The recent resurgence of the New World screwworm in Texas livestock has prompted concerns about the nation's food supply, but agricultural and health officials state the parasite does not contaminate meat, milk, or produce.
The U.S. Department of Agriculture (USDA) confirmed the first case of the New World screwworm in a three-week-old calf in Zavala County, Texas, on June 3. This marked the first detection of the parasite in the U.S. since its eradication in the 1960s, with the exception of a limited outbreak in Florida deer between 2016 and 2017. Since early June, the USDA has reported 33 screwworm infections in animals across Texas and New Mexico, including cattle, goats, and a pet dog.
No Threat to Food Supply
Experts emphasize that the screwworm is an animal health issue and not a foodborne pathogen. "The US food supply is not compromised by New World screwworm, which is an animal issue, but not a foodborne pathogen issue," Dr. Aaron Glatt, chief of infectious diseases at Mount Sinai South Nassau Hospital, told Fox News Digital. He further explained that screwworms die off during standard meat processing and cooking, and that animals destined for human consumption must pass USDA inspections before and after slaughter.
"An infestation or animal illness that makes meat unsafe for consumers will prevent the animal from entering the food supply," a USDA spokesperson stated. If an animal shows signs of illness at a slaughterhouse, it is isolated and subject to additional examination by a public health veterinarian. If an infection is detected prior to slaughter, a veterinarian will treat the animal and disinfect the wound. Livestock infected with New World screwworm are quarantined until their wounds heal.
Understanding the Parasite
The New World screwworm is a fly, typically similar in size to a housefly, that infects warm-blooded animals, including livestock, wildlife, and pets. Human infection is rare. The parasite's life cycle begins when a female fly lays eggs in an open wound on a live animal. These eggs hatch into larvae, or maggots, that feed on the host's living flesh. After about a week, the maggots drop to the ground, burrow, and develop into adult flies. The USDA confirmed that the screwworm spreads through fly eggs laid in wounds and not through the consumption of meat, poultry, or dairy products.
The parasite thrives in tropical and subtropical climates, and while colder temperatures limit its survival, some researchers have noted that climate warming could potentially expand its range. The current outbreak is primarily attributed to the parasite's northward migration from South America and the Caribbean through Central America and Mexico following outbreaks in Panama and Costa Rica in 2023.
Combating the Spread
The USDA is employing the Sterile Insect Technique to combat the current U.S. outbreaks. This method involves releasing sterile male flies that mate with wild females. Since female screwworm flies mate only once, those that breed with sterile males produce no viable offspring, leading to a gradual decline in the population. This technique was instrumental in eradicating the screwworm from the U.S. in the 1960s.
To bolster efforts, the USDA announced a $21 million investment in May 2025 to renovate a sterile screwworm fly production facility in southern Mexico, with production anticipated by summer 2026. Additionally, the agency plans to construct a new "fly factory" at Moore Air Base in Edinburg, Texas, scheduled to open by November 2027.
For individuals, the Centers for Disease Control and Prevention (CDC) recommends protective measures such as wearing long-sleeved shirts and pants, hats, and socks, and using EPA-registered insect repellent to prevent infection. Open wounds should be kept covered, and exposure to skin should be limited. In rare cases of human infection, symptoms include a persistent wound with increasing pain, redness, swelling, a crawling sensation, or visible larvae. Medical attention should be sought immediately in such instances. Maggots should not be removed without professional medical assistance, and if they fall to the ground, they should not be discarded in trash but placed in a leakproof container with alcohol to kill them.