African swine fever virus

African swine fever (ASF) is a contagious disease that can be fatal for all infected domestic pigs and wild boar.

Pigs are usually infected through direct contact with other infected pigs, or indirectly by eating infected meat or meat products. The African swine fever virus (ASFV) can also be spread by soft ticks and through contaminated objects such as vehicles, clothes and equipment.

ASF is now prevalent in many countries in Europe, Asia and Africa. ASFV was originally found throughout sub-Saharan Africa. The virus was first introduced to Europe in 1957 but was eradicated from the continent, with exception of Sardinia, by the mid-1990s. In 2007, there was a second incursion in the Caucasus, and since then the virus has spread across Eastern and Central Europe and into most of Southern and Eastern Asia. Outbreaks have also been reported in Papua New Guinea and on the Caribbean island of Hispaniola.

With such a high mortality rate, the disease is a significant animal welfare concern and hits smallholders especially hard. ASF has a huge social and economic impact, costing hundreds of millions of pounds in affected countries. It can also be devastating for national economies, potentially incurring years of international trade bans on live pigs or pork meat products. The presence of the disease in India, Bhutan, The Philippines and Indonesia means that ASF is now a huge conservation issue as critically endangered wild swine inhabit these parts of the world. 

  • African swine fever is a notifiable disease and should be reported.
    Please see the Defra website for advice on how to spot and report the disease. Guidance to pig keepers on preventing the disease is also available.

Clinical signs

The clinical signs of ASF can vary but are similar to some other pig diseases. Signs typically occur 3-15 days after infection. 

The early signs are non-specific and include:

  • High fever, lethargy, and loss of appetite.
  • Pigs may die suddenly without further disease signs.

At later stages, further signs may be observed including:

  • Reddening of the skin (visible only in pale-skinned pigs), with patches appearing on the tips of ears, tail, feet, chest, or under the belly.
  • Diarrhoea, vomiting.
  • Laboured breathing.
  • Swollen red eyes, eye discharge.
  • Abortions, still-births.
  • Increasing morbidity and unwillingness to get up.

In severe cases, death can sometimes be the only sign of infection, with a case fatality rate as high as 100%.

Images of ASF clinical signs:

Pictures copyright The Pirbright Institute.
For use of these images please email communications@pirbright.ac.uk.

Virology

ASFV is a large complex DNA virus and is the only member of the Asfarviridae family, genus Asfivirus. ASFV has several layers that surround a dense core containing its DNA genome. There are at least 23 genotypes.

There is currently no treatment or widely available vaccine and therefore biosecurity measures are essential to prevent an outbreak from spreading. Significant progress has been made in developing ASF vaccines and as of June 2024 these have only been licensed in Vietnam and The Philippines.

Prevention

There has never been an outbreak of ASFV in the UK, and ASFV-free countries in Western Europe have strict policies in place to prevent infected live animals and pork products being imported.

Feeding pigs with swill, which contains human food waste, is banned in the UK and EU to prevent contamination with infected pork products.  However, swill feeding remains popular elsewhere, especially among smallholders.

Eliminating the disease is difficult because the virus is infectious and very stable in the natural environment. In countries where ASFV is persistent, large numbers of wild pigs roam freely and can easily infect domestic pigs. 

Control

There is no treatment or vaccine available for ASFV. Measures to control the disease rely on effective surveillance, rapid diagnosis and movement restrictions. Control of ASFV can be particularly difficult among smallholders in lower income countries, where access to diagnostic tools and veterinary services can be limited.

Pirbright's research on African swine fever

Scientists at The Pirbright Institute have been working on understanding the virus since the 1960s.

Their expertise on how the virus works and how it interacts with the porcine (pig) immune system is crucial to the Institute’s vaccine development research.

Pirbright researchers are currently developing different types of ASF vaccines with the aim of producing one that will protect pigs from this deadly disease. 

As the World Organisation for Animal Health (WOAH) Reference Laboratory for ASF, Pirbright provides surveillance and diagnosis of ASF globally and continually works towards improving tests to detect the virus. Pirbright experts also provide advice to Department for Environment, Food and Rural Affairs (Defra) and WOAH, and have helped to provide resources for vets that will help them to identify ASF quickly should it ever present in the UK.

Resources

Research papers

Dixon L K, Chapman D A G, Netherton C L, Upton C (2013)

Virus Research 173 (1) , 3-14
Dixon L K, Abrams C C, Chapman D D, Goatley L C, Netherton C L, Taylor G, Takamatsu H H (2013)

Developments in Biologicals 135 , 147-157
Fishbourne E, Hutet E, Abrams C, Cariolet R, Potier M F l, Takamatsu H H, Dixon L K (2013)

Veterinary Research 44 , e87
Fishbourne E, Abrams C C, Takamatsu H-H, Dixon L K (2013)

Veterinary Microbiology 162 (2-4) , 937-943
Gomez-Villamandos J C, Bautista M J, Sanchez-Cordon P J, Carrasco L (2013)

Virus Research 173 (1) , 140-149

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