Wild Boar Diseases: ASF, Brucellosis, and Parasites

Wild boar (Sus scrofa) and feral pigs carry a wide array of diseases and parasites that affect animal health, livestock industries, and occasionally human populations. As wild boar numbers increase globally and their range expands into new areas, the disease risks they pose have become a major concern for veterinary authorities, wildlife managers, and public health agencies. Understanding the key diseases associated with wild boar is essential for anyone working at the interface of wildlife and agriculture.

African Swine Fever (ASF)

African swine fever is the most devastating disease threat to global pig populations, and wild boar play a critical role in its epidemiology. ASF is caused by a large, complex DNA virus (African swine fever virus, or ASFV) that infects domestic pigs and wild boar with typically catastrophic results.

Disease Characteristics

ASF causes hemorrhagic fever in infected pigs and wild boar. The acute form of the disease produces high fever, internal hemorrhaging, organ failure, and death, often within days of symptom onset. Mortality rates in naive populations (those with no prior exposure) approach 100 percent for the most virulent strains. There is currently no approved vaccine or treatment.

The virus is extraordinarily hardy in the environment. It can survive for months in contaminated meat products, soil, and fomites (contaminated objects), and it can persist in the carcasses of dead animals for extended periods. This environmental stability makes eradication extremely difficult once the virus becomes established in a wild boar population.

Global Spread

ASF was historically confined to sub-Saharan Africa, where it circulated among warthogs and bush pigs (which tolerate the infection without severe disease) and the Ornithodoros tick vectors. The virus escaped Africa and established in parts of Europe, spreading through domestic pig movements and contaminated pork products.

The disease spread through wild boar populations across Eastern Europe and into Western Europe. It has also swept through domestic pig industries in China, Southeast Asia, and other regions, causing enormous economic losses. The potential introduction of ASF to the Western Hemisphere — where millions of feral pigs could serve as a permanent reservoir — is a nightmare scenario for the pork industry.

Wild Boar as Reservoir

Wild boar complicate ASF control because they cannot be vaccinated or treated, they range freely across jurisdictional boundaries, and their carcasses can maintain infectious virus in the environment for months. Management strategies for ASF in wild boar populations include carcass search and removal, fencing to limit boar movement, population reduction in affected zones, and biosecurity measures at the wildlife-livestock interface. For more on wild boar management, see wild boar management and population control methods.

Brucellosis

Swine brucellosis, caused primarily by Brucella suis, is a bacterial disease that affects both wild boar and domestic pigs. In wild boar, the infection is often chronic and may not produce obvious clinical signs, allowing infected animals to serve as long-term reservoirs.

Transmission and Impact

Brucella suis is transmitted through contact with infected reproductive fluids, aborted fetuses, and contaminated environments. In domestic pig herds, brucellosis causes reproductive failure — abortions, infertility, and weak piglets. In wild boar, infected sows may show reduced reproductive success, but many carry the bacteria without apparent illness.

The disease is zoonotic, meaning it can infect humans. People who handle infected animals or their tissues without proper protection can contract brucellosis, which causes undulant fever — a debilitating illness with cyclical fever, joint pain, and fatigue. While treatable with antibiotics, human brucellosis can be a prolonged and unpleasant illness.

Seroprevalence studies (blood tests for antibodies) in feral pig populations across the southern United States have documented brucellosis exposure rates varying widely by region, with some populations showing substantial exposure levels. These findings underscore the importance of biosecurity when handling feral pigs.

Pseudorabies (Aujeszky’s Disease)

Pseudorabies is caused by suid herpesvirus 1 (SHV-1) and is endemic in many feral pig populations worldwide. In pigs and wild boar, the disease ranges from mild respiratory illness to reproductive failure, depending on the animal’s age and immune status. Adult wild boar often carry the virus without severe illness.

However, pseudorabies is nearly 100 percent fatal in most other mammalian species that contract it. Dogs, cats, cattle, sheep, and various wildlife species can develop rapidly fatal encephalitis after contact with infected pigs. This makes feral pig populations a significant risk to domestic animals and native wildlife in areas where they overlap.

Parasitic Infections

Wild boar harbor a diverse community of internal and external parasites that can affect both animal and human health.

Internal Parasites

Common internal parasites of wild boar include:

Kidney worms (Stephanurus dentatus) — Large nematodes that migrate through the liver and kidneys, causing tissue damage. More prevalent in tropical and subtropical populations.

Lungworms (Metastrongylus species) — Parasites that inhabit the bronchi and bronchioles, potentially predisposing animals to secondary bacterial pneumonia.

Stomach and intestinal worms — Multiple species of roundworms, hookworms, and whipworms inhabit the gastrointestinal tract of wild boar, with heavy infestations potentially affecting growth and condition.

Trichinella — The causative agent of trichinosis, this parasitic roundworm encysts in muscle tissue and can be transmitted to humans who consume undercooked infected meat. Trichinella prevalence in wild boar varies by region.

External Parasites

Ticks, lice, mites, and biting flies all parasitize wild boar. Ticks are of particular concern because they can transmit diseases to other wildlife, domestic animals, and humans. Wild boar may serve as hosts for tick species that carry Lyme disease, tick-borne encephalitis, and other pathogens. Wallowing behavior helps control ectoparasite loads, as described in our article on wild boar wallowing — mud bathing benefits.

Leptospirosis

Leptospirosis is a bacterial disease caused by various Leptospira species. Wild boar can carry and shed the bacteria in their urine, contaminating water sources and wet environments. The disease is zoonotic and can cause serious illness in humans, ranging from flu-like symptoms to kidney and liver failure in severe cases.

Implications for Livestock and Public Health

The disease burden of wild boar populations has significant implications at the wildlife-livestock-human interface. Where feral pigs and domestic livestock share landscapes, disease transmission risk is a constant concern. Biosecurity measures — fencing to prevent contact, avoiding shared water sources, and testing domestic herds in areas with feral pig activity — are essential components of livestock health management.

For public health, the key messages are straightforward: avoid direct contact with feral pig blood and tissues without appropriate protection, do not handle sick or dead feral pigs, and be aware that water sources contaminated by feral pig activity may carry zoonotic pathogens.

Key Takeaways

• African swine fever is the most significant disease threat, with near-100-percent mortality in naive populations and no vaccine available
• Wild boar serve as long-term reservoirs for brucellosis, pseudorabies, and leptospirosis
• Multiple parasitic infections affect wild boar, including several with zoonotic potential
• The expansion of wild boar populations increases disease transmission risk to domestic livestock and humans
• Biosecurity at the wildlife-livestock interface is essential in areas with feral pig activity
• Disease management in wild boar populations is complicated by the animals’ free-ranging behavior and large numbers

The disease ecology of wild boar underscores why their population management is not solely an agricultural or conservation concern — it is also a matter of veterinary and public health significance. As wild boar populations continue to expand globally, the disease risks they carry will only grow more relevant.