Report Suspected New World Screwworm (NWS) Immediately
Immediately report any suspected NWS case in animals to all of the following entities--
At the time of publishing, there have been
no detections of NWS in Military Working Dogs (MWDs). The risk of MWDs returning to the U.S. with screwworm infestation is assessed as
very low.
What is NWS?
NWS is the larval stage of a parasitic fly, Cochliomyia hominivorax. NWS larvae feed exclusively on the living flesh of warm-blooded animals, including humans. The adult fly is about twice the size of a house fly and is metallic blue-green with orange eyes. Female flies are attracted to open wounds, mucous membranes, and natural body orifices.
Why is NWS so Dangerous?
NWS infestations cause discomfort, extensive tissue damage and secondary bacterial infections. Common larval infestation sites include fresh wounds such as scratches, injuries, surgery, branding, tick bites and newborn navels. Untreated infestations can lead to debilitation and death within 7–14 days.
How to Prevent NWS
No products are specifically labeled for the prevention of NWS infestation in canines. Appropriate prevention protocol should be made by a veterinarian with a valid Veterinary-Client-Patient Relationship based upon an animal’s geographic location, assigned duties and environmental exposures.
Prevention Recommendations for MWAs
Products containing isoxazolines are preferred over others based on scientific literature, although any product’s duration of protection for NWS in canines has not been clearly defined. MWDs in areas at risk for NWS should use oral flea and tick products labeled for ticks and intestinal parasites in the relevant geographic location with at least 1-month duration of protection.
Topical or collar flea/tick preventives are likely ineffective at preventing NWS infestations.
Veterinarians should instruct all handlers traveling to Mexico and SOUTHCOM to inspect their MWDs daily for signs of myiasis and wounds. MWDs are required to comply with USDA-APHIS screwworm-free certification requirements for entry/re-entry into the U.S. if traveling from screwworm-endemic countries.
Military Working Equines (MWEs) should follow guidance from AVIC 
and SAHO . For more information, visit Pesticides to Potentially Use Against NWS in livestock and horses.
Treatment Recommendations for NWS in MWDs and Pets
The U.S. Food and Drug Administration (FDA) Center for Veterinary Medicine (CVM) has identified animal drugs for prevention or treatment of NWS. Product information and updates are available at New World Screwworm: Information for Veterinarians .
Why is NWS Important to Military Veterinary Personnel?
Military veterinary personnel may be the first line of defense for early NWS detection and response. Veterinary personnel are advised to provide prompt, effective wound care for all military animals, and educate handlers and owners on the need to keep wounds clean, dry and covered. NWS control measures should include minimizing fly populations in and around military animal facilities.
Potential pathways of entry in the U.S. include movement of infested live animals across the southern border; adult flies or larvae transported on vehicles, equipment or clothing; or infested humans returning from endemic areas. Military personnel and working animals deploying from or transiting through NWS-endemic regions could inadvertently transport larvae.
Image Courtesy of TAMU AgriLife Extension.
How to Identify NWS
Veterinary personnel should suspect NWS in animals with unexplained wounds or those recently returning from high-risk areas. Be alert for:
- Maggots in wounds
- Enlarging or deepening wounds, or wounds with a foul odor
- Irritated animal behavior such as head shaking, biting wounds, depression, and isolation
Examine all wounds carefully. A hotspot may not be just a hotspot. Meticulously examine and palpate all wounds, natural orifices and infestation-prone areas.
Larvae may be small to the naked eye and are typically head-down in wounds. NWS larvae are typically smaller and more tapered than other larvae. While NWS feeds on living flesh, wounds can become infested with other deadflesh-eating larvae. There are many morphologically similar species of fly that can cause myiasis, so differential diagnosis should incorporate travel and exposure history as well as clinical presentation.
If veterinary personnel see live animals with maggots, report as a suspected NWS infestation and annotate in the health record.
Collection of Maggots in MWAs or Pets
Any maggots or larvae found in MWAs or pets should be placed into a leak-proof container filled with 70% ethanol or 70% isopropyl alcohol. This will kill larvae and preserve them for diagnostic examination. If ethanol/alcohol is not available, water can be used to drown larvae.
Do not discard live maggots in the trash, medical waste or throw on the ground.
Traveling Internationally with a Pet
Visit New World Screwworm: What You Need to Know Before Traveling Internationally with a Pet to learn more about traveling to or from NWS-affected countries.
Additional Resources
