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African Swine Fever (ASF) in Pigs

Introduction

African Swine Fever (ASF) is a highly contagious and often fatal viral disease of domestic and wild pigs. It is characterized by hemorrhagic fever, high mortality, and severe economic losses in the swine industry. ASF is one of the most significant transboundary animal diseases due to its rapid spread and the absence of an effective vaccine.

Etiology
Causative Agent

ASF is caused by African Swine Fever Virus (ASFV), the only member of the family Asfarviridae, genus Asfivirus.

Virus Characteristics
  • Large, enveloped double-stranded DNA virus
  • Highly resistant in the environment and in pork products
  • Survives for long periods in blood, tissues, and processed meat
  • Infects macrophages and monocytes
Epidemiology
Species Affected
  • Domestic pigs
  • Wild boars
  • African wild suids (warthogs, bushpigs – usually asymptomatic carriers)
Geographic Distribution

Originally endemic in Africa, ASF has spread to Europe, Asia, and other regions, causing global concern.

Transmission
  • Direct contact with infected pigs
  • Ingestion of contaminated pork products (swill feeding)
  • Fomites (clothing, equipment, vehicles)
  • Biological transmission via soft ticks (Ornithodoros spp.) in endemic regions
Risk Factors
  • Poor biosecurity
  • Illegal movement of pigs and pork products
  • Feeding of untreated food waste
  • Contact with wild boar populations
Pathogenesis
Entry and Initial Infection

The virus enters via oral or nasal routes and infects macrophages and monocytes.

Systemic Spread
  • Rapid dissemination through bloodstream (viremia)
  • Widespread infection of lymphoid and vascular systems
Pathological Effects
  • Severe hemorrhages due to vascular damage
  • Lymphoid depletion and immunosuppression
  • Multi-organ failure
Clinical Signs
Peracute Form
  • Sudden death with few or no signs
Acute Form
  • High fever (40–42°C)
  • Depression and anorexia
  • Skin hemorrhages (ears, abdomen, limbs)
  • Respiratory distress
  • Vomiting and diarrhea (sometimes bloody)
  • Abortions in pregnant sows
  • High mortality (up to 100%)
Chronic Form
  • Weight loss
  • Intermittent fever
  • Skin ulcers
  • Joint swelling
Summary for Practitioners

ASF should be suspected in pigs with high fever, hemorrhagic signs, and sudden deaths, particularly in areas with known outbreaks or poor biosecurity practices.

Postmortem Findings
Gross Lesions
  • Enlarged, dark spleen (splenomegaly)
  • Hemorrhagic lymph nodes
  • Petechiae and ecchymoses in multiple organs
  • Pulmonary edema
  • Kidney hemorrhages (“turkey egg” appearance)
Microscopic Lesions
  • Severe lymphoid depletion
  • Vascular damage and hemorrhage
  • Necrosis in multiple organs
Diagnosis
Clinical Diagnosis

Based on high mortality, hemorrhagic signs, and rapid spread in pig populations.

Laboratory Diagnosis
  • PCR for ASFV DNA detection
  • Virus isolation
  • Serological tests (ELISA)
Differential Diagnosis
  • Classical swine fever (CSF)
  • Porcine reproductive and respiratory syndrome (PRRS)
  • Septicemic bacterial infections
  • Other hemorrhagic diseases
Summary for Practitioners

Definitive diagnosis requires laboratory confirmation due to similarity with other swine diseases, particularly classical swine fever.

Treatment
General Consideration

No effective treatment or vaccine is currently available for ASF.

Management
  • Culling of infected and exposed animals
  • Disposal of carcasses by approved methods
  • Strict movement control
Summary for Practitioners

Treatment is not possible. Immediate reporting and implementation of control measures are critical to prevent spread.

Control and Prevention
Biosecurity
  • Strict control of farm access
  • Disinfection of vehicles, equipment, and personnel
  • Prohibition of swill feeding
Surveillance
  • Monitoring of domestic and wild pig populations
  • Early detection and reporting systems
Outbreak Control
  • Stamping-out (culling infected herds)
  • Movement restrictions and quarantine
  • Zoning and compartmentalization
Summary for Practitioners

Prevention depends entirely on strict biosecurity and early detection. Rapid response is essential to control outbreaks.

Zoonotic Importance

African Swine Fever is not zoonotic and does not infect humans.

Economic Importance

ASF causes devastating economic losses due to high mortality, trade restrictions, culling of herds, and disruption of pork supply chains.

Summary

African Swine Fever is a highly lethal viral disease of pigs characterized by hemorrhagic fever and high mortality. With no effective vaccine or treatment, control relies on strict biosecurity, surveillance, and rapid eradication measures.