Global Strays Fights Screwworms' Terrible Toll
A small fly, the iridescent blue-green of a hummingbird, packs a nasty surprise.

If flies can be considered beautiful, you just might think that of the Cochliomyia Hominivorax. Unlike the housefly, its body is an iridescent blue-green reminiscent of a hummingbird. But it carries a deadly secret: this fly lays its eggs in mammals’ cuts and wounds, and its larva, New World Screwworms, hatch and painfully eat their way out, even killing animals–especially horses.
Three Decades After Eradicating Screwworm Nicaragua Faces a Deadly Resurgence
Working horses already faced unthinkable conditions in Nicaragua. Frequently underfed, overworked, and left with untreated wounds, the terrible lives that many of these horses endure can be difficult to comprehend. Compounding their misery, last year Nicaragua confirmed they found screwworms in cattle and horses, making the lives of working horses in this country that much harder. Being infected by this parasite is extremely painful, yet many owners don’t realize their animals are sick. At a slew of free Global Strays Horse Clinics last month, vets and techs identified screwworm cases and taught horse owners to recognize the signs of screwworm, including those in places like hooves and nasal cavities, which can be more difficult to notice. In just one month Global Strays screened 301 horses, treated those infected, and educated horse owners, ensuring they knew what to look for and how to treat their horses for screwworm.
Not seen in Central America since the 1990s, screwworm’s resurgence has left working horse owners in Nicaragua reeling, and closer to home it has put the US Department of Agriculture (USDA) and US Equestrian organizations on alert, because these parasites long thought eradicated could return.
For horses and people in Nicaragua the return of this deadly parasite is a tragedy. As Enrique Chamorro, a horse owner attending one of Global Strays free clinics, explains, “It’s a very harmful insect.That worm, that fly. It will kill any animal, so we have to be very careful–even for us because veins attract that insect.” Kenia Davila agrees, emphasizing the dangers posed by the fly “I know [it can affect humans], people have told me about cases, and I’ve seen a video.”

Healing Working Horses and Slowing Down The Rate of Infection
There is no simple veterinary solution to fully halt screwworms’ spread. However, Global Strays is working on the ground, making a real difference by treating horses and educating people about its dangers. At our working horse clinics in Nicaragua, we directly address infestations by thoroughly cleaning wounds, removing larvae, and giving horses medication–bringing these horses much needed relief.
Just as importantly, our team is taking the time to educate the community on a disease most have never encountered before. Each owner is shown how to identify and treat infections. This not only reduces suffering and saves their horses’ lives, it slows down infection rates of their neighbors’ animals as well.
A One Health, One Welfare Approach

Dr. Lester Tapia, lead veterinarian at our clinics, highlights the serious nature of this parasite “The screwworm infestation in Nicaragua is quite concerning. It not only poses a problem for working equines, I am particularly worried about human health, especially in the communities where we are working… We must continue to safeguard the health of these horses to maintain healthy populations, following the One Health, One Welfare approach.” (The One Health approach recognizes that human, animal and environmental health are all interconnected, and, because of this, emphasizes the importance of coordinated efforts.)
The overwhelming response to our free working horse clinics, which are filled to capacity, underscores the critical need for these interventions. By supporting Global Strays, you contribute to a holistic approach that protects animals and enhances the well-being of entire communities facing the persistent threat of screwworm.