22OCT

PAHO flags 1,355 human screwworm cases

2 min read

16:36UTC

PAHO issued a regional alert on 16 October after New World screwworm infested 1,355 people in six countries this year, 62% more than in all of 2025. Mexico has all five deaths.

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ScienceAssessed

Key takeaway

Human screwworm cases in the Americas are already 62% above all of 2025.

The Pan American Health Organization (PAHO) issued a regional alert on 16 October after 1,355 human cases of New World screwworm, a fly whose larvae eat living flesh in open wounds, and five deaths in six countries from January to September⁠¹. That is 62% more than the 837 cases in all of 2025. Mexico has 592 cases and all five deaths, one death more than its health ministry reported in September. Honduras (302) and Guatemala (295) together now outnumber it.

The fly was eradicated from Mexico in 1991 and from Central America by 2000, and has spread back since 2022. Females fly up to 50 km and ride on animals and vehicles, so PAHO wants vets and doctors reporting into one surveillance system⁠². It does not pass between people.

Deep Analysis

In plain English

New World screwworm is a fly that lays eggs in open wounds on animals and, sometimes, people. The larvae, or maggots, eat living flesh and can cause serious injury or death if untreated. The fly was wiped out in North and Central America decades ago by releasing huge numbers of sterile flies, which mate but produce no young. It has come back since 2022. It does not pass from person to person. Covering wounds and treating them quickly is the main protection.

Deep Analysis

Root Causes

The sterile insect technique works only if released sterile males outnumber wild ones across the whole infested area. Once the fly spreads faster than the production plants can supply sterile insects, the barrier breaks down region by region.

Cattle movements, legal and illegal, carry larvae in wounds across borders. Females fly up to 50 km, so an infested animal trucked north seeds a new population far ahead of the release zone.

Human cases cluster among people with untreated wounds and limited access to care, often in rural areas with livestock.

What could happen next?

Risk
Human cases will keep rising while the fly expands north through Mexico ahead of sterile-fly releases.
Consequence
Joint human and animal reporting may give earlier warning of the fly reaching new districts.

Source Landscape

This story draws on neutral-leaning sources

Primary parallel: In 1988 New World screwworm reached Libya in imported livestock, far from its native range. The UN Food and Agriculture Organization flew in sterile flies from Mexico and declared it eradicated by 1991, showing the method works when applied fast across a whole area.

Counter-parallel: A sterile-fly barrier in eastern Panama kept the fly out of Central America and Mexico from 2006, until it was breached and the fly spread north from 2022. Eradication held for years and still proved reversible once the barrier failed.

The United States suspended imports of live cattle from Mexico in 2025 because of screwworm, cutting off one of Mexico's main livestock exports and tightening beef supply north of the border.

For ranchers in Central America and Mexico, each infested animal means treatment, lost weight or death, and inspection costs at every movement. Sterile-fly plants take years to build, and governments share the bill.

Consensus view: PAHO wants human and animal health services reporting into one surveillance system, because people are infested where livestock are, and a case in a person usually means the fly is already established nearby.

Counter-view: Mexico's agriculture authorities and the US Department of Agriculture put the weight on the animal side: breeding and releasing sterile male flies, which mate with wild females and leave no offspring. On that view surveillance records the spread, but only sterile flies reverse it.

Key tension: Whether sterile-fly production can grow fast enough to cover a front that now runs from Central America deep into Mexico, while human cases keep rising.

Sources:PAHO

Mentions:PAHO →New World screwworm →Mexico →Honduras →Guatemala →Libya →Panama →Central America →North America →USDA →FAO →

First Reported In

Update #15 · Ebola travels to Kenya and Nigeria

PAHO· 22 Oct 2026

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Causes and effects

Caused by

Screwworm cases in Mexico rise fivefold

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

Occurred 18 Sept 2026

Read story →

This Event

PAHO flags 1,355 human screwworm cases

A flesh-eating fly pest eradicated from Mexico and Central America decades ago is now infesting more people each year, and PAHO wants vets and doctors on one reporting system.

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