New World Screwworm
High severityInfectiousAlso known as: NWS, Screwworm myiasis
A reportable parasitic infestation in which the larvae (maggots) of the New World screwworm fly burrow into the living flesh of warm-blooded animals. Wounds enlarge rapidly and can be fatal if untreated. After decades of US eradication, cases have re-emerged as the fly spreads north from Central America and Mexico.
Reported on ParvoMaps
Symptoms to watch for
- A wound that keeps enlarging instead of healing
- Visible maggots deep within a wound
- Foul-smelling or bloody discharge
- Pain, head-shaking, or constant licking of one spot
- Loss of appetite and lethargy
- Withdrawing from people or other animals
How it spreads
Adult female flies lay eggs at the edges of open wounds, even tiny ones like tick bites or scratches, or on moist tissue (nostrils, eyes, genitals). The hatched larvae feed on living flesh. Not spread directly dog-to-dog.
Prevention
Keep wounds clean and covered, treat injuries promptly, and inspect animals after travel to affected areas. Screwworm is a reportable foreign animal disease; if you suspect it, contact your veterinarian and state animal-health officials immediately.
Recent reports
Related infectious conditions
Frequently asked questions
What are the symptoms of New World Screwworm in dogs?
Common signs include A wound that keeps enlarging instead of healing, Visible maggots deep within a wound, Foul-smelling or bloody discharge, Pain, head-shaking, or constant licking of one spot, Loss of appetite and lethargy, Withdrawing from people or other animals. Signs vary by dog and stage — contact your veterinarian if you notice them.
How do dogs catch New World Screwworm?
Adult female flies lay eggs at the edges of open wounds, even tiny ones like tick bites or scratches, or on moist tissue (nostrils, eyes, genitals). The hatched larvae feed on living flesh. Not spread directly dog-to-dog.
How can I prevent New World Screwworm in dogs?
Keep wounds clean and covered, treat injuries promptly, and inspect animals after travel to affected areas. Screwworm is a reportable foreign animal disease; if you suspect it, contact your veterinarian and state animal-health officials immediately.
Is New World Screwworm dangerous to dogs?
New World Screwworm is considered high severity. A reportable parasitic infestation in which the larvae (maggots) of the New World screwworm fly burrow into the living flesh of warm-blooded animals. Wounds enlarge rapidly and can be fatal if untreated. After decades of US eradication, cases have re-emerged as the fly spreads north from Central America and Mexico.
Educational information only — not veterinary advice. If you think your dog is sick, contact your veterinarian.