New World Screwworm
New World Screwworm: A Reemerging Threat
New World screwworm (NWS), or Cochliomyia hominivorax, is a species of parasitic fly that can cause infestation in humans and animals. NWS larvae feed on live tissues of any warm-blooded animal. When larvae from the fly get into a wound or opening in the body, they cause myiasis, or an infestation of fly larvae.
NWS myiasis occurs when a female fly lays eggs near wounds or mucous membranes (eyes, ears, nose, mouth, genitalia) of an animal or person. Female flies can lay hundreds of eggs within minutes. When the eggs hatch, the immature flies (also known as larvae), burrow or “screw” into the opening with sharp mouth hooks and eat the flesh. This can be painful and can even cause death. There is currently no medication labeled to treat an NWS infestation in humans. The larvae must be removed by a healthcare professional for humans or by a veterinarian for animals.
NWS is generally an agricultural problem. Screwworm myiasis in cattle can lead to the animal’s death and can severely impact ranchers and the agricultural industry. Early detection can save lives and money.
If you suspect a pet, livestock, or wild animal has an NWS infestation, get help as soon as possible.
For pets or livestock, call your veterinarian and contact the Texas Animal Health Commission (TAHC) at 1-800-550-8242 or through your local TAHC regional office.
If you see a live wild animal with larvae, immediately contact Texas Parks and Wildlife (TPWD) through your local wildlife biologist at 1-512-389-4505.
For more information on New World screwworm, please visit screwworm.gov.
NWS and Humans
Though the risk to the public remains low, people can sometimes get an NWS infestation if they visit areas where the fly is present, such as Mexico, Central America or parts of South America and the Caribbean. People who do the following in areas with NWS might be at greater risk for infestation:
- People who sleep outdoors during the day (unhoused, campers)
- People who primarily work outdoors
- Ranchers and those who work with animals
- People with an open wound
- Those with diabetes or other skin conditions
DSHS urges people to take precautions by following these steps to prevent NWS infestation:
- Keep open wounds clean and covered
- Sleep indoors or in screened shelters, and keep window screens in good repair
- Wear loose-fitting, long-sleeved shirts and pants to prevent scrapes and insect bites
- Use an EPA-registered insect repellent to prevent insect bites
- Treat clothing and gear with products containing 0.5% permethrin, which is an insecticide and repellant
People who see or feel larvae in or on their wounds should immediately contact their healthcare provider. If you think you might have been exposed to C. hominivorax or think you might have an NWS infestation, contact your healthcare provider.
Information for Pet Owners
While livestock and wildlife represent most NWS cases, dogs and cats are also at risk. Pet owners are an important part of stopping the spread of this pest.
Check pets every day for wounds, including past tick bites. Watch for a bad smell, discharge, and larvae in or near the wound. Visit a veterinarian immediately if you suspect an infestation. Do not attempt to remove the larvae or treat the animal yourself.
For more information, visit the Texas A&M AgriLife Extension website.
Information for Healthcare Providers
Healthcare providers play a critical role in stopping NWS. If you suspect a patient might have myiasis caused by an NWS infestation, please contact your local health department to arrange testing. Any larvae collected for identification should be submerged in 70% alcohol (ethanol or isopropanol) in a plastic container with a screw cap that can be tightly sealed. DSHS Regional Zoonosis Control Offices will give providers further guidance on sample collection, submission, and interpretation of results.
Live larvae should not be thrown away in the trash or outside while they are alive. If larvae are not needed for testing, submerge them in 70% alcohol before disposing. This ensures that the larvae die and do not cause any further risk.
More recommendations for healthcare providers can be found at New World Screwworm Information for Healthcare Providers.
Identifying the New World screwworm
The DSHS laboratory accepts larvae extracted from wounds for rule out of myiasis in suspected human cases of New World Screwworm. Only healthcare providers can order these tests and submit specimens to the laboratory. The DSHS Lab does not accept specimens for NWS surveillance from the public. Specimens submitted by the public will be rejected and destroyed. If you believe you have a parasitic infection, contact your healthcare provider. Laboratory staff cannot provide medical advice.
Resources
DSHS is working with multiple state and federal partners in response to NWS. In Texas, the lead agency is the Texas Animal Health Commission (TAHC).
If you suspect an NWS infestation, please notify the following authorities immediately.
If you live or work with animals
Livestock: Call your veterinarian and the Texas Animal Health Commission at 1-800-550-8242 or through your local TAHC Regional Office.
Pets: Contact your veterinarian and the Texas Animal Health Commission at 1-800-550-8242 or through your local TAHC Regional Office.
Wildlife: Contact Texas Parks and Wildlife through your local wildlife biologist.
Animal Control Officer: If you suspect an animal has NWS, use this flowchart or pocket guide to determine who to notify.
- New World Screwworm Training Response, June 23, 2026
If you suspect you or another person has an NWS infestation
Contact your healthcare provider immediately. Your provider should contact your local health department or your regional public health office.
If you are a healthcare provider and need to get a sample tested:
The DSHS Laboratory can test samples from healthcare providers only. Contact your local Zoonosis Control Regional Office for instructions.
More recommendations for healthcare providers can be found at New World Screwworm Information for Healthcare Providers.
Visit the Communications Toolkit for materials in English and Spanish.