Power to the Parasites
An unusual study is infecting humans with a waterborne worm species to outsmart the neglected disease, schistosomiasis
In the late 18th century, the British doctor Edward Jenner scratched some pus from a Cowpox sore into the arm of an eight-year-old boy to see whether exposure to the virus it contained—vaccinia variola—would subsequently protect the child from its far deadlier relative, the smallpox virus. The experiment might have been highly unethical by current standards, but its success revolutionized preventive medicine, and laid the groundwork for the development of the first smallpox vaccine.
Because human infection challenge research involves the deliberate infection of volunteers with pathogens, however, these types of studies, can be ethically complex. Scientists have collaborated on human challenge studies to test drugs and vaccines for malaria, influenza, shigella, dengue, norovirus, tuberculosis, rhinovirus, Escherichia coli, typhoid, giardia, campylobacter and dengue.
An unusual study at Leiden University Medical Center covered this week by Science is also using this strategy with schistosomiasis. Seventeen volunteers have agreed to be infected with Schistosoma mansoni, one of five tiny waterborne worm species that cause the waterborne disease, schistosomiasis, which affects almost 240 million people worldwide living in tropical and sub-tropical areas, and in poor communities without potable water and adequate sanitation.
Human challenge studies have been avoided with schistosomiasis because the damage from the S. mansoni eggs can be irreversible, but the scientists who designed this experiment have has figure out a way to prevent the parasites from reproducing, which means the risk to volunteers should be extremely low.
With no vaccine or adequate treatments for schistosomiasis, this study is viewed by some as a quick way of fast-tracking viable vaccine candidates. But it is not without controversy, 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,” Daniel Colley, a schistosomiasis researcher at the University of Georgia in Athens, told Science report Kai Kupfershmidt.
If you are interested in reading more about neglected diseases, check out these first-person post about living with dengue or this Q&A with Peter Hotez. You can also pre-register to receive information about our 2nd Annual World Congress, with a focus on rare diseases and personalized medicine.