December 30, 2024 – AUSTIN — Texas Parks and Wildlife Department (TPWD) asks hunters and other outdoor enthusiasts in South Texas to monitor for animals affected by New World Screwworm (NWS) after a recent detection in Mexico.
This detection, found in a cow at an inspection checkpoint in the southern Mexico State of Chiapas, close to the border with Guatemala, follows the progressively northward movement of NWS through both South and Central Americas.
As a protective measure, animal health officials ask those along the southern Texas border to monitor wildlife, livestock and pets for clinical signs of NWS and immediately report potential cases.
What is New World Screwworm?
New World screwworms are larvae or maggots of the NWS fly (Cochliomyia hominivorax), that cause a painful condition known as NWS myiasis. NWS flies lay eggs in open wounds or orifices of live tissue such as nostrils, eyes or mouth. These eggs hatch into dangerous parasitic larvae, and the maggots burrow or screw into flesh with sharp mouth hooks. Wounds can become larger, and an infestation can often cause serious, deadly damage or death to the infected animal.
NWS primarily infests livestock but can also affect humans and wildlife including deer and birds.
The parasite was last eradicated from the U.S. in 1966, with costly efforts by federal and state animal health officials, livestock producers and veterinary practitioners. Eradication efforts have continued in Central America, but the pest is considered widespread in Cuba, Haiti, Dominican Republic and South American countries.
Clinical signs of NWS myiasis may include:
- Irritated or depressed behavior
- Loss of appetite
- Head shaking
- Smell of decaying flesh
- Presence of fly larvae (maggots) in wounds
- Isolation from other animals or people
Transmission
NWS infestations begin when a female NWS fly is drawn to the odor of a wound or natural opening on a live, warm-blooded animal, where she lays her eggs. These openings can include wounds as small as a tick bite, nasal or eye openings, navel of a newborn or genitalia.
One NWS female fly can lay up to 300 eggs at a time and may lay up to 3,000 eggs during her lifespan. Eggs hatch into larvae (maggots) that burrow into an opening to feed. After feeding, larvae drop to the ground, burrow into the soil and emerge as adult NWS flies. Adult NWS flies can fly long distances and the movement of infested livestock or wildlife can increase the rate of spread.
Prevention
When spending time outdoors (especially if traveling abroad to NWS-affected areas), be sure to clean and cover all wounds in addition to applying insect repellant to outdoor clothing to help avoid contact with NWS and other harmful insects.
How to Help
While in the field enjoying activities such as hunting, hiking or bird watching, hunters and outdoor enthusiasts are asked to report suspected signs of NWS. Any wildlife with suspicious clinical signs consistent with NWS should be immediately reported to a local wildlife biologist. Livestock reports should be made to the Texas Animal Health Commission (TAHC) or U.S. Department of Agriculture (USDA).
“Those enjoying Texas’ natural resources have an opportunity to serve as the first line of defense in protecting wildlife, livestock, and human health,” said TPWD wildlife veterinarian Dr. J Hunter Reed. “Their eyes and ears will be critical to quickly responding and managing this threat.”
Additional information about NWS can be found on TAHC, USDA and the Center for Disease Control NWS webpages.
