Texas is ramping up preparations to meet the looming invasion of New World screwworm, a parasitic fly threatening the state’s multibillion-dollar livestock industry.
The insect is typically found in South America and the Caribbean, but it found its way in late January to a northern Mexican state bordering Texas. The screwworm is now within 187 miles of the U.S. border, and it appears to be only a matter of time before it crosses into Texas, with officials gearing up to protect the community from parasitic invasion.
How do you combat screwworm?
Sterile fly release forms the basis of efforts to eradicate screwworms, which typically feed on live flesh by latching onto open wounds, proving potentially fatal to livestock. But current production capacity for sterile flies is far below what the state needs, and plans to expand volume won’t come to fruition until this summer, at the earliest.
Authorities hope to stave off a full-scale invasion of the screwworm through a variety of strategies until more sterile fly facilities are operating. The Texas Animal Health Commission is leading the state’s effort to combat the screwworm threat, which includes educating agriculture producers and veterinarians about how to recognize and address the parasite, one of the tactics viewed as key to buying the state time and keeping the situation from spiraling out of control.
Texas taking state action in preparation before things get ‘way worse’
TAHC communications director Erin Robinson told the Washington Examiner that authorities are prioritizing meeting with stakeholders, including cattle, equine, poultry, sheep, and goat producers, on a regular basis to raise awareness about the parasite. TAHC is encouraging livestock stakeholders to use fly surveillance traps, track wounds on animals, promote better animal husbandry systems, and build relationships with local veterinarians.
TAHC is also in talks with a slew of local officials, including judges, county commissioners, and law enforcement, who will help lead the response to screwworms when they cross the border. Educating veterinarians, possibly unfamiliar with screwworms, and raising awareness that the flies can also latch onto small pets are among other tactics the state is using to reduce the impact of the seemingly inevitable outbreak.
“Some of the biggest things that we’ve heard about is people don’t know what these screwworms are. … Therefore, there’s a possibility of the impact being way worse,” Robinson said. She said they’ve been meeting with Texas to help educate people on what to look for. So far, they’ve conducted 200 “producer meetings” where they’ve spoken to communities directly and at conferences.
“It really is going to take everybody doing their part to monitor their piece of the world, their livestock, their animals, to really prevent the spread,” she added.
The Department of Agriculture has facilitated efforts to keep the screwworm at bay through restricting animal movement into the United States and closing the border to Mexican livestock. That has helped restrict fly movement, because the parasites “can sure go a lot farther, if they’re on the back of a cow in a trailer,” Robinson said.
The Texas & Southwestern Cattle Raisers Association, which boasts around 28,000 members, is one of the groups TAHC is partnering with to prepare for the screwworm. TSCRA praised USDA for closing the border during an interview with the Washington Examiner, calling it a “big issue.”
“I think the protocols and measures are helping, and so I hope that that slows the progression until we can get more flies, or at least more drugs approved, conditionally approved, by FDA and EPA for us to use as ranchers and landowners if it does get here and we don’t have the flies yet,” TSCRA interim executive director of government relations Peyton Schumann said.
Gov. Greg Abbot’s (R-TX) move to authorize an emergency declaration on screwworms has also been pivotal, according to Schumann. The move eased fears about preparedness, as the state legislature is currently out of session and doesn’t convene until January 2027, meaning it could not approve new funding and resources needed to meet the threat.
Lack of action from Mexico threatens wildlife
But worries remain about the parasite spreading into Texas through wildlife movement. Mexico has been pressed, largely unsuccessfully, for data on what kind of surveillance is being done to track and report wildlife that crosses in and out of the Lone Star state, according to TSCRA. Schumann expressed concern that in the absence of proper surveillance, the impact for certain species could be even worse than a screwworm outbreak during the 1950s, which decimated around 80% of Texas’s whitetail fawn crop annually.
“We’ve got a species called Nilgai that are in South Texas that have a lot wider of a home range than white-tailed deer, meaning they travel a lot further. And they’re known to cross the Rio in Mexico and come back across,” he said. “We’re really concerned about the wildlife aspect, because of what type of money and the economic boost that hunting and wildlife bring to the state of Texas.”
Texas Commissioner of Agriculture Sid Miller echoed the concerns.
“I think everybody’s biggest concern here in Texas is our $30 billion livestock industry, right? And we have a very large wildlife industry. You know, hunting is big, brings in a lot of revenue. A lot of these ranches are nothing but game ranches,” he said.
US must ‘brace for impact’ without more sterile fly treatment
The biggest concern facing officials is the shortage of sterile flies, which are released to mate with wild flies as an eradication tactic to halt the advance of active screwworms. As females typically mate only once, sterile fly release prevents viable offspring and reduces the active population until it dies out in the treated area.
Robinson, with the Texas Animal Health Commission, said that access to a billion sterile flies weekly is ideal to address the looming threat. In the last major screwworm outbreak in Texas decades ago, the U.S. had around 700 million sterile flies on hand weekly. Texas now has access to only 100 million flies weekly, from a Panama-based production facility. That number met the need in years past, but fell short as increasing illegal movement in South America, combined with falling checkpoint activity during COVID-19, pushed screwworms out of the Darien Gap and into Mexico, inching them ever closer to the U.S. border, Schumann explained.
“Until we can get more flies, I don’t think any of us will feel just 100%,” he said.
Plans are in the works to build a domestic plant at Moore Air Base in South Texas capable of producing up to another 300 million sterile flies weekly, but it won’t be completed until 2027 at the earliest. The U.S. also sent Mexico $21 million to build out sterile fly production, but the development is still in the construction stage, with tentative plans to open sometime this summer.
“The reality is we will need more flies. 100 million flies are a lot, but we will certainly need more to keep these flies at bay. And so at this point, I think that there’s certainly a strong opportunity for us to keep New World squirm out of the United States for a little while, but if we do not get more sterile flies, I think that we’ve all braced for impact to respond to this,” Robinson said.
Officials are attempting to meet the moment by deploying sterile flies more strategically, including by using the USDA’s ARS system for a “dispersal polygon” operation. Dropping flies in an area the shape of a polygon allows for better saturation than dispersing in a straight line, maximizing the sterile insects’ limited supply.
“The thought is, you drop these flies at the northernmost part of incursion. You do it in this polygon shape. And that, hopefully, you know, you can use this 100 million to the best extent of what you’ve got,” Schumann said.
Newly approved treatments from the FDA, including Exzolt Cattle-CA1, are being hailed as one bright spot ahead of the seemingly inevitable parasitic invasion. Dr. Justin Welsh, the technical services lead for the Merck Animal Health team that helped develop the pour-on solution, said the solution could be used both as a treatment and as a preventive measure, which is key in a scenario like screwworms, where the parasites could spread throughout an entire herd within days.
Exzolt is a “little more” expensive than Ivermectin, another commonly used screwworm treatment, Welsh said, with a cost point of around $5 to treat a 500-pound calf. But it has higher efficacy, keeping cattle safe for two to three weeks after the solution is applied. That could be key to efforts to keep the infection contained, as the longer-lasting treatment would provide producers “a little bit of a buffer time,” he said.
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Robinson said at the end of the day, it’ll take individual ownership to keep the parasite at bay, particularly through animal surveillance.
“There’s not a magic bullet, as they say, to this situation. It’s going to take everybody, from veterinarians to the government to individual animal owners,” she said. “At the end of the day, if there are screw rooms in Mexico, Texas is going to be on high alert. There is a risk for Texas if screw worms are in Mexico.”
