Federal officials have confirmed the first U.S. case of New World screwworm in decades, marking a significant development for Texas ranchers and the broader livestock industry. The U.S. Department of Agriculture (USDA) announced Wednesday that laboratory testing verified an infestation in a three-week-old calf in Zavala County, South Texas.
The infected animal was located near La Pryor, and testing conducted at the USDA’s National Veterinary Services Laboratories in Ames, Iowa, confirmed the presence of the parasitic pest. Officials said no additional cases have been detected at this time, but surveillance efforts remain heightened across the region.
The confirmation follows months of preparation by state and federal agencies that had been monitoring the northward movement of screwworm through Central America and Mexico. The pest, once eradicated from the United States in the 1960s, has steadily advanced closer to the U.S. border in recent years, prompting concerns among agricultural leaders and ranchers.
New World screwworm poses a serious threat because its larvae feed on the living tissue of warm-blooded animals. The parasite can infect cattle, horses, wildlife, pets, and even humans by depositing eggs in open wounds. Once hatched, the larvae burrow into flesh, creating severe injuries that can lead to infection, significant suffering, and death if left untreated.
Agriculture officials emphasized that the discovery does not present a risk to the food supply. Screwworms do not infest meat products, fruits, or vegetables. However, the pest has the potential to cause substantial economic damage to livestock operations, particularly in Texas, where cattle production is a major component of the state’s agricultural economy.
Since early 2025, the USDA has significantly expanded surveillance efforts aimed at detecting the parasite before it could establish itself in the United States. More than 8,000 detection traps have been deployed, resulting in tens of thousands of samples being collected and tested from livestock and wildlife. Until this week’s confirmation, all tested samples had returned negative results.
The latest development comes amid increasing debate over the federal response to the screwworm threat. Agriculture Secretary Brooke Rollins stated that officials have been coordinating closely with Texas livestock producers, the Texas Animal Health Commission, Governor Greg Abbott, and other state leaders. Federal personnel were mobilized immediately after the suspected case was identified and have been working with local partners on containment efforts.
In an attempt to slow the pest’s advance, the USDA suspended imports of live cattle and other livestock from Mexico in May 2025. The move was designed to reduce the risk of infected animals entering the country, though it also tightened cattle supplies for producers and buyers in Texas.
Meanwhile, U.S., Mexican, and Panamanian authorities continue to rely on the sterile fly technique, the same strategy that successfully eradicated screwworm from the United States decades ago. The method involves releasing sterilized male flies into affected areas. Because female screwworm flies mate only once during their lifetime, reproduction is interrupted when they mate with sterile males, gradually collapsing local populations.
To strengthen eradication efforts, officials have expanded sterile fly production capacity beyond the long-standing facility in Panama. Additional facilities have been established in Mexico, while another production center is under development in Edinburg, Texas, with an expected opening in 2027. Fly dispersal facilities have also been launched to support rapid deployment where outbreaks occur.
The confirmed case has intensified calls for additional control measures. Texas Agriculture Commissioner Sid Miller has urged federal officials to consider deploying the Screwworm Adult Suppression System, an approach tested in previous eradication campaigns that combines bait and insecticides to reduce adult fly populations.
For now, officials are urging livestock owners and pet owners in South Texas to closely monitor animals for unusual wounds, signs of infection, or the presence of larvae. While only a single case has been confirmed, authorities view rapid detection and response as critical to preventing a larger outbreak that could threaten one of the nation’s most important agricultural sectors.
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