African Swine Fever in Pigs: Symptoms, Lesions and On-Farm PCR Testing

Last updated: 5 November 2026 · Clinical facts in this article come from the WOAH (World Organisation for Animal Health) technical disease card for African swine fever and the WOAH African swine fever disease page. Product data comes from Yinrui Bio's published specifications.

Quick Answer

African swine fever (ASF) cannot be confirmed by symptoms or post-mortem lesions alone. WOAH lists high fever (40.5–42°C), reddening of the skin on the ears, abdomen and legs, loss of appetite, vomiting, bloody diarrhoea, abortion and death within 6–13 days as typical of the acute form, with mortality close to 100% in domestic pigs. But classical swine fever (CSF) looks identical in the field, so WOAH states that laboratory confirmation is essential. PCR, which detects the ASF virus genome in blood or tissue, is the standard tool for that confirmation. ASF does not infect people.

Key takeaways

• Incubation: usually 4–19 days in nature; 3–4 days in the acute form (WOAH). The WOAH Code uses 15 days for regulatory purposes.
• Mortality: close to 100% for acute ASF in domestic pigs; roughly 30–70% for the subacute form (WOAH).
• Look-alikes: classical swine fever, PRRS, erysipelas, salmonellosis, Aujeszky's disease and pasteurellosis (WOAH differential list).
• Virus survival: ASFV can stay infectious for 3–6 months in uncooked pork products (WOAH), which is why swill feeding is a major transmission route.

What Is African Swine Fever?

ASF is a viral disease of domestic pigs and wild boar caused by African swine fever virus (ASFV), a large DNA virus and the only member of the family Asfarviridae. WOAH lists four transmission routes: direct contact between infected and healthy pigs; eating food waste, feed or garbage containing infected pork; contaminated fomites such as vehicles, clothing, footwear and equipment; and the bite of soft ticks of the genus Ornithodoros where they occur.

There is no treatment. Control relies on early detection, culling and safe disposal of infected herds, cleaning and disinfection, and movement controls. WOAH has also issued a statement warning about the risks of sub-standard ASF vaccines.

Symptoms of ASF by Clinical Form

WOAH describes four clinical forms. Which one you see depends mostly on the virulence of the strain.

Do not wait for mass deaths. ASF can spread slowly within a farm and mortality can be low at first, so a single pig with high fever, red or bluish skin, or an unexplained death is already a reason to suspect ASF, stop pig movements, report to the veterinary authority and have samples taken.

Post-Mortem Lesions of ASF

WOAH lists the following lesions for the acute form and notes that not all of them appear in every case:

• Pronounced haemorrhages in the gastrohepatic and renal lymph nodes
• Pinpoint (petechial) haemorrhages in the kidney cortex, and also in the medulla and pelvis
• Enlarged, congested spleen (congestive splenomegaly)
• Swollen areas of cyanosis on hairless skin; bruise-like haemorrhages on the legs and abdomen
• Excess fluid in the chest, around the heart and/or in the abdomen
• Petechiae on the larynx, bladder and the surfaces of internal organs
• Oedema in the mesentery of the colon and around and in the wall of the gall bladder

In the chronic form, lungs may show focal caseous necrosis and mineralisation, and lymph nodes are enlarged. Opening carcasses on the farm spreads virus-laden blood, so necropsy and sampling should follow your veterinary authority's biosecurity procedure.

Why Symptoms Are Not Enough: The CSF Problem

WOAH is explicit: it is not possible to tell ASF from classical swine fever by clinical signs or post-mortem examination. PRRS, erysipelas, salmonellosis, Aujeszky's disease (pseudorabies) and pasteurellosis also enter the differential list. The control measures for each are different, so a laboratory result is needed to confirm the cause. Containment and reporting should not wait for it.

If you run an on-farm panel, testing the same blood sample for ASFV, classical swine fever (CSFV) and PRRSV helps the differential diagnosis of the three most important look-alikes in one round. All 13 swine chips are listed on the swine PCR test kits page.

How ASF Is Diagnosed in the Laboratory

The WOAH disease card lists these laboratory methods:

Antibodies take time to appear, and pigs with acute ASF often die before they develop them, so serology is mainly a surveillance tool. For a sick or freshly dead pig, PCR is the practical test. Our PCR vs ELISA comparison explains the difference in more detail.

Which samples to collect

WOAH recommends blood collected in EDTA during the early fever stage, and spleen, lymph nodes, tonsil, lung, kidney and bone marrow kept at 4°C. Our veterinary sample collection guide covers labelling and transport.

On-Farm PCR Testing for ASF

Laboratory PCR is accurate, but samples must be packed, transported and queued, which can take hours or days in rural areas. A portable real-time PCR analyzer lets the farm vet or the field team of an integrator or distributor get a PCR result in under one hour while the farm is already in containment. It does not replace reporting: stop pig movements and notify the veterinary authority as soon as ASF is suspected, without waiting for any test result.

Workflow: collect whole blood, or prepare a tissue homogenate as described in the chip's instructions for use → add the sample to the chip → insert the chip into the CarryOn → extraction, amplification and detection run automatically → read the result and Ct value on the touchscreen.

Important: an on-farm PCR result is a screening and decision tool for the farm. Official confirmation of an ASF outbreak is made by the laboratory designated by your national veterinary authority. Movements should already be stopped on suspicion; a positive field result means: keep the pen isolated and make sure the authority has the result.

In herds vaccinated with a live attenuated ASF vaccine, the vaccine virus itself contains ASFV DNA. Our product pages do not claim that the ASF chip can distinguish vaccine strains from field strains, so interpret results in vaccinated herds with your veterinarian and the reference laboratory.

For distributors in Vietnam and Southeast Asia, see the Vietnam market page or contact us for a technical dossier and evaluation units.

Sources

• WOAH, African swine fever technical disease card (incubation, clinical forms, lesions, differential diagnosis, samples, laboratory methods).
• WOAH, African swine fever disease page (transmission routes, human health, control).
• WOAH Bulletin, on slow within-herd spread and initially low mortality delaying ASF recognition.
• Yinrui Bio published specifications for the CarryOn P1000Q and the ASF test chip.