The Texas Department of State Health Services (DSHS) has issued a health advisory to raise awareness about the New World screwworm (NWS), a parasitic fly that can affect both humans and animals. While there have been no recent cases in Texas, state and federal agencies are preparing for the possible reintroduction of the parasite into the United States.
New World screwworm myiasis occurs when larvae of Cochliomyia hominivorax infest wounds or mucous membranes in warm-blooded animals, including humans. The larvae feed on live tissue, causing pain and potentially severe tissue damage. After feeding, larvae drop to the ground to complete their lifecycle, which lasts between 14 and 54 days.
“NWS infestation cannot spread from one host to another without the completion of the fly’s life cycle, which ranges from approximately 14-54 days. NWS has the potential to significantly affect local animal populations, so awareness, surveillance, and control of NWS myiasis and C. hominivorax flies in both animals and humans are critical,” according to DSHS.
The parasite was eradicated from the United States in the 1960s but remains endemic in most of South America, parts of the Caribbean, and southern Panama. In 2023, NWS was detected throughout Central America and later identified in Mexico starting November 2024.
Although there is currently no immediate risk within the United States, travel-related cases remain a concern. People with painful wounds containing visible larvae after traveling to affected regions should seek medical attention promptly.
Healthcare providers are advised to consider NWS if patients present with very painful or foul-smelling wounds containing larvae—especially if they have recently traveled to areas where NWS is present—or if there is an egg mass near a wound or body opening. There is no approved medication for treating human NWS infestation; treatment involves removing all larvae manually or surgically if necessary.
Proper disposal procedures must be followed: “Larvae and eggs should be killed by placing them into a leak-proof container with 70% ethanol. The volume of liquid in the container should be enough to fully submerge the larvae,” DSHS stated. Extracted material should not be discarded until it has been properly treated as medical waste.
Diagnosis relies on identifying morphological features of collected larvae from different depths within wounds. All suspected cases must be reported immediately so samples can be sent for confirmation at specialized laboratories such as those operated by DSHS in Austin or by Centers for Disease Control and Prevention (CDC).
Individuals who travel to regions where NWS is known to occur—such as Mexico, Central America, South America, or certain Caribbean countries—are at higher risk if they spend time near livestock or outdoors with open wounds or weakened immune systems. Preventive measures include wearing protective clothing, using insect repellent on skin and gear treated with permethrin, keeping wounds clean and covered, sleeping indoors with screened windows, and seeking prompt medical care if symptoms arise.
Local public health departments offer further guidance on prevention strategies for communities at risk: https://www.dshs.texas.gov/regional-local-health-operations/public-health-regions/texas-local-public-health
For additional information about reporting requirements or clinical management questions related to New World screwworm cases, healthcare providers are encouraged to contact their local health department or consult with DSHS Zoonosis Control Branch.
