One of the vital profitable eradication applications within the historical past of American public well being and agriculture achieved one thing outstanding: the entire elimination of the New World Screwworm fly (Cochliomyia hominivorax) from the US in 1966. The screwworm — named for the screw-like movement its larvae use to burrow into the residing flesh of warm-blooded animals — is taken into account one of the crucial economically and medically devastating livestock parasites within the Western Hemisphere. For many years, its absence from U.S. soil has protected American cattle, horses, wildlife, and, in uncommon instances, people, from a situation that may be deadly if untreated.
That safety was breached in 2026. USDA Animal and Plant Well being Inspection Service (APHIS) confirmed the detection of New World Screwworm in cattle in Maverick County, Texas — a county alongside the Rio Grande in southwest Texas that borders Mexico’s Coahuila state. The detection adopted affirmation of the parasite’s re-emergence in livestock in Mexico in 2024 and 2025, the place USDA and Mexican authorities have been engaged in emergency sterile insect approach (SIT) operations to stop northward unfold. USDA closed the US-Mexico border to cattle imports in November 2024 following the preliminary Mexican detections, citing the danger of screwworm importation — a choice that proved prescient.
CDC confirmed on June 12, 2026 that it’s supporting the USDA and Texas Division of State Well being Providers in an ongoing investigation — an announcement that underscores each the agricultural and the human well being dimensions of this re-emergence.
What New World Screwworm Truly Does
The New World Screwworm fly (C. hominivorax) is a parasitic fly species that lays eggs completely in recent wounds, pure physique openings, or moist, heat pores and skin surfaces of residing warm-blooded animals. After hatching, the larvae burrow deeply into residing tissue — spiraling as they feed, which is the supply of the screwworm identify. Not like widespread maggots that decompose already-dead tissue, screwworm larvae eat solely residing flesh. The infestation, referred to as myiasis, grows quickly: a single wound can appeal to a number of feminine flies, every laying 200 to 400 eggs, and the ensuing mass of larvae can destroy giant portions of residing tissue in days.
In livestock, screwworm infestations kill cattle, horses, deer, pigs, sheep, and goats when untreated. The preliminary wound — which may be as small as a tick chew, a scratch, or a pure orifice — turns into a quickly enlarging, foul-smelling cavity teeming with larvae. Animals in screwworm-endemic areas with out enough veterinary consideration can die inside 7 to 14 days of preliminary infestation. The financial destruction in the course of the period of lively US screwworm infestation within the early twentieth century was estimated at tons of of hundreds of thousands of {dollars} yearly.
For people, screwworm myiasis is much less widespread however effectively documented. Instances have been reported in worldwide vacationers getting back from Latin America and in people with open wounds in areas of screwworm exercise. Infestations can happen in wounds, nasal passages, ear canals, and in extreme immunocompromised sufferers, in ulcerated pores and skin. Human screwworm myiasis is treatable with topical and mechanical elimination of larvae plus acceptable wound care, however requires immediate recognition and intervention.
The Eradication Program That Could Must Restart
The unique US screwworm eradication marketing campaign, carried out collectively between the US and Mexico from the Nineteen Fifties by means of the Nineteen Sixties, used a method referred to as the Sterile Insect Method (SIT): mass rearing of screwworm flies adopted by radiation-induced sterilization and mass aerial launch of sterile male flies into the setting. Sterile males compete with wild males for females, however their matings produce no offspring. Because the proportion of sterile males within the setting will increase, the wild inhabitants collapses. The identical SIT strategy is now being utilized in an emergency vogue in Mexico to create a organic barrier in opposition to northward unfold.
USDA APHIS maintains a standing New World Screwworm nationwide response plan for precisely this state of affairs. The detection of screwworm in Texas cattle triggers rapid tracing of animal actions, quarantine of affected premises, investigation of the wound website and larvae, laboratory affirmation, and deployment of emergency SIT operations to the affected space.
Any cattle producer, rancher, veterinarian, or wildlife supervisor in Texas and neighboring states who observes a wound in a warm-blooded animal — cattle, horses, deer, canines, goats — with uncommon tissue destruction, foul odor, or seen larvae ought to contact USDA’s Animal Illness Hotline at 1-866-536-7593 instantly.
Often Requested Questions
Q: What’s the New World Screwworm?
A: Cochliomyia hominivorax is a parasitic fly that lays eggs within the residing flesh of warm-blooded animals. Its larvae burrow into and eat residing tissue, inflicting infestations that may be quickly deadly in livestock and sometimes have an effect on people.
Q: When was screwworm eradicated from the US?
A: 1966, by means of a decades-long program utilizing the Sterile Insect Method — mass launch of radiation-sterilized male flies to break down the wild inhabitants. This system was one of the crucial profitable pest eradication campaigns in US historical past.
Q: How did screwworm return to Texas in 2026?
A: Following re-emergence in Mexican livestock in 2024 and 2025, cattle crossing the US-Mexico border into Texas served as an importation pathway. The US had closed the border to cattle imports in November 2024 in response, however the detection occurred regardless of these measures.
Q: Can people get screwworm?
A: Sure, although hardly ever. Human myiasis happens when fly larvae infest open wounds, pure physique openings, or pores and skin surfaces. It’s treatable however requires immediate identification and elimination. Vacationers to Latin America with open wounds ought to take specific care.
Q: What ought to ranchers or farmers do if they think screwworm?
A: Contact the USDA Animal Illness Hotline instantly at 1-866-536-7593. Don’t deal with the wound with out veterinary steerage, as correct pattern assortment for laboratory affirmation is crucial earlier than the wound is cleaned.
