Parasite That Can Lay Up to 3,000 Eggs in a Single Wound Detected in U.S. Wildlife for the First Time

The discovery of a flesh-eating parasite in an elk on a game ranch in Pecos County, Texas, has raised alarms among wildlife and livestock officials. The United States Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) confirmed on 21 October that the New World screwworm was found in the elk after a hunter harvested the animal. This incident marks the first identification of the parasite within U.S. wildlife, expanding the scope of an outbreak that has already affected livestock and domesticated animals across both Texas and New Mexico.

The New World screwworm is notorious for its potential to cause severe damage, as it is a parasitic fly that lays eggs in open wounds or body cavities of warm-blooded creatures. Once hatched, the larvae begin to consume living tissue, which can be fatal if not addressed promptly. The confirmation of this case adds a new and concerning dimension to an outbreak that initially began in June when the USDA reported the parasite within a calf in Zavala County, Texas. Since then, additional cases have surfaced in various livestock and dogs throughout the region.

In light of this new finding, both the USDA and Texas Parks and Wildlife Department are intensifying surveillance efforts around the affected game ranch. The Texas Animal Health Commission is also in the process of re-evaluating the boundaries of an infested zone previously established in order to enhance monitoring and response strategies. Under the regulations of this zone, animals must undergo inspection and treatment before being relocated, if necessary.

Officials have urged hunters and outdoor enthusiasts to remain vigilant for signs of infestation in wildlife. They are advised to report any animals exhibiting worsening wounds, visible maggots, or unusual behavioural patterns. The USDA has outlined specific indicators that could suggest an infestation, which include open wounds that appear to drain or progressively worsen, foul odours emanating from injuries, and changes in the animal’s behaviour such as lethargy or social withdrawal.

Dr. Theresa Kelliher, a delegate at the American Veterinary Medical Association (AVMA), emphasised the alarming efficiency of the screw-worm fly during a session in July. She noted that a single female fly can lay up to 3,000 eggs in a single wound, exacerbating the infestation potential within a short time frame. “A quarter-inch wound on Day 1 can become a five-inch wound by Day 2,” Kelliher stated, underlining the urgency of early detection and intervention.

The behavioural changes in afflicted animals can also serve as warning signs for owners and observers. Infested animals may display nervous behaviours, including head shaking, rubbing against objects, and a general refusal to eat. The flies are specifically drawn to the scent of blood, making newborns, animals recently given birth, and those recovering from surgery particularly susceptible to infestation.

The AVMA has recommended several measures to safeguard both pets and livestock from this hazardous parasite. Routine use of parasite preventatives is advisable, alongside maintaining clean and hazard-free environments in yards and animal pens. Immediate treatment of cuts, surgical sites, and fly bites with approved insecticides is also crucial in preventing infestations, thereby protecting animal health.

While the USDA has determined that the parasite does not pose a food safety risk, the occurrence of human cases associated with the screw-worm is rare but possible. Historically, the pest has been prevalent in South America and specific Caribbean regions and has been making its way northward through Central America and Mexico in recent years. A travel-related case in the U.S. in 2025 serves as a reminder of the potential for human exposure.

As animal health officials ramp up efforts to combat the spread of the New World screwworm, individuals who suspect any signs of an infestation in their animals are strongly urged to seek advice from veterinarians or contact state animal health officials without delay. The confirmation of the parasite in wildlife poses significant challenges, and swift action is essential to contain its spread and protect both animal and human populations in the affected areas.