The first confirmed case of a New World screwworm in a U.S. horse since the 1960s was detected Sept. 9 in South Texas, bringing a once-eradicated parasite closer to Florida’s horse industry and putting animal owners on heightened alert.
The case, confirmed in a working ranch horse in Presidio County, Texas, is the first equine case identified in the United States during the current outbreak. The live flesh-eating parasite was found on the horse’s hind limb.
In Texas, experts estimate a widespread outbreak could cost the economy up to $1.8 billion.
The development carries particular weight for Florida. The state is home to a major equine industry, with the Ocala-Marion County area officially known as the “Horse Capital of the World.” More than 70,000 acres in Florida are used for horse-related purposes, according to the Florida Department of Agriculture and Consumer Services.
The screwworm has not been detected in Florida, but University of Florida veterinarians say the state’s climate and large horse and livestock population make preparation critical.
“It would make sense that it would get to Florida at some point,” said Sally DeNotta, a UF veterinarian specializing in large animal internal medicine and infectious disease.
DeNotta said the current forecast suggests the pest could move through much of the Southern United States because Florida’s climate can support its life cycle year-round. She said the spread will also depend on the availability of sterile flies, which are a key part of the effort to control the pest.
For Florida animal owners, the question is increasingly not whether they should prepare, but when the pest could arrive.
New World screwworm is the larval stage of a shiny green blow fly. Female flies lay their eggs in or near wounds, and the larvae feed on living tissue.
That distinguishes screwworm from the maggots commonly associated with decaying animals.
“The New World Screwworm actually can attack live, healthy animals and cause disease by tissue disruption of their healthy tissues,” DeNotta said.
Edwin Burgess, a UF assistant professor of veterinary entomology, said the larvae can cause severe secondary infections and, in some cases, death.
“It can be difficult to control. It can be difficult to monitor those animals,” Burgess said. “So it just creates a lot of economic damage to the very, very, very high dollar industry in the United States.”
The pest was eradicated in the U.S. in the 1960s through a method called the Sterile Insect Technique, in which irradiated male flies are released into an area so they can mate with females without producing offspring.
The method pushed the screwworm population south through Mexico and Central America to the Darien Gap. But in recent years, the pest broke through that containment and began moving north.
DeNotta said officials have known for years that the pest could eventually reach the United States. This summer, it did.
Now, the first confirmed case in a U.S. horse adds another concern for Florida’s equine community.
The timing is particularly significant for Ocala and Marion County, where horses are central to the local economy and the area’s identity.
The Florida Department of Agriculture and Consumer Services describes Ocala-Marion County as the “Horse Capital of the World,” with nationally recognized equestrian events and facilities throughout the region.
For horse owners there and across North Central Florida, even a small cut could become a potential entry point for screwworm if the pest reaches the state.
At Mill Creek Farm, a nonprofit retirement home for horses, staff members have responded by paying closer attention to potential sources of wounds.
The 335-acre farm cares for elderly horses. President Paul Gregory said staff members are checking fence lines for loose nails, splinters and other hazards that could cut a horse.
“If there’s any blood, that’s where the screwworm can come in,” Gregory said.
Mill Creek also quarantines horses arriving from out of state for 30 to 60 days and monitors them for health concerns.
Gregory said the farm has always been attentive to injuries, but the screwworm threat has made staff members even more vigilant.
“Maybe now we’re even more on it,” he said.
At Beauty’s Haven Farm and Equine Rescue, president Theresa Batchelor said the nonprofit is not currently accepting new horses but continues to receive daily updates about the threat.
The farm maintains fly traps around its perimeter and interior fence lines. Horses receive hands-on attention every day, are routinely groomed and sprayed for flies, and most wear fly masks.
The farm also removes manure from paddocks daily and avoids standing water and spoiled hay, which can attract flies.
Florida agriculture officials have been preparing for the possibility of an introduction.
Burgess said the Florida Department of Agriculture and Consumer Services has assembled a task force focused on surveillance, insecticide supplies, identification training and preparations for sterile-fly releases if the pest reaches the state.
“The fly is currently not in Florida,” Burgess said.
Animal movement is another major concern. Burgess said the most common way screwworm has spread is through the movement of infested animals, making restrictions and inspections important ways to prevent the pest from reaching new areas.
DeNotta said UF is also focusing on education and awareness so animal owners know what to look for and can avoid misinformation.
“We want Floridians to be informed and ready, and level-headed about it, as opposed to reactionary and dramatic,” she said.
The new Texas horse case makes that preparation more immediate for Florida’s equine community.
DeNotta said the parasite is likely to remain a long-term problem. A USDA facility in Texas is being converted to produce sterile flies and is expected to begin production in early 2027. But she said the U.S. will need significantly more sterile flies to control the pest across its potential range.
Despite Florida being free of New World screwworm right now, veterinarians say preparation cannot wait until the first case reaches the state.
DeNotta said people are quite certain that the parasite will be eradicated in the U.S.
“The question, of course, will just be when,” she said. “The answer is probably not any time too soon.”