The mystery of a worm infestation discovered in a Vietnamese man last year has been answered, but not without adding yet another horrific twist to the story. The worms inside the man weren’t Guinea worms (Dracunculus medinensis), a now-rare parasite on the verge of extinction.
Instead, they were a closely related and unknown Dracunculus species that was most likely indigenous to the area. It is yet unknown whether or not this other worm offers a current or future hazard to humans.
In June 2020, Vietnamese news sites reported on a bizarre case involving a 23-year-old guy who had entered a hospital with abscesses on his arms and neck.
Doctors eventually identified and removed five adult worms, each about 1 to 2 feet long, as well as larvae, from the man’s wounds. Antiparasitics were provided to the individual, and no more infestations were discovered.
A doctor involved in the case was described at the time as noting that the man appeared to have Guinea worm illness, which would have been concerning for a number of reasons. Millions of people in Asia and Africa were infected with these agonizing and often permanently debilitating illnesses every year in the 1980s.
But, with the exception of a few African places, decades of arduous public health work have drove the creatures to near extinction. (Only 27 cases were reported in total in 2020.) Despite recent failures, it is hoped that Guinea worm will be the second human infection to be completely eradicated by 2030, following smallpox. So finding the Guinea worm thousands of kilometers distant from its last known traces, in a location where it had never been detected, would have been cause for concern.
Adam Weiss, director of the Carter Center’s Guinea Worm Eradication Program, a human rights group founded by former US President Jimmy Carter, even speculated that the man’s infestation could have been caused by a different species of Dracunculus. And it turned out that theory was correct.
The doctors who investigated the case published their findings in the International Journal of Infectious Diseases in March. Following the man’s treatment, they sent samples of the worm to the CDC in the United States for genetic testing, which verified that it wasn’t D. medinensis. But the enigma develops beyond that.
Dracunculus parasites infest a variety of primary species, as do many parasites. D. medinensis is the only known worm that has a specific appetite for human hosts, however other species prey on animals and reptiles. The doctors came to the conclusion that the man’s worms looked more like reptile-loving worms than any human or mammal worm.
However, only a few Dracunculus species have had their genes examined in detail, and the tested worm did not match any of them. It’s possible that the worm belongs to a species that’s already been discovered but hasn’t been genetically sequenced, but its identity remains unknown for the time being.
Another unanswered question is if this was a one-time occurrence or the first indicators of a growing sickness in the area. Dracunculus worms have their preferences, but they can cross species barriers on occasion—a capability that has hindered the Guinea worm eradication campaign in recent years, since the worms have begun to infest canines in some locations. Across addition, there have been intermittent reports of additional non-Guinea but Dracunculus human infestations in Asia over the years.
Just because this unknown worm doesn’t generally target humans doesn’t mean it won’t do so in the future. We also have no idea how the worms got into the man’s body, while the most popular theories are that he drank water polluted with infected copepods (small crustaceans that are part of the worms’ life cycle) or ate contaminated raw fish.
In an accompanying editorial, infectious disease doctors Martin Grobusch and Thomas Hänscheid set out the many unsolved concerns and advised against being too enthusiastic that this case was a rare occurrence, at least until additional research was done.