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The return of the New World screwworm – a meat-eating parasite that was eradicated in the US in the 1960s – has raised new concerns about whether it could threaten the nation's food supply.
Unlike other foodborne illnesses like norovirus, Ecoli and Salmonella, which sicken millions of Americans every year, experts say the screwworm is not a threat to the food on our dinner tables.
“The US food supply is not affected by the New World screwworm, which is an animal problem, but not a foodborne pathogen problem,” Dr. Aaron Glatt, chief of infectious diseases at Mount Sinai South Nassau Hospital, told Fox News Digital.
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“Although screwworm infestation is an infection of live animals, it does not cause meat, milk or produce to become infected.”
The worms die during normal meat processing and cooking, according to Glatt.
The return of the New World screwworm – a meat-eating parasite that was eradicated in the US in the 1960s – has raised new concerns about whether it could threaten the nation's food supply. (Stock)
While native to South America and the Caribbean, the screwworm migrated north through Central America and Mexico following 2023 outbreaks in Panama and Costa Rica, the CDC said.
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On June 3, health officials confirmed a single case in a three-week-old calf in Zavala County, Texas — the first detection in the US since it was eradicated in the 1960s (except for an outbreak in the Florida Keys deer area from 2016 to 2017), according to the US Department of Agriculture (USDA).
Since the beginning of June, the USDA has reported 33 cases of screwworm in animals in Texas and New Mexico – including cattle, goats and a pet dog.
Safety measures
Milk and food in the US are regularly inspected by regulatory agencies, according to Glatt.
“Animals used to produce human food must be inspected before and after slaughter to ensure that food safety and human handling requirements are met,” a USDA spokesperson told Fox News Digital.
“Infection or disease in animals that makes the meat unsafe for consumers will prevent the animal from entering the food supply.”
On June 3, health officials confirmed one case of screwworm in a three-week-old calf in Zavala County, Texas. (Stock)
If an animal at a slaughterhouse shows signs of illness, the USDA-directed meat inspection program separates it from the others and labels it a “US Suspect” — meaning it needs further testing by a public health veterinarian, according to USDA Food Safety and Inspection Service regulations.
If the infection is detected before the animal reaches the slaughterhouse, the veterinarian will treat and disinfect the wound to prevent the infection from spreading.
Any livestock infected with the new world worm should be isolated until all wounds have healed, according to the UDSA.
Transfer methods
A screwworm is a fly – usually the size of a common housefly or slightly larger. It infects warm-blooded animals — usually livestock, wild animals and pets — and rarely infects people, the CDC says.
Infection begins when the female fly lays eggs after being attracted to the smell of the wound, but the opening can be as small as the size of a tick bite. A single female can lay up to 3,000 eggs in her lifetime (about 10 to 30 days), according to the CDC.
The eggs hatch into maggots that “ready” the wound to feed on. After about a week, the maggots fall to the ground, burrow into the soil and transform into adult flies.
“Animals used to produce human food must be inspected before and after slaughter to ensure that food safety and human handling requirements are met,” a USDA spokesperson told Fox News Digital. (Images / Getty Images)
“It is only spread when the NWS fly lays its eggs in a wound, not through meat, poultry or dairy products,” said a USDA spokesperson.
“It's also important to note that people don't catch worms from other people, and they don't get infected by eating meat,” Dr. Bobbi Pritt, professor and chair of laboratory medicine and pathology at the Mayo Clinic in Rochester, Minnesota, told Fox News Digital.
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“The majority of people living in the US are very unlikely to ever encounter this animal.”
The fly thrives in hot and humid climates, while cold temperatures help reduce its survival. Some researchers warn that a warming climate could increase the areas where the insect can survive if it is established, although experts say that the current outbreak is mainly driven by its spread in northern Central America and Mexico.
Fighting the spread
The USDA is fighting the current outbreak in the US by sending male flies to mate with female flies using a technique known as the Sterile Insect Technique, which helped eradicate infestations in the 1960s, according to the USDA.
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Since female screwworm flies only mate once during their monthly cycle, those that breed with sterile females do not produce viable offspring, causing the population to slowly die out.
If the infection is detected before the animal reaches the slaughterhouse, the veterinarian will treat and disinfect the wound to prevent the infection from spreading. (AP Photo/Fernando Llano)
In May 2025, the USDA announced a $21 million investment to renovate a sterile fly production facility in southern Mexico, with production expected to begin in early summer 2026.
The agency also plans to spend $750 million on an “aviation factory” at Moore Air Base in Edinburg, Texas, which is expected to open in November 2027.
Symptoms, treatment and prevention
“In rare cases of human infection, symptoms that should prompt a person to seek medical attention include a non-healing wound with pain, redness and swelling that will worsen, a sensation of movement or crawling in the wound, and visible fly larvae in the wound,” Pritt told Fox News Digital.
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Maggots should not be removed without medical help, as attempting to do so can leave parts of the maggots behind and spread the infection, according to the CDC.
To protect against infection, the CDC recommends wearing long-sleeved shirts and pants, hats and socks, and using an EPA-registered insect repellent. (Stock)
If any worms fall to the ground, they should not be thrown in the garbage, because this may spread the disease. Instead, they should be placed in an airtight container filled with alcohol to kill them, and a doctor should be consulted to safely remove the remaining worms.
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To protect against infection, the CDC recommends the following steps.
- Keep any open wounds closed
- Minimize skin exposure by wearing long-sleeved shirts and pants, hats, and socks
- Use an EPA-registered insect repellent
- Protect clothing and gear with products containing 0.5% permethrin.
- Avoid sleeping outside or sleeping in tents with screens
- Sleep in a room with closed or screened windows
