New World Screwworm Outbreak Puts the Americas on Veterinary Alert

A renewed parasitic threat is testing livestock surveillance, pet health response, wildlife monitoring and cross-border animal movement controls across Central America, Mexico and the United States.

June 2026: New World Screwworm, a parasitic fly once pushed back through decades of eradication work, has again become a major veterinary concern across the Americas. The disease is caused by the larvae of Cochliomyia hominivorax, which infest wounds and feed on living tissue in warm-blooded animals, including livestock, pets, wildlife and, less commonly, people.

The current outbreak has moved northward since 2023 through Central America and Mexico. On June 3, 2026, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service confirmed New World Screwworm in a calf in Zavala County, Texas. The confirmation changed the risk calculation for the region because the parasite had long been considered eliminated from the United States.

Why the Outbreak Matters

New World Screwworm is not a food safety issue in the usual sense. Its impact is on live animals, farm productivity, animal welfare and trade. Untreated infestations can damage tissue, cause secondary infections, reduce production and result in animal losses. The disease can also trigger quarantine measures and livestock movement restrictions, creating pressure on cattle, sheep, goat, horse and pet sectors.

According to the U.S. Centers for Disease Control and Prevention, the current outbreak has primarily affected livestock, pets and wildlife, while human cases have also been reported in parts of Mexico and Central America. No locally acquired human infestations have been reported in the United States in the current outbreak.

Outbreak Mapping: Main Affected Areas

Region/Country	Current Concern	Key Source
Panama	Frontline eradication zone; sterile fly production and field surveillance remain central to control.	COPEG Panama
Central America	Regional spread reported across Belize, Costa Rica, El Salvador, Guatemala, Honduras and Nicaragua.	WOAH
Belize	One Health surveillance increased after animal and human case concerns.	PAHO/WHO Belize
Mexico	Major escalation front; livestock movement and disease-free northern areas under pressure.	SENASICA Mexico
Texas, United States	Confirmed U.S. animal cases have led to quarantine, surveillance and sterile fly response.	USDA/APHIS Current Status
New Mexico, United States	Pet-related detection has increased attention on companion animal preparedness.	FDA Emergency Use Authorization

Why USDA, FDA, CDC and WOAH Are Focused on It

The leading U.S. animal health agency in this response is USDA/APHIS. Its concern is linked to livestock protection, wildlife surveillance, sterile fly release, animal movement control and agricultural trade. USDA says it continues to disperse sterile insects in Mexico and along the U.S.-Mexico border as part of the containment strategy.

The U.S. Food and Drug Administration has also issued emergency authorization for generic nitenpyram tablets for eligible dogs and cats with New World Screwworm infestation. This shows that the outbreak is no longer being viewed only as a cattle issue, but also as a pet health and veterinary preparedness concern.

The World Organisation for Animal Health has called for stronger surveillance, transparent reporting, veterinary certification and cross-border collaboration. The disease is important internationally because it can move with animals, affect multiple species and create trade disruption.

Sterile Insect Technique Remains the Main Control Tool

The Sterile Insect Technique remains the backbone of the response. In this system, sterile male flies are released into affected areas. When wild female flies mate with sterile males, their eggs do not hatch, reducing the population over time. This same approach helped eliminate New World Screwworm from the United States and other regions in the past.

USDA has also announced the New World Screwworm Grand Challenge, supporting innovation in sterile fly production, surveillance tools, traps, lures, treatments and preparedness systems.

Trade and Field-Level Impact

The outbreak is already affecting animal movement and livestock trade. Reuters reported that Mexico blocked most live animal imports from the United States after screwworm detections in Texas and New Mexico. The restrictions reflect the seriousness of the disease for cattle, horses, pigs, sheep and goats.

Regional media in Texas have reported rising concern among ranchers and veterinarians as cases were detected in cattle, goats and dogs. Local reporting from Midland Reporter-Telegram and MySA has highlighted quarantine zones, pet infections and animal movement restrictions.

What the Outbreak Shows

The 2026 New World Screwworm situation shows how an old parasite can quickly become a modern veterinary emergency. It links livestock production, pet care, wildlife health, public health, quarantine systems and international trade. The disease has no vaccine, making early detection, wound inspection, rapid reporting and sterile fly release essential.

For the global veterinary community, the message is clear: eradication does not mean permanent safety unless surveillance continues. New World Screwworm has returned as one of the most important transboundary animal disease stories of 2026.