The Texas Department of State Health Services (DSHS) has issued a health advisory to inform public health professionals, clinicians, and the public about the New World screwworm (NWS), a parasitic fly that poses risks to both humans and animals. Although there have been no recent cases in Texas, state and federal agencies are preparing for the possible reintroduction of this parasite into the United States.
New World screwworm myiasis occurs when larvae of Cochliomyia hominivorax infest wounds or mucous membranes of warm-blooded animals. The fly lays eggs near wounds, which hatch within a day, and the larvae begin feeding on live tissue. Symptoms include pain and movement in the affected area. After feeding, larvae drop to the ground to complete their lifecycle.
NWS cannot spread directly from one host to another without completing its life cycle, which lasts between 14 and 54 days. The parasite can significantly impact local animal populations, making surveillance and control efforts important for both animal and human health.
The United States eradicated NWS in the 1960s, but it remains present in most of South America, parts of the Caribbean, and southern Panama. In 2023, detections occurred throughout Central America; by November 2024, NWS was found in Mexico.
While there is currently no immediate risk within the U.S., travel-related cases remain possible. People returning from areas where NWS is present should be aware of symptoms such as painful, foul-smelling wounds with visible larvae or egg masses.
“There is currently no medication approved for treatment of NWS infestation in humans,” according to DSHS guidance.
Treatment involves removing all larvae from wounds; surgical removal may be necessary if larvae burrow deeply. Secondary bacterial infections are possible and should be assessed clinically. Extracted larvae or eggs must be killed by submerging them in 70% ethanol before disposal to prevent environmental contamination.
Diagnosis relies on identifying larval features. Healthcare providers are instructed not to dispose of larvae or eggs improperly: “Failure to kill and properly dispose of all larvae or eggs may result in the new introduction and spread of NWS in the local environment.”
Suspected cases should be reported immediately so samples can be sent to DSHS laboratories for identification with confirmation by CDC experts. Public health consultation is available through local departments coordinating with DSHS.
Travelers who spend time around livestock or outdoors in regions where NWS is present—including Mexico, Central America, South America, and some Caribbean countries—face higher risk if they have open wounds or certain medical conditions like diabetes or immune deficiencies.
Preventive measures include wearing long clothing, treating clothes with permethrin products, keeping wounds clean and covered, sleeping indoors with screens, and seeking prompt medical attention if larvae are noticed in wounds. Larvae removal should only be performed by healthcare professionals.
Additional information about regional public health operations can be found at https://www.dshs.texas.gov/regional-local-health-operations/public-health-regions/texas-local-public-health.
