A parasite that vanished from American soil more than half a century ago has returned.
A parasite eradicated from American soil in the 1960s has returned to Texas, where a second confirmed screwworm case has prompted Governor Abbott to expand a disaster declaration and Canada to ban Texas cattle imports. The screwworm — larvae that burrow into living flesh through open wounds — once required a generation of coordinated biological warfare to defeat, and its reappearance asks whether the tools of that era can hold in a warmer, more interconnected world. What was once a hard-won continental victory now stands as a fragile thing, tested again by the persistence of nature and the porousness of borders.
- A flesh-eating parasite absent from the U.S. for over sixty years has now been confirmed twice in Texas within weeks, transforming an isolated incident into a spreading emergency.
- Canada has already moved to ban Texas cattle imports, sending a financial shockwave through ranching communities already operating on thin margins.
- Screwworm larvae do not distinguish between cattle, deer, wild pigs, or humans — any open wound is an entry point, and infected wildlife become untreatable, mobile carriers.
- Texas summer heat is arriving, creating ideal conditions for fly reproduction and threatening to accelerate the outbreak before containment can take hold.
- Governor Abbott's expanded disaster declaration unlocks broader state powers, while veterinarians and animal health officials intensify surveillance in a race against the parasite's spread.
A parasite that vanished from American soil more than half a century ago has returned. Texas confirmed a second screwworm case this week, escalating what began as an isolated discovery into a spreading agricultural and public health emergency. Governor Greg Abbott expanded the state's disaster declaration — a formal signal that the threat is no longer contained to a single animal or location.
Screwworms are the larvae of a particular fly species. Once they enter an open wound, they burrow into living flesh and feed, creating the spiral pattern that gave the parasite its name. The infestation is agonizing and, left untreated, fatal. The United States had been free of it since the 1960s, when a successful campaign of releasing sterile male flies disrupted breeding cycles and drove the parasite from the continent. That long-standing victory now appears to be unraveling.
The first Texas case emerged weeks earlier, suggesting the parasite had crossed from Mexico, where it remains endemic. Screwworms do not discriminate between species — cattle, deer, javelinas, and other animals with open wounds are all vulnerable. Canada responded swiftly with a ban on Texas cattle imports, adding financial pressure to ranchers already facing a biological crisis. Wildlife, unlike livestock, cannot be systematically treated, making infected deer or wild pigs mobile reservoirs capable of carrying the parasite across county and state lines.
The expanded disaster declaration gives authorities broader powers to coordinate containment, but the window of vulnerability is narrowing. Texas summer is arriving, and warm conditions favor fly reproduction. The question now is whether the tools that worked sixty years ago — sterile fly releases, rapid response, regional coordination — can succeed again in a more complex and interconnected world. The second confirmed case suggests the answer will not come easily.
A parasite that vanished from American soil more than half a century ago has returned. Texas confirmed a second case of screwworm infection this week, escalating what began as an isolated discovery into a spreading public health and agricultural emergency. Governor Greg Abbott expanded the state's disaster declaration in response, a formal acknowledgment that the threat extends beyond a single animal or location.
Screwworms are the larvae of a particular fly species. Once they enter an open wound—on livestock, wildlife, or theoretically a human—they burrow into living flesh and feed. The infestation is agonizing and, left untreated, fatal. The parasite earned its colloquial name from the spiral pattern it creates as it tunnels through tissue. For decades, the United States had been free of it. The last confirmed case on American soil occurred in the 1960s, the result of a successful eradication campaign that relied on releasing sterile male flies to disrupt breeding cycles. That victory, hard-won and long-standing, now appears to be unraveling.
The first Texas case emerged weeks before this second confirmation, signaling that the parasite had crossed the border from Mexico, where it remains endemic. The discovery triggered immediate concern among ranchers and wildlife managers. Screwworms do not discriminate between species. Cattle, deer, javelinas, and other animals with open wounds become vulnerable. A single infected animal can harbor dozens or hundreds of larvae. The economic and ecological consequences ripple outward quickly.
Canada responded swiftly by banning cattle imports from Texas, a trade restriction that underscores the seriousness with which neighboring countries view the outbreak. Livestock commerce depends on disease-free status; a single confirmed case in a major cattle-producing state threatens market access and prices. For Texas ranchers already managing thin margins, the ban adds financial pressure to an already urgent biological crisis.
The expanded disaster declaration gives state authorities broader powers to coordinate response efforts, mobilize resources, and implement containment measures. It signals preparation for the possibility that more cases will be found as surveillance intensifies. Veterinarians and animal health officials are likely increasing inspections of livestock and wildlife, looking for signs of infection. Treatment exists—topical insecticides and antibiotics can kill the larvae and prevent secondary infection—but only if the infestation is caught and identified.
What makes this moment particularly precarious is the window of vulnerability. The parasite thrives in warm climates, and Texas summer is arriving. Conditions are becoming ideal for fly reproduction and transmission. The longer the outbreak persists uncontained, the greater the chance it establishes itself more broadly across the state and potentially beyond. Wildlife, which cannot be treated the way livestock can, poses an additional complication. A infected deer or wild pig becomes a mobile reservoir, capable of spreading the parasite across county lines and state boundaries.
The return of screwworm after sixty years of absence represents a failure of the biological barriers that once protected the continent. Climate change, shifting wildlife patterns, and the sheer persistence of the parasite in Mexico's warm regions all likely played roles. The question now is whether the tools that worked in the 1960s—sterile fly releases, coordinated regional efforts, rapid response to new cases—can work again in a more complex, interconnected world. The second confirmed case suggests the answer will not come easily.
Notable Quotes
The parasite earned its colloquial name from the spiral pattern it creates as it tunnels through tissue.— Biological description of screwworm behavior
The Hearth Conversation Another angle on the story
Why does a parasite that was eradicated sixty years ago suddenly matter now?
Because it never actually left the Western Hemisphere. It stayed in Mexico, waiting in the warm climate. One infected animal crossing the border, or one infected animal brought across, and suddenly it's back in Texas. The eradication was real, but it was always conditional on keeping it out.
What does the parasite actually do to an animal?
It enters through any open wound—a cut, a scrape, an insect bite. The larvae burrow into living tissue and feed. The animal feels it. It's painful, and if you don't treat it, the infection spreads and the animal dies. For wildlife, there's no treatment option. A deer with screwworms just suffers until it doesn't.
Why is Canada banning Texas cattle?
Because if even one infected animal makes it into Canada, they have the same problem Texas has now. Trade is built on trust that animals are disease-free. One case breaks that trust. The ban is both practical and protective.
Can humans get it?
Theoretically, yes. If someone has an open wound and a screwworm fly lays eggs in it, the larvae can infect that wound just like they would an animal's. It's rare, but it's possible. That's part of why this matters beyond just ranching.
What does the disaster declaration actually do?
It gives the state more authority to act quickly—to move resources, coordinate across agencies, maybe even restrict animal movement if needed. It's a signal that this is serious and that normal procedures might not be fast enough.
Is this going to spread?
That depends on how fast they find and treat infected animals, and how well they can keep the parasite from establishing itself in wildlife. Summer is coming, which is when the flies reproduce most actively. The next few weeks matter a lot.