In less than a week, federal officials confirmed five cases of New World screwworm in Texas livestock by Monday, a pest declared eradicated from the U.S. decades ago. These flesh-eating larvae are now burrowing into calves, dogs, and goats across the state. The United States has been free of New World screwworms for decades, but new cases are rapidly emerging and spreading across multiple states, challenging long-standing biosecurity protocols.
A new NWS case was confirmed in a calf in La Salle County, Texas, bringing the total cases in the United States to six, according to Texas Public Radio. This rapid increase and geographic spread of confirmed cases make intensified federal and state control measures, including widespread surveillance and potential animal movement restrictions, likely to prevent a full-scale re-establishment of the pest.
A Decades-Old Threat Returns
New World Screwworm (NWS) larvae burrow into the flesh of living animals, feeding on tissue and causing severe wounds that can lead to death if untreated, according to aphis. This parasitic behavior directly threatens livestock health and the economic viability of the agricultural industry. After decades of successful eradication, this re-emergence forces ranchers to brace for widespread losses and increased veterinary costs, suggesting a significant setback for U.S. biosecurity.
A Rapid Resurgence: Tracing the Outbreak
- June 3, 2026: New World Screwworm (NWS) was confirmed in a calf in Zavala County, Texas, according to the Texas Animal Health Commission.
- Early June 2026: A NWS case has been detected in a calf in La Pryor, Texas, approximately 30 miles from the US-Mexico border, according to BBC News.
- Monday, June 8, 2026: Federal officials confirmed three additional cases of NWS, including two in Texas. This brought the state's total to five confirmed detections in less than a week, as reported by Texas Public Radio.
- Tuesday, June 9, 2026: A new NWS case was confirmed in a calf in La Salle County, Texas, bringing the total cases in the United States to six, according to Texas Public Radio.
These initial detections near the US-Mexico border and subsequent rapid confirmations suggest a potential re-entry point and swift internal spread. The escalating challenge for control measures is evident, raising questions about border biosecurity effectiveness.
The Expanding Front: Cases Across State Lines
Beyond initial detections, cases emerged in a calf in La Salle County, a dog in Andrews County, and a goat in Gillespie County, according to The Texas Tribune. The dog in Andrews County originated from Lea County, New Mexico, marking that state’s first screwworm case. This cross-state transmission via a domestic pet, combined with the variety of affected hosts (livestock and pets), reveals a critical vulnerability in US biosecurity. The swift confirmation of six screwworm cases across two states within a week indicates that US biosecurity is reacting to an established, mobile threat rather than preventing its initial entry, a critical failure in proactive defense.
Urgent Measures for Screwworm Control
The USDA confirmed three additional cases of New World screwworm in livestock—two in Texas and one in New Mexico—according to The Guardian. These ongoing confirmations demand immediate, aggressive surveillance and control to prevent the screwworm from establishing a permanent foothold. With cases spanning from the US-Mexico border to central Texas and New Mexico, this re-emergence is not isolated. It presents a widespread, multi-front challenge that threatens to overwhelm localized containment and may necessitate a national emergency response. The involvement of diverse livestock and domestic animals means economic and animal welfare risks extend beyond traditional ranching, requiring a broader public health and agricultural response that includes pet owners. The USDA and state agricultural departments face pressure to demonstrate effective control measures by Q3 2026, or risk an escalating crisis for ranchers and pet owners across affected states.
Frequently Asked Questions About Screwworms
What are the symptoms of screwworms in animals?
Animals infested with screwworms typically exhibit a wound with a discharge that attracts adult female flies, which then lay eggs in the wound. Other symptoms include restlessness, reduced appetite, and a distinctive foul odor from the infested area. Without treatment, the continuous feeding of larvae can lead to severe tissue damage and death.
How are screwworms spread?
Screwworms spread when the adult female fly lays eggs in open wounds of warm-blooded animals. The larvae hatch and feed on living tissue, then drop to the ground to pupate. After emerging as adult flies, they can travel several miles, mating and continuing the cycle, with animal movement, including domestic pets, significantly aiding dispersal.
Can humans get screwworms?
Yes, humans can contract myiasis from screwworms, although it is rare. Infestations typically occur when flies lay eggs in open wounds or mucous membranes. Symptoms are similar to those in animals, involving larvae burrowing into flesh, and require medical intervention for removal and treatment to prevent further tissue damage.
