First Human Case of Flesh-Eating Screwworms Detected in the U.S
- TPP
- Aug 27
- 5 min read
First New World Screwworm Infestation in U.S. in Decades — Larvae of ‘Man-Eater’ Fly Pose Greater Threat to Livestock than Humans.
The United States Department of Health and Human Services (HHS) has confirmed the first human case of New World screwworm infestation in the U.S. in decades. The case, reported on August 4, 2025, involved a Maryland resident who had recently traveled to El Salvador, one of several Central American countries currently facing an ongoing outbreak of this devastating parasite.
Although the immediate risk to public health remains low, experts warn that the real danger lies in the potential spread of screwworms to U.S. livestock, which could have catastrophic economic and ecological consequences.
What Are Screwworms?
Screwworms are the larvae (maggots) of the fly species Cochliomyia hominivorax — a name that literally translates to “man-eater”. Unlike most maggots that feed on dead tissue, screwworm larvae burrow into the living flesh of warm-blooded animals, including humans, making them uniquely dangerous.
Female flies lay up to 300 eggs at a time, typically inside open wounds, soft tissues, or even nasal cavities.
Across her 10–30 day lifespan, one female can lay up to 3,000 eggs.
Within 12–24 hours, eggs hatch into larvae, which corkscrew into the flesh — a motion that gives the parasite its name.
Over 3–7 days, larvae feed on tissue, then drop to the ground, burrow into the soil, and pupate before emerging as adult flies.
One female mates only once in her lifetime, a trait that plays a critical role in eradication strategies.
Definition: New World screwworm myiasis refers to parasitic infestations caused by screwworm larvae feeding on living tissue. If left untreated, infestations can rapidly progress, causing tissue destruction, sepsis, and even death.
The Maryland Case: Why Experts Are Concerned
According to HHS spokesperson Andrew Nixon, this is the first U.S. human case of travel-associated screwworm myiasis since the country successfully eradicated the parasite in the 1960s.
While prompt treatment prevented further spread, experts stress that infected travelers can inadvertently introduce larvae into non-endemic areas. Dr. Sonja L. Swiger, a veterinary entomologist at Texas A&M University, explains:
“A human coming back with larvae is generally not going to lead to an outbreak because those humans get treated quickly. But these larvae are horrible. They literally eat your body.”
Symptoms of Screwworm Infestation
Screwworm infestations are extremely painful and can progress rapidly if untreated:
Open, foul-smelling sores that enlarge quickly
Visible maggots burrowing within wounds
Severe pain, swelling, and fever
Secondary bacterial infections due to tissue damage
In animals: weakness, weight loss, behavioral changes, and reduced mobility
Warning: If untreated, screwworm infestations can lead to sepsis, loss of vital tissues, or even death.
How Are Screwworm Infestations Treated?
Currently, there are no FDA-approved drugs specifically for screwworm treatment, making manual removal of larvae the primary solution:
Manual Extraction – Each larva must be carefully removed, often through surgery.
Disinfection – Wounds are cleaned and sterilized to prevent re-infestation.
Antibiotics – Prescribed to combat secondary infections.
Pain Management – Necessary due to extreme discomfort.
In Animals – Veterinary protocols involve topical/systemic insecticides and off-label antiparasitic drugs.
In response to the growing outbreak, the FDA’s Center for Veterinary Medicine has fast-tracked efforts to approve antiparasitic drugs for livestock.
Why Livestock and the U.S. Meat Industry Are at High Risk
The real danger lies in livestock, not humans. Screwworm infestations can wipe out herds and devastate the cattle industry:
Newborn calves are especially vulnerable because their postpartum navels provide ideal egg-laying sites.
The U.S. legally imports over a million heads of cattle from Mexico annually — a critical pathway for potential parasite introduction.
According to the USDA, a widespread outbreak could cost Texas alone nearly $1.8 billion in livestock deaths, labor costs, and medical expenses.
Nationwide, the economic impact on the cattle and livestock sector could exceed $100 billion.
How Screwworms Spread
Contrary to common fears, adult screwworm flies are poor long-distance travelers, moving only ~12 miles within their 30-day lifespan.
Instead, spread occurs primarily via infected animals transported across regions:
Legal livestock imports → tightly regulated, but still vulnerable
Illegal cattle smuggling → a major threat, often tied to Central American drug cartels
Wildlife vectors → if screwworms infect wild deer populations, eradication becomes nearly impossible
Current Geographic Spread
Endemic Regions: Cuba, Haiti, the Dominican Republic, and parts of South America
Recent Expansion: Outbreaks reported in Panama, Costa Rica, Nicaragua, Honduras, and El Salvador
Northern March: Now detected in southern Mexico, roughly 595 km (~370 miles) from the U.S. border
Government Measures to Contain the Threat
1. Sterile Insect Technique (SIT)
The U.S. originally eradicated screwworms in the 1960s using SIT, which involves:
Breeding millions of male flies
Sterilizing them using radiation
Releasing them into the wild, where females mate only once, producing no viable offspring
This method successfully eliminated screwworms from the U.S., Mexico (1970s), and Central America (2000s). It was even reactivated in Florida in 2017 to control a localized outbreak.
2. New Facilities and Funding
Panama Facility → Co-managed by the USDA and Panama to produce sterile flies for Central America.
Mexico Plant → A $51M facility currently under construction to support SIT campaigns.
Texas Plant → The USDA recently announced plans for a U.S.-based sterile fly production facility.
3. Regulatory Actions
Livestock imports from affected Mexican regions are temporarily suspended.
Enhanced border inspections to identify infected animals.
Coordinated response efforts involving the USDA, HHS, the CDC, and the Food and Agriculture Organization (FAO).
A Potential Ecological Game-Changer
Experts warn that if screwworms establish permanent populations in states like Texas or Florida, they could persist year-round due to favorable climates.
Dr. Swiger cautions:
“If these parasites get into wild animal populations, it’s a game-changer. Those are the animals we cannot control.”
How to Protect Yourself and Your Animals
Cover all wounds — even minor scratches or insect bites
Use insect repellents when traveling in affected regions
Monitor pets and livestock for open wounds and signs of infestation
Seek medical help immediately if you suspect infection
Report unusual livestock symptoms to veterinarians or local agricultural authorities
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