African swine fever – clinical signs and current status - Veterinary Practice
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African swine fever – clinical signs and current status

ASF is a notifiable disease with risk of transmission from human-mediated routes currently deemed high, necessitating continued stringent surveillance

African swine fever (ASF) continues to spread across Europe, posing a current and real threat to both the commercial and domestic pig populations, as well as to the wild boar population, across the United Kingdom (UK). An incursion of this disease into the UK would have adverse effects on pig health and welfare, commercial productivity and the ability of the UK to sell pork. Globally, the spread of ASF is having detrimental effects on biodiversity alongside severe economic consequences.

This article seeks to describe the global spread of ASF, its agent and clinical signs to look out for in pigs. Most importantly it also outlines what anyone working with or keeping pigs, as well as the public, can do to help keep the UK free from this disease.

What is ASF?

ASF is a highly contagious viral haemorrhagic disease caused by a large double-stranded DNA virus from the family Asfarviridae. The virus is known to infect all pigs, including wild pigs (such as warthogs and wild boar). ASF does not affect humans and as such does not pose a significant, direct threat to human health.

Following initial exposure to the virus it can take from 5 to 15 days before first clinical signs are seen

In pigs, the virus exhibits a variable incubation time. Following initial exposure to the virus it can take from 5 to 15 days before first clinical signs are seen. This can create a lag between incursion and detection, which can allow for considerable spread prior to detection if biosecurity is suboptimal.

Clinical signs

ASF is distinct from the better-known classical swine fever (CSF); however, similar clinical signs are often seen. This means that it is impossible to distinguish between ASF and CSF on clinical signs alone, with laboratory testing required to differentiate between the two diseases. When investigating clinical suspicion of either disease, the competent authority will always test for both concurrently.

Pigs suffering from ASF can show varied clinical signs depending on the strain of infecting virus. Mild strains may cause few or no clinical signs, while acute strains cause severe clinical signs and death within 10 days. The case fatality rate can be as high as 100 percent in severe cases.

Common early clinical presentations include malaise, high fever and inappetence, though in severe cases sudden death with no obvious premonitory signs can occur. Pigs can also present with:

  • Diarrhoea and vomiting
  • Dark red or purple ears, snout, tail or feet
  • Reddening of the skin on the ventrum or chest

Respiratory distress, ataxia or weakness, red eyes with or without discharge, and abortion and still births in pregnant gilts and sows can also be seen in the later stages of the disease.

African swine fever is a notifiable disease and any suspicion must be reported to the competent authority immediately. The Pirbright Institute is the World Organisation for Animal Health (WOAH) reference laboratory for ASF and has a lot of useful information on its website including a helpful factsheet. Defra has also published photos of affected pigs to aid in recognition of the disease.

African swine fever is a notifiable disease. Failure to report a notifiable disease is an offence. Any suspicion of this disease must be reported at once:

In England contact Defra Rural Services Helpline on 03000 200 301. More information can be found here. In Wales, contact 0300 303 8268. In Scotland, contact your local APHA Field Services office. More information can be found here. In Northern Ireland, contact your local DAERA Direct Regional office. More information can be found here.

Control and treatment

There are currently no vaccines available to control or prevent ASF in porcine populations. However, researchers are working hard to identify new vaccine candidates. Despite promising early results, commercial production of any vaccine is expected to be several years away and although researchers are also working on antivirals to help control progress of the disease, no cure is currently available for individual animals infected with the disease. Therefore, the most important form of control is prevention of infection and early detection of any incursion. This can be achieved via surveillance, strict biosecurity, import controls and the education of both pig owners and anyone coming into contact with domestic or feral pigs.

Despite promising early results, commercial production of any vaccine is expected to be several years away

The risk

Pigs are at risk of contracting the disease through contact with infected animals, either directly or indirectly by contact with infected animals’ faeces or body fluids. This can also include contact with contaminated fomites (eg clothes, vehicles, footwear or equipment). The ASF virus can survive for months to years in smoked, dried, cured and frozen meat so there is a significant risk from pigs consuming meat or meat products from infected animals. Pigs can also contract ASF through the bite of an infected Ornithodoros tick, but these are not currently found in the UK.

