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New World screwworm is a parasitic fly whose larvae—not adult flies—feed on living tissue. It can seriously affect people and animals, but the CDC says the current risk to people and animals in the United States is very low; anyone who sees or feels larvae in a wound should seek medical or veterinary care immediately and must not try to remove them at home.
Pets can be affected, especially when they have open wounds or spend time in areas where the flies are present. Keep wounds clean and covered, inspect them regularly, and call a veterinarian promptly about a painful, worsening, foul-smelling, bleeding, or nonhealing wound.
What “flesh-eating flies” actually means
New World screwworm (NWS) is a species of parasitic flies that feed on live tissue, according to the CDC. Adult female flies lay eggs in wounds or body openings; the eggs hatch into larvae that burrow into and consume living tissue. This infestation is called New World screwworm myiasis.
That differs from ordinary fly activity around a wound. Some fly larvae feed on dead or damaged tissue, but Cochliomyia hominivorax larvae are parasites of living flesh. Symptoms alone cannot confirm the species, so a clinician or veterinarian must assess a suspected case.
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What the outbreak evidence shows
CDC’s outbreak summary, accessed October 7, 2026, reports more than 209,400 animal cases and more than 2,700 human cases in Central America and Mexico. The summary does not give an “as of” date beside those totals, so they should not be treated as a dated snapshot. CDC reports the first animal case in the current outbreak in the United States on June 3, 2026, and no locally acquired U.S. human cases; its current assessment is that risk to people and animals in the United States is very low.
| Evidence or guidance | What it means |
|---|---|
| CDC regional totals | More than 209,400 animal cases and more than 2,700 human cases in Central America and Mexico; the summary does not specify an as-of date beside these totals. |
| CDC U.S. status | First U.S. animal case in the current outbreak was reported June 3, 2026; CDC reports no locally acquired U.S. human cases and assesses current U.S. risk as very low. |
| Mexico animal-health report | SENASICA reported 1,905 active cases as of August 29, 2026. This is a dated active-case figure, not a cumulative regional total. |
| CDC-published Mexico study | A retrospective analysis examined 202 confirmed human cases with adequate case-level information from April 13, 2025, through March 14, 2026. These study findings are not current cumulative totals. |
The CDC-published study found that the analyzed cases were concentrated in southern Mexico, particularly Chiapas, followed by Yucatán, Oaxaca, and Quintana Roo. In that dataset, 71.8% of cases were in men, mean patient age was 61.1 years, 55.0% affected lower limbs, and 76.7% of patients had more than one concurrent condition. Six deaths were reported, with one attributed directly to NWS myiasis at the time of reporting. These statistics describe the study period and dataset, not present-day totals.
SENASICA also reported inspecting 80,750 shipments carrying 5,081,531 head of cattle between October 28, 2024, and June 8, 2026. These are official Mexican animal-health figures, distinct from human case counts and CDC’s regional aggregate totals.
How a pet can become infested
Female flies are attracted to wounds and body openings, including the nose, eyes, ears, and mouth. Small skin breaks such as scratches, insect bites, and recent surgical wounds may attract flies. CDC says a female may lay 200–300 eggs at a time and up to 3,000 during a 10–30 day lifespan; larvae feed for about seven days before dropping to the ground and continuing development.
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Risk is most relevant where the flies are present and animals have accessible wounds. Pay particular attention to pets with:
- cuts, scrapes, bites, punctures, or surgical wounds;
- skin injuries that are difficult to see under fur;
- wounds around the face, ears, nose, eyes, mouth, or genitals;
- prolonged outdoor exposure or contact with livestock and other warm-blooded animals; or
- conditions that cause bleeding, sores, or delayed wound healing.
Livestock are a major concern, but pets and wildlife may also be affected. Risk varies by location and exposure; the current U.S. risk assessment should not be confused with conditions in affected parts of Mexico and Central America.
Signs of screwworm in animals and people
Warning signs can include seeing or feeling larvae in a wound or body opening, painful wounds that worsen within days, foul odor, and bleeding. Bacterial infection may also occur and can cause fever or chills. These signs do not identify the species by themselves.
