African swine fever (ASF) is a severe viral disease that infects pigs and wild boar, causing internal bleeding, high fever, and death rates that can reach 100% in its most virulent form. It does not infect humans. Despite decades of effort, there is still no commercially reliable vaccine, making ASF one of the most devastating livestock diseases in the world. Since 2018, outbreaks have killed or led to the culling of hundreds of millions of pigs across Asia, Europe, and parts of the Caribbean.
The Virus Behind ASF
ASF is caused by a large, complex DNA virus in the family Asfarviridae. It’s unusually tough for a virus. It survives across a wide pH range, remains infectious for years at room temperature or below, and requires heating to at least 60°C (140°F) for 30 minutes to be killed. Standard disinfectants like formaldehyde and sodium hydroxide can destroy it, but it takes extended contact times of one to six days depending on concentration.
This durability is a major reason ASF is so hard to control. The virus persists in frozen meat for months, in chilled pork fat for over two years, and in frozen spleen tissue for at least 735 days. Even cured pork products can harbor the virus for weeks to months. Salami cured for 27 days still tested positive 18 days into processing. Longer-cured products like Serrano ham (cured 180 to 365 days) eventually test negative, but shorter curing times are not reliably safe.
How It Spreads
Among domestic pigs, ASF spreads primarily through direct contact with infected animals or indirectly through contaminated meat products, equipment, vehicles, and clothing. Feeding pigs kitchen scraps or improperly treated food waste containing infected pork is a well-documented route of transmission. The virus can also travel on boots, tires, and shared farm tools.
In eastern and southern Africa, the disease originally circulated in a cycle between wild warthogs and soft-bodied ticks of the Ornithodoros genus. These ticks act as both vectors and long-term reservoirs, capable of harboring the virus for months. During a resurgence in Portugal in the 1990s, a native tick species allowed the virus to persist in the environment long after outbreaks in pigs had been controlled.
However, the role of ticks in the current global spread appears limited. The wave of ASF that has swept through Europe and Asia since 2007 has been sustained entirely through pig-to-pig transmission and contaminated pork products, with no significant involvement of tick vectors. Wild boar populations in Europe have become a major reservoir, making eradication extremely difficult in affected regions.
Symptoms in Pigs
ASF takes several forms depending on the virulence of the virus strain involved. The most common and most feared are the acute and peracute forms.
After an incubation period of 3 to 7 days, pigs develop a high fever (up to 42°C or about 107.5°F), stop eating, become uncoordinated, and collapse. Some die at this stage before showing any other signs. Those that survive longer develop reddening or blue discoloration of the ears and snout, which spreads across the body. Bleeding from the nose and rectum follows. Pregnant sows abort. Vomiting and labored breathing are common. Mortality in the acute form approaches 100%.
Lower-virulence strains produce a chronic form with vague symptoms: weight loss, swollen joints, and respiratory problems. These cases are harder to diagnose because the signs overlap with many other pig diseases, and chronically infected pigs can continue shedding virus for extended periods.
No Risk to Humans
ASF does not infect people. You cannot catch it by handling pork, eating pork products, or being around infected animals. The concern is entirely economic and animal welfare related. The virus is strictly limited to members of the pig family, including domestic pigs, wild boar, warthogs, and bushpigs.
Global Economic Damage
The scale of destruction from ASF is staggering. China lost approximately 225 million pigs between 2018 and 2019 to death or culling, with estimated economic losses approaching $119 billion over a decade. Vietnam lost 20% of its pig population within the first five months of its outbreak, costing between $880 million and $4.4 billion in 2019 alone. India lost over $37 million from pig deaths in a single outbreak period in 2020.
As of late 2024, active outbreaks continue across multiple European countries including Germany, Italy, Poland, Romania, Hungary, Serbia, Ukraine, and Bosnia and Herzegovina. New cases were reported in Albania and Hong Kong in November 2024. The disease has never been detected in the United States, Australia, or New Zealand, but authorities in those countries treat the threat as serious and imminent.
Why There’s Still No Vaccine
The ASF virus is genetically complex, with a genome of 170,000 to 194,000 base pairs encoding over 150 proteins. This complexity has made vaccine development extraordinarily difficult. Live attenuated vaccines, which use weakened versions of the virus, are currently considered the most promising approach, and some candidates have shown significant protection in trials.
But safety remains a problem. A recent meta-analysis of vaccine candidates found that about 24% of vaccinated pigs developed fever and 11% showed clinical reactions. These side effects, combined with concerns about the weakened virus reverting to a more dangerous form, mean no vaccine has yet achieved the safety profile needed for widespread commercial use. Vietnam approved a domestic vaccine in 2023, but reports of adverse effects in the field prompted its suspension. The global pork industry continues to rely entirely on prevention and culling to manage outbreaks.
How Outbreaks Are Controlled
Without a vaccine, controlling ASF depends entirely on biosecurity, surveillance, and rapid response. When an outbreak is confirmed, every pig on the affected farm is typically culled, and movement restrictions are imposed on farms within a surrounding zone. Contaminated carcasses, feed, and bedding are destroyed.
For pig farmers, prevention centers on a few core practices. Keeping outside food products away from animals is critical because the virus survives for months in pork. All vehicles and equipment entering or leaving a farm site need thorough cleaning and disinfection. New animals should be quarantined before joining an existing herd. Feral pigs and wild boar should be kept away from domestic pig areas through fencing and habitat management.
For countries that remain ASF-free, border control plays a major role. Travelers are prohibited from bringing pork products from affected regions, and customs agencies actively screen for illegally imported meat. A single contaminated sandwich discarded near a pig farm could theoretically spark an outbreak, given how long the virus survives in processed pork.