Texas confirmed the first U.S. case of the New World screwworm on June 3, marking the parasite’s return to the country nearly 60 years after it was eradicated in 1966
By the end of June, the U.S. Department of Agriculture confirmed 30 cases in Texas across 13 counties, prompting state and federal officials to quarantine more than 20 counties to help slow the spread.
A separate case initially attributed to Andrews County in June was later reclassified as a New Mexico case after officials confirmed the affected dog lived in that state.
As cases continue to be confirmed in July, here’s your guide to navigating and understanding the New World screwworm outbreak in Texas.
What is a screwworm?
According to the USDA, the New World screwworm is a parasitic fly that affects livestock, pets, wildlife and — less commonly — people and birds. The fly’s larvae feed on the living tissue of warm-blooded animals.
Screwworm infestations begin when a female fly lays eggs on a wound or body opening. The eggs hatch into larvae that burrow into the wound and feed on living tissue; then, after about seven days of feeding, the larvae drop to the ground, burrow into the soil and pupate.
What a screwworm looks like
Adult New World screwworms have orange eyes, a metallic blue or green body and three dark stripes across the back, according to the USDA.
The telltale signs of a screwworm infection are the growing wounds or lesions and the presence of feeding maggots on still-alive animals.
Screwworm risk in dogs, pets
So far, there have been two dog-related cases of the screwworm — one in Texas and another in New Mexico.
The Texas Animal Health Commission — the state agency tasked with leading Texas’ response to the screwworm — says people should conduct daily pet checks to ensure their pets are not infected with screwworms.
Here are two stories to read to learn how best to protect your pet and what to do if your pet becomes infected.
Screwworm risk to humans
The risk of a screwworm infecting a human “remains very low,” according to the Centers for Disease Control and Prevention.
Since screwworm’s re-emergence in Central America and Mexico, one case was confirmed in August 2025 in a person who returned to the U.S. after traveling to El Salvador.
Certain factors raise the risk of infection. Those include living, working or spending significant time around livestock or other warm-blooded animals in areas where screwworm flies are present.
For more on screwworm infections in humans, visit cdc.gov/new-world-screwworm.
Screwworm map
Mateo Rosiles is the Texas Connect reporter for USA TODAY and its regional papers in Texas. Got a news tip for him? Email him at mrosiles@usatodayco.com.
This article originally appeared on San Angelo Standard-Times: What is a New World screwworm? What to know as cases continue in Texas
Reporting by Mateo Rosiles, USA TODAY NETWORK / San Angelo Standard-Times
USA TODAY Network via Reuters Connect
By Mateo Rosiles, USA TODAY NETWORK | USA TODAY Network
