22OCT

Screwworm cases in Mexico rise fivefold

2 min read

16:36UTC

Mexico's health ministry recorded 575 human screwworm cases in 2026 to 18 September, against 117 in all of 2025, El Universal reported.

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Key takeaway

Mexico's screwworm outbreak in livestock is now infesting people in 27 states.

Mexico's Secretaría de Salud, the federal health ministry, recorded 575 human cases of New World screwworm in 2026 to 18 September, against 117 in all of 2025, as reported by El Universal⁠¹. screwworm larvae hatch from fly eggs laid in open wounds and feed on living tissue. The parasite mainly attacks livestock, and it has now infested 692 people in 27 states since April 2025.

Four have died, all this year, in Oaxaca, Querétaro, Veracruz and Yucatán. Chiapas, on the Guatemalan border, has the most cases at 165. Any untreated wound, on an animal or a person, can host the larvae, so human cases rise with the number of flies in the field. The Secretaría de Salud is fighting the parasite alongside a measles outbreak that accounted for more than half the Americas' cases in the first five months of the year, and is now declining.

Deep Analysis

In plain English

The maggots of the New World screwworm fly eat living flesh. It usually attacks cattle, but it can infest people through open wounds, the nose or ears. The fly was wiped out in North and Central America decades ago by releasing sterile flies that cannot breed. Since 2023 it has spread north again from Panama through Central America into Mexico. This year Mexico has recorded 575 human cases, five times last year's total, and four deaths. Cases are mainly in the south, near Guatemala.

Deep Analysis

Root Causes

screwworm flies lay eggs in open wounds on warm-blooded animals, including people. The larvae eat living flesh, so untreated wounds on cattle, dogs or people in rural areas become breeding sites.

The barrier in Panama failed partly because cattle moved north illegally through Central America, carrying larvae past the sterile-fly zone. Once breeding populations formed in Guatemala and southern Mexico, sterile-fly supply could no longer cover the area.

Human cases cluster among older people, people with chronic wounds and those living near livestock in hot rural areas.

What could happen next?

Risk
Further spread north could bring screwworm to the US border states, risking a repeat on the mainland of the 2016 outbreak among deer in the Florida Keys.
Consequence
Mexico's live-cattle exports to the United States will stay constrained while the fly spreads.

Source Landscape

This story draws on centre-leaning sources from Mexico

Mexico

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Primary parallel: The United States eradicated screwworm in the 1960s by releasing billions of sterile male flies, and Mexico was declared free in 1991. A barrier zone was then pushed south to Panama's Darién Gap from 2006, and its breach in 2023 opened the current northward spread.

Counter-parallel: screwworm reached Libya in 1988, its first appearance outside the Americas, and was eradicated by 1991 with sterile flies shipped from Mexico. That success depended on a single, isolated outbreak and an existing fly factory, neither of which holds in Mexico now.

Mexico's cattle exports to the United States took the first hit in 2025. The United States suspended imports of live cattle from Mexico in 2025, which hit northern Mexican ranchers who sell feeder calves to US feedlots.

In the longer run, the cost lies in treatment and fly production. Each infested animal must be found and treated, and new sterile-fly capacity takes years to build.

Consensus view: Mexico's Secretaría de Salud runs a dedicated surveillance system for screwworm myiasis, and its figures, relayed by El Universal, show human cases tracking the fly's northward spread: Chiapas 165, Veracruz 116, Oaxaca 68, Puebla 61 and Yucatán 47. The official reading treats human infestations as a by-product of an animal-health failure.

Counter-view: The US Department of Agriculture has handled screwworm as a livestock trade threat, suspending imports of live Mexican cattle in 2025. On that view the binding constraint is sterile-fly supply, not human medical care. The plant run by the Panama-US commission COPEG near Panama City was the region's only producer until a second plant opened at Metapa, in Chiapas, Mexico, in June 2026.

Key tension: Whether sterile-fly releases can be scaled fast enough to push the barrier back south before the fly reaches the US border states.

First Reported In

Update #14 · River boat carries Ebola 1,000 km downriver

El Universal· 3 Oct 2026

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Causes and effects

This Event

Screwworm cases in Mexico rise fivefold

A livestock parasite that feeds on living flesh has now infested 692 people across most of Mexico and killed four this year.

Led to

PAHO flags 1,355 human screwworm cases

Mexico's human screwworm cases rose to 592 as PAHO counted 1,355 across six countries.

Occurred 16 Oct 2026

Read story →

Different Perspectives

Pan American Health Organization

PAHO warned on 20 October that El Niño is set to intensify as the dengue season begins, and issued a regional screwworm alert on 16 October. It wants veterinary and human health workers reporting into one surveillance system.

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ECDC

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Ghana Ministry of Health

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Government of Côte d'Ivoire

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World Health Organization

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Written with AI from Lowdown's published reporting. Not individually reviewed by an editor. Editorial standards.