New World Screwworm
You may have recently seen updates from the United States Department of Agriculture (USDA) and the California Department of Food and Agriculture (CDFA) regarding New World Screwworm (NWS).
While there are currently no known cases of New World Screwworm in California, recent detections in Texas and northern Mexico have put veterinarians and agricultural officials on heightened alert. Because animal movement is the primary way this pest spreads, staying informed and proactive is our best defense.
As your holistic and integrative Sonoma County vet, Wise and Wonderful Integrative Veterinary Center is here to partner with you in providing the best possible care for your pet and provide everything you need to know about New World Screwworm, signs to watch for, and how to keep your animals safe.
What Is New World Screwworm?
The New World Screwworm (Cochliomyia hominivorax) is a parasitic fly. While common houseflies lay eggs in decaying matter or dead tissue, female screwworm flies lay their eggs on open wounds of living, warm-blooded animals.
Within 12 to 24 hours, these eggs hatch into larvae (maggots) that burrow into healthy living flesh to feed. Left untreated, screwworm infestations cause severe tissue damage, intense pain, secondary infections, and can be fatal.
Who Is at Risk?
All warm-blooded animals can be affected, including:
Pets: Dogs, cats, and small animals.
Livestock and Equines: Horses, cattle, sheep, goats, and pigs.
Newborns: Neonatal animals are particularly vulnerable around the umbilical area.
Signs and Symptoms to Monitor
The key to treating screwworm is early detection. Inspect your animals regularly, paying extra attention to cuts, bites, or recent surgical sites.
Common warning signs include:
Unhealing or Worsening Wounds: A minor scratch, bite, or umbilical site that suddenly gets bigger, deeper, or inflamed.
Visible Eggs or Larvae: White fly eggs or maggots active inside or around the edges of a wound or body orifice (ears, eyes, nose, or mouth).
Foul Odor: A distinct, unpleasant smell coming from the wound site.
Signs of Discomfort: Excessive licking, biting, scratching at a specific area, or signs of intense pain and restlessness.
How to Protect Your Animals
Preventing screwworms boil down to basic wound management and insect control:
Clean and Cover Wounds Promptly: Treat even small scrapes, bug bites, or surgical incisions right away. Keep them clean and covered with bandages or protective sprays whenever possible.
Keep Up with Parasite Control: Use vet-approved flea, tick, and fly preventatives. Minimizing bug bites reduces the scratches and sores where screwworm flies like to lay eggs.
Be Cautious When Traveling: If you travel with pets or transport livestock out of state (especially to or through areas with active detections, like Texas or Mexico), inspect your animals daily during and after the trip. Check current CDFA import requirements before moving animals back into California.
Inspect Newborn Animals: Make sure umbilical cords on newborn calves, foals, kids, or puppies are properly disinfected and monitored closely.
What to Do If You Suspect Screwworm
If you notice maggots or suspicious, fast-worsening wounds on your animal, take action immediately, but take specific safety precautions:
IMPORTANT: Do NOT throw live maggots or eggs into the trash, flush them down the drain, or wash them into the soil. Improper disposal of screwworm maggots can allow the screwworm to continue its lifecycle and potentially establish itself in California.
Collect a sample safely: If larvae or eggs fall off or can be removed easily, place them directly into a sealable container filled with 70% rubbing alcohol (isopropyl alcohol) to preserve and neutralize them. Note: common flies can inhabit the necrotic tissue left behind by burrowing screwworm, so be sure to collect larvae from the deepest portion of the wound, where screwworms will burrow into living tissue.
Contact your veterinarian immediately: Screwworm is a reportable condition in California. Call your veterinarian right away so your animal can be evaluated, report the findings to state authorities, and start proper, safe treatment.
We’re Here to Help
While California remains free of New World Screwworm, vigilance from pet owners, ranchers, and veterinarians is what will keep it that way.
Please reach out to Wise & Wonderful Integrative Veterinary Center, 707-546-4646, your local Santa Rosa, CA, animal clinic, if you have questions about insect prevention, travel safety guidelines, or an unusual wound on your pet
