Key points
- New World screwworm (NWS) is a fly that lays its eggs in open wounds and body openings such as the eyes, ears, nose, mouth, or genitals.
- NWS eggs hatch into parasitic maggots that burrow into and feed on living tissue or flesh.
- You are at higher risk for NWS if you live or travel to areas where NWS flies are found, spend a lot of time outside where flies are, and if you have an open wound.
Overview
New World screwworm (NWS), or Cochliomyia hominivorax, is species of parasitic fly that completes part of its lifecycle by feeding on the tissue or flesh of warm-blooded animals and people. NWS flies are attracted to wounds and body openings like the nose, eyes, ears, and mouth, where they lay eggs. The eggs hatch into maggots (larvae) that eat live tissue, causing a worsening, often painful and foul-smelling wound.
NWS is typically found in South America and parts of the Caribbean. However, the fly has steadily moved northward from South America through every country in Central America and Mexico since 2023.
NWS infestations (presence of maggots on or in the body) do not regularly occur in the United States, but cases have occurred in travelers returning from areas where flies are present. If you travel to these areas, have an open wound and spend a lot of time outdoors, you may be at greater risk of becoming infested with NWS.
Symptoms
Symptoms can include
- Feeling maggots (larvae) move or seeing maggots within a skin wound or sore, or in the ears, nose, eyes, or mouth.
- Painful skin wounds or sores that worsen within a few days.
- A foul-smelling odor from the site of the infestation.
- Bleeding from open sores.
Bacteria can also infect wounds where NWS maggots are present and may cause infection that can lead to symptoms like fever or chills.
Risk factors
You may be at an increased risk for NWS if you are in areas where the flies are present and
- Spend a lot of time outdoors during the day, especially if sleeping or unable to keep flies away.
- Have any open wounds. Even small breaks in the skin, including from a scratch, insect bite, or recent surgery may attract NWS flies.
- Have a medical condition that can cause bleeding or open sores, such as from skin or sinus cancer, or from treatments that create breaks in the skin.
If you live, work, or spend an extended amount of time with (or near) livestock or other warm-blooded animals in areas where NWS flies are present, you could also be at a higher risk for NWS.
How it spreads
New World screwworm infestations begin when a female fly lays eggs on open wounds or other parts of the body in live, warm-blooded animals. Most infestations occur in animals, but they also occur in people. The smell of a wound or body opening such as the nose, mouth, eyes, ears, or genitals can attract female flies. Wounds as small as a tick bite may attract a female fly to lay her eggs. One female can lay 200 – 300 eggs at a time and may lay up to 3,000 eggs during her 10- to 30-day lifespan.
Eggs hatch into maggots that burrow into the wound to feed on the living flesh. After feeding for about 7 days, larvae drop to the ground, burrow into the soil, and emerge as adult screwworm flies.
Prevention
Preventing breaks in the skin and avoiding NWS flies is key to protecting yourself in areas where the flies are present.
- Keep open wounds clean and covered, no matter how small or location on the body.
- Sleep indoors with closed windows or screened open windows. If you are outside, sleep under a bed net or inside a screened tent.
- Protect your skin and prevent insect bites by
- Using an EPA-registered insect repellent.
- Treating clothing and gear with products containing 0.5% permethrin.
- Wearing loose-fitting, long-sleeved shirts and pants, hats, and socks to limit access to your body by NWS flies and biting insects.
Treatment
- If you see or feel maggots in or on a wound or other area of your body, contact your healthcare provider immediately. Tell them if you have recently traveled to Central or South America, the Caribbean, or Mexico.
- Your healthcare provider will need to remove each maggot, sometimes surgically.
- Do not try to remove any maggots or egg masses yourself. If maggots or eggs fall out of the wound, place them in a leak-proof container with rubbing alcohol to kill them. Bring them with you to your healthcare provider.
Urgent
Animal impact
NWS maggots can infest any warm-blooded animal, including birds. NWS can be particularly devastating to livestock health with serious economic impacts. If you see maggots on any animal, whether livestock, pets, or wildlife, contact your veterinarian. Visit screwworm.gov for more information about NWS in animals.
Veterinarians should report any suspicious cases immediately to their state animal health official and APHIS office.
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