Wild boar pose disease risk to humans, domestic pigs

Escaped wild boar and feral pigs occupy the nebulous grey zone between wildlife and agriculture livestock and have been left to their own devices with limited control efforts.

The animals, which were introduced to Canada in the 1990s through agriculture diversification programs, subsequently escaped or were deliberately released to establish free-roaming wild populations.

They can be found on the Prairies and in almost the entire continental United States.

Eradication is hampered by their lack of natural predators, ability to exist on varied food sources and nocturnal behaviour that impedes hunting efforts.

The potential for reintroduction exists even if eradication efforts are successful because these animals are still raised for food and the trophy hunt farm industry.

Pigs were originally domesticated from wild boar in Europe and Asia, so the two species are closely related. Interbreeding between wild boar and feral pigs can occur.

Feral domestic pigs begin to resemble their wild boar cousins after a few generations in the wild, making it difficult to distinguish the source of free-roaming pigs.

Populations have grown exponentially in other areas where wild boars have been introduced, which compounds the risk of contact between domestic pigs and people.

University of Saskatchewan professor Ryan Brook has begun to research wild boar numbers in Saskatchewan to get a handle on the current situation. A Facebook page, Wild Hog Watch, has been set up to engage the community.

However, little has been said about the disease risks posed by this introduced species.

Trichinella, the pesky muscle worm that causes fever and muscle pain when it inadvertently infects people, is an important disease of wild boar elsewhere in the world.

The parasite, which has been eradicated from commercial hog production in Canada, is the reason cooking recommendations for pork suggest it should be well done.

There is no information about the rates of infection in Canadian wild boar, although a recent U.S. study found that 13 percent of wild boar had evidence of exposure to the parasite.

Hepatitis E virus, brucellosis and tuberculosis could also be carried by wild boar and transmitted to people.

The potential for transmission to Canadian populations is great if wild boar are diseased in the United States. We all know animals don’t respect human-made borders.

Commercial hog operations in Canada use biosecurity and caesarean-derived specific pathogen free breeding programs to eliminate many important swine diseases.

Wild boar could potentially reintroduce disease by contaminating food and the environment surrounding indoor commercial hog operations.

Feral pigs can also contact domestic pigs that are raised outdoors. Diseases of concern to domestic hog operations include porcine circovirus, reproductive and respiratory syndrome virus, parvovirus, swine influenza and pseudorabies.

Wild boar in other parts of the world can be affected by African swine fever, foot-and-mouth disease and classical swine fever, also known as hog cholera, although they are not currently found in North America.

A large free-ranging pig population could serve as a reservoir should any of these reportable diseases be introduced.

Wild boar can contaminate fresh produce with E. coli and campylobacter and were responsible for a large outbreak of food-borne illness in California in 2006.

Hunting wild boar requires little more than landowner permission because they are labelled as pests in Alberta and strays in Saskatchewan. Brucellosis and trichellosis are the two diseases most likely to affect hunters of wild boar.

Twenty-one wild boar were submitted to the Canadian Cooperative Wildlife Health Centre’s diagnostic service for autopsy examination this winter.

All animals were in good body condition with ample fat stores, and the females were found to be pregnant.

This initial assessment suggests that these boar are finding ample food despite the heavy snow pack we’ve experienced this winter in Saskatchewan. The deer and elk I’ve autopsied this season are usually down to the last of their internal fat stores.

Further testing of these animals for disease is being considered.

Determining the true disease risk that wild boar pose to commercial hog production and people is hampered by the lack of information about wild boar population numbers and what diseases they currently carry.

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