The U.S. Department of Agriculture (USDA) has confirmed multiple detections of New World screwworm (NWS) in livestock in Texas and New Mexico, prompting federal quarantine zones, movement restrictions, and import limitations from Canada and several U.S. states.
Detection and Timeline
On June 3, 2025, USDA’s Animal and Plant Health Inspection Service (APHIS) confirmed the first U.S. case of New World screwworm in a three-week-old calf in Zavala County, Texas, approximately 50 kilometers from the Mexican border. Larvae were identified in the calf’s umbilical area.
A second case was subsequently confirmed in a one-month-old calf in Zavala County, approximately 5.6 miles (9 kilometers) from the first detection. Additional samples from the surrounding area tested negative.
In New Mexico, additional detections have also been confirmed, though the number and specific locations of those cases have not been detailed in the provided sources.
"The pest was declared eradicated in the United States in 1966. It reappeared in Central America and moved into Mexico in 2023."
Federal and State Response
Quarantine and Movement Restrictions
- A 20-kilometer (12-mile) infested zone has been established around the initial detection site in Texas.
- Movement of animals, including pets, is prohibited within this zone.
- The USDA has activated an Incident Command Team in coordination with the Texas Animal Health Commission.
- Surveillance traps have been increased along the U.S.-Mexico border.
Pest Control Measures
- Sterile male insects are being released in the affected area to suppress the pest population.
- The affected animals are being treated, which includes manual removal of larvae, wound disinfection, antibiotics, and insecticides.
Trade and Interstate Movement Restrictions
- The Canadian Food Inspection Agency has imposed temporary restrictions on importing livestock from affected U.S. areas. Animals originating in or present in Texas within 21 days before crossing the border are barred from Canada.
- The Idaho State Department of Agriculture (ISDA) issued an administrative order restricting entry of warm-blooded animals from affected states:
- Animals from designated infested zones require a Certificate of Veterinary Inspection issued within five days of travel and documentation of authorized departure from the infested area.
- Animals from states with detected cases but outside infestation zones must have a health certificate issued within five days before entering Idaho.
- USDA officials stated that the U.S. food supply remains safe, as New World screwworms do not infest food products.
Background on New World Screwworm
New World screwworm is caused by the larvae of the fly Cochliomyia hominivorax. Female flies lay eggs in wounds, scratches, or orifices of warm-blooded animals, including humans. The larvae feed on living tissue, causing severe wounds that can be fatal without treatment.
"Since September 2024, at least 26,216 cases have been identified in Mexico, with over 2,700 currently active as of the most recent reporting."
Mexico confirmed 41 human cases in 2024, primarily in Chiapas. The U.S. had its first reported human case of New World screwworm in August 2024 in a patient who returned from El Salvador to Maryland. That individual recovered, and no transmission to others or animals was found.
Potential Economic Impact
The USDA estimates potential losses of $1.8 billion to the Texas economy in the event of a widespread outbreak. The U.S. halted cattle imports from Mexico for the past year due to the pest’s spread, a factor that has contributed to rising beef prices.
Expert Commentary
Dr. Cheryl Whitehorn, a medical entomologist at the London School of Hygiene & Tropical Medicine, described the initial case as a locally acquired infestation. She stated that the primary measures are vigilance, identification and isolation of cases, treatment and elimination of larvae, and controlling movement of animals, and that a program of sterile male release is the best long-term method of control.
"USDA has not wasted any time in this fight, we have defeated New World screwworm before, and we will do it again." — Dudley Hoskins, USDA Under Secretary for Marketing and Regulatory Programs
"Livestock owners and all Texans should remain vigilant. Surveillance and reporting are a priority. The quicker an infestation is found, the quicker the New World screwworm can be eradicated." — Russell Boening, President of the Texas Farm Bureau
Reporting Requirements
Suspected infestations of New World screwworm must be reported to a veterinarian immediately. The disease is a mandatory reportable condition in affected states.