Potentially deadly, flesh-eating parasite breaches Texas border threatening local wildlife and livestock
The USDA confirmed the parasite was discovered in the umbilical area of a three-week-old calf in Zavala County, prompting immediate state and federal containment action.
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A potentially deadly, flesh-eating parasite has officially crossed into Texas. The U.S. Department of Agriculture (USDA) confirmed Wednesday that the New World screwworm was detected in Zavala County, posing a serious threat to local livestock and wildlife, and, in rarer cases, to humans and birds.
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According to the USDA, the screwworm larvae were discovered in the umbilical area of a three-week-old calf. Officials confirmed that there have been no other detections so far.
State and federal agriculture officials are taking immediate action to combat the threat.
The New World screwworm is a parasitic fly species that feeds on the tissue or flesh of warm-blooded animals and people to complete parts of its life cycle, the Centers for Disease Control and Prevention (CDC) said.
The infestation begins when adult females are attracted to open wounds and body openings, such as the eyes, nose, mouth or genitals.
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They lay their eggs — usually 200 to 300 at a time — in these vulnerable areas, which quickly hatch into maggots that burrow into the wound or opening to feed on the flesh. After about seven days of feeding, the larvae then drop to the ground, pupate and eventually emerge into an adult screwworm.
Larvae, at stage 3 of their development, are in bio-waste. (GUILLAUME SOUVANT/AFP via Getty Images / Getty Images)
This is not only harmful to the infected but also leads to economic loss.
Recently, in April, the NWS was confirmed in a young calf in the Mexican state of Nuevo León, just 60 miles from the Texas border.
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State officials immediately sounded the alarm. "It is a direct and imminent threat to Texas, and we are treating it that way. This is a high-stakes situation for our ranchers, our livestock industry and our food supply, and we are moving aggressively to stay ahead of it," Texas Agriculture Commissioner Sid Miller said.
The New World screwworm is a species of the parasitic fly that completes part of its lifecycle by feeding on the tissue or flesh of warm-blooded animals and people. (USDA / FOX Weather)
That said, in 2023, Panama and Costa Rica identified an outbreak of the New World screwworm. Since then, all countries in Central America and Mexico have reported cases among animals and people.
In 2025, a Maryland resident traveling back to the U.S. from El Salvador contracted the parasite. The patient fully recovered, and no further spread was reported from that case.
The incident marked the first confirmed human case in the U.S. in years.
When contracting the parasite, human patients typically experience symptoms such as feeling or seeing maggots in the skin, a foul-smelling odor from the site of infection, and bleeding open sores, the CDC said.
The USDA is urging all residents in the area to monitor pets and livestock for indications of NWS by looking for draining or enlarged wounds and signs of discomfort.
Cattle are detained in the pens of the Chihuahua Regional Livestock Union. (Christian Torres/Anadolu via Getty Images / FOX Weather)
Residents should also look out for screwworm larvae around open wounds and body openings. If signs are present, "Contact your state animal health official or USDA area veterinarian in charge immediately," the USDA said.
To contain and eradicate the pest, officials are executing an aggressive response playbook that includes implementing quarantines, forming a unified Incident Command Team with state animal health authorities, expediting the release of sterile flies, and increasing trapping along the border.
Under Secretary for Marketing and Regulatory Programs Dudley Hoskins highlighted that the USDA has invested in the best tools needed to combat the NWS threat since cases started increasing. "The United States has defeated this pest before, and we will do it again," he said.
To learn more about the New World screwworm and ongoing federal containment efforts, visit Screwworm.gov.