DSHS provides precautions following animal New World screwworm case in Texas

The Department of State Health Services is alerting Texans to the presence of New World screwworm in the state following confirmation of an NWS detection in a bovine in Zavala County. The three-week-old, affected calf was found with larvae from the parasitic fly in its umbilical area. New World screwworm flies have been moving north through Mexico since they were first detected there in November 2024.

NWS flies were endemic in Texas and many southern states until their eradication from the U.S. mainland in 1966. NWS flies are endemic in Cuba, Haiti, the Dominican Republic and parts of South America. The current outbreak is considered to have begun in Panama in 2022, with the flies migrating north since that time. NWS flies are now present in all countries of Central America and much of Mexico.

The larvae of the parasitic fly primarily infests livestock, pets, wildlife, and other warm-blooded animals, including in rare cases people. NWS flies lay eggs on or near open wounds and body openings, such as the eyes, ears, nose mouth or genitals. When the eggs hatch, the larvae burrow into and feed on the living tissue of the mammal, which can cause severe harm and even death. While not common in people, if you notice a suspicious lesion on your body or suspect you may have contracted screwworm, seek immediate medical attention.

"DSHS and other state agencies have worked closely with the federal government and local partners to monitor the screwworm fly as it made its way toward our southern border," said Imelda Garcia, MPH, DSHS chief deputy commissioner. "Now with confirmation of its presence in South Texas, we ask all healthcare professionals and clinicians to be on the lookout for NWS larvae infestations in their patients and to alert their local health departments immediately if they suspect a screwworm case."

Providers should consider NWS in patients who have traveled in areas with animal or human cases of NWS and who suffer from a painful, foul-smelling wound containing visible larvae. Deep wounds with extensive tissue damage are also evidence of larval infestation, even if no larvae are seen on initial examination. There is no human-to-human transmission of NWS infestation.

More recommendations for healthcare providers can be found in a Sept. 26, 2025 DSHS Health Alert and on the DSHS website.

Texans may be at risk if they live in areas where the flies are present and they spend a lot of time outdoors during the day. Sleeping outdoors and working or living with animals near reported NWS fly populations are also risk factors. Because any break in the skin can attract NWS flies, open wounds of any size should always be cleaned and covered.

EPA-registered insect repellents are also recommended when outdoors in areas where the flies are present to deter biting insects. Wearing loose-fitting, long-sleeved shirts, pants, and socks will also limit the areas where scrapes or insect bites may occur. Clothing should be treated with a 0.5% permethrin insecticide.

Anyone who sees or feels larvae in a wound should cover the wound and contact their healthcare provider immediately. Larvae should only be removed by a healthcare provider to prevent further tissue damage and illness. Do not attempt to remove or dispose of eggs or larvae yourself.

The food supply in Texas is safe from screwworm. Current state or federal meat inspectors examine each animal to ensure they do not have signs of disease or pests, including screwworm.

Additional resources include:

• DSHS Regional Zoonosis Control offices
• New World Screwworm (NWS) | Texas DSHS
• Center for Disease Control and Prevention's NWS webpage
• Texas Animal Health Commission's information on reporting and responding to NWS in animals in Texas
• Stop Screwworm: Unified Government Response to Protect the United States

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