PAHO alert: human New World screwworm cases in the Americas jump 62 percent in 2026

The New World screwworm is not a worm. It is the larval stage of Cochliomyia hominivorax, a fly whose maggots feed on the living tissue of warm blooded animals, enlarging wounds that will not heal and, in severe and untreated cases, killing the host. For decades the species looked like a solved problem. Campaigns built on the sterile insect technique cleared it from the United States in 1966, from Mexico in 1991, and from Central America between 1994 and 2000.

That achievement has come undone. From 2022, with a marked increase reported by Panama in 2023, the fly was documented again in Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Panama and the United States. The leading edge has crept north through Mexico, and the border with the United States is now part of the planning of veterinary and public health agencies.

On October 16, 2026, the Pan American Health Organization, the regional office of the World Health Organization, issued an epidemiological alert on human myiasis caused by Cochliomyia hominivorax. PAHO/WHO reported on October 16 that 1,355 confirmed human cases and five deaths had been recorded across six countries between January 1 and September 2026. That compares with 837 cases and four deaths in eight countries during the whole of 2025, a rise of 62 percent. The alert asks member states to strengthen epidemiological surveillance, ensure timely diagnosis and clinical management, and reinforce coordination among human health, animal health and environmental sectors under a One Health approach.

Key Facts

PAHO/WHO reported on October 16 that the 2026 total covered six countries. Mexico carried the largest share, with 592 confirmed cases and five deaths as of epidemiological week 37. Honduras followed with 302 cases as of epidemiological week 38, Guatemala with 295, Panama with 101, Costa Rica with 57 and Belize with eight. El Salvador and the United States recorded no human cases in the period.

Within Mexico, the outbreak is concentrated in the south and southeast. PAHO reported on October 16 that 61 percent of cases, 359 of them, were recorded in five states: Veracruz with 115 cases including two deaths, Chiapas with 77, Oaxaca with 64 including one death, Puebla with 64, and Yucatan with 39 including one death. Patients ranged in age from one to 98 years, with a mean of 63, and 63 percent of cases, 372 people, were aged 60 or older. Of all Mexican cases recorded in 2025 and 2026, 81 percent needed hospital care, a total of 574 patients.

The US Centers for Disease Control and Prevention reported on October 14 that countries in Central America and Mexico have together recorded more than 209,400 animal cases and more than 2,700 human cases of New World screwworm since 2023. In a situation summary dated October 7 and last modified October 14, the agency said the current risk to the public and to animals in the United States is very low. No locally acquired human infestation has been reported in the United States. One case was confirmed in August 2025 in a person who returned to the country after travelling to El Salvador. On June 3, 2026, USDA-APHIS confirmed the first American animal case of the current outbreak.

A study published on August 5, 2026 in Emerging Infectious Diseases, the CDC journal, examined 202 Mexican cases drawn from the national surveillance system between April 13, 2025 and March 14, 2026. It found that 71.8 percent of patients were men, the mean age was 61.1 years, and lower limbs were the most frequently reported site at 55.0 percent. Some 76.7 percent of patients had more than one concurrent condition, most commonly diabetes, alcoholism, cancers and skin conditions. Six deaths were recorded, although at the time of reporting only one was attributed directly to screwworm myiasis, with other causes listed as cancers, encephalitis, respiratory failure and septic shock. The mean age of patients who died was 79.5 years.

The tempo also changed. The journal study recorded 111 cases during the 2025 reporting period, a mean of three confirmed cases per epidemiological week, then 91 cases in the first 10 epidemiological weeks of 2026, an average of 9.1 per week, roughly a threefold increase. By week 10 of 2026, 12 of Mexico's 32 states had reported confirmed human cases, and Chiapas alone accounted for 119 of 204 cases, or 58.3 percent. Houston Public Media reported on October 5 that the United States had confirmed 53 animal cases since June, 51 in Texas and two in New Mexico, with the most recent found on October 2 in a dog in Brewster County, Texas.

