The New World screwworm, a parasitic fly, poses a significant threat to livestock and can also be dangerous to pets. Recently, two out of 34 animals affected by screwworm since early June were dogs. One case occurred in New Mexico, and the other in Texas. While the risk to most pets in the U.S. remains low, those residing in areas with confirmed screwworm cases, including specific counties in New Mexico and Texas, face an elevated risk.
Screwworm infestations are a disturbing phenomenon. The adult female fly, Cochliomyia hominivorax, deposits its eggs in open wounds or body openings of warm-blooded animals. Upon hatching, the larvae feed on the host’s flesh, causing severe tissue damage, potential infections, and in critical cases, death, especially if not addressed promptly.
Fortunately, preventative measures and treatments are available. Many flea and tick medications, specifically isoxazolines, can help protect pets. These medications not only eliminate fleas and ticks but also kill screwworm larvae. While they don’t prevent flies from laying eggs in wounds, they stop the larvae from causing the devastating damage associated with infestations. The Food and Drug Administration (FDA) has issued emergency use authorizations for several treatments for dogs and cats, including NexGard and Credelio. These prescription medications, designed to prevent flea and tick infestations, are expected to offer protection against screwworm as well.
Beyond preventative medications, the FDA has also approved nitenpyram (Capstar, CapAction) as a treatment for existing screwworm infestations in dogs and cats. This over-the-counter medication rapidly kills adult fleas and has shown effectiveness in eliminating screwworms within 24 hours. Following treatment, a veterinarian may need to manually remove any remaining larvae to prevent further complications.
For pet owners in affected areas, daily inspection of pets that spend time outdoors is recommended. While keeping pets indoors is a more cautious approach, it is generally advised if a pet has an open wound. Given the current screwworm outbreaks in Texas and New Mexico, limiting pets’ unsupervised outdoor time, especially around livestock and where flies are present, is a sensible precaution.
The challenge of controlling this screwworm outbreak is considerable. While one of the recently affected dogs in New Mexico recovered, the dog in Texas succumbed to the infestation. Eradicating screwworm historically involves releasing sterile flies to disrupt the reproductive cycle, a process that can be lengthy and complex. This particular outbreak is expected to be a persistent issue for some time.