The New World screwworm—a flesh-eating parasite that burrows into living tissue—has re-emerged along the U.S.-Mexico border, triggering alarms from public health officials, cattle ranchers, and veterinarians. In a span of weeks, the U.S. has confirmed its first human infection in 60 years, a case in a traveler returning from El Salvador, and a separate infection in a South Texas calf. Meanwhile, Mexico's Ministry of Health reports more than 500 human cases since the fly reinvaded the country in 2024, with the pace of infestation accelerating.

The developments mark an unsettling reversal for a pest that was officially eradicated from the United States in 1966 after a multi-decade campaign. The New World screwworm fly (Cochliomyia hominivorax) lays hundreds of eggs in wounds, mucous membranes, or orifices of warm-blooded animals. Within a day, the larvae hatch and begin feeding on living flesh, creating wounds that can be fatal if untreated.

A Growing Outbreak in Mexico

A study published this week in the journal Emerging Infectious Diseases analyzed more than 200 confirmed human cases reported in Mexico between April 2025 and March 2026. The researchers found that infestations are increasing, and they documented six deaths—at least one directly caused by the maggots' destruction of tissue. Mexico's national surveillance report from July 2025 tallies over 500 human cases across multiple states, a sharp rise from the initial cases detected in 2024.

“The infestation pace is increasing,” the researchers wrote, warning that without aggressive control measures, the parasite could spread further into Central and North America. The fly is already known to affect dozens of warm-blooded species, including dogs, cats, and wildlife, making containment challenging.

First U.S. Human Case and Cattle Infection

The first human case in the U.S. since the 1960s was confirmed by the Department of Health and Human Services (HHS) in a person who had traveled to El Salvador. The infection was detected during routine health screening, and officials have not disclosed additional details about the patient's condition. The same week, the U.S. Department of Agriculture (USDA) confirmed a New World screwworm infestation in a calf in South Texas, marking the first livestock case on U.S. soil since the pest was eradicated.

“This is exactly the scenario we feared,” said Texas State Veterinarian Dr. James Rich, speaking to local media. “The fly does not respect borders, and with movement of animals and people, these cases will likely continue.”

The Texas case has prompted a swift response: Canada has temporarily banned the import of Texas livestock, and several U.S. states—including Arizona, New York, Pennsylvania, North Carolina, and Wyoming—are urging veterinarians and pet owners to watch for signs of screwworm infestations.

Economic Fallout for the Cattle Industry

Beyond the human health threat, the screwworm's arrival is a significant economic blow. The cattle industry, already grappling with drought and market volatility, now faces potential quarantine zones, treatment costs, and disrupted exports. The Los Angeles Times highlighted that if the parasite becomes established, it could stress the beef supply chain and ultimately raise prices at the grocery store.

“A single fly can lay thousands of eggs, and each larva can cause a wound that ruins an animal for market,” said Dr. Angela Chen, an agricultural economist at Texas A&M University. “The cost of surveillance and treatment is piling up, but the cost of doing nothing is catastrophic.”

In Mexico, livestock losses have already been reported in the millions of dollars. Ranchers along the border are bracing for similar fallout. “We've been here before, and we know how bad it gets,” said a third-generation rancher in Starr County, Texas, near the border, in an interview with Dallas News. “We're hoping the government acts fast.”

How the U.S. Plans to Fight Back

The USDA has activated its emergency response plan, which includes increased inspection of animals at ports of entry, the use of insecticide-laced baits, and the release of sterile flies—the same technique used to eradicate the screwworm in the 1950s and 1960s. This method, which involves rearing and releasing millions of sterile male flies to mate with wild females and produce no offspring, is credited with eliminating the pest from the U.S. and much of Central America.

However, experts note that the sterile insect technique requires a sustained, region-wide effort. “You can't just do this at the county level,” said Dr. Martha Rodriguez, a veterinary entomologist at the University of California, Davis. “The fly flies up to 200 kilometers in its lifetime, and it can move through animal transport networks. We need a coordinated international response.”

The USDA is also considering temporary restrictions on animal movement from affected areas, and Mexico has begun vaccinating livestock with a new preventive product. But the parasite is notoriously resilient: the larvae can survive in a wound for up to a week, and adult flies can live and reproduce year-round in warm climates.

Different Outlets, Different Frames

Coverage of the outbreak reflects varied priorities. Tech and science outlets like Ars Technica emphasize the biological nightmare and the surveillance data, describing the maggots as “ravenously feasting” on victims. Local news outlets from Arizona to New York are focusing on whether the pest is in their backyard, with headlines like “Is it in Arizona?” and “Should you worry?”. The Chicago Tribune and others stress the economic angle, linking the parasite to burger prices. Meanwhile, outlets like Defector approach it with dark humor—“Welcome, Screwworms! Make Yourself At Home”—while urging practical precautions.

Belize and other Central American nations have also issued public warnings, and Canadian media are covering the border implications. The common thread is a sense of urgency: this is not a distant problem but one that is literally crawling closer.

What the Public Should Know

For humans, the risk remains low—the fly typically infects open wounds, so basic hygiene and wound care prevent most infestations. But pet owners and livestock producers are advised to check animals for maggots, especially in any skin abrasion, navel, or other opening. All cases should be reported to state veterinary authorities.

As one researcher put it, “The screwworm is a disease of poverty and neglect, but in an interconnected world, it can become everyone's problem.” The coming months will be critical in determining whether the U.S. can stop this pest at the border or face a larger, costlier battle.