- The first confirmed U.S. human case of New World screwworm, a flesh-eating parasite, has been reported in Maryland, following the patient’s travel to El Salvador.
- Federal and state officials emphasize that the risk of spread remains low, although the incident has raised concerns among farmers and veterinarians about potential communication lapses.
- The U.S. is preparing to combat the parasite with sterile fly–release programs, a proven strategy previously used to eliminate the pest, though it may take years to scale.
Food & Wine has been monitoring the progress of the New World screwworm (NWS), a tiny, flesh-eating parasite, since late 2024, when it was discovered in the cattle supply in Mexico. It was then that the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service halted all cattle imports from Mexico in an effort to protect both the U.S. cattle supply and public health. However, now the Centers for Disease Control and Prevention (CDC) and the Maryland Department of Health are confirming that the first case in the U.S. has been identified. The case was confirmed on August 4; however, according to some state officials, they were never informed directly.
According to exclusive reporting from Reuters, on Sunday, the U.S. Department of Health and Human Services (HHS) announced the first human case in a man who had traveled to El Salvador and returned infected with the parasite.
HHS spokesman Andrew G. Nixon told NPR, “This is the first human case of travel-associated NWS myiasis from an outbreak-affected country identified in the United States … Currently, the risk to public health in the United States from this introduction is very low.”
Still, this news has unsettled both some state officials and the farming industry overall, including Beth Thompson, South Dakota’s state veterinarian, who told Reuters that she was informed about the human case by someone with direct knowledge of it, rather than the CDC itself.
“We found out via other routes and then had to go to CDC to tell us what was going on,” Thompson told Reuters. “They weren’t forthcoming at all. They turned it back over to the state to confirm anything that had happened or what had been found in this traveler.”
The good news is that David McAllister, a spokesperson for the Maryland Department of Health, told NPR that there is no indication that the infection has spread beyond this one individual. “The investigation confirmed there is no indication of transmission to any other individuals or animals,” he shared, adding that this serves as a “timely reminder for health care providers, livestock owners, and others to maintain vigilance through routine monitoring.”
The U.S. also has a plan to combat the spread of the parasite. In early July, Food & Wine reported on the government’s plan to breed millions of sterile flies at a facility in Texas, just a few miles from the Mexico border, which will be released to mate with wild female flies and prevent them from laying eggs in cattle wounds, where flesh-eating larvae can develop.
The strategy that has been proven effective in the past, including through another sterile fly factory in Panama, which successfully kept the flies out of that nation in 2024. The U.S. also used this approach in the 1960s, when the parasite once threatened the cattle supply. The process then eradicated the fly from the U.S. Still, it won’t be a quick process, with Rollins previously stating that the facility could take several years to build.
As for how bad things could get if the parasite spreads to the U.S. cattle supply, the Texas Farm Bureau wrote in a letter to Rollins on August 1 that an outbreak in “Texas cattle alone could result in $1.8 billion in annual losses, including $732 million in direct impacts to producers. But the damage wouldn’t stop there.”
It added that across the U.S., millions of farm animals could be at risk, including more than 71 million pigs, 5 million sheep, 2.5 million goats, more than 9 billion chickens, and 6.65 million horses. “If an outbreak were to spread across states within the historic NWS range, national livestock losses could exceed $4.3 billion annually, with total economic damages surpassing $10.6 billion. The U.S. horse industry alone contributes $177 billion to the national economy and stands to suffer significant losses should NWS spread.”
And that’s before considering wildlife losses, including game and nongame animals, which would “threaten our $400 billion wildlife-recreation economy and North American Model of Conservation Funding that it supports. Rural economies and the viability of working lands are closely tied to the health and sustainability of our native wildlife populations. Also of great concern are potential threats to the costly ongoing recovery of threatened and endangered species nationwide. Losses to the nation’s wildlife and livestock are not hypothetical; they are real, and they are preventable.”
What pet owners need to know about the New World screwworm
- Could pets be affected? Yes. Dogs, cats, horses, and other animals with open wounds are vulnerable if they come into contact with screwworm flies. The flies lay eggs inside wounds, and the larvae feed on living tissue. Even a small cut or scratch could attract them in outbreak areas.
- What homeowners should know: If you live near farms, travel with pets, or own livestock, regular monitoring is essential. Keep wounds clean and covered when possible, and seek veterinary care promptly for any injuries. If traveling to Central America or regions affected by outbreaks, consult a vet before leaving and after returning.
- Signs of infection: Watch for wounds that do not heal or get worse. Swelling, foul smells, and small white larvae inside the wound are warning signs. Animals may become restless, lose their appetite, or avoid being touched. If you suspect an infection, contact a veterinarian immediately — early treatment can prevent serious damage or death.
