African Swine Fever
What is it?
African Swine Fever (ASF) is a highly contagious disease of swine (Sus scrofa), including domesticated pigs, European wild boar and American wild (feral) pigs. Wild African suids, such as warthogs (Phacochoerus spp.), are reservoir species - they rarely show clinical signs, but maintain the virus in the environment in a sylvatic cycle with Ornithodoros ticks. The virus has the capability to manifest with a wide range of clinical signs and lesions. It can spread very rapidly in pig populations. ASF cannot be differentiated from classical swine fever by either clinical or postmortem examination.
ASF in Hispaniola
ASF was reported in the Dominican Republic in July 2021, and in Haiti the following September. Introduction of ASF to the Dominican Republic is thought to have happened in April, but it is not known when it was introduced to Haiti. The presence of ASF in the Caribbean poses a risk to other countries in the region, including the U.S. ASF introduction to the U.S. would result in severe economic consequences due to disruption of the production cycle through quarantine, culling, and trade sanctions. USDA is providing support to the Dominican Republic and Haiti in combating ASF and is working with Canada and Mexico to prevent introduction to North America.
Signs and Symptoms
Mortality rates vary depending on the virulence of the virus; highly virulent virus presents as peracute or acute disease. In peracute forms of the disease, pigs die suddenly with minimal clinical signs. Acute disease has an incubation period of three to seven days, followed by a high fever, decreased appetite, weakness, coughing and difficulty breathing, vomiting and diarrhea, red blotchy skin or skin lesions, abortion, and death within 10-20 days. Hemorrhages primarily occur in lymph nodes, kidneys, and on visceral surfaces of organs; enlarged spleen, skin bruising, swollen bluish color of hairless skin, and fluid around the lungs, heart and abdomen may also be present. Mortality in domestic swine is close to 100% in these forms of disease.
Moderately virulent ASF incubation can be longer (up to 15 days), and manifests as subacute disease. Clinical signs include slight fever, low appetite, lethargy, and abortion. Death occurs in 15-45 days, with a wide variation in mortality (30-70% reported).
The chronic form of ASF results from moderate to low virulence virus. This form is characterized by emaciation, swollen joints, waxing/waning fever, respiratory problems, and ulceration and necrosis of skin. Pathologic lesions may include focal caseous necrosis and mineralization of lungs, and lymph adenomegaly.
Transmission
ASF is endemic in sub-Saharan Africa. It is also found in areas of Asia, Europe, Russia, and now Hispaniola. The virus is found in all body fluids and tissues. Pigs become infected by direct contact with infected pigs, their bodily fluids, or feces. or indirectly by ingestion of unprocessed infected pig meat or products, including frozen meats or improperly cooked food waste. Ticks, environmental contamination, and fomites can also spread the virus.
Although people cannot get African swine fever, they can carry it on clothing, shoes, and equipment. Sources of the infection include garbage feeding, contaminated personnel, equipment and vehicles, contaminated feed, or water, infected domestic or wild pigs, soft ticks, stable flies and semen. The most common sources of transmission include:
Direct Contact: Direct contact occurs when healthy pigs have contact with infected domestic or wild swine or come in contact with infected saliva, urine, feces, or aerosolized respiratory secretions via coughing or sneezing.
Indirect transmission: Indirect transmission happens when healthy pigs eat virus-contaminated feed, pork products, or come into contact with the virus on clothing, shoes, equipment, vehicles, or food waste.
Insect-borne transmission: This occurs when a soft tick acts as a vector, feeding on infected pigs and spreading the virus to healthy swine. Other insects like stable flies, leeches, and swine lice may also spread it.
ASF Virology
The ASF virus is the only member of the Asfarviridae family; there are two distinct genotypes of ASF virus, and a recombinant virus was recently isolated in China, Russia, and Vietnam. The virus is stable in a wide pH range, and in cold temperatures. The virus can remain infectious for many months at room temperature. Virus is reported to be inactivated at 133⁰F for 70 minutes, or 140⁰F for 20 minutes; virus in infected pig meat can remain viable for several weeks to months.
Diagnosis
The University of Minnesota Veterinary Diagnostic Laboratory is an ASF-approved testing laboratory. The test for ASF is run on whole blood samples, tonsil, spleen and lymph nodes. As with other reportable diseases, the USDA’s National Veterinary Services Laboratory is the nation’s confirmatory lab. If you suspect that pigs may be infected, contact the BAH immediately and we will arrange an investigation and sample collection.
Human Risk
ASF affects members of the pig family, and it is not known to be a human health risk.
Prevention
Biosecurity and prevention are our best methods to help protect the swine population. There is no treatment for ASF, and while several vaccines are in development, none have been licensed. Successful eradication involves rapid diagnosis, quarantine, slaughter and disposal of all animals on an infected farm, and disinfection of infected premises. African swine fever has never been found in the United States, and we want to keep it that way.
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