06/13/2026
New World Screw Worm
New World screwworm (NWS) myiasis is a serious disease that affects livestock, pets, wildlife, occasionally birds, and in rare cases, people. The disease is most often detected in cattle, swine, horses, small ruminants, and dogs.
NWS flies are attracted to wounds. Animals that have given birth, suffered an injury, or had a surgical procedure, such as dehorning or branding, are most vulnerable. Even tick bites can attract NWS flies.
NWS can also infest mucus membranes. Dogs and cats at higher risk include those that:
Spend significant time outside
Have skin folds, long hair, allergies, or medical conditions
Are recovering from surgery or have recently given birth
Are infested with mites, fleas, or ticks
What to look for
Maggot in wounds or other body openings, such as the nose, ears and genitalia or the navel of newborn animals.
Wounds that have bloody discharge and foul odor
Wounds that become deeper and larger as the maggots grow and feed on living tissue
Please contact your veterinarian if you see wounds that you see maggots and/or becoming deeper and larger.
Treatment and Control
The current status of NWS and the authorized treatments available
Approved or Conditionally Approved by FDA for NWS are:
Credelio Quattro
Emergency Use Authorizations (EUA) Issued by the FDA for NWS for dogs and cats are:
Credelio Chewable tablets
Credelio Cat Chewable tablets
Nexgard chewable tablets
Nexgard Combo Topical for Cats
