First Human Case of Screwworm Myiasis Reported in Mexico
- TPP
- Apr 23
- 3 min read
Recently, Mexico’s Health Ministry has confirmed the first-ever human case of myiasis caused by the New World screwworm (NWS). The infection was detected in a 77-year-old woman from Acacoyagua, a municipality in the southern state of Chiapas. Authorities have reported that the patient is in stable condition and currently undergoing antibiotic treatment.
This case brings renewed attention to a parasitic disease that, while more common in animals, has the potential to affect humans under specific conditions.
Understanding Myiasis
Myiasis is a parasitic infection that occurs when fly larvae (maggots) infest human or animal tissue. The larvae feed on living or necrotic flesh, typically entering through open wounds, mucous membranes, or natural body openings such as the nose, eyes, or mouth. If left untreated, this infestation can lead to severe tissue damage, secondary infections, and significant pain, although it is generally not fatal.
About the New World Screwworm
The New World screwworm (Cochliomyia hominivorax) is a fly species known for its aggressive parasitic behavior. It is named for the unique, spiral-like motion of its larvae as they burrow ("screw") into living tissue. According to the Centers for Disease Control and Prevention (CDC), NWS infestations are primarily found in livestock, but in rare cases, they can also affect pets, birds, and humans.
Screwworm flies are attracted to open wounds and mucous membranes, where they lay clusters of 200–300 eggs. Over a female fly's 10–30 day lifespan, she may lay up to 3,000 eggs. After hatching, the larvae tear into living tissue using sharp mouth hooks, feeding and causing extensive tissue damage. They eventually drop to the ground to pupate, later emerging as adult flies, thereby continuing the cycle.
Historical Context and Spread
Historically, the New World screwworm was eradicated from the United States and Mexico through sustained control programs involving the release of sterile male flies. However, the species remains endemic to parts of South America and the Caribbean, posing a continuous threat to regions with tropical or subtropical climates.
In humans, cases are extremely rare but possible, especially in areas where the fly is present and risk factors such as open wounds, poor hygiene, or proximity to livestock exist.
The Chiapas Case: A Public Health Wake-up Call
The confirmed case in Chiapas represents the first documented human infection with NWS in Mexico, highlighting a potential public health risk, especially for rural populations in tropical regions. The patient—a 77-year-old woman—presented with symptoms consistent with screwworm myiasis, including a painful, worsening wound from which maggots were visible.
Authorities report that she is responding well to antibiotic therapy, but this case emphasizes the importance of early detection and immediate treatment.
Symptoms of Screwworm Myiasis
While not usually fatal, screwworm myiasis can be extremely painful and debilitating. Symptoms may include:
Unexplained skin lesions or wounds that do not heal
Painful sores that worsen over time
Bleeding or discharge from open wounds
A foul-smelling odor from the infested area
Sensation of movement under the skin or in natural openings like the eyes, nose, or mouth
Visible maggots (larvae) in or around the affected site
Fever or chills in cases of secondary bacterial infections
These symptoms should prompt immediate medical attention, especially following travel to endemic areas.
Who is at Risk?
According to the CDC, the risk of NWS myiasis is significantly higher for individuals who:
Travel to endemic areas in South America or the Caribbean
Have open wounds, even as small as insect bites or scratches
Have weakened immune systems due to HIV, cancer, or immunosuppressive medications
Sleep outdoors or work in close proximity to livestock
Suffer from chronic medical conditions that cause open sores, such as skin or sinus cancers
The elderly, those in rural communities, and agricultural workers are particularly vulnerable.
Treatment and Management
The only effective treatment for screwworm myiasis is the physical removal of the larvae, often performed through minor surgery. Antibiotics may be prescribed to prevent or treat secondary infections. Self-removal is strongly discouraged, as it may cause further tissue damage or incomplete larval extraction.
Prevention Strategies
Preventing screwworm infestation is crucial, especially for those in or traveling to endemic regions. Key measures include:
Keeping open wounds clean and properly covered
Using EPA-registered insect repellents
Wearing protective clothing (long sleeves, pants, socks)
Treating clothing with permethrin (0.5%)
Avoiding sleeping outdoors or using insect-proof screens
Practicing good personal hygiene and wound care when handling livestock
Public health awareness and ongoing surveillance are essential in preventing the re-emergence of NWS in previously eradicated areas.
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