The U.S. Department of Agriculture (USDA) has confirmed the presence of the New World screwworm, a flesh-eating parasite, in a 3-week-old calf in Zavala County, Texas. This detection marks the first occurrence of the parasite in the United States in decades, raising concerns among livestock owners, pet owners, and wildlife experts.
The USDA’s Animal and Plant Health Inspection Service (APHIS) announced the finding on Wednesday, June 3, 2026, and has since initiated containment and eradication measures. The parasite, which is the larval stage of a fly, lays eggs in open wounds or body openings of warm-blooded animals. Once hatched, the larvae burrow into living tissue, causing painful and potentially deadly infections.
The Threat of the New World Screwworm
The New World screwworm, Cochliomyia hominivorax, is not a new adversary for U.S. livestock. The parasite was endemic across the southern United States for much of the 20th century before a decades-long eradication campaign cleared it from the country by the 1960s. The approach involved releasing mass-reared, radiation-sterilized male flies that mate with wild females, producing no offspring and collapsing the population over successive generations.
Despite its eradication, the pest has resurfaced periodically. A 2016–2017 outbreak in the Florida Keys, centered on endangered Key deer, marked the first local U.S. detection in more than 30 years before it was again eradicated. The current threat traces back to 2026, when the screwworm began advancing northward through Central America and into Mexico, with case numbers climbing steadily toward the southern border.
Impact on Texas and Beyond
Texas, home to the largest cattle industry in the nation, faces significant economic consequences if the pest spreads. Federal officials have established quarantine zones, increased surveillance efforts, and begun releasing sterile flies to stop the pest from becoming established in the United States. The discovery comes after the parasite steadily moved north through Central America and Mexico over the past several years, prompting growing concern among agriculture officials.
While there have been no reported screwworm cases in the Houston area, officials stress that the current detection is limited to a single calf in South Texas. However, Houston’s large population of pet owners, horse owners, and backyard animal enthusiasts may want to stay informed as state and federal agencies monitor the situation.
Response and Prevention Efforts
The USDA and Texas Animal Health Commission have established a unified incident command structure and imposed a 20-kilometer quarantine zone surrounding the detection site. Officials are implementing movement controls, enhanced surveillance, and increased trapping efforts in the region. The agency is also accelerating the release of sterile male screwworm flies, a strategy that proved successful during the original eradication campaign.
USDA has supported new sterile-fly production and dispersal facilities in Mexico and South Texas while increasing surveillance efforts along the border. The agency has also suspended imports of live cattle, horses, and bison from Mexico to slow the parasite’s advance. For ranchers, the stakes are substantial, as the larvae of the New World screwworm fly invade open wounds and body openings, consuming living tissue and potentially leading to severe health issues and economic losses.
Public Health and Food Safety
USDA officials emphasize that the parasite does not contaminate meat or other food products. The primary concern is animal health and the potential economic impact if the pest spreads among livestock populations. For now, officials are emphasizing rapid response measures and say there is no evidence of widespread infestation in Texas. Surveillance and containment efforts remain underway.
Experts recommend checking animals for unusual wounds that appear to be getting larger, draining excessively, or attracting flies. Pet owners and livestock producers should contact a veterinarian immediately if they suspect an infestation. Anyone who notices a suspicious lesion or suspects infection should seek medical attention.
The detection of the New World screwworm in Texas serves as a reminder of the ongoing vigilance required to protect animal health and the agricultural industry. As crews work to prevent the parasite from gaining a foothold in the state, residents are urged to remain informed and proactive in monitoring their animals for any signs of infestation.