(The latest human case may mark a “first” in the US in that it may be the first travel-related case from a country in Central America experiencing an outbreak since the previous eradication.)
Screwworms—or technically New World Screwworms (NWS)—are parasitic flies that spawn hundreds of ravenous larvae in the wounds and orifices of a wide range of warm-blooded animals. The parasites get their names from the larvae, which look and act like screws, boring and twisting into their victim’s flesh. As the larvae feast on living flesh, they create repulsive, excruciatingly painful festering wounds that can easily turn fatal in wild animals and livestock. The US Department of Agriculture has estimated that an outbreak of screwworms in Texas—a major cattle-producing state—could cause $1.8 billion in economic damage.
While the infection is typically not fatal in humans, it is still extremely painful and gruesome. Adult female flies can lay up to 400 eggs at a time, and each larva in a human patient has to be physically dug out from infected flesh. As CDC Medical Officer Rebecca Chancey remarked in a clinical presentation last October about their resurgence, the larvae are “pretty tenacious and hang on pretty tightly, so oftentimes, you know, a great deal of force is required to remove them.” After that, treatment can involve removing necrotic tissue, cleaning the wounds, and treating for secondary infections while trying to manage the pain.
Gruesome cases
While details of the case in Maryland are not known, the CDC in that presentation last year laid out details of three other travel-related cases. One case in 2024 was in a Florida man who had traveled to the Dominican Republic and unknowingly had a screwworm fly lay eggs in his nose. The man had previously had a cancerous tumor removed from his nose and was immunosuppressed. Back in Florida, his face abruptly began swelling, and he developed constant nose bleeds. When he went to the hospital, doctors were shocked to find his nose and sinus cavities erupting with 100 to 150 larvae.
