Earlier this week, the Department of Health and Human Services (HHS) confirmed the first case of a human infected with New World screwworm (NWS) in the United States. A Maryland resident had recently traveled to El Salvador and returned with the parasitic infection, as reported by an HHS spokesperson to ABC News. This incident arises amidst an ongoing outbreak of the parasite affecting livestock in Mexico and Central America.
What is New World Screwworm?
The New World screwworm, scientifically known as Cochliomyia hominivorax, is a parasitic fly that poses a significant threat due to its larvae’s tendency to consume living tissue. This condition, known as myiasis, can occur in various animals, including livestock, pets, and wildlife, and in rare cases, humans.
Lori Ferrins, an associate professor of pharmaceutical sciences at Northeastern University, explained, “New World screwworm kind of gets its name because these are little parasites and, when they actually land on an open wound, they’re going to screw down into the wound — that’s how they burrow in — and actually consume tissue.” The female NWS finds a living host and lays between 200 to 300 eggs in an exposed wound, leading to painful infestations as the hatchlings burrow deeper into the tissue.
Currently, NWS is not typically found in the U.S. but is present in regions across Central and South America and the Caribbean, as stated by the Centers for Disease Control and Prevention (CDC).
Symptoms and Treatment
Infections can produce a range of symptoms, including:
- Non-healing or worsening skin lesions
- Painful open wounds or sores
- Bleeding from sores
- Visible maggots in wounds
- Unpleasant odors from the site of infestation
According to the CDC, maggots can also be found in various body openings such as the eyes, nose, and mouth. Dr. Shira Doron, chief infection control officer for Tufts Medicine Health System, remarked, “The larvae of the New World screwworm are particularly nasty, and that’s why it has been given this name. Here in the hospital, we may have a patient come in and, with a painful open wound, we may notice that there are larvae or maggots in it.”
Currently, there is no drug that can eliminate NWS, but effective treatments exist. If someone suspects an infection or sees maggots, they should seek medical attention immediately. Physicians may need to perform surgical procedures to remove the larvae. Doron emphasizes the importance of not attempting to remove the maggots without professional assistance: “We want to physically remove those, kill them, and send them off to a special lab to see if we’re dealing with something from another country, which then implies the need for a more robust public health response to prevent it from becoming a widespread problem.”
Preventing Infection
For travelers venturing to areas where NWS is prevalent, Doron recommends:
- Covering open wounds
- Using EPA-approved insect repellents
- Wearing long sleeves and pants, with pants tucked into socks
Ferrins noted ongoing efforts to prevent the parasite’s reintroduction into the U.S., including establishing a sterile fly production facility in Texas. “There are steps we can take … to then control or eliminate the presence of [NWS], just like we did in 1966,” she explained. The prior eradication involved breeding and dispersing sterilized male flies that would mate with wild females, preventing egg hatching and disrupting the life cycle.
Current Risk Assessment
Since the successful eradication of screwworm in the U.S. in 1966, infections have been rare, with only a notable outbreak occurring in the Florida Keys in 2017, affecting only animals. Ferrins reassured, “The risk of infection is currently low in the U.S., so there is no cause for major concern.” She advised, “My advice to people would be: be on your guard but ultimately, there’s no active signs of infection here, locally acquired infection in the United States.” ABC News’ Youri Benadjaoud contributed to this report.
