New World screwworm has returned to North America after decades of eradication. The University of Minnesota is working with veterinarians and ranchers to strengthen preparedness for future cases.
Guillermo Arcega Castillo visits a swine farm as part of his work during his time in the Veterinary Public Health and Preventive Medicine Residency.
While its scientific name means “man-eater,” the New World screwworm has posed the greatest threat to animals, namely livestock, which suffer serious and often deadly damage from the parasite burrowing into their flesh.
For the first time in 60 years, New World screwworm (NWS) has been detected in the United States, with animal cases confirmed in Texas and New Mexico raising concerns among health officials and livestock producers in the U.S.
Among those working to help prevent the next stream of outbreaks from spreading are researchers at the University of Minnesota (UMN) College of Veterinary Medicine (CVM), who seek to fill gaps in veterinarian knowledge regarding a disease once considered eradicated in North America.
“It’s an animal health emergency,” says Guillermo Arcega Castillo, a Veterinary Public Health and Preventative Medicine resident in the Center for Animal Health and Food Safety (CAHFS). “It affects wildlife, livestock, companion animals and sometimes people.”
The parasite returned to North America after spreading across the Darién region, a strip of dense rainforest and wetland that separates Panama and Colombia. In 2023, NWS worked its way up north from Central America and then reached Mexico in 2024, a country in which the parasite had been eradicated for more than 30 years.
Last year, Arcega Castillo was among a group of UMN researchers that received funding from the Center for Global Health and Social Responsibility for a project that seeks to understand how to best support veterinarians and producers in Mexico and Central America to respond to the new One Health crisis.
“This is a parasite we have not seen in decades, so it’s natural for people to not know much about it,” says Arcega Castillo, adding that in his own veterinary school experience in Mexico, he remembers encountering the topic only twice in his coursework.
They started with a knowledge, attitudes and practices survey that asked veterinarians and cattle producers in Mexico and Central America to report what they understand about NWS and their experience with preventing and reporting cases. Next, they will visit veterinarians and producers in Mexico, Guatemala and Panama.
“The field visits will help us better understand what is happening,” he says. “Online surveys are a helpful place to start, but they can only tell you so much.”
The team will share their findings with partner organizations that can implement the research into tailored workshops, training and communication materials that can fill knowledge or reporting gaps. In the long term, the same approach can be customized for other threats, such as African swine fever or foot-and-mouth disease.
“Veterinarians and cattle producers play a huge role in responding effectively to outbreaks because they are usually the first to detect an infestation when it happens,” Arcega Castillo says. “Instead of sending a general message that may not be effective, we need to customize and tailor training to what we are hearing from veterinarians and those working with animals every day about where these gaps are.”
Arcega Castillo says his VPHPM residency has allowed him to learn from different aspects of veterinary public health and apply newly acquired skills to his next projects. The opportunity to work on NWS infestations in Mexico will not only bring a new level of understanding to this public health threat but also help protect communities like the one he grew up in along the Sonora-Arizona region.
“The Veterinary Public Health and Preventive Medicine Residency at UMN gives you access to a wide variety of projects, but also the flexibility to align those projects to what experience you would like to get,” he says.
For more information about New World screwworm and preventing its possible spread to Minnesota, visit the Minnesota Board of Animal Health’s resource page.
