Flesh-Eating Screwworms Surge in Mexico With Over 2,300 Human Cases Reported

A parasitic fly once pushed to the brink of eradication from North America has roared back with a vengeance. New World screwworm larvae now bore into living flesh across Mexico, leaving painful, expanding wounds in their wake. Human infections have climbed past 2,360 according to the latest tally from U.S. health authorities. And the numbers keep rising.

The Ars Technica report from earlier this week first spotlighted the human toll exceeding 500 cases drawn from 2025 and early 2026 surveillance data. But fresh figures released by the Centers for Disease Control and Prevention paint a far larger picture. As of July 31, 2026, Mexico and Central American nations have logged more than 189,000 animal cases alongside those 2,360 human infestations. The CDC updated its situation summary just days ago on August 4.

These maggots do not wait for death. Female Cochliomyia hominivorax flies detect the slightest open wound, even a small cut or mucous membrane. They deposit hundreds of eggs. Within a day the larvae hatch and begin feeding on living tissue. The result is tissue destruction that can reach muscle, cartilage and bone. Secondary bacterial infections follow. Sepsis becomes a real threat. Left unchecked, the infestation can kill.

One study examined 202 confirmed human cases between April 2025 and March 2026. Six patients died. At least one death was directly linked to the screwworm infestation. The patients skewed older with a mean age of 61. Three-quarters suffered from underlying conditions such as diabetes or cancer. Men accounted for 72 percent of the cases. Many infections struck the lower limbs. Others attacked the head and neck. The pattern tracked closely with animal outbreaks spreading northward. The researchers published their findings in Emerging Infectious Diseases.

“Because animal and human cases reflect northward spread of the NWS fly and that spread is expected to continue, surveillance, diagnostic preparedness, animal movement controls, and fly-suppression activities should be implemented proactively at the leading edge of expansion, rather than only after human cases are detected,” the authors wrote. They stressed coordination across human health, animal health, wildlife and agriculture sectors.

The resurgence caught officials off guard. Screwworms once plagued the southern United States and Mexico. A massive campaign in the mid-20th century released billions of sterilized male flies. Females mate only once. The sterile males crashed the population. Mexico celebrated eradication in 2003. A sterile fly barrier held in Panama. Then the barrier broke in 2022. Cases surfaced in Central America in 2023. By 2024 the fly had reclaimed ground in Mexico. The outbreak accelerated from there.

Animal infections tell the bigger economic story. Mexican authorities reported more than 36,000 total cases with nearly 2,000 still active as of August 5. Livestock bear the heaviest burden. Cattle, goats, dogs and wildlife all fall victim. The pain and tissue loss translate into lost productivity, carcass condemnation and expensive treatments. Ranchers face mounting pressure.

The United States has not escaped entirely. The first domestic animal case appeared in Texas on June 3, 2026. USDA tallies now stand at 37 domestically acquired animal infections. Three additional cases surfaced in June across Texas and New Mexico, according to a Guardian article from that period. No locally acquired human cases have surfaced on U.S. soil. The CDC maintains the risk to people here remains very low. One traveler returned from El Salvador in August 2025 with an infestation. That remains the sole imported human case.

Yet anxiety grows along the border. Earlier detections placed the fly within 25 miles of U.S. territory. A Reuters story from June 2 detailed a case in a young goat in Coahuila state. Agriculture Secretary Brooke Rollins called the situation “a very, very serious threat to our livestock.” The U.S. responded by suspending livestock imports from Mexico in May 2025. Debate now swirls around when or whether to reopen the border. Trade groups such as the National Cattlemen’s Beef Association push for resumption as early as August 24. Independent ranchers worry about new outbreaks and who would shoulder the losses.

Mexico’s own surveillance shows the human side accelerating. A February report from the Center for Infectious Disease Research and Policy noted six new cases in a single week, pushing the total to 141 across eight states with the majority in Chiapas. That was early in the outbreak. Numbers have since multiplied. The July Ministry of Health report captured the jump past 500. The CDC’s broader regional count reflects continued transmission into 2026.

Prevention remains straightforward but demanding. Keep wounds clean and covered. Wear long sleeves and pants. Apply insect repellent. Treat clothes with permethrin. Sleep indoors or behind screens. The CDC lists these steps clearly on its outbreak page. For animals the sterile insect technique once worked wonders. A new production facility opened in Edinburg, Texas, to ramp up sterile fly releases. Officials hope to contain the advance before it reaches deeper into American herds.

The human cases, though fewer than animal ones, reveal vulnerabilities. Older adults with comorbidities face the highest risk. Wounds on the legs invite infestation during outdoor work or daily life in affected regions. The larvae create foul-smelling, bleeding sores that grow larger each day. Patients describe feeling movement inside the tissue. Some require surgical removal of dozens or hundreds of maggots. The psychological toll adds to the physical damage.

But the economic stakes may ultimately drive policy. Millions of dollars in livestock losses loom if the fly establishes itself north of the border. The last major U.S. outbreak ended decades ago. Memory has faded. Preparedness has gaps. The CDC situation summary urges vigilance. So does the agricultural community. Coordination between sectors has become non-negotiable.

Recent social media chatter on X reflects the tension. Posts from early August show Mexican officials updating active case maps. Rancher accounts debate border reopening. One independent group highlighted that current low U.S. numbers exist precisely because imports remain restricted. The clock ticks. Fly populations peak in warmer months. Northward pressure continues.

Health officials stress early detection. Unexplained painful wounds that worsen or emit odors demand immediate medical attention. Doctors must consider screwworm in travelers from affected areas even if the risk at home stays low. Diagnostic labs need training to identify the larvae quickly. Delays allow deeper tissue invasion.

The story echoes past battles against invasive species. Success once seemed permanent. Sterile flies and strict barriers held the line for years. complacency crept in. A breach in Panama allowed reinvasion. Now the fly exploits wounds in humans and animals alike with ruthless efficiency. The coming months will test whether renewed sterile releases, tighter surveillance and cross-border cooperation can blunt the advance. Or whether the screwworm carves out a permanent foothold once again. The human cost already exceeds two thousand confirmed cases. The animal toll runs into the hundreds of thousands. Neither side can afford to lose this fight.