New World Screwworm Frequently Asked Questions
New World screwworm is a parasitic fly with larvae that feeds on living tissue. Outbreaks of NWS are most likely to happen in cows, pigs, and other livestock, though it can also infest pets like dogs and cats. Though rare in humans, it can be very painful and even cause death. Below are some frequently asked questions about the pest.
General Information
What is New World screwworm?
Despite its name, the New World screwworm is actually a species of fly also known as Cochliomyia hominivorax. NWS larvae feed on live tissues of any warm-blooded animal. When fly larvae get into a wound, they cause myasis, or an infestation of fly larvae.
Can I get NWS from an animal or someone who is infested?
No, you cannot directly catch NWS myasis from an infested animal or person. However, adult flies can lay eggs on and infest different people living in the same space
What are the symptoms of NWS infestation in humans?
NWS infestations are very painful. If you have an NWS infestation, you may see larvae around or in an open wound. They could also be in your nose, eyes, mouth, or other mucous membranes. Tell your healthcare provider of any recent travel to Central or South America, the Caribbean, or Mexico.
Symptoms can include:
- Feeling larvae moving within a skin wound, sore, ears, nose, eyes, or mouth
- Seeing larvae around or in open sores
- Painful skin wounds or sores
- A foul-smelling odor from the site of the infestation
- Unexplained skin wounds or sores that do not heal within a few days
- Bleeding from open sores
Bacteria can also infect wounds where NWS larvae are present, which may lead to fever or chills. (CDC)
How can I protect myself from NWS?
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 socks and loose-fitting, long-sleeved shirts and pants
- Use an EPA-registered insect repellent
- Treat clothing and gear with products containing 0.5% permethrin, which is an insecticide and repellant
What should I do if I think I have an NWS infestation?
If you think you might have an NWS infestation, keep your wound covered and see your healthcare provider as soon as possible. Because NWS larvae can burrow deep into wounds, you can hurt yourself if you try to remove the larvae on your own. Your healthcare provider will be able to safely remove the larvae. Your provider should contact newworldscrewworm@dshs.texas.gov for more information.
Does the NWS affect our food supply?
Our DSHS Consumer Protection Division team has been working closely with state and federal partners over the past six months to ensure the food supply is safe. The food supply is safe from New World screwworm.
Is meat safe to eat? Is our meat inspected?
Yes, meat is safe to eat. Every single animal is inspected both before and after harvest. Our Texas Meat Safety Assurance personnel are trained to identify suspicious larvae. DSHS then collaborates with Texas Animal Health Commission to respond appropriately.
Who does the inspection?
Current state or federal meat inspectors examine each animal to ensure they do not have signs of disease or pests, including NWS. This includes an inspection of the live animal prior to harvest as well as an inspection of the carcass after harvest. Meat processing operations also receive inspection on every day of production.
Our Texas Meat Safety Assurance personnel are trained to identify suspicious larvae and collaborate with Texas Animal Health Commission to respond appropriately.
Is Texas dairy safe to drink and eat?
Yes. If there are signs of NWS, there are drugs (similar to Ivermectin) that dairy farmers may choose to use on affected cows or calves. If drugs like this are used on dairy cows, the dairy farmer is not allowed to use milk from those cows for a period of time to ensure the drug is cleared from the cow.
Our Texas Milk and Dairy personnel are trained to identify approved and non-approved drugs for lactating and non-lactating dairy cows. We are notified when a new drug is approved for use in dairy cows and update our drug monitoring procedures for routine inspections.
What should I do if I think my pet or livestock has an NWS infestation?
Animals with an NWS infestation typically display:
- Irritation or discomfort
- A smell of death or decay around a wound or orifice
- Open wounds or sores
- Wounds where larvae are visible
If you see or suspect any of these symptoms, contact your veterinarian so the animal can be assessed quickly.
If your pet or livestock is diagnosed with NWS infestation, you or your vet should contact the Texas Animal Health Commission (TAHC). If you see a live wild animal with larvae, report the sighting to Texas Parks and Wildlife (TPWD).
Didn't the U.S. eradicate the New World screwworm?
NWS was previously eradicated from the U.S. in the 1960s. The fly continues to be endemic in most of South America, parts of the Caribbean, and southern Panama. Since 2023, NWS has been detected throughout Central America. NWS was detected in southern Mexico beginning in November 2024. To learn more about the history of NWS and eradication efforts, visit the U.S. Department of Agriculture (USDA) website.