First human case of flesh-eating parasite detected in the US; Symptoms, risk factors, and safety measures to follow

In a startling development, US health officials have confirmed the first human case of the flesh-eating parasite, the New World screwworm (Cochliomyia hominivorax), in decades. Detected in Maryland on August 4, 2025, the individual had recently returned from El Salvador. Although such infections are rare, they can cause severe tissue damage if untreated. Although the risk to the general public remains very low, as per experts, this incident has reignited prevention efforts and prompted renewed action to protect both human health and livestock.


What is the new world screwworm?

The New World screwworm is not a bacterium or virus, but a parasitic fly whose females lay hundreds of eggs in open wounds or natural orifices of warm-blooded animals, cattle, wildlife, and sometimes humans. Upon hatching, the larvae (maggots) burrow into living flesh, causing intense pain and potentially fatal tissue destruction. The larvae eventually drop to the ground to pupate and grow into adult flies. The larvae's feeding mechanism has been likened to a screw boring into wood, hence the gruesome name. This life cycle typically spans around 20 days.

Historically, the screwworm was eradicated in the United States of America in the 1960s using a sterilization program involving the release of sterile male flies, a highly effective biological control method.


The Maryland case: What happened?

This recent case involves a Maryland resident who had traveled to El Salvador, a country currently experiencing outbreaks among livestock. The US Department of Health and Human Services confirmed the diagnosis on August 4, following laboratory confirmation by the CDC. Conflicting reports earlier suggested Guatemala as the origin, but updated information pointed to El Salvador.


The infected individual has thankfully recovered, and authorities have found no evidence of transmission to others or to animals. Officials have emphasized that the public health risk remains very low.


Symptoms to watch for

Infestations typically start in wounds, nasal passages, eyes, or mouth, where screwworms lay their eggs. As larvae develop, symptoms of screwworm infestation in humans include:

Severe pain, often with visible or palpable maggots

A feeling of movement under the skin

Potentially deep tissue destruction if left untreated

The site may be red, swollen, and painful, potentially draining fluid or bleeding

The infection is distinct from bacterial "flesh-eating" diseases like necrotizing fasciitis, though both can involve rapid tissue loss. Without timely intervention, the infestation can escalate to severe tissue destruction or death.



Risk factors

Though rare in humans, certain individuals face a higher risk:

Travel to outbreak regions like Central America or southern Mexico

Exposure to livestock or wildlife, or outdoor environments with open wounds

Having unclean/uncared-for wounds exposed to flies, particularly those in rural or livestock-heavy areas

Those working with or near animals without protective measures



Current response and safety measures

US authorities have quickly responded with a comprehensive plan to prevent further spread and protect agriculture and public health:

Sterile fly program revival: The USDA is reviving the sterile insect technique, which is the mass breeding and release of sterilized male screwworm flies to disrupt reproduction. This successful method dates back to the 1960s when the parasite was eradicated in the US. Plans are underway to reopen a sterile male fly facility in Texas, able to produce hundreds of millions of sterile flies weekly, to disrupt screwworm breeding, echoing past eradication methods.

Border and livestock measures: The USDA has suspended some livestock imports from Mexico, especially from outbreak regions, as part of preventive controls.

Surveillance enhancements: Officials are deploying surveillance tools, such as traps, mounted patrols, and detector dogs, to monitor for any emerging infestation near the US-Mexico border.

Emergency animal treatment approvals: The FDA has issued emergency animal health authorizations for drugs used to treat or prevent screwworm infestations in livestock.


How you can stay safe

To stay protected:

Protect wounds: Keep any scratches or cuts clean, covered, and properly treated.

Be aware when traveling: If you go to areas with known screwworm outbreaks, avoid exposing wounds and seek medical help if symptoms arise. Cover any open wounds, wear protective clothing, and avoid outdoor sleeping in rural zones.

Seek prompt care: Regularly check wounds or skin for unusual swelling or movement. Unusual pain, movement under your skin, or visible larvae should trigger immediate medical evaluation. Seek prompt medical care if symptoms arise. Early removal and sterilization are key.

Stay informed: Agricultural workers, veterinarians, and healthcare providers should stay alert and report suspect cases quickly.


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