Cochliomyia hominivorax, commonly referred to as the New World Screwworm (NWS) or primary screwworm, is a species of fly that can cause disease in humans and animals.  NWS larvae feed on live tissues of any warm-blooded animal.  When larvae from the fly get into a wound, they cause a disease called screwworm myiasis- or an infestation of fly larvae.

NWS is generally an agricultural problem.  Myiasis in cattle can lead to animal death, and can severely impact farmers and the agricultural industry.  Occasionally humans can be at risk for NWS infestations, and those with open wounds or other conditions like diabetes are at greater risk for myiasis. 

Through the work of the United States Department of Agriculture (USDA), NWS was eradicated from the US in the 1960s.  However, NWS is now present in areas of Central America, and other areas where it was previously eliminated.  In 2024, NWS reemerged in Southern Mexico.  

NWS is a serious disease.  If you think you might have been exposed to C. hominivorax and might have an NWS infestation, please see your primary healthcare physician. 

Suspicious animal observations must be reported to Texas Animal Health Commission.

Information for Healthcare Providers

As part of their Clinician Outreach and Communication Activity (COCA) call series, the Centers for Disease Control and Prevention (CDC) held a webinar on NWS myiasis.  A recorded version of that COCA call hosted by CDC here contains more information on identifying and reporting NWS myiasis cases in humans. 

If you suspect your patient might have myiasis caused by a NWS infestation, your local health department can help you arrange testing. Any larvae collected for NWS identification should be submerged in 70% alcohol (ethanol or isopropanol), in plastic container with a screw cap that can be tightly sealed.  Regional Zoonosis Control Offices can give healthcare providers further guidance on sample collection, submission, and interpretation of results. 

The DSHS Laboratory does not accept parasitology specimens from the public.  Only healthcare providers can order parasitology tests and submit specimens for testing.  Specimens submitted by the public will be rejected and destroyed.  If you believe you have a parasitic infection, please talk with your healthcare provider. Laboratory staff cannot provide medical advice. 

Human Sample Submission Information

Download instructions on how to submit a sample

View the latest information from the USDA on NWS northward movement

Screwworm Eradication

The release of sterile insects among native insect populations is the most common approach to successful control of NWS.  The technique, known as the Sterile Insect Technique (SIT) was conceived by Edward F. Knipling in the early 1900s.  By the early 1950s, Knipling and colleagues had completed the development of SIT.  The product of these efforts was be put into practice soon after and  eradicated the pest from the United States by 1966.  SIT programs abroad eventually pushed the pest down to south of Panama by 2000.

Images of Adult Fly and Larvae                        

Learn more about NWS

Texas Animal Health Commission  
Texas’ lead agency regarding NWS
https://www.tahc.texas.gov/animal_health/feverticks-pests/EMGuide-NewWorldScrewworm.pdf
https://www.tahc.texas.gov/animal_health/feverticks-pests/

Texas Parks and Wildlife 
TPWD works with TAHC regarding Texas wildlife
https://tpwd.texas.gov/huntwild/wild/diseases/screwworm/

TAMU AgriLife Extension Service
New World screwworm fact sheet - Texas A&M AgriLife Extension Service

Screwworm Coalition of Texas
https://screwwormtx.org/
 

USDA  
Find updated information on NWS outbreaks as well as historical and general information about the NWS.
New World Screwworm

CDC  
Find updated information on human symptoms, risk factors, how NWS myiasis is spread, and how to prevent it from happening to you.
About New World Screwworm Myiasis | Myiasis | CDC
 

Panama-United States Commission for the Eradication and Prevention of Screwworm Infestation in Livestock (COPEG)  copeg.org/en/
Find updated information on the current NWS situation in the Americas and how the sterile insect technique works.