Science revisits one of my childhood nightmares (one of many blessings from frequent family visits to South Africa) with news of researchers infecting volunteers with what my aunts called “bilharzia” and what scientists now call “schistosomiasis.” Seventeen people intentionally let snail-borne parasitic worms burrow into their skin in order to find new ways to stop the deadly disease… if possible:
The light and warmth signal hundreds of tiny larval parasites to stream out of the mollusk. Now, the clock starts ticking for Meta Roestenberg, an infectious disease physician here at Leiden University Medical Center. She has about 4 hours to launch a unique, controversial experiment in which she will let the parasites burrow into the arms of four healthy volunteers. If she waits too long, the larvae start to die.
Roestenberg and her colleagues are infecting people with Schistosoma mansoni, one of five tiny waterborne worm species that cause schistosomiasis, a disease that sickens millions of people in Africa, the Middle East, and Latin America and kills thousands each year. There is no schistosomiasis vaccine and only one old, inadequate drug, praziquantel, to treat it. Infecting humans could help speed up the development of new interventions. Roestenberg has designed the experiment to prevent the parasites from reproducing, and she says the risk to volunteers is extremely low.
But not low enough, some scientists argue, because there is no guarantee that subjects will get rid of their parasites when the study is over. “I would not volunteer for this study and if I had a son or daughter who wanted to volunteer, I would recommend against it,” says Daniel Colley, a schistosomiasis researcher at the University of Georgia in Athens.
Studies in which people are purposely infected with malaria, cholera, and flu are on the rise, but they haven’t been done with schistosomiasis, in part because damage from the S. mansoni eggs can be irreversible. The goal of the current study, which began in early 2017, is to find out whether Roestenberg’s infection model is safe; if so, she hopes to test a vaccine later this year.
In nature, people become infected with both male and female parasites, but Roestenberg uses only males, so there will be no eggs and thus, she says, no symptoms. And when the study ends in 12 weeks, the volunteers will be given praziquantel to cure them.
That drug, Colley emphasizes, is “not terribly effective.” But Roestenberg says that even if it fails, volunteers needn’t worry. “The ethics board asked me: ‘If one worm survives even after multiple treatments, what will happen to that person?’ And I said: ‘They’ll probably live to be 100.’” The board gave her its blessing. Colley agrees the risk is low, but still, S. mansoni has an average life span of 5 to 10 years. “That is a long time to have something as ugly as a schistosome living in your blood vessels, putting out excrement and things.”
Once infected, the volunteers will return to the lab every week so the research team can test their blood for a molecule called CAA, which the worms regurgitate from their stomachs. CAA’s presence will indicate that the worms are still alive; in future trials, its absence might mean that a vaccine or drug has worked.
The full story has more, including a vivid microscopic photo of one of the teeny tinyworms and a wonderful quote from one of the volunteers describing how it feels to have a pack of them burrowing through your skin and into your bloodstream.