For an animal, seek immediate veterinary attention for a painful, worsening, foul-smelling, bleeding, or nonhealing wound, especially if larvae are visible or suspected. A veterinarian can examine the animal, collect a specimen, arrange identification, and advise on reporting.
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For a person, contact a healthcare provider immediately if larvae are seen or felt. Tell the provider about relevant travel or residence. Do not attempt to remove larvae yourself. CDC advises placing any larvae or eggs that fall out in a leak-proof container with rubbing alcohol and bringing them to the provider; do not discard live larvae outdoors or in the trash.
What to do if your pet has a suspicious wound
- Call a veterinarian promptly. Explain the wound, symptoms, any visible larvae, and why you are concerned about possible screwworm.
- Do not try to remove larvae or self-treat. Do not probe the wound or apply pesticides, solvents, or chemicals not directed by a veterinarian.
- Keep the animal calm and safely contained. Avoid unnecessary handling, squeezing, or probing of the wound during transport.
- Share exposure details. Tell the veterinarian about travel, outdoor exposure, contact with livestock or wildlife, recent injuries, and any prior treatment.
- Follow professional instructions. Your veterinarian can advise about specimen handling, treatment, and any animal-health reporting.
A wound may still need examination even if larvae are no longer visible. Do not assume it has healed without professional advice.
How to reduce exposure
CDC prevention guidance for areas where NWS flies are present focuses on reducing access to skin and wounds. These measures lower exposure risk but do not guarantee protection and are not treatment for a suspected infestation.
- Keep every open wound clean and covered, however small.
- Sleep indoors with closed or screened windows, or use a bed net or screened tent.
- Use an EPA-registered insect repellent according to its label.
- Treat clothing and gear with products containing 0.5% permethrin, following product directions.
- Wear loose-fitting long sleeves and pants, a hat, and socks to limit exposed skin.
- Inspect pets regularly, including under fur and around healing wounds; ask a veterinarian about precautions before travel to affected areas.
For routine wound care, clean cuts, scrapes, and bites promptly and keep them covered with an appropriate dressing while they heal. A dressing does not kill larvae or replace urgent care for a suspicious wound.
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How authorities are responding
Control measures include releasing sterile male flies, animal surveillance, movement controls, wound inspection, rapid case detection, laboratory diagnosis, and public education. The CDC-published study notes that Mexico was declared free of NWS in 2003, with animal cases reported again since 2024 and human cases since 2025. It describes sterile-fly release, quarantine, and treatment of infested animals as elements of prior eradication efforts.
In its September 2, 2026 report, SENASICA described intensified surveillance in southern and southeastern Mexico and reported livestock shipment inspections. Its active-case count is a dated snapshot and should not be mixed with cumulative human or animal totals.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Frequently Asked Questions
What is New World screwworm?
It is a parasitic fly species. The adult female lays eggs in wounds or body openings, and the hatched larvae feed on living tissue.
Can New World screwworm infest dogs and cats?
Yes. Pets can be affected, particularly if they have open wounds and are exposed where the flies are present. Contact a veterinarian promptly about a suspicious wound.
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Is screwworm affecting people in the United States?
CDC reports the first animal case in the current U.S. outbreak on June 3, 2026, and no locally acquired U.S. human cases. CDC’s current assessment is that risk to people and animals in the United States is very low.
What are the signs and symptoms?
Possible signs include larvae seen or felt in a wound or body opening, worsening pain, foul odor, and bleeding. Fever or chills may occur with bacterial infection. Symptoms do not confirm the species; seek prompt professional care.
Should I remove larvae from my pet’s wound myself?
No. Do not probe or try to remove larvae, and do not apply unapproved chemicals. Call a veterinarian immediately.
How can I prevent New World screwworm?
In areas where the flies are present, keep wounds clean and covered, sleep behind screens or indoors, use an EPA-registered repellent, treat clothing and gear with 0.5% permethrin as directed, and cover exposed skin with clothing.
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