What is New World screwworm (NWS)?
New World screwworm (NWS) is a type of parasitic fly (Cochliomyia hominivorax) that infests or produces maggots in open wounds of animals and sometimes people. When screwworm maggots infest the skin, they can cause serious skin damage and even death if not treated.
Adult screwworm flies are about the size of a common housefly. They have orange eyes, a metallic blue or green body, and three dark stripes along the back.
[Actual Size]
Image source: CDC
The NWS fly is currently established in:
- Mexico
- Central America
- Caribbean islands, including Cuba, Haiti, and the Dominican Republic
- South America
Who needs to be worried about NWS?
Anyone who goes to an area where NWS is present (whether for work, school, vacation, visiting family, or other activities) needs to be aware of screwworm and protect themselves while in these areas. Because animals (including pets) can be infested, it's especially important for people who travel with their animals, or people who buy or adopt animals outside of the United States, to be aware of NWS and protect their animals.
Pet owners and ranchers along the U.S.-Mexico border should be on alert for signs of possible NWS infestation in their animals.
Veterinarians and human healthcare providers who work along the border should also watch for any infestations in their patients.
Signs and Symptoms
General signs of NWS infestation in people and animals:
Unexplained skin wounds or sores that do not heal or get worse within a few days
Painful skin wounds or sores
Feeling maggots (fly larvae) moving in a skin wound or sore or in the ears, nose, eyes, or mouth
Seeing maggots in or around open sores
A bad-smelling odor from the site of the infestation
Additional signs of possible NWS infestation in animals include:
Agitated behavior
- Head shaking