New Feral Swine Research Helps Pinpoint Anthrax Risk Zones

A microscopic anthrax spore can lie dormant in the soil for decades until it ends up in a suitable host. Factor in feral swine and their natural tendency to root and wallow, and whose exploding population is estimated at over six million in the U.S. alone, and a concerning scenario emerges.

Rachel Maison, a Ph.D. student in Colorado State University's Department of Biomedical Sciences, recently published an innovative study that tested feral swine blood samples for the presence of anthrax antibodies in and around the "anthrax triangle," an area of southwest Texas where high numbers of anthrax cases have occurred in domestic livestock and farmed deer populations. This promising research, never before done in the U.S., was featured on the Centers for Disease Control and Prevention podcast as well as its March 2022 Zoonoses & One Health Updates webinar and provides an important tool for better monitoring and responding to the dangerous pathogen.

"Rachel's work is a stellar example of how important it is to bring together humans, animals, and the environment when assessing the threat of zoonotic diseases," said Angela Bosco-Lauth, Maison's adviser and an assistant professor in the Department of Biomedical Sciences. "From management practices to invasive species to environmental conditions, we can't ignore the impact that each factor has on disease risk. And as an individual, Rachel's background in conservation, wildlife, and disease make her the ideal researcher to tackle these complex topics."

A conservation mindset

Maison grew up in Glenwood Springs, Colorado, where she developed a passion for wildlife conservation. After earning a bachelor's degree in fish, wildlife, and conservation biology from CSU, she was hired as a biological science technician with the USDA National Wildlife Research Center's National Wildlife Disease Program and later joined its National Feral Swine Damage Management Program, which works to protect agricultural and natural resources, property, and animal and human health and safety by managing damage caused by feral swine.

Through this work she was introduced to her now co-advisers, Bosco-Lauth and Richard Bowen, a professor in the Department of Biomedical Sciences, who both closely collaborate with the USDA in their wildlife, zoonotic, and infectious disease research efforts. Maison's research centers around investigating pathogens that might be carried or influenced by feral swine in the U.S. and focused on anthrax for this study.

"Because pigs in general are pretty resistant to developing anthrax, they seem to be a good species for mapping out risk regions," Maison said. "I knew through my undergraduate coursework that feral swine were a very problematic invasive species. Working with the USDA inspired me to further pursue wildlife disease surveillance work and to look at how invasive species might contribute to not only human health, but also the health of native wildlife populations and threatened or endangered species."

An ancient—and stealthy—disease + a destructive invasive species

Anthrax, caused by the bacteria Bacillus anthracis, is a rare but serious infectious disease that is thought to date back to at least 700 B.C. While uncommon, it can infect humans, and sporadic outbreaks occur in wild and domestic animal populations. It is also an extremely important pathogen to track and better understand due to its past and potential use in bioterrorism attacks.

Anthrax infections can occur when B. anthracis is inhaled, ingested, or comes into contact with broken skin. Ruminant species like cattle and deer are very susceptible to even small doses of anthrax spores and will often quickly fall fatally ill after exposure. Their bodies may then be scavenged by other animals, which can release spores back into the environment.

Once B. anthracis vegetative cells are exposed to oxygen, they expertly enter a dormant state and become spores that are highly resistant to environmental degradation, allowing them to be present on the landscape for indefinite lengths of time. Once they enter a new host, they can quickly come back to life and resume the infectious cycle.

About half of the nation's six million feral swine live in Texas, home to the anthrax triangle, and though they spend a great deal of time rooting around in the soil with their long snouts, they are mostly resistant to the disease.

Not your average farm pig, feral swine are typically more aggressive, can run up to 30 miles per hour, and often sport thick skin, coarse hair, and sharp tusks. They descended from escaped or released pigs that were first brought to the U.S. in the 1500s as a food source and Eurasian wild boars introduced in the 1900s for sport hunting.