Why United States Pork Producers Should Be Concerned About African Swine Fever
In July 2021, the United States Department of Agriculture’s (USDA) Foreign Animal Disease Diagnostic Laboratory confirmed that African swine fever (ASF) had been found in samples collected from pigs in the Dominican Republic. Outbreaks were discovered in 11 of the country’s 32 provinces, resulting in the slaughter of tens of thousands of pigs. This operation to hopefully eradicate the disease will take at least five months to complete. ASF has never been found in the U.S., but an outbreak here would be devastating, and U.S. pork producers should take the necessary steps to protect their farms, and the domestic pork industry, from this serious threat.
What is African swine fever?
ASF is a double-stranded deoxyribonucleic acid (DNA) virus that infects domestic swine, warthogs, bushpigs, and wild boar. The soft tick Ornithodoros moubata can also be infected. Transmission primarily occurs through the upper respiratory tract, where the virus replicates in the tonsils and lymph nodes draining the head and neck. The infection is rapidly disseminated through the bloodstream, causing high virus concentrations in all body tissues. The body’s blood clotting mechanism is severely disrupted, resulting in hemorrhagic lesions. Clinical signs vary depending on the swine species, and the virus’ virulence.
- Subclinical form — Wild species can have an infection that is not apparent, making them infection reservoirs.
- Chronic form — ASF caused by low virulence isolates produce clinical signs that can last for extended periods. Signs include skin necrosis, arthritis, stunted growth, emaciation, respiratory issues, and abortion. These cases are observed infrequently in the Iberian Peninsula and the Dominican Republic, and this form is hypothesized to have evolved from ASF isolates employed in the early failed vaccine trials carried out in the Iberian Peninsula in the 1960s.
- Subacute form — ASF caused by moderately virulent isolates produces signs such as high fever and vascular changes, including hemorrhages and edema. These changes can be more pronounced than those in the acute form. Mortality rates range from 30 to 70 percent.
- Acute form — ASF caused by highly or moderately virulent isolates produces signs including high fever, appetite loss, and lethargy. Cyanosis is typically seen in the ears, snout, limbs, abdomen, tail, and perianal area. Respiratory distress is common, and skin hemorrhages are usually observed, especially on the ears, abdomen, and limbs. Other signs include bloody nasal discharge, vomiting, diarrhea, and abortions. Mortality rates can reach up to 100 percent in seven days from disease onset.
- Peracute form — ASF caused by highly virulent isolates is characterized by a rapid clinical course involving high fever, loss of appetite, lethargy, and sudden death.
How is African swine fever diagnosed?
The clinical signs seen in pigs with ASF are similar to several diseases, including erysipelas and salmonellosis, but classical swine fever (CSF) is the main differential diagnosis. Viral tests are essential for diagnosis confirmation, and samples of blood, spleen, kidney, lymph nodes, and tonsils should be collected for viral isolation, antigen detection, and polymerase chain reaction (PCR) testing for viral DNA.
Where is African swine fever found?
Until 1957, ASF was believed to be restricted to subSaharan Africa, but other outbreaks have occurred, including:
- 1957 — An outbreak occurred in Portugal on the Iberian Peninsula, after pigs were fed waste from airline flights near the Lisbon airport.
- 1964 — France
- 1967 — Italy
- 1978 — Malta
- 1986 — Netherlands
- 2007 — An outbreak that began in Georgia spread to western Russia, Armenia, Azerbaijan, Ukraine, Belarus, Lithuania, Latvia, Poland, and Estonia.
- 2018 — An outbreak occurred in China, and spread to many neighboring countries, including Mongolia, Cambodia, India, Laos, Vietnam, the Philippines, North and South Korea, Maynmar, Timor-Leste, and Papua New Guinea. The virus also spread across Europe, infecting pigs in Romania, Serbia, Slovakia, Bulgaria, and Greece, as well as wild boar in Belgium, Czech Republic, and Hungary. Belgium and the Czech Republic have since eradicated the disease.
- 2021 — Three cases of ASF were confirmed in farm pigs in the eastern German state of Bradenburg. Outbreaks in 11 of the Dominican Republic’s 32 provinces were identified.
How is African swine fever treated and prevented?
No effective treatment or vaccine exists to manage ASF, making prevention key in safeguarding the pork industry. The USDA prohibits the entry of pork products from areas, such as the Dominican Republic, where ASF has been identified. Also, the Department of Homeland Security’s Customs and Border Protection (CBP) is increasing inspections on Dominican Republic flights, to ensure travelers do not bring prohibited products to the United States. The CBP will also be ensuring that the garbage from these airplanes undergoes proper disposal, to prevent ASF transmission. U.S. pork producers should also prepare for a potential ASF outbreak here by following these protocols:
- Traceability and surveillance — Swine movement records should be kept on paper or electronically, with these protocols:
- Assign a premises identification number (PIN) to each production site.
- Geolocate each PIN to the pigs’ housing.
- Include the PIN on all animal movements, semen shipments, and diagnostic submissions.
- Record all human, vehicle, and equipment movements on and off each site.
- Onsite preparedness — Planning ahead can help ensure disease containment in the case of an ASF outbreak.
- Create a site-specific biosecurity plan.
- Train all production employees to recognize ASF signs.
- Observe pigs daily for ASF signs, and document and report any concerns.
- Perform diagnostic tests, as directed by the herd veterinarian.
- Develop welfare and disposal plans in case a quarantine is necessary.
ASF is a concerning disease that could cause devastating effects in a U.S. outbreak. However, by taking the appropriate precautions, U.S. pork producers can help prevent the disease from damaging the domestic pork industry.
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