Two cases of the New World screwworm in dogs in Texas and New Mexico have prompted warnings from veterinarians and humane societies for pet owners to remain vigilant. This marks the parasite's return to the U.S. more than 50 years after it was largely eradicated.
The New World screwworm is the larval stage of a fly that consumes live flesh and bodily fluids. While its migration north from Panama, through Mexico, poses a threat to the U.S. cattle industry, the larvae can develop in any mammal, including wildlife, pets, and occasionally humans.
The problem begins when a female screwworm fly lays eggs in open wounds or mucous membranes. The hatched larvae feed for approximately one week before maturing, dropping to the ground to develop into adult flies.
Newborn animals, those with open wounds, or pets that have recently undergone surgery are particularly vulnerable, according to the American Veterinary Medical Association. Even a tick bite can become an entry point for infestation. Signs of an infestation include visible maggots or movement within a wound, a foul odor, or noticeable anxiety and restlessness in an animal. Pets may also repeatedly focus on or chew a specific area of their body.
Veterinarians and humane society officials advise pet owners in affected areas, currently southern and southwestern Texas and southeastern New Mexico, to regularly examine their animals for any wounds, cuts, or bites. If any signs are observed, contacting a veterinarian immediately is recommended, as untreated infestations can be fatal due to shock, infection, or the larvae moving into vital organs.
To prevent infestations, shelters in Texas are administering prescription flea and tick medications to animals, a practice recommended for pet owners as well. These medications contain chemicals that kill the larvae upon ingestion of blood and tissue.
Veterinarians can treat screwworm infestations, and animals can recover with prompt medical attention, which may include antibiotics. The parasite is only considered fatal if left untreated.
Federal and state agriculture officials are employing an eradication method used decades ago: releasing sterile male flies. Female screwworm flies mate only once in their lifespan, and if their partner is sterile, their eggs will not hatch, leading to a decline and eventual disappearance of the population in a given area. The USDA has invested $21 million to establish a facility in southern Mexico for breeding sterile flies and plans to open a new $750 million facility in Texas next year.