Texas and federal animal health officials have confirmed New World screwworm in a three-week-old calf in Zavala County, a South Texas detection that triggered quarantine and surveillance measures aimed at keeping the fly-borne parasite from spreading.
The Texas Animal Health Commission said it received confirmation on June 3, 2026, after a sample from a calf with an umbilical lesion was identified as New World screwworm by the National Veterinary Services Laboratories in Ames, Iowa. TAHC said there were no further confirmed detections in animals in Texas at the time of its notice.
USDA's Animal and Plant Health Inspection Service also confirmed the detection in a bovine in Zavala County. Federal officials said the affected animal was a three-week-old calf and that larvae were identified in its umbilical area.
What New World screwworm is
New World screwworm is a parasitic fly, not a worm. Its larvae can infest livestock, pets, wildlife and, in rare cases, people. According to CDC and Texas DSHS guidance, female flies lay eggs on or near open wounds or body openings such as the eyes, ears, nose, mouth, genitals or the navel of newborn animals. When the eggs hatch, larvae burrow into living tissue and feed there.
That is why officials treat the pest as an urgent animal-health and public-health concern. DSHS says there is no human-to-human transmission of New World screwworm infestation. The infestation requires the fly life cycle, beginning with eggs laid by a female fly.
What Texans should watch for
DSHS said people should seek immediate medical care if they notice a suspicious lesion or believe they may have contracted screwworm. The agency said providers should consider New World screwworm in patients who have traveled in areas with animal or human cases and who have a painful, foul-smelling wound containing visible larvae, or a deep wound with extensive tissue damage.
Anyone who sees or feels larvae in a wound should cover the wound and contact a health care provider immediately, according to DSHS. The agency warns people not to try to remove or dispose of eggs or larvae themselves because improper removal can cause further tissue damage and mishandled live larvae could create a risk of spread.
For animals, DSHS says signs can include irritation or discomfort, the smell of decay around a wound or body opening, open wounds or sores, and visible larvae. Pet and livestock owners who suspect an infestation should contact a veterinarian quickly. Livestock and pet cases should be reported to TAHC.
State and federal response
USDA said response steps include forming a unified Incident Command Team with TAHC, establishing a 20-kilometer infested zone around the detection, implementing quarantines and movement controls, increasing trapping, conducting wildlife surveillance and carrying out targeted local outreach. USDA also said officials are expediting targeted release of sterile New World screwworm flies, a technique intended to reduce reproduction.