Screwworm: The Plague Threatening the U.S. and Mexico

Screwworm: the plague threatening the U.S. and Mexico.
The return of the screwworm raises concern for livestock.
The parasite that harms cattle ranching.

A Silent Threat to Livestock

The screwworm (Cochliomyia hominivorax) is a parasite that feeds on the living tissue of warm-blooded animals, including livestock and, in some cases, humans.

Its presence represents a serious problem for animal health and the economy, since an infestation can cause the death of cattle, horses, and other farm animals.

In addition, it implies millions of dollars in expenses for treatments, veterinary controls, and productive losses for ranchers.

In recent history, both Mexico and the United States managed to eradicate the screwworm through intensive campaigns that included the use of sterile flies to break the parasite’s reproductive cycle.

However, recent outbreaks in Latin America and the Caribbean have revived fears of reintroduction in territories where it had already been eliminated.

Screwworm: The Plague Threatening the U.S. and Mexico

PROTECT YOUR LIVESTOCK AND PREVENT THE SCREWWORM

Cattle Screwworm can cause serious damage if not detected in time. With these actions, we prevent its spread and protect livestock production.

Check, detect, and report any suspected case to 800… pic.twitter.com/9kWX8mGR2s

— Gobierno de Oaxaca (@GobOax) August 17, 2025

The concern is twofold: health-related and economic. In Mexico, cattle ranching is one of the pillars of the agricultural economy and a strategic sector for exports.

In the United States, the meat industry is one of the largest in the world, with billions of dollars at stake.

A reinfestation of the screwworm would not only affect animal health but could also hit international trade by imposing sanitary restrictions in key markets.

The risk increases due to factors such as climate change, which favors the spread of pests, and the movement of animals across borders. A single uncontrolled outbreak could spread quickly in livestock regions, forcing strict biosecurity measures and constant monitoring.

The Problem of Control and Prevention

🚨🐛 Attention! If you visit rural areas or spend time outdoors, protect your health and that of your animals from cattle screwworm.

🧼 Hygiene is key to prevention. @Gob_Puebla #PorAmorAPuebla #PensarEnGrande pic.twitter.com/5QpdwDvnps

— Secretaría de Salud (@SaludGobPue) August 20, 2025

Combating the screwworm requires a coordinated binational effort. Joint surveillance programs, fumigation campaigns, and the release of sterile flies are strategies that have been successfully used in the past. However, the cost is extremely high: millions of dollars annually invested to keep the pest at bay.

At a social level, the problem is also concerning because infestations can affect rural communities and people with limited access to medical services.

In regions where livestock is the economic backbone, the presence of the parasite means animal losses, reduced income, and added pressure on daily life.

The battle against the screwworm is far from over. For Mexico and the United States, the challenge is to maintain a pest-free border that threatens animal health, agricultural production, and the economic stability of two of the most important industries in the region.

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