Since 2023, an outbreak of New World screwworm (NWS) has advanced north through Central America and Mexico, predominantly affecting livestock, pets, and wildlife, but also people. On June 3rd, 2026, the United States Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) reported the first animal cases of New World screwworm (NWS) in the United States from this outbreak and subsequently more animal cases have been identified in both Texas and New Mexico. No locally acquired human cases have been reported in the United States at this time.
Additional information about the current NWS outbreak is available here.
More information about NWS in animals can be found at screwworm.gov.
Background
NWS is a fly (Cochliomyia hominivorax) whose larvae (maggots) feed on the living tissue of warm-blooded animals, including humans. The adult fly lays eggs in open wounds or body openings. After the eggs hatch, the maggots burrow into and consume living tissue, causing painful and rapidly worsening wounds.
NWS is endemic to the American tropics and subtropics, including most countries in South America, as well as Cuba, Haiti, and the Dominican Republic. It was eradicated from the United States in the 1960’s and was pushed all the way out of Mexico and Central America by the early 2000’s but remained endemic in South America and few places in the Caribbean. There has been one other outbreak in the United States in the Florida Keys in 2016-2017, but the flies were once again eradicated from the U.S. after a very large, coordinated response. However, since 2023, its range has been expanding northward into Central America and Mexico since the recent breakdown of the biologic barrier zone at the Darien Gap at the Panama-Colombia border.
How it Spreads
People can become infected when a screwworm fly lays eggs on open cuts or wounds (even small ones), surgical sites, insect bites, or body openings such as the nose, ears, eyes, or mouth. NWS does not spread from person to person or from animal to person.
Signs and Symptoms
Symptoms usually begin within a few days of exposure and may include:
- Visible movement or presence of maggots in a wound or in the ears, nose, eyes, and mouth
- A painful wound that worsens in a few days
- Foul-smelling drainage from the infestation site
- Bleeding from open sores
Who Is at Risk?
People may be at a higher risk for NWS if they are in places where the flies are found and:
- Have open sores or wounds, even small ones, or recent surgical sites
- Spend a lot of time or sleep outdoors
- Are physically or mentally unable to keep flies away
- Have medical conditions that may cause open sores or bleeding
Others who may be at higher risk for NWS infestation include those who live, work, or spend long periods of time around livestock or other warm-blooded animals in areas where NWS flies are present.
Testing and Diagnosis
Diagnosis is based on maggot identification, which is coordinated with state and federal partners. Do not throw any live maggots in the trash or outside, as this could result in NWS spreading in your area. All larvae and eggs should be submerged in either 70% ethanol or ≥70% isopropanol to kill them. Do not put them in formalin as this will make identification more difficult or even impossible.
Treatment
All visible larvae and eggs should be removed (and submerged in either ethanol or isopropanol as described above) for identification/testing as well as to ensure they are dead for disposal. This may require surgical intervention depending on the extent of infestation. Healthcare providers should monitor and treat any secondary bacterial infections.
Prevention
In areas where NWS is present, people should:
- Clean and cover all wounds, regardless of size or location on the body
- Protect skin and prevent insect bites by:
- Using an EPA-registered insect repellant
- Treating clothing with products containing 0.5% permethrin
- Wearing loose-fitting, long-sleeves, long pants, hats, and socks
- Avoid sleeping outdoors, especially in the daytime. If sleeping outdoors cannot be avoided, sleep inside a screened tent or use a bed net.
Resources for the Public
- CDC: About NWS
- A brief (2-page PDF) about NWS for the public can be found at: NWS: What You Need to Know (Spanish version).
Resources for Healthcare Providers
- CDC: Clinical Overview of NWS
- Brief CDC guidance (2-page PDF) about NWS for healthcare providers can be found at NWS: Recommendations for Healthcare Providers and at Project Firstline and NWS: What Healthcare Workers Need to Know
- CDC recorded webinar: Resurgence of NWS in the Americas: What Healthcare Providers Need to Know
Resources for NWS in Animals
- Arkansas Department of Agriculture: NWS
- Report suspicious cases by submitting information, including location and photographs, to the Arkansas Department of Agriculture through an online reporting tool or call (501) 823-1746 or email [email protected].
- If NWS is suspected, isolate the affected animal immediately and avoid moving any animals off premises, as movement can rapidly spread the pest.
- A one-page PDF on how agriculture employees can stop NWS can be found at: Stop New World Screwworm: agriculture employees (Spanish version)
- A one-page PDF on how agriculture producers can stop NWS can be found at: Stop New World Screwworm: agriculture producers (Spanish version)
- Report suspicious cases by submitting information, including location and photographs, to the Arkansas Department of Agriculture through an online reporting tool or call (501) 823-1746 or email [email protected].
- Arkansas Game and Fish Commission
- Contact the Arkansas Game and Fish Commission at [email protected] to report a suspect case of NWS in wildlife.
- University of Arkansas Division of Agriculture Research & Extension: NWS
- Screwworm.gov | Unified Government Response To Protect the United States
- FDA: NWS Information for Veterinarians
- American Veterinary Medical Association: NWS
Resources for Laboratories
- NWS larval identification is carried out in collaboration with state and federal partners, and these documents explains how to distinguish NWS larvae from other species.
Helpful Links
Public Health Reporting in Arkansas
Report immediately to:
Arkansas Department of Health
Zoonotic Disease Section
Phone: 501-280-4136
After hours: 1-800-554-5738
[email protected]