. Pigs can therefore become infected by eating contaminated food (feeding on leftover kitchen waste, for example – or “swill feeding”), by direct contact with infected pigs or from contaminated soil or farm equipment.
As its name implies, ASF was originally identified in Africa, where it is endemic in Sub-Saharan countries and circulates between domestic pigs and wild African pig species, such as warthogs. Curiously, warthogs don’t develop the disease, but become infected for life and can be a source of infection for domestic pigs. In Africa, certain species of ticks also play a role in the spread and maintenance of ASF, but do not seem to be important for transmission outside Africa.
A major factor in the spread of the disease is human behaviour and activities. Illegal movement of pigs or pork products across borders by traders or foreign workers, improper disposal of food waste at entry ports, swill feeding and the illegal sale of pigs from infected herds all contribute to the spread of ASF.
There is no vaccine available to prevent this disease, which, together with the involvement of wildlife and the environmental stability of the virus, means that ASF is very difficult to control. The only effective measures following an outbreak are the enforcement of strict quarantine and biosecurity, animal movement restrictions and culling infected or exposed herds. Cleaning and disinfection of infected properties and monitoring surrounding pig farms and wildlife are also important in preventing secondary outbreaks.
ASF can have devastating effects on farming communities, particularly small backyard pig farmers, whose livelihoods may be destroyed. More broadly, ASF leads to trade restrictions, which can result in lost markets and decreases in local pork prices.
One of the worrying features of ASF is its propensity to spread over very long distances. In 1957 and again in 1960, outbreaks occurred in Portugal, originating from West Africa. Over the next three decades, the disease spread to Spain and other European countries, as well as to the Caribbean and Brazil. It wasn’t until 1995 that the disease was finally eradicated from the Iberian Peninsula, at great economic cost.
In 2007, the virus emerged in Georgia in the Caucasus. It quickly spread to neighbouring countries, including Russia. From there, it steadily marched eastward, re-emerging in the European Union in 2014. Two recent long-range jumps of the virus into wild boar populations in the Czech Republic (June 2017) and Belgium (September 2018) were most likely caused by human introductions.
In Russia, ASF spread westward into Siberia. Outbreaks in Irkutsk and others near the Chinese border in 2017 preceded the recent outbreaks in China. While there is no direct evidence that the virus responsible for the Chinese outbreaks came from Russia, the genetic sequence of the Chinese strain is closely related to the pan-Russian strain of ASF virus.
At the time of writing, 22 outbreaks of ASF in China have been reported to the World Organisation for Animal Health (OIE) by the China Animal Disease Control Centre. The first was on a farm near the city of Shenyang in the northeast province of Liaoning on 3 August. Subsequent investigations found that ASF was probably present from mid-June. Since then, over a 10-week period, outbreaks have been reported from six other provinces, including neighbouring Heilongjiang and Inner Mongolia, the central province of Henan, and Jiangsu, Zhejiang and Anhui in the east. These locations span a distance of approximately 3,000km north to south. To put this into context, the spread of ASF from Georgia to the Czech Republic, over roughly the same distance, took 10 years.
Although China has long been expecting and preparing for ASF, animal health authorities now face a daunting task in controlling the disease. So far, over 40,000 pigs have died or been culled as part of control efforts. Millions of pigs have also been inspected at farms, markets and abattoirs across China.
Of major concern now is the potential for onward spread of ASF throughout Southeast Asia – and the socio-economic consequences. Indeed, further spread into the region seems inevitable. The recent detection of ASF DNA in food brought into South Korea by a returning traveller from China highlights the risk to nearby countries.
What does this mean for the Southeast Asian region? All countries are now on high alert for ASF. In response to the Chinese outbreak, the UN’s Food and Agriculture Organization (FAO) convened an emergency meeting in early September to address regional preparedness for ASF. Representatives from countries most at risk, as well as laboratory and veterinary experts from Asian countries and overseas, participated. Since ASF does not recognise international borders, a coordinated regional response was recognised as being the most effective means to combat this disease.
The most urgent action needed now is for at-risk countries to ensure they are prepared to deal with an incursion of ASF. Key elements of this include the capacity to perform rapid field investigations and laboratory diagnosis for early detection of ASF. Underlying this is an effective veterinary service and a sound understanding of the pig value chain, which may be complex and involve cross-border trade.
Communication and engagement with pig farmers and stakeholders will also be critical in raising awareness of the disease and minimising risky practices such as swill feeding. Border biosecurity and quarantine inspections will be important to prevent the importation of infected animals and pork products. National emergency contingency planning will be central to effective and coordinated rollout of control measures.
There is no question that China and the region are facing a major threat to food biosecurity. The fight against ASF will be won through shared responsibility for implementing preventative measures – as well as open, collaborative and coordinated outbreak response involving all affected or at-risk countries. Organisations like the FAO and OIE can also be relied on to continue their excellent work towards facilitating these goals.
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