Screwworm case confirmed next door to Llano County

A confirmed New World screwworm infection was documented next door to Llano County on Monday, June 8, just a few days after the flesh-eating parasite was first documented in the United States. Federal, state, and local authorities are cautioning Texas residents to keep a close eye on livestock, pets, and wildlife amidst the outbreak. 

The first U.S. case was documented on June 3. Since then, four cases have been confirmed– one in New Mexico and three in Texas– including a goat in Gillespie County on Monday. 

“This situation is evolving, and we expect new information to emerge as our investigation continues,” reads a statement from United States Department of Agriculture Under Secretary for Marketing and Regulatory Programs Dudley Hoskins. “USDA is committed to sharing what we learn quickly, accurately, and transparently so animal owners and local communities have the information they need to stay vigilant. We are working closely with our partners in New Mexico, Texas, and across the region to ensure we identify, contain, and respond to any potential cases as swiftly as possible.”

The New World screwworm is the larva of the New World screwworm fly. These flies lay their eggs on open wounds or openings in the bodies of warm-blooded animals. Once the eggs hatch, the screwworms burrow or “screw” into the flesh of the host animal causing tissue damage, infection, stress, and in some cases death. This is of special concern to ranchers due to potential impacts on livestock, and to populations of wild mammals, like white-tailed deer herds. The bug can also infect pets, and people in some instances. 

A northward progression of the New World screwworm has been on the U.S.’s radar since 2023, when infections were observed in Central America. Federal and state governments began warning about a possible U.S. outbreak in 2025. 

According to the USDA, there were 2,077 documented active cases in Mexico as of June 3, and 4,214 total cases documented in that country between Sept. 20, 2025 and June 3, 2026. 

Background

The fly was a problem in the United States for decades, first becoming a threat in the 1930s, although it had been in the American Southwest since at least 1842. The pest was effectively eradicated in the United States in the 1980s, but not without some devastating consequences. In 1976 alone, the Texas economy lost about $329.59 million due to livestock deaths from a New World screwworm outbreak. Accounting for inflation, that would have been $1.8 billion in 2024. About 1.48 million cattle were reportedly infected in that outbreak. 

Since eradication in the 1980s, screwworms have had a minimal impact on U.S. ranchers, but even the threat of a potential outbreak is enough to raise the alarm. The U.S. Department of Agriculture estimates a screwworm outbreak could cost the Texas cattle industry $1.8 billion in annual losses and up to $10.6 billion in national economic damages.  

Combating the worm

The New World screwworm was originally eradicated in the United States using the “sterile insect technique” which is done by releasing massive numbers of sterilized male flies into infected areas, leading to infertile eggs and breaking the screwworm’s breeding cycle. 

“Targeted releases of sterile (New World screwworm) flies are being expedited to eliminate any reproducing populations in the area associated with the detection,” reads the June 3 TPWD media release. “When combined with enhanced surveillance, movement restrictions, prompt treatment of wounds, and education and outreach efforts, the sterile insect technique is a proven and effective tool for controlling and eradicating this pest.”

The United States Department of Agriculture is already releasing large numbers of sterile flies along the U.S.-Mexico border and building a dedicated sterile fly production facility at Moore Air Base in Edinburg, Texas. 

Resources

All southern ports of entry are currently closed to livestock trade according to the USDA.

See a gallery of images from the USDA showing what New World screwworm infections may look like at this link. The images have not been included in the article due to their graphic nature. 

Signs of New World screwworm infection include:

• Feeling larva move or seeing maggots within a skin wound or sore, or in the ears, nose, eyes, or mouth
• Painful skin wounds or sores that worsen within a few days
• A foul-smelling odor from the site of the infestation
• Bleeding from open sores

Prevention methods:

• Make sure pets traveling internationally are inspected for screwworm
• Handle livestock carefully and inspect pens and equipment for sharp objects that can cause wounds
• Treat the umbilical cords of newborn animals and all wounds immediately with an approved insecticide
• Protect pets and livestock from other wound-causing parasites such as ticks

If you are concerned about a possible New World screwworm infection, contact your local veterinarian or the Texas Animal Health Commission at 1-800-550-8242. 

dakota@thepicayune.com