About New World Screwworm

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Key points

  • Myiasis is a parasitic infestation of fly larvae (maggots) in human tissue.
  • New World screwworm (NWS) is a species of parasitic fly that can cause myiasis and feeds on live tissue.
  • It primarily affects livestock, but it can also infest people.
  • NWS is typically found in South America, Cuba, Haiti, and the Dominican Republic.
  • You are at higher risk for NWS if you travel in these areas, are around livestock in rural areas where the flies are, and if you have an open wound.
Two individual larvae on a blue background

Overview

New World screwworm (NWS) infestation occurs when NWS fly larvae (Cochliomyia hominivorax) infest the tissue or flesh of warm-blooded animals and people. Screwworm flies are attracted to and lay eggs on and in open wounds. NWS does not regularly occur or spread in the United States. The parasite is typically found in South America and the Caribbean, although Mexico and countries in Central America are reporting cases in animals and people. If you travel to areas where the flies are present, have an open wound, spend time among livestock animals, or sleep outdoors, you may be at greater risk of becoming infested with NWS.

Resource

NWS: What You Need to Know

Symptoms

NWS infestations are very painful. If you have an NWS infestation, you may see maggots around or in an open wound. They could also be in your nose, eyes, or mouth. Tell your healthcare provider of any recent travel to Central or South America, the Caribbean, or Mexico.

Symptoms can include

  • Feeling maggots (larvae) moving within a skin wound or sore, ears, nose, eyes, or mouth.
  • Seeing maggots around or in open sores.
  • Painful skin wounds or sores.
  • A foul-smelling odor from the site of the infestation.
  • Unexplained skin wounds or sores that do not heal or worsen within a few days.
  • Bleeding from open sores.

Bacteria can also infect wounds where NWS maggots are present and may cause fever or chills.

For Health Care Providers Clinical Overview of New World Screwworm

Risk factors

You may be at an increased risk for NWS if you are in areas where the flies are present and

  • Have an open wound, from a scratch or cut, from an insect bite, or from a recent surgery.
  • Have a weakened immune system, for example from HIV, cancer treatment, or medications that weaken your immune system.
  • Have a medical condition that can cause bleeding or open sores, such as from skin or sinus cancer.
  • Sleep outdoors, especially during the day.

If you live, work, or spend an extended amount of time with (or near) livestock or other warm-blooded animals in these areas, 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. It primarily affects livestock but can also infest birds and people. The smell of a wound or an opening such as the nose, mouth, or eyes, umbilical cord of a newborn animal, or genitals, will attract the female flies. Wounds as small as a tick bite may attract a female fly to feed and 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, larvae drop to the ground, burrow into the soil, and emerge as adult screwworm flies.

Prevention

Prevention is key to protecting yourself from NWS in areas where the flies are present.

  • Keep open wounds clean and covered.
  • Prevent insect bites, especially when visiting areas where NWS files are present.
  • Wear loose-fitting, long-sleeved shirts and pants, and socks to limit areas where you could get bitten.
  • Use an EPA-registered insect repellent.
  • Treat clothing and gear with products containing 0.5% permethrin.
  • Sleep indoors (if the room has windows, the windows should be screened). If you are outside, sleep under a bed net or inside a screened tent.

Treatment

  • If you see or feel maggots in or on a wound or other area of your body, contact your healthcare provider immediately.
  • Your healthcare provider will need to remove each maggot, sometimes surgically.
  • Do not try to remove any maggots or egg masses yourself. Do not throw any in the trash or outside as this could result in NWS spreading in your area.
  • If maggots or eggs do fall out of the wound, place them in a leak-proof container with rubbing alcohol. If you do save the maggots and eggs in a container, bring them with you to your healthcare provider.

Reminder

If you are a healthcare provider removing larvae from a patient, place all larvae in a leak-proof container, directly into 70% ethanol (or other alcohol) and contact CDC's DPDx lab for specimen submission instructions.

If you think your patient has NWS, report it immediately to your local or state health department by contacting the appropriate Epi on Call.

Animal impact

If you see maggots on an animal, contact your veterinarian. Visit USDA's website for more information about NWS in animals.

Veterinarians should report any suspicious cases immediately to their state animal health official and APHIS office.

Resources

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Content Source:
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)