For the first time since testing began several years ago, feral pigs in North Carolina have tested positive for Brucella suis, an important and harmful bacteria that can be transmitted to domestic pigs and people.

The results surfaced in a North Carolina State University study conducted to test the state’s feral pig populations for several types of bacteria and viruses. Researchers found about 9 percent of feral pigs studied in Johnston County and less than 1 percent surveyed randomly at 13 other sites across the state showed exposure to B. suis.

Suzanne Kennedy-Stoskopf, a North Carolina State research professor of wildlife infectious diseases, says that testing positive for antibodies to B. suis means the feral pigs have been exposed to and mounted an immune response against the bacteria. Antibodies do not eliminate B. suis from pigs, so the animals are considered infected and capable of transmitting the bacteria to other pigs and people. The United States has long had a swine brucellosis control and eradication program, which by the late 1990s eliminated the disease from all commercial pig populations.

For the domestic swine herd, the risk is that the bacteria can spread beyond feral hogs and cause abortions in affected swine. Kennedy-Stoskopf says that B.suis can be transmitted when pigs ingest infected tissue or fluids. Also, direct contact with infected pigs or ingestion of contaminated food and water could cause currently uninfected pig populations to become infected. Biosecurity protocols in place to prevent herd exposure to other pathogens are important in preventing the spread of B.suis into a domestic herd.

“Spillover from infected feral pigs to commercial pigs is an economic and a public-health concern,” Kennedy-Stoskopf says. “The biggest public-health risk is to pork processors and hunters who field dress feral pigs.”

The study’s co-author, Chris DePerno, associate professor of forestry and environmental resources at North Carolina State, points out the bacteria are transmitted to humans by unsafe butchering and consumption of undercooked meat. “Now that exposure to Brucella suis has been found in North Carolina’s feral pig populations, people need to take care when hunting, butchering and cooking feral pigs,” he says. “That means wearing gloves when field dressing feral pigs and cooking the meat to the proper temperature.”

Kennedy-Stoskopf emphasizes that although cases of brucellosis are rare in the United States, people need to understand the clinical signs, which mimic the flu and feature intermittent fevers and persistent headaches. “Because clinical signs are so non-specific, it’s important to tell your physician if you have had any exposure to feral swine carcasses and meat,” she adds.

Feral pig populations are exploding across the country, and are in nearly every state. Efforts to control them often meet with controversy.

“Control of feral pig populations is difficult at best,” DePerno says. “Research indicates that about 70 percent of the population will need to be removed each year to keep a wild population stable. Regarding feral pigs, hunting usually removes from 8 percent to 50 percent of a given wild population.”

DePerno hopes that more research on how far feral pigs travel – and increased scrutiny of hunters who move feral pigs from place to place – will help keep feral populations from spreading.

The North Carolina State research is published in Journal of Wildlife Diseases.