Flesh-eating fly found in a wild animal in the US for the first time: how dangerous is screwworm for dogs and cats?

What was found in Texas

On 21 October 2026 the US Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) confirmed the country's first detection of New World screwworm in a wild animal. The larvae were found in an elk on a hunting ranch in Pecos County, Texas. The animal had been taken by a hunter who noticed the lesion and reported it. Veterinary authorities regard reports like this from hunters, farmers and animal owners as the main way of spotting the parasite in new places in time.

Following the find, the Texas Animal Health Commission will adjust the boundaries of the previously declared infested zone, and the Department of Agriculture and Texas Parks and Wildlife will step up surveillance of wildlife in the area.

Early reporting is one of the most important tools we have to protect wildlife, livestock and pets in the United States.

US Animal and Plant Health Inspection Service (APHIS)

What kind of parasite it is

The New World screwworm (Cochliomyia hominivorax) is related to ordinary blowflies, but with one dangerous difference. Most flies lay their eggs on dead tissue and rotting remains, whereas the female of this species lays them in fresh wounds and natural openings of living warm-blooded animals: the nose, mouth, ears, eyes and genitals. Even a small scratch, a tick bite, a fresh surgical wound or the navel of a newborn calf can become the site of infestation. A single female lays hundreds of eggs at a time, so even one visit by a fly to a wound can lead to a severe infestation.

The larvae hatch within hours and burrow into living tissue, enlarging the wound. The parasite is called "screwworm" because the larvae look like small screws and anchor themselves firmly in the tissue. The smell of the wound attracts more flies, and the lesion grows quickly. According to APHIS, infested animals die quickly without treatment.

Why a find in a wild animal matters

According to APHIS, all warm-blooded wild animals are susceptible to the parasite. Wild animals travel long distances and cross state lines, so they can carry the parasite to places where it is not yet present. Monitoring wildlife therefore protects livestock and pets too. In addition, infested animals that go untreated die quickly, which can reduce wild populations.

How the parasite came back

The New World screwworm was once common in the southern USA and caused huge losses in livestock farming. In the 20th century it was defeated in an unusual way: millions of flies were reared in special facilities, the males were sterilised with radiation and released into the wild. Females that mated with sterile males laid unfertilised eggs, and the parasite's numbers fell. In 1966 the USA first declared itself free of the fly, and it was later pushed out of Mexico and Central America as far as Panama, where a "barrier" of sterile flies was maintained for many years.

In recent years the parasite has moved north again through Central America and Mexico, and in 2026 it returned to the southern USA. The last outbreak in the USA itself before that was in 2016 on the Florida Keys, where the parasite affected small deer; it too was eradicated with sterile flies.

The parasite's return has already cost America dearly. Because of it the USA suspended imports of live cattle from Mexico, and the authorities of both countries are increasing production of sterile flies — without them it is practically impossible to stop the parasite spreading. Vets point out that fighting it is a shared task for farmers, hunters, animal owners and vets.

Dogs and cats are at risk too

The New World screwworm infests any warm-blooded animal, including dogs and cats. In 2026, among several dozen confirmed cases in Texas and New Mexico, there were also cases in dogs. US veterinary organisations stress that the overall risk for most dogs remains low, especially away from the southern border, but an infestation can be very severe and needs immediate help.

The animals most at risk are those with open wounds, fresh surgical stitches, weeping patches of skin or discharge from the eyes and ears, as well as old and bedridden animals that cannot chase flies away themselves.

People can also be infected if they have an open wound, but such cases are rare. In recent years the USA has described isolated cases linked to travel to countries where the parasite is widespread. So when caring for an affected animal, wear gloves and wash your hands thoroughly.

How to recognise an infestation

Be alert to:

• a wound that does not heal or keeps getting bigger;
• an unpleasant, putrid smell from the wound;
• larvae visible in the wound or natural openings;
• discharge or blood from the wound;
• restlessness, with the animal constantly licking or rubbing one spot;
• lethargy, fever, loss of appetite and weight.

If you see larvae in a wound, do not try to remove them yourself — take the animal to a vet immediately.

How it is treated

Treatment is carried out by a vet: they remove the larvae, clean the wound and prescribe medicines that kill any remaining larvae, plus antibiotics and pain relief if needed. In the USA several products familiar to owners as flea and tick treatments — for example those based on lotilaner and afoxolaner — are authorised for dogs and cats, some of them on an emergency basis. The FDA has issued emergency use authorisations for four products against this parasite. They should be used only as prescribed by a vet. After treatment the wound is checked by the vet over several days: it is important to make sure no larvae remain and that healing has begun. While the wound is open, it is best to keep the animal indoors where there are no flies.

What owners in the US are advised to do

• Check your pet every day, especially if it has wounds or has recently had surgery.
• Clean and cover wounds, and keep an eye on stitches after neutering and other operations.
• Do not leave dogs with wounds outdoors for long in warm weather when flies are active.
• See a vet straight away about wounds that do not heal or that smell.
• Report suspicious lesions in wild animals to the veterinary or wildlife authorities — in Texas that is Texas Parks and Wildlife.

What this means for Europe

There is no New World screwworm in Europe. Warm regions of Africa, the Middle East and Asia are home to its relative, the Old World screwworm, which also infests the wounds of living animals. European countries are protected by strict veterinary rules on animal imports.

Europe also has its own experience of fighting this parasite close to home. In 1988 the New World screwworm was accidentally introduced into Libya and began to spread across North Africa. Using the same sterile fly technique, with flies flown in from Mexico, the outbreak was eradicated by 1991. That episode showed how quickly the parasite can establish itself in a new region with a suitable climate.

For pet owners in Europe something else matters. If you have travelled with your dog or cat to Mexico, Central or South America or the southern USA, check any wounds carefully for several weeks after you return and show anything suspicious to a vet straight away. If you have brought an animal from there, be sure to tell your vet where it has been. The same applies to dogs adopted from shelters and rescue programmes in Latin American countries.

A similar problem in Europe — summer myiasis

Although the New World fly is not found in Europe, European animals can suffer a similar problem — myiasis, or "fly strike". In summer ordinary blowflies lay eggs in soiled fur and wounds, and the larvae damage the skin. Rabbits with dirty fur under the tail, sheep, and old or immobile dogs and cats with wounds or incontinence are most often affected. The rules are the same: check animals daily in summer, keep their coat clean and see a vet straight away if you spot larvae.

What happens next

The US authorities are expanding wildlife surveillance and preparing further measures against the parasite, including releases of sterile flies. Vets are being offered materials for hunters and landowners on how to recognise an infestation and where to report it. For dog and cat owners in the USA, the key is to pay attention to any wound. For Europeans, the story is a reminder of why border veterinary checks and animal import rules matter so much. And one more simple rule that is useful in any country: any wound on a pet deserves attention, and one that does not heal and smells unpleasant deserves an urgent trip to the vet.