Schistosomiasis, a disease caused by (a parasitic worm) affects 200 million people in the world today. 200,000 die from the disease annually: symptoms of infection including cough, fever, diarrhea and genital sores. Despite the magnitude of the problem, there is only one drug available for mass treatment: praziquantel, raising the question of whether we need to look for an additional or alternative schistasoma treatment. This topic has been tackled by Alan Fenwick of Imperial College London in the latest, freely available issue of Future Medicinal Chemistry.
By next year, Merck KGaA will be providing 250 million tablets of praziquantel to combat the disease and will continue doing so until at least 2020. Other groups providing praziquantel include USAID, DFID, the World Bank and World Vision. With the widespread coverage that should be possible with these supporters, there has been a worry that resistance may arise. There has been a well documented rise in artemisinin resistance in malaria, so will praziquantel suffer the same fate? Professor Fenwick argues that it won’t for a few of reasons:
·Schistosoma worms which have had tolerance to praziquantel induced in the lab appear to show lower reproductive success than normal worms.
·The drug is thought to work by inducing an immune response, thus the worm would have to develop immunity to the varied tools of the immune system, rather than the drug itself.
One of the main existing problems with pranziquantel is that the treatment comes in the form of a large bitter pill which children who are the most vulnerable to Schistosomiasis find difficult to take. However, the bitter taste has been linked to an inactive isomer and if it could be made economical to produce the drug without this isomer, it may solve both the bitterness and the pill size in one go.
For more of Professor Fenwick’s analysis, you can read the whole editorial here