The U.S. Department of Agriculture (USDA) has confirmed a concerning rise in New world screwworm infestations, with 41 cases identified, including 40 in Texas and one in New Mexico. This resurgence of the flesh-eating parasite has prompted swift action from federal and state officials to contain its spread.

The most recent detection occurred in a baby calf in Western Starr County marking the first case in the Rio Grande Valley. This area is now under an active quarantine, following a previous detection in neighboring Jim Hogg County which has led to stringent livestock inspections before any movement is permitted.

The nature of the New World screwworm threat

The New World screwworm despite its name, is not a worm but the larval stage of a parasitic fly (Cochliomyia hominivorax). This pest targets warm-blooded animals, laying its eggs in open wounds or natural body openings. Within hours, the eggs hatch, and the larvae begin feeding on living tissue, unlike common maggots that feed on dead or decaying matter.

As the larvae burrow deeper, the wounds enlarge and often become infected. Without prompt treatment, these infestations can be fatal. The screwworm primarily affects livestock and wildlife, posing a significant threat to Texas ranchers and animal health officials.

Animals at risk and human concerns

The screwworm infestation poses a risk to a variety of animals, including:

  • Cattle
  • Horses
  • Sheep and goats
  • Pigs
  • Deer and other wildlife
  • Dogs and, less commonly, cats

Human infestations are rare and typically occur when untreated wounds are exposed in areas where the fly is circulating. The current outbreak primarily affects livestock, wildlife, and pets. The USDA assures that the screwworm is not considered a food safety threat, as it feeds on living tissue in open wounds rather than meat intended for consumers.

Symptoms and early detection

Early detection is crucial for managing screwworm infestations. Infected animals may exhibit:

  • Wounds that worsen instead of healing
  • Bloody, thick, or foul-smelling drainage
  • Swelling around an injury
  • Visible larvae moving inside a wound
  • Signs of pain, restlessness, or unusual behavior

Veterinarians recommend regular inspections of animals after injuries, surgical procedures, branding, or any condition that creates an open wound.

The broader impact on Texas

Texas, with its vast livestock industry and abundant wildlife populations, is particularly vulnerable to screwworm infestations. A widespread outbreak could lead to rapid spread through livestock and wildlife, increased veterinary and inspection costs, economic losses for ranchers, and potential impacts on livestock trade. Additionally, wildlife, particularly white-tailed deer, could face significant threats.

The Texas Animal Health Commission and the USDA have expanded surveillance, increased monitoring of animal movement, and encouraged rapid reporting of suspected infestations. Researchers at the newly opened Knipling-Bushland U.S. Livestock Insects Research Laboratory in Kerrville are building on past successes to combat this resurgence.

Historical context and future outlook

The United States previously eradicated screwworm using the sterile insect technique a method that involved releasing millions of sterile male flies to disrupt the breeding cycle. This strategy successfully eliminated the pest from the United States and much of North America. However, the parasite remains present in parts of Central and South America, posing a continuous risk of reintroduction.

For most Texans, daily activities need not change, as the greatest risk remains to livestock, pets, and wildlife. Animal owners are advised to inspect wounds regularly, contact a veterinarian immediately if a wound worsens or contains larvae, avoid transporting animals with suspicious wounds, and report suspected infestations to state animal health officials. Hunters should also inspect harvested game for unusual wounds or signs of infestation and report suspected cases to wildlife officials.

For the latest information and guidance, visit the Texas Animal Health Commission resources, USDA Screwworm.gov and the USDA Current Status dashboard. Additionally, consult your local veterinarian or county extension office for further assistance.