Diagnosing African Swine Fever: Laboratory Approaches and Practical Sample Selection for Field Veterinarians

African swine fever (ASF) presents a significant diagnostic challenge because its clinical signs and gross lesions can resemble those of several other hemorrhagic diseases affecting pigs. Although fever, hemorrhages, splenomegaly, and increased mortality may strongly raise clinical suspicion, these findings alone cannot establish a definitive diagnosis. Laboratory confirmation remains essential before implementing disease-specific control measures¹. 

For practicing veterinarians, appropriate sample selection and an understanding of available diagnostic methods are critical for achieving accurate and timely diagnosis, particularly during the early stages of an outbreak. 

Why Laboratory Confirmation Is Essential 

The clinical presentation of ASF varies depending on the virulence of the virus, infectious dose, and stage of disease. Acute, subacute, and chronic infections may all present differently, making diagnosis based solely on clinical examination unreliable¹. 

Rapid laboratory confirmation not only supports clinical decision-making but also plays a vital role in surveillance, outbreak investigation, movement control, and implementation of biosecurity measures. Selecting appropriate samples and using the correct diagnostic test improves the likelihood of detecting infection during different stages of disease. 

Selecting the Right Samples 

Successful diagnosis begins with proper sample collection. 

In live animals, whole blood is one of the most valuable specimens because infected pigs develop high levels of circulating virus during the acute stage of infection. Blood collected with anticoagulant is commonly used for molecular detection and virus isolation. 

Following necropsy, tissues containing high viral loads provide excellent diagnostic material. Samples commonly collected include: 

• Spleen 

• Lymph nodes 

• Tonsils 

• Lung 

• Kidney 

• Liver 

These tissues are particularly useful because ASFV replicates extensively in macrophages, resulting in widespread distribution of viral particles throughout lymphoid and visceral organs^2,3. 

Proper handling and transport of specimens remain essential to preserve sample quality and reduce the risk of contamination before laboratory analysis. 

Molecular Detection: The Primary Diagnostic Tool 

Polymerase chain reaction (PCR) remains one of the most important laboratory techniques for confirming ASF infection because it directly detects viral DNA. 

ASFV possesses a large double-stranded DNA genome measuring approximately 170–194 kb, making nucleic acid detection highly suitable for laboratory diagnosis³. PCR enables rapid identification of viral genetic material in blood and tissue samples, even before detectable antibody responses have developed. 

Because viral replication begins soon after infection and large quantities of viral DNA accumulate within infected tissues, molecular testing is particularly valuable during acute disease when animals exhibit clinical signs and high levels of viremia³. 

The reliability of PCR depends heavily on appropriate sample selection and proper specimen handling throughout collection and transport. 

Additional Diagnostic Approaches³ 

Although molecular testing is widely used, several other laboratory methods contribute to ASF diagnosis depending on the stage of infection and diagnostic objective. 

Virus isolation confirms the presence of infectious virus by demonstrating viral replication under controlled laboratory conditions. While highly informative, this method requires specialized laboratory facilities and is generally less practical for routine field diagnosis. 

Antigen detection methods identify viral proteins within infected tissues or blood samples. These techniques may support diagnosis during active infection when sufficient viral antigen is present. 

Antibody detection becomes valuable later in infection, particularly in animals that survive long enough to develop an immune response. Since antibody production requires time following infection, serological testing should always be interpreted alongside clinical findings and, when appropriate, molecular diagnostic results. 

Each laboratory method provides different information, making test selection dependent on the stage of disease, available samples, and the specific diagnostic question being addressed. 

Interpreting Diagnostic Findings in Clinical Practice 

Laboratory results should always be interpreted alongside clinical observations and pathological findings. 

For example, pigs presenting with high fever, hemorrhagic lymph nodes, marked splenomegaly, and positive PCR results strongly support a diagnosis of ASF. Conversely, negative laboratory findings from poorly collected or unsuitable samples should be interpreted cautiously, particularly if clinical suspicion remains high. 

Understanding the disease timeline is equally important. Viral DNA and antigen are most readily detected during active infection, whereas antibody detection becomes increasingly useful in animals that survive beyond the acute stage. 

Conclusion 

Accurate diagnosis of African swine fever relies on combining careful clinical evaluation with appropriate laboratory testing. Selecting suitable samples, understanding the strengths of different diagnostic methods, and interpreting results within the clinical context allow veterinarians to recognize suspected cases promptly and support effective outbreak response. Because no single clinical sign is pathognomonic for ASF, laboratory confirmation remains the cornerstone of definitive diagnosis. 

References 

1. Sánchez-Vizcaíno JM, Mur L, Gomez-Villamandos JC, Carrasco L. An update on the epidemiology and pathology of African swine fever. Journal of comparative pathology. 2015 Jan 1;152(1):9-21. https://www.researchgate.net/profile/Librado-Carrasco/publication/269180289_An_Update_on_the_Epidemiology_and_Pathology_of_African_Swine_Fever/links/622b08309f7b324634211eba/An-Update-on-the-Epidemiology-and-Pathology-of-African-Swine-Fever.pdf 

2. Alonso C, Galindo I, Cuesta-Geijo MA, Cabezas M, Hernaez B, Munoz-Moreno R. African swine fever virus-cell interactions: from virus entry to cell survival. Virus research. 2013 Apr 1;173(1):42-57. https://pmc.ncbi.nlm.nih.gov/articles/PMC7114420/pdf/main.pdf 

3. Li Z, Chen W, Qiu Z, Li Y, Fan J, Wu K, Li X, Zhao M, Ding H, Fan S, Chen J. African swine fever virus: a review. Life. 2022 Aug 17;12(8):1255. https://www.mdpi.com/2075-1729/12/8/1255