Agricultural workers are among the highest risk group for human infection during the screwworm outbreak in the American south, yet they frequently face challenges in accessing public health – an ongoing concern amid zoonotic spillovers such as H5N1 bird flu.
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.
Despite being at greater risk of spillover, farm workers are frequently disconnected from healthcare; they often work long hours after clinics close for the day, live on-site and in remote locations, lack insurance or the financial resources to pay for healthcare, 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.
These factors make it more difficult to prevent and treat emerging diseases, and it makes it harder for public health to stop outbreaks at their source, including monitoring diseases, known as disease surveillance.
Ranchers talk among themselves before a New World screwworm press conference at the Knipling-Bushland US Livestock Insects Research Laboratory on 8 June in Texas. Photograph: Brandon Bell/Getty Images
“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,” said Rebekah Stewart, a clinical educator and care coordinator with the Migrant Clinicians Network and a family nurse practitioner. “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. And any opportunity that we can reduce those barriers is going to be not just good for the individuals and their community, but good for all of us.”
The main risk during the New World screwworm outbreak is to animals, including the $347.7bn meat and poultry industry. Before the parasitic fly was pushed out of the US four decades ago, it caused hundreds of millions of dollars in losses.
As the insects moved back up through Central America, the livestock industry has prepared for cases in the US. In recent months, it has become a matter of when, not if, the screwworm would arrive, said Tom Paterson, the 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,” he said.
Though the risks to humans are significantly lower, those who work closely with animals are the most likely to encounter screwworm.
An aerial view of cattle, detained in the pens of the Chihuahua Regional Livestock Union, at the Jerónimo-Santa Teresa border crossing in Ciudad árez, Mexico, on 27 November 2024. Photograph: Anadolu/Getty Images
“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 Stewart.
If a farm worker is working long hours and needs to rest outside, they may fall asleep and not notice a fly landing on them. If they open windows or doors without screens for air circulation in their living quarters, the flies could come inside.
The fly lays its eggs in wounds as small as a tick bite. “Cleaning and covering wounds is really important,” Stewart said.
Paterson emphasized that “it can happen, and people have got to pay attention.”
“Here on my ranch, we’ve been discussing the New World screwworm. All my guys wear long-sleeve shirts, long pants, gloves and a hat,” he said.
Protective clothing like this also shields them from the sun and other insects; insect repellent may also help.
Paterson’s ranch is off the electricity grid, running on solar and batteries, so there’s no air conditioning. They open doors and windows to cool off, but they have screens to keep the insects out.
There are also larger barriers to agricultural workers accessing healthcare, Stewart said.
“Something that farm owners or anyone who’s employing farm workers could think about is trying to partner with migrant health programs, so that people, when they have health concerns, have a way to access healthcare easily, quickly, readily, that’s close to them,” said Stewart.
Cattle are herded at Lew Thompson’s ranch on 17 June in Frio county, Texas. Photograph: San Antonio Express-News/Hearst Newspapers/Getty Images
Agricultural workers may delay care “for any number of reasons”, she said. “It could be because they’re trying to get as much work as possible in during the day. It could be that their working hours overlap with when the clinics or the health centers are open … it could be because of concerns about being able to pay for the services or lack of insurance, and it could be also because of fear of interacting with the public health or other healthcare systems.”
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 Donald Trump’s January 2025 order on immigration.
“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 US Food and Drug Administration (FDA) has issued emergency use authorizations for anti-parasitic medications for animals, and manufacturers are ramping up production to meet increasing demand. But there are no specific treatments for human cases beyond manual extraction and off-label anti-parasitic medications.
Stopping the outbreak in animals would also make agricultural workers safer.
Industry groups in affected areas are informing members of the warning signs of animal infection. They’re also urging them to postpone elective procedures that would create open wounds and to make sure they are giving antiparasitic medications to any livestock with wounds.
Last week, Paterson was working with some cattle, including branding, castrating, vaccinating and ear-tagging animals, noting that “whenever we do that, we also treat for worms, so we went ahead and gave everything that we processed a shot of Dectomax last week.”
Paterson is optimistic that this outbreak will be contained, but for producers with cases in their herds, “it’s a huge pain”, he said. Responding aggressively to the outbreak and working with other countries will be key to stopping infections and eradicating the fly in the US once more, Paterson said.
“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,” he said. “No one needs this. No one needs this.”