The ASF virus can survive for months to years in smoked, dried, cured and frozen meat so there is a significant risk from pigs consuming meat or meat products from infected animals

The international disease monitoring team at Animal and Plant Health Agency (APHA) currently considers the “overall” risk of entry of the ASF virus into the UK from a combination of all pathways to be medium, but considers the risk from human-mediated routes (for example, pigs having access to infected fomites or meat and meat products) to be high.

The historic situation

ASF emerged in the early 1900s in East Africa and subsequently spread across sub-Saharan Africa, where it is now considered to be endemic. It was first seen in Europe in 1957 with an incursion of the disease to Lisbon, Portugal, from where it spread across Europe. However, it was eradicated from all affected countries in Europe – with the exception of Sardinia, where ASF has been endemic since 1978 – by the mid-1990s.

More recently, following its first confirmation in Georgia in 2007, ASF has gradually spread into the Russian Federation and Eastern Europe affecting both domestic pigs and wild boar. Continual spread led to the first record of ASF in the European Union (EU) in January 2014, initially in Poland and the Baltic states from whence the spread continued. To date ASF has been confirmed in 16 European countries, although two countries (Belgium in 2020 and the Czech Republic in 2018) have since been able to eradicate the disease within their borders (World Organisation for Animal Health, 2022a).

In its latest situation report, WOAH states that as of July 2022, ASF has been reported in a total of 74 countries

ASF was first reported in China in 2018, severely impacting a country that is home to around half of the global pig population. The disease continues to spread in Asia affecting 16 countries as of 2021 (World Organisation for Animal Health, 2022b).

ASF continues to be reported in previously unaffected countries and previously unaffected areas of affected countries. Locally, continuous spreading is mostly facilitated by wild boar, while in longer-distance events human-mediated transmission is suspected to be involved. Commercial pig farms, smallholdings, pet pigs and wild boar have all been affected. In its latest situation report, WOAH states that as of July 2022, ASF has been reported in a total of 74 countries (World Organisation for Animal Health, 2022a).

Keeping ASF out of the UK

Increased awareness of the risks, enhanced surveillance and stringent biosecurity around pigs are key to minimising the risk of an outbreak of ASF in the UK. Adherence to the following can help to achieve this.

If visiting an affected country/area:

  • Footwear, clothing, vehicles and equipment must be thoroughly cleansed and disinfected before returning to the UK. This is especially important for those in contact with pigs or visiting areas where wild boar reside
  • Pork or pork products must not be brought into the UK from affected areas
  • While it is legal to bring other meat and meat products from EU affected areas into the UK, it is essential that this does not come into contact with pigs or wild boar in the UK
  • It is illegal to bring personal meat or dairy products into the UK from Asia or Africa whether from an affected area or not (failure to adhere to this rule may result in prosecution and a large fine)

Pig keepers and those going into areas where pigs/wild boar reside in the UK:

  • Footwear, equipment, clothing and vehicles should be thoroughly cleansed and disinfected when entering and leaving pig areas
  • No catering or domestic food waste (including any meat products) should be fed to pigs – this is illegal (this includes catering waste from vegetarian or vegan kitchens)
  • No meat products should be taken into areas where wild boar or pigs live
  • All edible waste must be disposed of in a wildlife-proof fashion
  • Only essential visitors should be allowed to have contact with pigs. If contact is necessary, protective clothing must be worn. Protective clothing must be clean and, if not disposable, thoroughly cleansed and disinfected on leaving the area
  • Pig keepers and vets must be aware of the typical clinical signs of ASF and report any suspicion to the local competent authority


ASF continues to spread globally, affecting biodiversity and economies. Until effective vaccines or treatments are available, the methods that remain to slow or stop this spread are surveillance, vigilance, biosecurity and education. An awareness of the risks and clinical signs, exercising caution when travelling and strict adherence to biosecurity protocols in and around areas where pigs reside can make all the difference in stopping this disease spreading to and within the UK. Please spread the word and help to keep UK pigs free from this devastating disease.

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