What is myiasis?
Myiasis is a parasitic infection of fly larvae (maggots), also known as maggot infestation or flystrike. Certain species of flies lay their eggs in wounds or, less commonly, on healthy skin, especially near the eyes, ears, or nose.
Many species of flies can cause this infection, including blow flies and flesh flies. However, the New World screwworm (Cochliomyia hominivorax) is most concerning, as infestations with this parasite can be very aggressive. It was previously eradicated from North America, but is now being seen in Mexico and, as of June 2026, has been reported in animals, including a dog in the southwestern United States.
How are dogs and cats infected?
Infection occurs when a fly lays eggs on an animal’s skin or mucous membranes, such as inside the nose, eyes, ears, mouth, or genital area. Flies are particularly attracted to wounds, moist or infected skin, and soiled areas. Once the eggs hatch, they result in hundreds or thousands of larvae, which may or may not be visible.
Most fly larvae (maggots) feed on necrotic (dying) or diseased tissue. However, screwworm larvae are much more aggressive. They burrow into and feed on healthy, living tissue, including tendon sheaths and tissues in the abdomen. As the larvae burrow, they create deeper wounds, attracting more adult flies, and leading to a worsening cycle of infestation. Mature larvae drop into the soil and develop into adult flies, which can start the cycle again.
What pets are most often infected?
Infection risk increases with many conditions, including:
- Open wounds or surgical wounds
- Skin disease
- Weakness
- Other illness
- Incontinence
- Being housed in unsanitary conditions
- Living in warmer, wet areas
- Spending a lot of time outdoors (although indoor pets are still at risk)
- Having recently given birth
Screwworm cannot survive the cold winters of northern U.S. states and Canada. However, animals infested in affected areas can carry larvae into these regions during warmer months.
What are the signs of myiasis?
Signs of maggot infestation depend on the location of infection and may include:
- A foul odor of decay
- Skin wounds or fistulae (tunnels under the skin) that enlarge or even coalesce (merge together)
- Wounds that appear around the eyes, nose, mouth, anus, or near previously noted wounds
- Round nodules under the skin
- Draining tracts (small holes in the skin that ooze liquid)
- Irritability or restlessness
- Depression
- Poor appetite
- Maggots or eggs visible in wounds or mucous membranes
- Screwworm larvae burrow deep into the tissue, so they are less often visible.
If you suspect myiasis in your pet, notify your veterinarian right away for prompt treatment. Let them know all regions your pet has been in the past month. Early veterinary treatment can improve your pet’s outcome.
How is myiasis treated?
- Maggots will be removed by thoroughly cleaning and flushing any wounds and removing any dead tissue (debridement).
- One or a combination of parasite medications may be recommended to kill any remaining larvae/maggots, such as ivermectin, nitenpyram, milbemycin, sarolaner, or afoxolaner.
- Due to the emerging concern of screwworm infestation, the FDA has temporarily approved the use of certain medications for screwworm treatment, including:
- Nexgard® (afoxolaner), Credelio™ (lotilaner), and Credelio Quattro™ (lotilaner, moxidectin, praziquantel, pyrantel) for dogs.
- Nexgard®Combo (esafoxolaner, eprinomectin, and praziquantel topical solution) and Credelio™ Cat (lotilaner) for cats.
- Antibiotics may be needed for any infections that occur secondary to maggot infestation.
- Therapy will be provided for any underlying condition, such as ear or skin infections.
- In severe cases, supportive therapy may be recommended, such as fluids, special diet, and pain medication.
How do I prevent myiasis?
- Keep your pet clean and dry.
- Ensure any open wounds are treated quickly and effectively and monitored at least daily.
- Manage allergic skin disease.
- Ensure items like collars aren’t creating skin irritation.
- Keep your pet at an ideal weight.
- Limit outdoor exposure, reducing exposure to flies, especially if your pet is at higher risk.
- Use routine parasite prevention, including repellents, as recommended by your veterinarian.
If you have any concerns, contact your veterinarian immediately. Screwworm infestations can worsen extremely quickly. A false alarm is better than missing an infestation in the early stages.
Can I travel with my pet if I live in a vulnerable region?
There are increasing restrictions on pet travel as the screwworm outbreak progresses. It is important to keep aware of any updated requirements or restrictions before traveling with your pet.
Can humans or other pets be affected?
If your pet becomes infested with screwworm, they cannot directly infect you or other pets. However, it means that screwworm flies are around you, which increases your risk of infection.
