Growing Concern Over New World Screwworm Infestations in the U.S.

The U.S. Department of Agriculture has reported an increase in confirmed New World screwworm cases, reaching 45 incidents by August 2026. The most recent detection occurred in Terrell County, Texas, involving a domesticated sheep. So far, the screwworm has been found exclusively in animals such as cattle, sheep, and dogs following its entry into the U.S. during the summer. However, humans are not entirely free from risk, as screwworm flies can lay eggs on any warm-blooded host, including humans.

The eggs develop into parasitic larvae that consume surrounding flesh as they burrow in. If not treated, these infestations can be deadly. Unlike the cyclospora parasite, which affects people through food, the New World screwworm releases eggs into live tissue. These can enter through wounds or cavities like noses, mouths, eyes, or ears.

(USDA Agricultural Research Service via AP)

According to the Centers for Disease Control and Prevention, wounds as minor as tick bites can attract female screwworm flies to lay eggs. A single female can lay between 200 to 300 eggs at once and up to 3,000 during her lifespan of 10 to 30 days. Outdoor enthusiasts and those near animals face a higher exposure risk, particularly if they have open cuts.

To combat screwworm infestations, the CDC recommends removing all eggs and larvae from infected areas, which might require surgery for deeply embedded maggots. Efforts to halt the parasite’s spread, posing a significant threat to the cattle industry, are ongoing. Infestations mostly remain concentrated in Texas, with one case also reported in New Mexico.

The Department of Agriculture is deploying sterile flies to prevent rapid screwworm reproduction. In response to the crisis, the Food and Drug Administration has authorized emergency use of a medication aimed at prevention.