New World Screwworm Expansion in Texas Raises Alarms for Livestock Producers Across the South

AUSTIN, Texas - Veterinary officials and livestock producers are sounding the alarm as confirmed cases of the New World screwworm continue to expand across parts of Texas, marking the most significant U.S. spread of the parasite in decades. The flesh‑eating larvae, known scientifically as Cochliomyia hominivorax, pose a severe threat to cattle, horses, wildlife, and even pets, prompting state and federal agencies to intensify surveillance and containment efforts.

The New World screwworm is infamous for its ability to infest living tissue. Female flies lay eggs in wounds-sometimes as small as a tick bite or branding mark-and the hatched larvae burrow deeper in a corkscrew pattern, feeding on the host's flesh. Without rapid treatment, infestations can become fatal.

Recent Spread and Confirmed Cases

Texas animal‑health officials began investigating suspected screwworm cases earlier this summer after ranchers in South Texas reported unusual wound infestations in cattle and deer. Laboratory testing confirmed multiple positive cases, initially concentrated near the Rio Grande corridor. Over the past several weeks, however, detections have expanded northward and eastward, raising concerns that the parasite may be establishing a broader foothold.

The Texas Animal Health Commission (TAHC) has not yet released exact case counts, but field veterinarians report a "clear uptick" in confirmed infestations across ranches in the southern half of the state. Wildlife biologists have also documented screwworm activity in white‑tailed deer, feral hogs, and exotic game species-an indicator that the parasite is circulating beyond domestic herds.

Why the Expansion Matters

The New World screwworm was eradicated from the United States in 1966 through a landmark sterile‑fly program. Since then, only rare, isolated introductions have occurred-typically linked to imported animals or wildlife migrating from affected regions. A sustained expansion inside Texas represents a serious threat to livestock industries across the South, especially states like Alabama, where cattle operations, deer populations, and warm weather create ideal conditions for parasite spread.

If the screwworm continues moving north or east, producers could face:

Severe animal losses from untreated infestations

Costly veterinary interventions including wound care, larvicides, and quarantine

Movement restrictions on cattle, horses, and wildlife

Economic strain on ranches already dealing with heat stress, drought, and rising feed costs

Response Efforts Underway

Federal and state agencies have activated enhanced surveillance zones, deploying traps, conducting field inspections, and working with ranchers to identify suspect cases quickly. The USDA's Sterile Insect Release Program-still active in Panama as a continental barrier-is preparing contingency plans should Texas require emergency fly‑suppression operations.

TAHC is urging producers to inspect animals daily, especially during peak fly season. Even minor wounds should be treated immediately, and any suspicious infestation-characterized by foul odor, deepening wounds, or visible larvae-should be reported to veterinarians or state officials.

What Producers Should Watch For

Livestock owners should monitor for:

Unexplained wound deterioration

Animals separating from the herd

Visible maggots in wounds

Sudden weight loss or lethargy

Wildlife carcasses showing signs of screwworm activity

Early detection is critical. When caught quickly, screwworm infestations can be treated with larvicides, wound debridement, and strict isolation to prevent fly spread.

Looking Ahead

Experts warn that Texas may face a months‑long battle to contain the parasite, especially if warm weather persists into fall. While there is no evidence yet of spread into Louisiana, Arkansas, or Alabama, veterinary officials across the Southeast are preparing guidance for producers should the situation escalate.

For now, Texas ranchers remain on high alert. As one South Texas cattleman put it, "We beat screwworm once. We can beat it again. But it's going to take every rancher paying attention."