African Swine Fever (ASF) is a dangerous disease that can lead to hemorrhaging in domestic pigs and wild boars. While ASF does not infect humans, it can lead to 100% mortality in pigs, making this virus one of the most devastating diseases in pig rearing and pork production worldwide. ASF threatens food security and the livelihoods of smallholder farms. The people most at risk are those in lower-income countries where sanitary measures for disease management and control are often too expensive to implement.
A Disease With a Century-Long History
The virus was first described in Kenya in 1921 and now affects up to 35 African countries, including the islands of Mauritius and Madagascar. The first report in Tanzania occurred in 1962. Since then, ASF has been reported in 15 local Tanzanian municipalities and poses a substantial threat in the southern highlands. Outbreaks are attributed to poor conditions on pig farms, including insecure transport systems, feeding pigs contaminated food, and a lack of quarantine measures for sick animals.
How African Swine Fever Spreads: Three Transmission Cycles
ASF has a complicated transmission cycle with three main avenues. First, the domestic cycle, in which pigs can pass the virus directly to each other. Second, the domestic pig-tick cycle, in which infected ticks transmit the virus to domestic pigs during feeding. Third, the wild warthog cycle, in which the virus can pass directly between wild pigs or be transmitted via ticks.
These three overlapping cycles make the virus extremely difficult to control and monitor. A particularly vulnerable point is where domestic and wild pigs come into contact due to inadequate infrastructure, weak fencing, exposure during transportation, or overlapping shared spaces.
The Role of Ticks — and Why It Is So Poorly Understood
Very little is known about how the soft tick, Ornithodoros species, is capable of transmitting ASF to pigs. Securing pigpens and transport vehicles to protect against tick exposure is something rarely considered or implemented across Africa as well as parts of Asia.
In Europe, laws require vector management to protect animals from dangerous insect bites, though flying insects are typically given priority over ticks. Animals can be sprayed with acaricides, chemicals that kill ticks and mites. However, these chemicals carry significant risks: toxicity to the animal, tick-acquired chemical resistance, and the potential for contaminated meat, which can pose a threat to human health. Vaccines that protect against tick bites have been proposed as a safer alternative to interrupt ASF transmission.
Biosecurity on Smallholder Farms: Simple in Theory, Difficult in Practice
Many steps can be taken on smallholder farms to help secure the livelihoods of farmers and the safety of animals through well-defined biosecurity practices — measures that help prevent the spread of disease between animals, from animals to humans, or between farms. Examples include controlling animal movements between facilities, cleaning equipment before and after contact with animals, isolating sick animals, safely disposing of dead animals or contaminated feed, and limiting contact with outside animals or ticks.
While many of these practices are straightforward in theory, numerous factors make implementation expensive or impractical for farmers with limited resources.
Why Tanzanian Farmers Struggle to Implement ASF Controls
A study in Tanzania examined the barriers farmers face in implementing biosecurity practices against ASF. Given the economic pressure to succeed, some farmers feared losing profit from quarantining or culling sick animals and instead chose to sell them — prioritizing short-term income over disease containment. Access to veterinary and government assistance was also limited, making treatment difficult and compensation for losses unlikely. Increasing demand for pork has further led to more frequent pig transport and movement of pork products, raising the risk of contamination across wider areas.
African Swine Fever Goes Global
ASF has now spread well beyond Africa. Early outbreaks occurred in Europe, South America, and the Caribbean but were eradicated by the mid-1990s. However, the current epidemic is attributed to a second introduction of the virus in Europe, in the Republic of Georgia in 2007. This triggered the spread of ASF into vulnerable Asian markets, with outbreaks confirmed in Mongolia, Cambodia, and Indonesia in 2019. As of 2021, ASF has resurfaced in the Dominican Republic and Haiti after a 40-year absence.
African Swine Fever is now a growing epidemiological threat for swine worldwide — and the communities that depend on them.
