Myiasis

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 of emerging concern, as infestations with this parasite can be very aggressive. It was previously eradicated from North America, but is now being seen in Mexico and is at risk of coming back to the United States.

What pets are most often infected?

Both dogs and cats can be infected and are at higher risk if they have open wounds, are weak or ill, are incontinent, or live in unclean conditions. Animals living in warmer, wet areas are also more likely to become infected.

Once eggs are laid, they hatch and result in hundreds or thousands of larvae, which may or may not be visible. Skin infections are often visible, but infections in the nose or intestine are not.

What signs does myiasis cause?

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 merge together (coalesce)
• Wounds that appear around the eyes, nose, mouth, anus, or near previously noted wounds
• Round nodules under the skin
• Irritability or restlessness
• Depression 
• Poor appetite

How is myiasis treated?

Treatment includes:

• 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.
• 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.
• Keep your pet at an ideal weight.
• Limit outdoor exposure, reducing their exposure to flies.
• Use routine parasite prevention, including repellants, as recommended by your veterinarian.