Swine fever is a highly contagious viral disease that infects domestic pigs and wild boar, often causing severe hemorrhaging, high fever, and death. It does not infect humans and poses no food safety risk, but it devastates pig populations and can cripple a country’s pork industry. There are actually two distinct diseases that share the name: African swine fever (ASF) and classical swine fever (CSF). They look similar in a sick pig but are caused by completely different viruses and require different control strategies.
Two Different Diseases, Similar Names
African swine fever is caused by a large DNA virus in the Asfarviridae family. It is the only known DNA virus spread by arthropods (specifically ticks). Classical swine fever, sometimes called hog cholera, is caused by a small RNA virus in the Flaviviridae family, making it a relative of the viruses behind dengue and Zika. Despite the overlapping symptoms, the two viruses are not closely related.
The practical difference that matters most is vaccination. Effective vaccines exist for classical swine fever, and vaccinated pigs develop neutralizing antibodies that provide strong, cross-protective immunity across different virus strains. African swine fever is a different story entirely. The virus evades the immune system in ways researchers still struggle to counter; infected pigs do not produce useful neutralizing antibodies. As of mid-2025, the first international standards for ASF vaccine production were adopted by the World Organisation for Animal Health (WOAH), and several modified live vaccine candidates are being approved or tested in individual countries, but no widely available commercial vaccine exists yet.
How Swine Fever Spreads
Both viruses spread through direct contact between pigs and through contaminated materials like clothing, equipment, vehicles, and feed. Pork products that haven’t been properly heat-treated can carry the virus over enormous distances, which is why border inspections at airports and ports focus heavily on confiscating meat. In the Dominican Republic alone, canine detection units have seized more than 2,000 kilograms of food items destined for the United States since early 2024.
African swine fever has an additional transmission route that classical swine fever lacks: soft ticks. Soft ticks of the genus Ornithodoros are the only confirmed biological vector for ASF. These ticks feed on blood multiple times during their lives, picking up the virus from infected warthogs or pigs and passing it along during future feedings. The virus can even move from one tick generation to the next through eggs, meaning tick populations serve as a long-term reservoir. In eastern and southern Africa, a cycle between warthogs and soft ticks in underground burrows has maintained the virus for centuries.
Classical swine fever spreads efficiently through all bodily secretions and has one particularly dangerous trick: the virus crosses the placental barrier. Pregnant sows can pass the infection to their unborn piglets, producing offspring that are born persistently infected. These piglets appear healthy for a time but shed virus continuously until they eventually die, silently seeding outbreaks in herds.
What Swine Fever Looks Like in Pigs
Both diseases range from sudden death to chronic, drawn-out illness depending on the strain’s virulence and the pig’s age. In the acute form, pigs develop high fevers (above 40°C or 104°F), stop eating, become depressed, and may show an unsteady gait, diarrhea, vomiting, or coughing. Skin reddening or bluish discoloration, particularly on the ears, tail, and belly, is a hallmark sign visible before slaughter.
Internally, the damage is more dramatic. In African swine fever, the spleen often becomes massively enlarged and turns dark red to nearly black from hemorrhage. Widespread pinpoint hemorrhages appear on the kidneys in roughly 20 to 25 percent of infected pigs, and hemorrhaging in the lymph nodes is common across all confirmed cases. Bleeding can also appear on the intestinal surfaces, the lining of the heart, and the urinary bladder, though at lower rates.
Classical swine fever in its acute form looks strikingly similar, with hemorrhaging in the lymph nodes, kidneys, and other organs. Piglets are hit hardest, often developing neurological signs like tremors and convulsions before dying. The chronic form of CSF is subtler, producing vague symptoms like intermittent fever and poor appetite that drag on for two to three months before the animal dies.
Mortality Rates
Highly virulent strains of African swine fever kill 90 to 100 percent of infected domestic pigs. There is no treatment. Pigs that survive infection with lower-virulence strains can become long-term carriers, shedding virus and potentially sparking new outbreaks.
Classical swine fever is similarly lethal under the wrong conditions. Highly virulent CSF strains in young or immunologically naive pigs produce case fatality rates of 80 to 100 percent. An analysis of CSF outbreaks in Japanese wild boar estimated the overall case fatality ratio at roughly 96 percent, with recovery occurring at an extremely low rate. Older domestic pigs exposed to less virulent strains fare better and can develop lifelong immunity if they survive.
No Risk to Humans
Neither African nor classical swine fever infects people. You cannot catch swine fever by handling pigs, and eating properly prepared pork from an affected region carries no health risk. The concern is entirely economic and agricultural. Swine fever is devastating to pig farmers, to pork supply chains, and to the millions of smallholder families in Asia and Africa who depend on pig farming for their livelihoods.
Economic Damage and Trade Disruption
When ASF arrives in a country, the consequences extend far beyond the farm. Because no widely available vaccine exists, the primary control tool is mass culling of infected and exposed herds, followed by strict trade restrictions. The Dominican Republic offers a case study in these costs: as of September 2024, the country had culled over 210,000 pigs and processed $28.4 million in compensation payments to more than 5,000 producers. The United States contributed approximately $15 million toward that total.
The ripple effect on trade is enormous. With domestic production gutted, the Dominican Republic’s pork imports surged 153 percent between 2020 and 2023, jumping from about 40,000 metric tons to over 101,000 metric tons. Through the first half of 2024, imports were still climbing. Countries that detect ASF typically lose access to export markets overnight, as trading partners impose immediate bans on pork products from affected regions.
Prevention and Biosecurity
For classical swine fever, vaccination is the frontline defense. Modified live vaccines, chimeric vaccines, and subunit vaccines are available depending on the country. Some newer vaccines come with companion blood tests that can distinguish vaccinated pigs from truly infected ones, which is critical for trade and eradication programs. Oral vaccines have also been deployed in wild boar populations to reduce virus circulation in the wild.
For African swine fever, prevention relies almost entirely on biosecurity. That means controlling who and what enters a pig farm, disinfecting vehicles and equipment, sourcing feed carefully, and keeping domestic pigs away from wild boar and their habitats. On surfaces, the virus is remarkably tough but can be killed with the right chemicals and enough contact time. Sodium hypochlorite (bleach) at 600 parts per million eliminates the virus from plastic, steel, and sealed concrete within five minutes. Citric acid at 2 percent concentration inactivates the virus in dried feces on steel in about two minutes, though the presence of blood significantly reduces its effectiveness. Potassium peroxymonosulfate-based commercial disinfectants achieve effective kill rates on packing plant surfaces after 10 minutes of contact. Porous materials like wood require higher concentrations and longer soak times than smooth surfaces like steel or plastic.
How Swine Fever Is Diagnosed
Because the symptoms of ASF and CSF overlap heavily with each other and with other pig diseases, laboratory confirmation is essential. For African swine fever, the standard approach uses PCR testing to detect viral DNA in blood or tissue samples. Newer real-time PCR methods are more sensitive than older versions and can pick up infection in animals that have survived the acute phase. Antibody detection through blood testing (ELISA screening confirmed by additional assays) identifies pigs that were previously infected, which matters for surveillance in regions where the virus circulates at lower levels.
Classical swine fever diagnosis follows a similar two-track approach of virus detection and antibody screening. The key diagnostic challenge with CSF is identifying those persistently infected piglets born to infected sows. These animals do not produce antibodies against the virus, so they test negative on standard blood screens despite actively shedding virus. Detecting them requires direct virus testing rather than antibody-based methods.