Development of a vaccine against schistosomiasis
Seventeen volunteers got themselves blood suckers
A pilot study was conducted at the University of Leiden (the Netherlands), during which 17 people voluntarily allowed themselves to be injected with Schistosoma – parasitic worms that cause the disease schistosomiasis. Every year it takes the lives of up to 200,000 people around the world. Scientists have reduced the risk of negative consequences for the participants of the experiment as much as possible, but some risks remain, reports Science (Seventeen volunteers let this worm live inside them to help defeat a dangerous disease).
Schistosomes, better known as blood flukes, belong to the class of trematodes (Digenea). These parasites penetrate through the skin and settle in the human bloodstream, where they lay eggs, affecting the bladder, liver and other organs. In recent years, this disease has begun to affect not only the poor population of Asian and African countries, but also tourists from Western countries. Praziquantel is currently used for its treatment, but many experts consider it insufficiently effective, especially against neglected cases of the disease.
As with other parasitic diseases, the best method for testing new drugs or vaccines is to use them on infected people (human challenge model). Previously, prisoners often took part in such experiments, but currently there are many ethical and legislative restrictions for conducting such experiments.
Infectious disease specialist Meta Roestenberg and her colleagues from the University of Leiden have been developing a new vaccine against schistosomiasis for a long time, but in order to test it in a series of clinical trials, they had to make sure that the experimental infection of the subjects would be safe, and the presence of live worms in their body could be tracked by special biochemical markers.
To do this, scientists found 17 volunteers – ordinary Dutch people who agreed to put parasites in their blood for a while. The subjects are injected with 20 Schistosoma mansoni specimens grown in the laboratory. At the same time, only males – this is done so that parasites do not multiply and do not lay eggs, which cause the most severe consequences of schistosomiasis (tissue fibrosis).
Scientists will observe volunteers for 12 weeks and analyze their blood for the presence of a special serum protein amyloid A, which signals inflammatory and other immune reactions caused by schistosomes. During a future trial of the vaccine, it is the level of this protein in the blood that will determine whether it is effective against parasites or not. After the experiment, the scientists plan to destroy all parasites in the blood of volunteers using the old drug praziquantel.
There is no guarantee that all schistosomes will be destroyed, Rostenberg admits. But one or two surviving parasites probably will not affect the health and well-being of the host in any way. According to her, this was one of the most pressing issues when discussing the experiment with the ethics commission.
The volunteers are aware of all the risks, but this did not change their determination to participate in the study. Among them there are scientists, doctors and people from tropical regions who know firsthand about the danger of schistosomiasis and want to help defeat this disease. If the experiment goes according to plan, trials of the new vaccine will begin at the end of 2018.
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