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1. Disease Information1

1.1 General Disease and Pathogen Information: African swine fever (ASF) is an 

infectious disease of both domestic and wild pigs2 caused by the African swine fever 

virus (ASFV), a DNA virus and the only member of the Asfarviridae family. It can be 

transmitted through direct or indirect contact or by ticks of the genus Ornithodoros. The 

incubation period in nature is usually 4–19 days but can be up to 21 days, or in the 

acute form 3–4 days. For the purposes of the World Organisation for Animal Health 

(WOAH) Terrestrial Animal Health Code, the incubation period in Sus scrofa is 15 

days. Infection can be subclinical, peracute, acute, subacute, or chronic. Pigs that 

recover from infection can become persistently infected carriers of the virus. ASF is 

present in wild or domestic pigs in regions of Asia, Europe, Africa, and the Americas.

1.2 Clinical Signs:

1.2.1 Peracute: Caused by highly virulent strains. Pigs are typically found dead, 

sometimes without clinical signs of disease or any post-mortem lesions.

1.2.2 Acute: Caused by highly virulent strains. Clinical signs include fever, increased 

pulse and respiratory rate, lethargy, anorexia, and recumbency. Jaundice, 

vomiting, bloody diarrhea, eye discharge, bloody nasal discharge, and abortions 

may be observed. Pigs commonly exhibit reddening, hemorrhage, and/ or 

petechiation of the skin. One to two days before death the pig may develop 

anorexia, depression or listlessness, cyanosis, and incoordination. Death occurs 

2-13 days after infection. Mortality rates approach 100 percent. Commonly seen 

post-mortem lesions include enlarged, and often friable spleen, enlarged liver, 

renal petechiae/ hemorrhages, hemorrhagic and enlarged lymph nodes (most 

commonly gastrohepatic and renal), and hemorrhages/ petechiae in other 

organs including urinary bladder, lungs, heart, stomach, and intestines.

1.2.3 Subacute: Caused by moderately virulent strains. Clinical signs are similar to the 

acute form but are less severe. The duration of illness is 5-30 days and mortality 

rates are lower (30-70 percent). Death occurs 15-45 days after infection. Postmortem lesions are similar to those seen with the acute form, but typically less 

severe.

1.2.4 Chronic: Caused by lowly virulent strains. Clinical signs develop over 2-15 

months, are variable, and may include weight loss, fever, respiratory signs, skin 

1 In the 2018 ASF outbreaks in both China and Russia, the disease presented in the acute form.

2 Suids include all varieties of Sus scrofa (pig), both domestic and wild, and African wild suid species 

including warthogs (Phacochoerus spp.), bushpigs (Potamochoerus spp.) and the giant forest hog 

(Hylochoerus meinertzhageni).

Case Definition

African Swine Fever (ASF)

(Notifiable) March 2023
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necrosis, pericarditis, lung adhesions, and joint swelling. Mortality rates are low. 

Post-mortem lesions can include emaciation and focal caseous necrosis and 

mineralization of the lungs. 

2. Laboratory Criteria

2.1 Agent Isolation and Identification: Collect whole blood (EDTA and heparin), spleen, 

lymph nodes, and tonsils. Keep samples as cold as possible without freezing, unless 

using inactivating media. Tests include real-time polymerase chain reaction (PCR), 

immunohistochemistry (IHC), and virus isolation (VI). 

2.2 Agent Characterization: Genome sequencing is critical to differentiate viral strains.

2.3 Serology: Antibody (Ab) detection in serum can be evaluated by enzyme-linked 

immunosorbent assay (Ab ELISA), indirect fluorescent antibody test (IFAT), and 

indirect immunoperoxidase test (IPT). Antibodies typically develop 7-10 days postinfection and can persist for life. Pigs infected with highly virulent ASFV strains can die 

before antibody production occurs.

3. Case Classification

3.1 Suspect Case: a suid with

3.1.1 clinical signs consistent with ASF; OR 

3.1.2 an epidemiologic link to ASFV; OR

3.1.3 a non-negative result by a serological antibody screening assay conducted as 

part of a national surveillance activity. 

3.2 Presumptive Positive Case: a suspect case with 

3.2.1 a non-negative test result for ASFV PCR from a NAHLN or other APHISapproved screening laboratory.

3.3 Confirmed Positive Case: 

3.3.1 ASF virus has been isolated and sequenced at NVSL; OR

3.3.2 A suid with clinical signs consistent with ASF or an epidemiologic link to ASFV or

cause for suspicion of previous association or contact with ASFV; AND 

3.3.2.1 an ASF PCR3 positive result with genomic sequencing at NVSL; OR

3.3.2.2 antibodies specific to ASFV are identified by Ab ELISA and confirmed 

by IPT at NVSL.

4. Reporting Criteria ASF is a U.S. foreign animal disease (FAD) that is immediately 

reportable under the APHIS National List of Reportable Animal Diseases (NLRAD).

4.1 NLRAD reporting in accordance with the NLRAD Standards for notifiable diseases; 

and by APHIS to the World Organisation for Animal Health (WOAH); AND

3 Once first identification has occurred at NVSL, ASF PCR positive result at a NAHLN approved 

laboratory or NVSL
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4.2 For FAD or Emerging Disease Incidents (EDI) also follow standard procedures 

according to the Policy for the Investigation of Potential Foreign Animal 

Disease/Emerging Disease Incidents.