For decades, the New World screwworm was considered a problem of the past in the United States. After an extensive eradication campaign, the pest was eliminated from the U.S. in 1966 through the use of sterile fly technology. Unfortunately, that changed in June 2026 when USDA confirmed the first domestic screwworm case in nearly 60 years.
The initial detection occurred in a calf in South Texas, triggering an aggressive response from federal and state animal health officials. Since then, additional cases have been identified in Texas and New Mexico, raising concerns across the livestock industry and prompting increased surveillance efforts throughout the region.
Current Situation
As of late June, USDA has confirmed 15 cases of New World screwworm in the United States. Confirmed infestations have been found in calves, sheep, goats, and even a pet dog. Most cases have occurred in Texas, with an additional case reported in New Mexico.
The parasite remains a significant concern throughout Mexico and Central America. According to federal animal health officials, more than 185,000 animal cases and over 2,100 human cases have been reported across affected countries since the current outbreak began. USDA continues to monitor the situation closely while coordinating response efforts with international partners.
Why Screwworm Is Different
Unlike many livestock parasites that feed on dead or decaying tissue, screwworm larvae consume living flesh. Adult flies are attracted to wounds, navels of newborn animals, branding sites, dehorning wounds, tick bites, and other openings. After eggs hatch, the larvae burrow deeper into the tissue, causing severe damage and potentially leading to death if left untreated.
Cattle, sheep, goats, horses, wildlife, pets, and even humans can become infected. Because Wagyu producers often invest significant resources into genetics and herd health, early detection is especially important.
What Producers Should Watch For
Producers should monitor cattle closely for:
- Open cuts, wounds, or sores
- Maggots present in a wound
- Animals acting uncomfortable or stressed
- Separation from the herd
- Loss of appetite
- Excessive head shaking
- Strong or unusual odor from a wound
- Signs of fly infestation around wounds
Newborn calves deserve particular attention, as the healing navel can provide an entry point for infestation.
“Early detection and rapid response are our best tools. Producers should inspect their livestock regularly, report suspicious wounds immediately, and work closely with their veterinarians and animal health officials.” — Texas Agriculture Commissioner Sid Miller
Response Efforts Continue
USDA is responding with one of the largest sterile fly release programs in North America, currently dispersing approximately 100 million sterile flies per week in Mexico and along the U.S.-Mexico border. Additional surveillance, movement restrictions, and inspection efforts have also been implemented to slow the spread and protect the nation’s livestock industry.
While the current number of U.S. cases remains relatively small, animal health officials continue to emphasize vigilance. Early detection and rapid reporting remain the most important tools producers have in helping prevent further spread of this costly and destructive pest.
For the latest updates and reporting information, producers should contact their veterinarian, state animal health officials, or USDA APHIS.