First U.S. Case of Travel-Related New World Screwworm Identified in Maryland: Health Officials Investigate Flesh-Eating Parasite Outbreak

In a notable development, health authorities have confirmed a case of travel-related New World screwworm in Maryland. The patient, who had recently returned from El Salvador, was identified by the US Department of Health and Human Services (HHS).

The Centers for Disease Control and Prevention (CDC) and the Maryland Department of Health are now investigating this case, with HHS spokesman Andrew Nixon confirming the parasitic infestation on August 4. Details regarding the patient’s current condition remain undisclosed.

According to Nixon, this is the first human case of New World screwworm myiasis (infestation by fly larvae) from an outbreak-affected country reported in the United States. He emphasized that the risk to public health from this introduction is currently very low.

Since early 2023, an outbreak of New World screwworms has been spreading across Central America, affecting countries such as Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, and Panama. This fly species, known for nesting in the wounds of warm-blooded animals and consuming their flesh, reached southern Mexico towards the end of last year.

The outbreak has sparked concerns among US agricultural industry officials, leading to closures of border-area cattle, horse, and bison trading ports this year. To combat this threat, the US Department of Agriculture (USDA) announced plans to construct a fly production facility in Edinburg, Texas, at Moore Air Force Base. This facility could produce up to 300 million sterile flies per week to mate with wild female flies and control the population.

USDA Secretary Brooke Rollins stated that this domestic production of sterile flies would ensure the United States continues to be a leader in combating this destructive pest, as its absence is crucial for maintaining the nation’s food supply.

In addition, USDA plans to provide up to $100 million for advanced technologies, including traps and lures, therapeutics, and techniques to enhance fly production. The agency also plans to employ “Tick Riders” for surveillance and train screwworm detection dogs to identify outbreaks among livestock.

This month, HHS issued an emergency declaration, granting the US Food and Drug Administration (FDA) more flexibility in authorizing animal drugs for treating and preventing New World screwworm infestations. Although no FDA-approved drugs for this parasite are available in the United States, this declaration allows the agency to authorize drugs for emergency use.

New World screwworms are the larval form of the metallic blue blow fly species Cochliomyia hominivorax. Unlike other blow flies native to the Western Hemisphere, these maggots feed on the flesh of living animals rather than dead ones. The infestation process begins when a female fly lands on a wound and lays eggs, which hatch and burrow into the host’s tissue within 12 to 24 hours, causing extensive wounds.

If left untreated, these flesh-eating maggots can kill an animal in a matter of one to two weeks and spread to others. Treatment for infested cattle typically involves cleaning, antiseptic treatment, and wound coverings.