First human case of flesh-eating parasite detected in the US; How is it different from the flesh-eating bacteria

In a rare and unsettling turn of events, the first human case in years of a flesh-eating parasite, called the New World screwworm, has been confirmed in the United States of America. Detected in a Maryland traveler who recently returned from El Salvador, the case was confirmed on August 4.

Unlike the more familiar flesh-eating bacteria (necrotizing fasciitis), this threat comes from fly larvae that burrow into living flesh. This parasite lays eggs in open wounds; the larvae then burrow into live flesh, causing extreme pain and tissue destruction. It differs fundamentally from the more well-known "flesh-eating bacteria" (necrotizing fasciitis), because one is caused by larvae physically consuming tissue, while the other stems from bacteria releasing toxins.

The patient, a traveler recently returned from El Salvador, has recovered. While health officials emphasize that the risk to the general public remains very low, they are also ramping up prevention efforts to shield both people and animals from this newcomer.


What is the New World screwworm parasite?

The New World screwworm (scientifically known as Cochliomyia hominivorax) is a type of blowfly whose larvae, or maggots, feed on living tissue. Female flies lay their eggs in open wounds, natural orifices, or soft parts of warm-blooded animals. Within hours, when eggs hatch, the larvae burrow deep into living flesh, hooking on, feeding, and causing severe damage and painful lesions. The larvae deepen wounds, potentially leading to severe destruction, and if untreated, can be fatal. This aggressive feeding behavior is unlike other maggots that usually target dead or decaying flesh. This particular larval feeding behavior gives the parasite its dramatic name.

Symptoms include visible maggots in wounds, a sensation of movement under the skin, foul odors, bleeding, and wounds that worsen rather than heal. Secondary bacterial infections may lead to fever or chills.



The Maryland case: What happened?

On August 4, Maryland health officials confirmed the first human case of screwworm infestation in the US in decades. The patient had recently returned from El Salvador, a region confronting an ongoing outbreak among livestock. Thankfully, the person has fully recovered, and there is no evidence of transmission to others or to animals. Authorities stress that the infection is not contagious and the public health risk remains very low.


How is it different from flesh-eating bacteria?

Unlike necrotizing fasciitis, commonly known as flesh-eating bacteria, which involves bacteria destroying tissue from the inside out, screwworm myiasis involves live insect larvae actively eating live flesh.

Bacterial infections like necrotizing fasciitis (from groups like Streptococcus or Vibrio) typically develop through bacterial invasion into soft tissue, causing rapid tissue death, such as skin, fat, and fascia. Symptoms emerge swiftly, within hours, and include extreme pain, swelling, redness that progresses to purplish or black skin, fever, and systemic signs like vomiting and shock.

In contrast, screwworm larvae literally consume living flesh mechanically and physically. Both cause rapid tissue destruction and are dangerous, but their causes and treatment approaches differ significantly.



Why screwworms are especially dangerous

Rather than the flesh-eating bacteria, flesh-eating parasites are more dangerous, because:

Direct consumption of healthy tissue: Screwworm larvae prefer living tissue, increasing risks of intense pain and severe damage.

Fast progression: Once inside, larvae rapidly burrow, making early detection challenging but vital.

Economic threats: While human risk remains low, screwworms pose a grave threat to livestock industries if they gain a foothold.

Both infections are serious, but they require starkly different responses. Knowing whether you face larva infestation or bacterial infection directs the correct treatment. For screwworm, physical removal of the larvae is critical. For necrotizing fasciitis, emergency surgery paired with antibiotics saves lives.


What actions are the authorities taking?

In response to the detection, US agencies are implementing several proactive measures:

Sterile-fly release program: The US Department of Agriculture (USDA) is reviving a successful eradication strategy from the 1960s, mass breeding and release of sterile male screwworm flies to disrupt reproduction. Plans include new production facilities in Texas and Mexico, generating hundreds of millions of sterile flies weekly.

Border and livestock controls: Stricter regulations and suspensions on livestock imports from affected regions, especially Mexico, are in place to prevent further entry of screwworms.

Surveillance and monitoring: Enhanced surveillance efforts include traps, patrols, and trained detector dogs to catch any emerging outbreaks near the US-Mexico border.

Emergency treatment approvals for animals: The FDA has granted emergency authorizations for animal treatments to combat screwworm infestations in livestock.


What you should do

What must you do to keep yourself safe?

Cover wounds: Treat and keep cuts or open sores clean and covered, especially when outdoors or near livestock.

Stay cautious while traveling: If visiting outbreak areas like parts of Central America, take precautions like wearing protective clothing and avoiding exposure of wounds.

Seek help quickly: Feel something moving under your skin? See larvae or feel unexplained pain around a wound? Immediate medical attention is critical.

Inform professionals: Agricultural workers, veterinarians, and farmers should stay alert and report any potential cases or unusual wounds.


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