From Tropics to Maryland: Renewed Vigilance Against Screwworm Threat

By Ruha Lee

Earlier this August, there authorities reported the screwworm diagnosis in Maryland. A tourist, after a brief trip to El Salvador, was found to have contracted a case of the New World screwworm, a flesh-eating fly larva. Vets and doctors state that this parasite is not expected to pose a large threat to human health in the United States. However, populations in regions such as South and Central America and the Caribbean Islands have prompted U.S. government agencies to strengthen monitoring and prevention efforts.

Cochliomyia hominivorax, otherwise known as the New World screwworm fly or screwworm, is a parasitic blowfly belonging to a family whose larvae feed on the living tissue of warm-blooded animals. As the name suggests, it is found mostly in New World tropics such as South America, Central America, the Caribbean Islands, and southern North America. Of species in the genus Cochliomyia, C. hominivorax is the one primarily responsible for parasitic infestations in healthy tissue. Infestation of a living vertebrate animal by a maggot is referred to scientifically as myiasis. While most fly maggots feed on dead or decaying flesh, screwworm maggots are unusual in how they infest healthy tissue. This increases the risk of infection even more, and infected tissue can attract additional flies.

This case was quickly brought under control but raised alarm among researchers who monitor the potential re-emergence of this parasite in the United States. The U.S. eradicated screwworms in the 1960s by carrying out a program of releasing millions of sterile male flies to reduce the breeding population. The program was so successful that it became a model for pest control worldwide. With increased global travel and climate shifts, however, there is concern that screwworm populations could re-establish themselves if not carefully monitored.

According to the U.S. Department of Agriculture [USDA], agricultural economists warn that even a small outbreak could result in billions of dollars in losses. Texas, Florida, and other southern states with large cattle industries are most vulnerable since the larvae most easily attack livestock. Untreated infection can result in extensive tissue damage, suffering, and death in infected animals. The economic effects would extend to the meat and dairy sectors, increasing costs for consumers and impacting export markets. 

To prevent such an infestation, the USDA is building a new sterile fly production facility in Edinburg, Texas, designed to flood susceptible areas with sterilized males should any wild populations arise. Veterinarians are also increasing surveillance, requesting farmers to report unusual wounds on animals immediately. Rapid response teams can then quarantine, treat, and test cases before they spread. This plan relies on cooperation not just from large ranches but also smaller farms and pet owners who might unknowingly have infected animals.

Outside the borders, U.S. agencies work with partners in Panama and Mexico, where permanent screwworm control zones are maintained. These programs periodically release sterile flies in buffer areas to keep populations from moving northward. According to the U.S. Department of Agriculture [USDA], specialists warn that cutting funding for these programs would be a costly mistake, as prevention is far cheaper than eradication after an outbreak takes hold.

Public health administrators emphasize the importance of early detection and treatment. Although the Maryland case did not pose a risk to the general population, it reminds individuals who have traveled to tropical regions to seek medical assessment if they notice unusual skin lesions, particularly those that do not heal or appear to move. Complete recovery usually follows early removal of the larva and treatment with antiparasitic medication.

Scientists continue to explore improved treatments and surveillance tools. Current options rely on ivermectin and careful wound care, which can be labor-intensive for large herds. Advances in biotechnology could one day allow faster prevention or early diagnosis but are still in development.

Researchers stress that biosecurity is an ongoing process. Pests and diseases once thought eradicated can reappear under the right conditions. As global temperatures rise and the range of many insect species expands, the fight against screwworms is one example of how human health, agriculture, and climate are interconnected. 

For now, officials emphasize caution rather than panic. The Maryland case has served as a reminder to veterinarians, farmers, and public health authorities that this ancient foe is never entirely gone. Whether the United States can keep screwworms from regaining a foothold will depend on rapid detection, sound science, and continued cross-border collaboration.