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Deadly African swine fever arrives in China, the world’s largest producer of pigs


Africa swine fever, which recently appeared in Shenyang City, in Liaoning Province, northeastern China, threatens the USD150-billion global pig industry.

This article is written by Vish Nene, co-leader of ILRI’s animal and human health program, and Han Jianlin, a population geneticist based in Beijing at the Joint Laboratory on Livestock and Forage Genetic Resources, which is run by ILRI and the Chinese Academy of Agricultural Sciences’ Institute of Animal Sciences.

Long feared, it’s now finally happened. African swine fever (ASF), an infectious and highly lethal viral disease of pigs, has for the first time reared its head in China. Just two weeks ago, African swine fever was confirmed as the cause of death of pigs on a small farm in Shenyang City, in Liaoning Province, located in the northeast, bordering North Korea and the Yellow Sea.

China is the largest pig producer in the world, raising more than 500 million animals—about half of the global pig population.

The introduction of this pig disease in China could have devastating consequences, especially as small-scale, backyard pig-keeping remains central to the livelihoods and food security of many farmers.

African swine fever is a highly contagious and deadly disease of domestic pigs. No vaccine or treatment for the disease yet exists. This disease, which is listed by the World Organisation for Animal Health (OIE) as a significant transboundary disease, poses a huge risk to the global pig industry, valued at some USD150 billion.

Fortunately, China had prepared itself to address this disease threat. Following detection of African swine fever in the Caucasus region in 2007, the China Animal Disease Control Center (CADC) and the China Animal Health and Epidemiology Center (CAHEC) of the Ministry of Agriculture and Rural Affairs began to prepare the country for actions to take in the event the disease entered China. The disease progressively spread west and east from the Caucasus. Following its detection in 2017 in Irkutsk, a city in eastern Siberia, Russia, only some 1000 km from China, Beijing issued a countrywide warning to enable government agencies and personnel at all levels to respond to a possible outbreak in China.

In the present case, some sick pigs died on the afternoon of 1 Aug 2018, with a preliminary diagnosis of African swine fever made by the Liaoning Animal Disease Control Center, in Shenyang. Samples were sent to the National Research Center for Exotic Animal Disease (NRCEAD) of CADC, in Qinghao, for testing on 2 Aug and confirmed as African swine fever the next day.

After this, all governmental agencies began implementing a level-II response action plan. Pigs in an area within 3 km of the infected farm were culled and the area was disinfected. As an additional precaution, the area was closed for the next six weeks. Furthermore, the media are being encouraged to talk about this case and its potential risk to aid the control and elimination of the disease.

On the morning of 7 Aug, an article reporting the clinical symptoms and laboratory diagnostic results of this first outbreak of African swine fever in China was published online. The nucleic acid positive result and sequencing analysis of the 417 base pairs of B646L/p72 gene of the virus confirmed that it shares 100% identity with the current prevalent Georgian strain of the virus in Russia and Eastern Europe (Wang et al., 2018).

The cause of this outbreak is still under investigation. The goal of researchers is to control the current outbreak as quickly as possible.

An ILRI staff member assesses a pig’s health in Busia, western Kenya (photo credit: ILRI/Charlie Pye-Smith).

Although African swine fever has been long-established in wild African pigs, the first scientific reports of an outbreak in domestic pigs came from Kenya in 1909 following the introduction of exotic pigs to the country. African swine fever is now present in much of sub-Saharan Africa. Outbreaks, both within endemic areas and in naive pig populations in Africa, are on the increase, with mortality rates as high as 100%.

Disease outbreaks outside Africa have occurred since 1957. These affected Belgium, France, Italy, Malta, the Netherlands. Portugal and Spain in Europe and Brazil and the Caribbean in Latin America. After many years of implementing intensive control measures, the virus was successfully eliminated from all these areas, with the exception of the island of Sardinia.

Following a subsequent lull, a new outbreak of the African swine fever virus was reported in Armenia, Georgia and the Russian Federation in 2007, which has since spread to Belarus, Estonia, Latvia, Lithuania, Poland and the Ukraine. In 2017 the virus was reported in the Czech Republic, Moldova and Romania. It has now arrived in China.

As mentioned, no drugs or vaccines exist for treating or stopping African swine fever. Unlike other viral pathogens, the causative virus of this disease is remarkably stable, with contaminated pork products, waste and fomites (materials likely to carry infection, such as vehicles, clothes and equipment) significant and long-lasting sources of infection.

In Africa there are reservoirs of the virus in soft-bodied ticks and in disease-resistant wild pigs. The epidemiology of African swine fever outside Africa is further complicated by spread of the virus by wild boars and there is good evidence that different breeds of pigs and wild boars have different levels of sensitivity to the virus.

With China home not only to half the world’s total pig population but also to unique pig breeds and to a large population of wild boars, it is vital that the current outbreak of the disease is successfully controlled.

Two collaborative research projects are being implemented by scientists at the International Livestock Research Institute (ILRI) and Huazhong (Wuhan) and China (Beijing) agricultural universities on the genomic characterization of domestic pigs and wild boars in Asia and the genetic resistance of domestic pigs and wild boars to African swine fever. These research projects are jointly funded by the National Natural Science Foundation of China and by ILRI.

With others, ILRI is working to develop a vaccine that will protect pigs from this lethal and economically devastating disease.

Related ILRI collaborative research activities on African swine fever conducted with partners in Europe and the USA focus on the socioeconomic impacts and epidemiology of the disease, surveillance of the disease, the response mechanisms pigs make to the disease, bio-security protocols in place in different pig value chains, and the comparative evolutionary biology of the African swine fever virus.

Reference
Wang QH, Ren WJ, Bao JY, Ge SQ, Li JM, Li L, Fan XX et al. 2018. The First Outbreak of African Swine Fever was Confirmed in China. China Animal Health Inspection, http://kns.cnki.net/kcms/detail/37.1246.S.20180807.0908.002.html.

Links to related ILRI information
Sequencing swine leucocyte alleles for vaccine development, by Lucilla Steinaa, Sonal Henson, Soren Buus, Annette Stryhn, Morten Nielsen, Nicholas Svitek, Cynthia Onzere, Edwina Bochere, Gideon Ndambuki and Richard Bishop, Apr 2018.

Pig diseases in Uganda: Impacts on pig production, human health and nutrition, by Michel Dione, Lucilla Steinaa, Edward Okoth, Kristina Roesel and Barbara Wieland, Dec 2016.

Pig vaccines and diagnostics for African swine fever in Uganda, by Lucilla Steinaa, Richard Bishop, Edward Okoth, Nicholas Svitek and Victor Riitho, Dec 2016.

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