The rare parasite known as the New World screwworm has now infected a human in the U.S.
Health officials have confirmed the first U.S. human case of a rare flesh-eating parasite called the New World screwworm. The parasite, which feeds on living tissue, has historically been a serious threat to livestock across the Americas but only rarely infects people.
According to the U.S. Department of Agriculture (USDA), outbreaks in animals were once widespread before eradication programs nearly eliminated the pest in the United States. The new case highlights how dangerous the parasite can be and why scientists are urging vigilance to prevent its spread back into vulnerable ecosystems and human populations.
1. What exactly is the New World screwworm?
The New World screwworm is the larval stage of a parasitic fly (Cochliomyia hominivorax). Unlike common maggots that feed on decaying matter, screwworm larvae eat living tissue, making them especially destructive.
Female flies lay their eggs in open wounds or sores. When the larvae hatch, they burrow deeper into the flesh, causing painful and often life-threatening infections. For decades, the parasite was a major concern for livestock across the Americas, costing farmers millions until eradication programs brought it under control in the U.S.
2. Why this first human case matters
Human infections are rare, but when they occur, they can be severe. The confirmation of the first U.S. human case is alarming because it signals that the parasite may still pose risks despite decades of eradication efforts.
The case demonstrates that even diseases thought to be eliminated in a region can resurface under the right conditions. Experts say it’s a reminder of how fragile eradication programs can be and why continued surveillance is essential.
3. The parasite’s history in the United States
The New World screwworm was once widespread in the southern U.S., devastating cattle and wildlife populations. By the mid-20th century, infestations were so common that they caused severe economic losses for farmers.
In response, the USDA launched an ambitious program using sterilized male flies to collapse populations. The campaign was successful, and by 1966 screwworms were declared eradicated from the U.S. The success was hailed as one of the greatest victories in veterinary science, but the new human case shows the threat isn’t gone.
4. How the parasite infects humans
While screwworms typically target livestock, humans can become accidental hosts. Infection usually begins when a fly lays eggs in an open wound, surgical site, or even inside the nose or ears.
Once hatched, the larvae feed aggressively on living tissue, worsening the wound and making recovery difficult. Without swift treatment, infections can spread and lead to serious complications. Doctors must remove the larvae and treat the patient with medication to prevent reinfestation.
5. The case that alarmed health officials
According to reports, the confirmed U.S. case involved an individual diagnosed after doctors discovered the parasite inside a wound. The infection was verified using laboratory testing, confirming it as the first human case in the country.
While the patient received treatment, officials are working to trace where the infection originated. The incident underscores how easily parasites can cross borders and appear where they were thought to be eliminated.
6. Symptoms people should know
Early symptoms of screwworm infection can resemble those of a typical wound—pain, swelling, or irritation. But unlike normal infections, screwworm larvae burrow deeper over time, enlarging the wound instead of allowing it to heal.
Patients may also notice a foul odor or movement within the tissue. Left untreated, infestations can cause severe tissue damage, systemic illness, or even death. Awareness is key because the earlier treatment begins, the greater the chance of recovery.
7. The role of livestock in spreading screwworms
The parasite primarily affects cattle, sheep, and other animals, where open wounds provide an easy site for flies to lay eggs. Infected animals can suffer immense pain and, if untreated, may die from the infestation.
When livestock populations are infected, the risk to humans increases. That’s why agricultural agencies stress the importance of ongoing monitoring. Protecting herds isn’t just an economic issue—it’s also a public health safeguard.
8. Why eradication efforts must continue
The U.S. eradication campaign was groundbreaking, but experts warn that complacency is dangerous. Border surveillance programs and sterile fly releases must be maintained to keep screwworms from reestablishing.
Reintroductions have occurred before in parts of Central and South America, showing how quickly populations can rebound. The first U.S. human case makes clear that vigilance must remain high. Eradication is not a one-time achievement—it’s an ongoing responsibility.
9. Global risks of screwworm outbreaks
Outside the U.S., screwworms still pose a serious problem in parts of South America and the Caribbean. Outbreaks have been reported in recent decades, costing farmers and governments millions in control measures.
As climate change alters ecosystems and global travel increases, the risk of screwworm spread grows. Experts say international cooperation is vital, since parasites don’t respect borders. A single introduction can undo decades of work if not caught early.
10. What people can do to protect themselves
For most Americans, the risk of screwworm infection remains extremely low. Still, simple precautions can help. Cover wounds properly, seek prompt medical care for injuries, and be alert when traveling in areas where the parasite still exists.
If infections occur in livestock, report them immediately to authorities. Swift action prevents outbreaks and protects both humans and animals. Experts stress that awareness is the strongest line of defense against this flesh-eating parasite.