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.