The U.S. Department of Agriculture (USDA) confirmed a second case of the New World screwworm parasite in Texas on Friday, according to the USDA’s Animal and Plant Health Inspection Service (APHIS). The parasite was found in a one-month-old calf in Zavala County, less than six miles from a previously confirmed case; this is only the second confirmed case in Texas since 1966.

Parasite Spreads from South America

The New World screwworm is a parasitic fly species that feeds on the living tissue of warm-blooded animals, including humans, according to the Centers for Disease Control and Prevention (CDC). The larvae burrow into wounds or skin, causing painful, often foul-smelling injuries. The parasite has been spreading northward from South America into Central America and Mexico since 2023, and experts had predicted its arrival in the U.S. as early as last year.

“USDA has responded expediently with respect to this second detection, demonstrating our utmost preparedness,” Dudley Hoskins, the department’s under secretary for marketing and regulatory programs, said in a statement. Other samples tested in the surrounding area have come back negative, according to APHIS.

Human Infections and Past Outbreaks

While rare, human infections can occur. In Guatemala. 80 cases were reported by September 2025; in Costa Rica, about 70; and in Mexico, 44, In the U.S., a case was previously reported in a person from El Salvador. One of the most severe cases occurred in Mexico, where an 86-year-old woman with pre-existing health conditions died after being infected — Dozens of other people in the southern Mexican states of Campeche and Chiapas were treated for the infection, according to local reports.

And, in 2024, a case was reported in Florida where a person who had visited the Dominican Republic was found to have between 100 and 150 screwworm larvae in their body, according to Texas authorities. Hospital staff noted the sheer number of larvae clogged their suction equipment.

Control Measures and Emergency Response

Concerned about the spread. Texas Governor Greg Abbott declared a state of emergency on May 5 before any local cases were confirmed. In a statement, Abbott said, “Texas law allows for preemptive action to prevent the spread of pests that could harm livestock, wildlife, and property.” He added that the state would not wait for the damage to occur before acting.

To combat the parasite, Texas authorities have established a joint task force involving the state’s Parks and Wildlife Department and the Animal Health Commission. A large-scale infrastructure project is also underway to stop the parasite’s spread. The plan involves releasing sterile male flies to disrupt the parasite’s reproduction — a method successfully used in the 1960s to eradicate the screwworm from the U.S.

According to APHIS, the USDA is also working with state and industry partners to contain the outbreak. A 20-kilometer quarantine zone has been established around the affected area to prevent movement of potentially infected animals. Affected animals can be treated, but the process is time-consuming and expensive, requiring the removal of hundreds of larvae and wound disinfection.