The New World screwworm was detected on June 3 in a three-week-old calf in Zavala County by the U.S. Department of Agriculture. Since this initial discovery, the agency has reported additional screwworm infestations in Texas.
This parasitic fly presents a potential multibillion-dollar crisis for the state’s cattle industry, which generates $41 billion annually. Officials warn that an outbreak could also lead to an increase in already record-high beef prices across the nation. While the full extent of cases in Texas remains unclear, Mexican officials have reported nearly 28,000 cases in Mexico since November 2024.
State and federal officials have been actively tracking the northern migration of the screwworm since 2023. In response to the confirmed cases, the USDA and the Texas Animal Health Commission have significantly increased animal surveillance efforts in designated zones around each detected infestation. Animals are prohibited from leaving these infested areas without undergoing proper inspection.
Control measures include increasing the number of fly traps, enhanced surveillance of wildlife, and the release of sterile flies. This last method aims to break the parasitic screwworm fly’s reproductive cycle by preventing fertile offspring.
New World screwworm is a parasitic fly that seeks out living tissue. The flies burrow their larvae into open wounds, and after hatching, the maggots feed on the living flesh, causing severe damage to the host animal. If left untreated, these infestations can be fatal. The screwworm can also burrow through other natural openings in the skin, such as the corner of an eye or through the nose.
Biologically, all mammals are vulnerable to screwworm, including domestic pets and humans. However, livestock and wildlife are generally the most susceptible because they spend their entire lives outdoors, increasing their exposure to the fly. Dogs and cats can become vulnerable through small wounds or scratches that break the skin.
Casey Locklear, a veterinarian and parasiticides lead for Elanco Animal Health, advises pet owners to medicate their pets for fleas and ticks year-round. Locklear emphasized the importance of early intervention, stating that if a pet owner notices a wound on their dog or cat, "especially if it’s foul smelling, it’s enlarging, you may actually see the maggots," they should seek treatment promptly. Early treatment, whether for a pet or a person, is key to managing an infestation.
State and federal agencies will continue their surveillance and control efforts to prevent further spread of the New World screwworm in Texas.
