Louisiana puts restrictions on animals entering state after screwworm reaches Texas

Louisiana officials have tightened restrictions on animals entering the state, with five cases of the flesh-eating parasite confirmed so far in the United States.

The presence of the New World screwworm was confirmed last week in Zavala County, Texas, near the Mexican border. The U.S. Department of Agriculture initially reported a 3-week-old calf was infected, and four additional cases have since been confirmed.

Screwworm infections occur when the parasitic fly lays its eggs in open wounds and body openings of warm-blooded animals. Their developing larvae can cause painful lesions, infections and death if left untreated.

Livestock are most vulnerable to the screwworm, though wildlife and pets are also susceptible. Medications are available to treat infected animals, and the parasite is not believed to pose a food risk. 

Human cases have historically been exceedingly rare, though the U.S. Centers for Disease Control and Prevention reports more than 2,100 people in Mexico and Central America have been infected since the parasite was initially reported in 2024.

The first two cases in the U.S. were just miles apart in Zevala County. A third infected calf was reported in adjacent LaSalle County, southwest of San Antonio, and the USDA reported Monday a goat in Gillespie County, to the north of San Antonio and west of Austin, was inflected. 

A screwworm case found in a dog first linked to Texas last week has since been attributed to Lea County, New Mexico, with officials now tracking where the animal has recently traveled.

Scientists eradicated the screwworm in 1966 through introducing sterile flies into infected areas. The federal government currently doesn’t have an adequate supply of sterile flies to conduct a similar effort, the San Antonio Express-News reported.

Federal and Texas officials have tracked the spread of the parasite through northern Mexico over the past several months. The CDC said more than 185,000 animals have been infected since the initial case was reported in 2024.

Dr. Daniel Myrick, Louisiana’s state veterinarian, issued an emergency order Friday that allows animals coming from a screwworm-infected state to enter Louisiana only if they do not originate from or pass through an “infected zone.” The animals also need an official inspection certificate declaring they are free from infection. The certificate is good for only seven days after the inspection.

Animals that come from or pass through an infected zone must first pass “movement requirements” from their state of origin, obtain an inspection certificate and receive a permit from the Louisiana’s Office of Food Health and Safety, part of the state agriculture department, according to Myrick’s order. 

The public is asked to report any suspected screwworm cases to the Louisiana Department of Agriculture and Forestry at (225) 925-3980 or [email protected].