Analysis

The bigger picture here is that the 62 percent jump measures two things at once, and only one of them is a worsening outbreak. Wider testing and stronger reporting after years of under detection will inflate any case count, and PAHO frames the alert around surveillance capacity. But the geography is harder to explain away. Human cases are appearing in Mexican states that had not reported them before, animals have been found infected in Texas and New Mexico, and a wild fly turned up in a surveillance trap in Brewster County on September 25. Better detection explains part of the rise. Movement of the fly explains the rest.

The clinical profile points to a second problem, which is late presentation. In Mexico the mean patient age is 63 and 63 percent of cases are in people aged 60 and over. The CDC journal study found that 76.7 percent of patients had at least one concurrent condition, most often diabetes, and 81 percent of Mexican cases across 2025 and 2026 required hospitalisation. These are not exotic infections in healthy travellers. They are wound complications in older, often rural patients whose underlying illnesses and living conditions leave them exposed. The parasite can only establish itself in an open wound, which means many of these cases were preventable with basic wound care.

What this really means is that the response cannot rest on the sterile insect technique alone, however impressive the industrial scale of that effort has become. The USDA says it has released more than 1 billion sterile flies in Texas since February 2026 and aims to raise production to 500 million flies per week by summer 2027, a target set for next year rather than today. Agriculture Secretary Brooke Rollins said officials are making progress containing the outbreak but warned the threat has not passed, particularly in Arizona and New Mexico. Until that capacity arrives, the human side of the equation depends on clinics recognising a rare infestation, laboratories confirming it, and health departments reporting it quickly.

PAHO's technical notes add detail that shapes the risk map. Adult female flies can travel up to 50 km, and they are rarely found above 2,100 metres, so altitude offers some protection to highland communities and little to anyone else. The re-emergence has already touched eight countries since 2022, and an eradication programme that depends on uninterrupted cross border coordination does not stay inside one jurisdiction.

Why It Matters

For individuals and clinicians, the practical stakes are high but manageable. CDC advises people in affected areas to keep open wounds clean and covered, wear long sleeves and pants, use EPA registered insect repellent and permethrin treated clothing, and sleep in screened rooms. Symptoms to watch for include unexplained painful wounds that do not heal, foul smelling discharge or bleeding, and visible maggots or a sensation of movement in wounds, nose, mouth, eyes, ears or genitals. Healthcare providers who suspect an infestation must report it immediately to their local or state health department.

For governments, the alert is a test of the One Health machinery that PAHO invoked by name. The CDC says it is working with USDA, the Department of the Interior and state, local and tribal partners, and that the USDA led strategy combines sterile fly releases, animal movement controls, surveillance and outreach in affected areas. USDA considers the screwworm not a food safety threat, but livestock movement restrictions and the cost of suppression carry real economic weight for farming communities in Mexico, Central America and the southern United States.

The regional arithmetic is sobering. More than 209,400 animal cases and more than 2,700 human cases since 2023, 592 human cases in Mexico in 2026 alone and five deaths there this year make this the largest sustained human exposure to Cochliomyia hominivorax that the Americas have recorded since eradication was declared. Rare does not mean trivial when the patient is elderly, diabetic and living where the fly has returned.

Next Up

The markers to watch are weekly case counts in Mexico, Guatemala and Honduras, whether the United States confirms any locally acquired human case, and whether the USDA reaches its production target of 500 million sterile flies per week by summer 2027. The three active animal cases reported in early October, the dog in Brewster County, the goats in Crockett County confirmed on September 26, and the horse in Grant County, New Mexico confirmed on September 17, will show whether the northern front is expanding or contracting.

The authors of the Emerging Infectious Diseases study argue that because animal and human cases reflect the northward spread of the fly, surveillance, diagnostic preparedness, animal movement controls and fly suppression should be put in place proactively at the leading edge of expansion, rather than after cases appear. PAHO's October 16 alert asks member states for the same thing. The question for the next reporting period is whether the region can act ahead of the fly rather than behind it.