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. ASFV can also be spread by soft ticks and through contaminated objects such as vehicles, clothes and equipment.

ASFV is prevalent in most countries of sub-Saharan Africa. The virus was first introduced to Europe in 1957, but was eradicated from everywhere other than Sardinia by the mid-1990s. In 2007 there was a second incursion in the Caucasus, and since then outbreaks in the Russian Federation and bordering countries. ASFV was introduced into Poland and the Baltic States in 2014 and has continued
to spread in wild boar and cause outbreaks in domestic pigs.

ASF has a huge social and economic impact; costing hundreds of millions of pounds in affected countries.

With such a high mortality rate, the disease hits smallholders especially hard. It can also be devastating for national economies, potentially incurring years of international trade bans on live pigs or pork meat products.

  • 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.

Virology

African swine fever virus (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 24 genotypes.

There is currently no treatment or vaccine widely available and therefore biosecurity measures are essential to prevent an outbreak from spreading.

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.

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 highly infectious. 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 awareness of the
infection signs tends to be low. This means farmers may not put controls in place quickly enough, enabling the disease to spread. 

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 Envionment, 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

Moorton M, Tng PyL, Innoue R, Netherton CL, Gerner W, Schmidt S (2024)

Frontiers in Veterinary Science 11
Franzoni G, Fiori MS, Mura L, Carta T, Nardo AD, Floris M, Ferretti L, Zinellu S, Angioi PP, Sechi AM, Carusillo F, Brundu D, Fadda M, Bazzardi R, Giammarioli M, Cappai S, Giudici SD, Oggiano A (2024)

Veterinary Research 55 (1)
Cackett G, Sýkora M, Portugal R, Dulson C, Dixon L, Werner F (2024)

frontiers in Immunology 15
Goatley LC, Freimanis G, Tennakoon C, Bastos A, Heath L, Netherton CL (2024)

American Society for Microbiology
Goatley LC, Freimanis G, Tennakoon C, Foster TJ, Quershi M, Dixon LD, Batten C, Forth JH, Wade A, Netherton C (2024)

PLOS ONE

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