Screwworm has been detected in goats and sheep in three Texas counties in recent days, bringing the total to 16 known cases among animals and none reported in people, according to the Guardian. The parasitic fly, which was pushed out of the United States four decades ago, lays its eggs in wounds as small as a tick bite. The resulting infestation can be fatal to livestock and, in rare cases, affects humans who work closely with animals.
“The fly tends to lay its eggs more commonly in mammals and we see it a lot in livestock, so you’re going to see a greater density of flies in those areas – and people who are living and working in those areas are going to be the most at risk,” said Rebekah Stewart, a clinical educator and care coordinator with the Migrant Clinicians Network and a family nurse practitioner.
Stewart said farm workers frequently are disconnected from healthcare: they often work long hours after clinics close, live on-site in remote locations, lack insurance or the financial resources to pay for care, and face language barriers. Migrant workers and people of color may also fear seeking healthcare or even driving outside work as the Trump administration clamps down on immigrants.
“If they’re not in touch with the healthcare system, they’re very likely not going to be picked up by any of the surveillance that is being done,” Stewart said. “It’s like a jungle gym, the number of hoops and barriers that a person has to jump over to get from the farm to a healthcare system.”
About 84% of clinicians who regularly work with immigrant populations said in a recent survey that they were seeing very serious delays in patients seeking healthcare since President Donald Trump’s January 2025 order on immigration, the Guardian reported. “Anyone who is delaying care or not seeking care for a wound, for some reason, could potentially also be at an increased risk,” Stewart said.
The main economic risk of the outbreak is to the $347.7 billion meat and poultry industry. Before the fly was eradicated in the U.S., it caused hundreds of millions of dollars in losses annually, the Guardian reported. As the insects moved back up through Central America, the livestock industry prepared for cases in the U.S. In recent months it became a matter of when, not if, the screwworm would arrive, said Tom Paterson, president of the New Mexico Cattle Growers’ Association and a cattle rancher in Catron County.
Earlier in the year, “we transitioned from describing New World screwworm and what the problems are with it, to advising our cattle producer members about what to do when they get it,” Paterson said.
Paterson emphasized that human infection, though lower risk, “can happen, and people have got to pay attention.” On his off-grid ranch, workers wear long-sleeve shirts, long pants, gloves and a hat, and screens keep insects out of open windows and doors used for cooling instead of air conditioning. He noted that cleaning and covering wounds is important.
The U.S. Food and Drug Administration has issued emergency use authorizations for anti-parasitic medications for animals, and manufacturers are ramping up production to meet increasing demand, the Guardian reported. There are no specific treatments for human cases beyond manual extraction and off-label anti-parasitic medications.
Industry groups in affected areas are informing members of warning signs of animal infection and urging postponement of elective procedures that would create open wounds, as well as ensuring antiparasitic medications are given to any livestock with wounds. Paterson said that when his crew branded, castrated, vaccinated and ear-tagged cattle last week, they also treated the animals for worms with Dectomax.
Paterson expressed optimism that the outbreak will be contained, but acknowledged that for producers with cases in their herds, “it’s a huge pain.” He called for aggressive response and cooperation with Mexico and Central American countries: “Hopefully, we get our sterile flies in place. We don’t get lax down the road. We cooperate with Mexico, we cooperate with the Central American countries, and we push it back into South America. No one needs this. No one needs this.”