A Dangerous Cattle Parasite Is Back in Texas After 60 Years

The U.S. Department of Agriculture confirmed on June 3, 2026 that a parasitic fly called the New World screwworm (Cochliomyia hominivorax) was found in a cow in Zavala County, Texas. This marks the first time the parasite has been detected in the continental United States since it was wiped out in 1966 — a 60-year gap. Federal and state officials are now activating emergency containment plans.

The detection isn't entirely a surprise. Over the past five months, this parasite has been moving northward through Mexico, getting steadily closer to the U.S. border. On May 29, authorities found it in a sheep in Mexico's Coahuila state, just 31 miles from Texas — closer than it had come during this outbreak.

What Is the New World Screwworm?

The New World screwworm is a parasitic fly whose larvae burrow into the skin and living tissue of warm-blooded animals like cattle, sheep, and horses. The infestation causes severe wounds and can kill livestock if left untreated. It got its name because the larvae leave a screw-like pattern as they tunnel through flesh. The World Organization for Animal Health considers it serious enough to require immediate reporting across borders because it spreads quickly and causes major economic losses.

The U.S. Was Already Preparing

The good news is that officials saw this coming and had already set up defenses. In February 2026, USDA Secretary Brooke Rollins and Texas Governor Greg Abbott opened a new facility at Moore Air Base in Edinburg — about 150 miles from where the parasite was just found. This facility breeds sterile male screwworms in a laboratory and releases them into affected areas.

The technique works like this: sterile male flies mate with wild females, but their offspring cannot survive. Over time, this crashes the wild population. It sounds strange, but it's been proven to work. The U.S. actually relied on a similar facility operated jointly with Panama (called COPEG) for decades to keep the parasite out of the United States by containing it in South America.

The Edinburg facility is the first domestic screwworm production center the U.S. has operated since the original eradication campaign in the 1960s. A companion dispersal facility at the same location will handle releasing the sterile flies across affected areas.

How Close Did It Get?

The outbreak in Mexico started in the south and crept northward throughout 2026. Texas Agriculture Commissioner Sid Miller first warned in January after a case appeared in González, Tamaulipas — 215 miles from Texas. By April, another case turned up 62 miles from the border in Nuevo León. Then in May, a case in Coahuila was found only 119 miles away.

Ranchers weren't caught off guard. Extension services held information sessions throughout South Texas in May to teach farmers what to watch for and how to respond if they found infected animals.

What Happens Next?

The Zavala County case triggers strict quarantine rules across South Texas. Infected animals must be isolated, and livestock in surrounding buffer zones will face enhanced monitoring. Cattle shipments from the affected area will face extra checks and paperwork before crossing state lines — a serious disruption during peak selling season.

International trading partners will also tighten restrictions on cattle and breeding materials from Texas and potentially other states. Any cattle or genetic material exported will require additional testing and proof of safety.

The outcome now depends on how fast and effectively officials can contain the outbreak. The 2017 Florida Keys outbreak showed that the system can work — officials caught it, stamped it out, and kept the damage localized. The U.S. has the experience, the facilities, and the protocols in place. Whether it works this time depends on catching and killing the parasite before it establishes itself across a broader region.

The fact that the parasite made it this far north in Mexico before crossing the border is not a sign that containment failed. It reflects how coordinated response efforts can slow and hinder an organism's advance. But once it crosses into U.S. cattle herds, the race is on.