What Is New World Screwworm?
Cochliomyia hominivorax is a parasitic blowfly whose larvae feed exclusively on living tissue. Unlike most wound parasites that target dead tissue, NWS larvae burrow into healthy flesh and consume it, causing progressive myiasis. Untreated infestations can be fatal within days.
The fly lays eggs near any open wound, including wounds as small as a tick bite, a surgical incision, or a minor scratch. Larvae hatch within 12 to 24 hours and begin feeding immediately. Adult flies are metallic blue-green, similar in size to a common housefly.
The US eradicated NWS in 1982 using the sterile insect technique. The June 3, 2026 confirmation in Zavala County, Texas marks the first domestic detection in over four decades. [Source: USDA APHIS · aphis.usda.gov/screwworm]
Any warm-blooded mammal: cattle, deer, horses, dogs, cats, and occasionally humans. Not species-selective.
Any open wound: tick bites, surgical sites, ear canals, skin abrasions, umbilical areas in neonates.
Eggs hatch in 12 to 24 hours. Larvae burrow within 1 to 2 days. Clinical signs appear rapidly.
Year-round in tropical areas. Peak risk in summer in the US as warm temperatures accelerate the fly life cycle.
Source: CDC DPDx; USDA APHIS; Emerging Infectious Diseases (CDC), Feb 2019; screwworm.gov
Who Is at Risk?
Any dog or cat that has travelled through South Texas (Zavala County and surrounding counties) or southern New Mexico since June 3 should be considered at elevated risk. Summer is peak travel season, and companion animals frequently accompany families on road trips through outbreak zones.
- •Open wounds, skin abrasions, or recent injuries
- •Chronic ear infections
- •Post-surgical patients with healing incisions
- •Off-leash dogs in rural/brush areas of TX, NM, AZ
- •Hunting, trail, and camping dogs
- •Outdoor or indoor-outdoor cats in affected corridors
- •Cats with fight wounds or abscesses
- •Cats travelling with families through outbreak areas
Restlessness near a wound area
Wound odor or unusual discharge
Small larvae visible in or around wound
Wound appears larger or deeper than expected
Rapid tissue destruction
Systemic illness: fever, lethargy, anorexia
Visible larval movement in wound
Wound fails to heal or suddenly worsens
Source: USDA APHIS; CDC DPDx (New World Screwworm Myiasis); FDA CVM Dear Veterinarian Letter, June 5, 2026
Clinic Talking Points
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Client FAQs
The eight questions clinics and commercial teams are hearing most. Factual answers as of June 2026.
As of June 2026, confirmed cases are limited to South Texas and southern New Mexico. Pets that have not travelled to those areas and have no open wounds are at very low risk. Monitor the live case map at screwworm.gov as the situation evolves.
Early signs include unusual odor from a wound, a wound appearing to enlarge or deepen unexpectedly, and small cream-colored larvae (1 to 15mm) visible in or around the wound. The animal may show pain, agitation, or systemic illness. Any suspected case should be seen by a veterinarian immediately.
Yes. Several products have received Emergency Use Authorization (EUA) or FDA Conditional Approval for companion animal NWS treatment. Your veterinarian can advise on which product is appropriate. Physical removal of larvae is also a component of treatment.
Most prescription products (Credelio, NexGard) require a veterinary prescription. One generic nitenpyram product has received an OTC EUA. Always consult your veterinarian for diagnosis and treatment decisions. The FDA Dear Veterinarian letter from June 5, 2026 provides full prescribing guidance at fda.gov/animal-veterinary.
Yes. Cats are warm-blooded mammals and are susceptible to NWS myiasis. Two products are specifically authorized for cats: Credelio CAT (Elanco, EUA) and NexGard Combo (Boehringer, EUA). Outdoor and indoor-outdoor cats in affected corridors should be monitored.
NWS myiasis is not directly contagious between pets. Infestation requires an adult NWS fly to lay eggs in a wound. However, a heavily infested animal may attract NWS flies that could then infest other animals with open wounds nearby. Keep wounds covered and clean.
Current guidance is not to cancel travel, but to take precautions: keep wounds clean and covered, avoid areas with heavy wildlife or livestock activity, and inspect your pet daily. If your pet has a healing surgical wound, consult your veterinarian before travelling to affected areas.
screwworm.gov has live case tracking and client-ready resources. USDA APHIS situation reports are at aphis.usda.gov/screwworm. FDA CVM veterinary guidance is at fda.gov/animal-veterinary. Competitive intelligence for commercial teams at vetlaunchlab.com.
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Key Resources
Educational and awareness content only. This guide is for commercial intelligence and educational purposes and is intended to support animal health commercial teams and the veterinary community. This is a rapidly evolving situation, authorization status, case counts, and official guidance may change at any time. Always refer to official government sources: screwworm.gov, aphis.usda.gov/screwworm, and fda.gov/animal-veterinary for current information. All clinical and treatment decisions must be directed by a licensed veterinarian. This content does not constitute veterinary or regulatory advice. Information current as of June 20, 2026.