By Jack Schouten | Missouri Independent
(Republished with minor formatting edits)
State and federal officials are preparing to stop the advance of a parasitic insect known as the New World screwworm fly, which is currently less than 70 miles from the United States’ southern border.
Since Nov. 25, at least 10 new cases involving the fly have been confirmed within 400 miles of the U.S.–Mexico border. The species has been steadily moving north since it breached a biological barrier created by Panama’s narrow geography in 2022.
“There is a threat of it maybe getting into the southern United States, and then it would most likely end up in Missouri, too — at least maybe some isolated cases,” said State Veterinarian Steve Strubberg. “It’s conceivable that it could happen in the coming year or two.”
Deb Hudman, health section chief for the Missouri Department of Conservation, said transportation of infected animals is the most likely way the parasite could enter the state.
Experts are hoping for a long winter and a cold spring to slow the fly’s spread.
“The cold weather is good,” Hudman said. “Anything as low as 48 degrees Fahrenheit stops larvae and pupae development, and anything below 59 degrees significantly drops the activity of adult flies.”
Federal response underway
Local and federal agencies are working to take advantage of colder weather while preparing additional defenses. Last month, the U.S. Department of Agriculture launched a website aimed at centralizing information about the flesh-eating fly.
“The USDA remains focused on implementing our sweeping five-pronged plan to combat New World screwworm,” said USDA spokesperson Lyndsay Cole in an email. “As part of these critical efforts, USDA is working on both sides of the border to ensure a comprehensive response.”
That plan includes $29.5 million in investments to renovate an existing fruit fly production facility in Metapa, Mexico, and to build a sterile insect dispersal facility at Moore Air Base in south Texas. The Mexico facility is expected to open as early as next summer, and planning is underway for an additional production site in Texas.
“Unfortunately, there won’t be enough of those sterile flies available to us for a few years,” Strubberg said. “It takes a long time to ramp up those production facilities, so we are hoping it stays in Mexico.”
Currently, only one sterile-fly production plant exists in Panama, producing about 100 million flies per week. A former plant in Mexico that produced 500 million flies weekly shut down in 2012 for economic reasons.
Sterile insect techniques were key to eradicating screwworm from the U.S. in the 1960s by preventing female flies — which mate only once — from reproducing.
A costly potential return
Screwworm was eradicated in the United States in 1966 at a cost of roughly $750 million. If the parasite returns, the USDA’s Economic Research Service estimates losses to the Texas economy alone could reach $1.8 billion within a year.
Cattle producers would bear much of that burden, with projected losses of $730 million. According to USDA data, nine of the last 10 confirmed cases near the U.S. border involved cattle.
“If it would come in, we would have such a great expense of eliminating it,” Strubberg said. “There are just so many different areas of added expense for individual producers.”
Consumer impacts are harder to predict but could include higher prices driven by reduced supply and increased treatment costs.
Strubberg encourages livestock owners to register their premises with the Missouri Department of Agriculture to help officials respond quickly if an outbreak occurs.
Cows, pets and wildlife at risk
The New World screwworm can infest all warm-blooded animals, including humans, pets, livestock and wildlife. Warning signs include open wounds that appear infected, reduced activity and animals isolating themselves.
“The larvae are basically maggots,” Strubberg said. “They are much more aggressive than the normal maggots of the common flies we have around Missouri, and they cause significantly more damage.”
Animals can recover fully if treated early. Treatment may involve surgical removal of larvae and systemic medications.
The FDA recently conditionally approved a new topical treatment for cattle over two months old, Exzolt Cattle-CA1, for prevention and treatment of screwworm infestations.
“Pets are also an easy way for screwworm to be transported,” Strubberg said, urging owners to monitor animals closely, especially after travel to regions with known screwworm activity.
Hudman added that wildlife populations would be extremely difficult to protect.
“Deer would be something to keep an eye on because they have lots of wounds from running, vehicle strikes and fences,” she said. “Really any warm-blooded species with an open wound.”
While large wild populations would be nearly impossible to treat, smaller, localized populations — such as Missouri’s elk herd — might be manageable.
Identification challenges
Missouri officials also face the challenge of distinguishing screwworm larvae from a similar blowfly species that feeds only on dead tissue.
“It’s going to be very tricky for the general public to tell the difference,” Hudman said.
The Missouri Department of Conservation, Missouri Department of Agriculture and USDA are working together to develop a response plan, including placing microscopes across the state so trained personnel can quickly identify larvae.
This story from the Missouri Independent is published under a Creative Commons license. The Missouri Independent is a nonpartisan, nonprofit news organization covering state government, politics and policy. This article was originally published in the Columbia Missourian.