Current status of sensitivity to praziquantel in a focus of potential drug resistance in Egypt

A decade ago, a study revealed that praziquantel (PZQ) failed to cure 1.6% of those with intestinal schistomiasis in five villages of the Nile delta region. The recommended dosage of PZQ is a single 40 mg/kg oral dose, and each of these patients continued to pass viable Schistosoma mansoni eggs despite three successive doses at or above this level. The eggs passed by these uncured villagers produced adult worms that were, in most cases, significantly less responsive to PZQ in vitro. This report investigates the current sensitivity of S. mansoni infections to PZQ after 10 years of therapeutic pressure in the same villages, testing the hypothesis that the number of drug failures would have increased as continued drug pressure selected for worms with diminished sensitivity to PZQ. The data show that these villages have experienced a significant decrease in the prevalence and intensity of S. mansoni infections, with present infection rate of 10.9%, compared with 25.1% in 1994. The first treatment resulted in normal range of cure rates, between 73.8 and 92.3% in each of the five villages in the study. After three successive doses (40, 40, and 60 mg/kg, the same treatment protocol applied a decade ago) there were no uncured patients remaining in the study. This shows that there has not been an increase of drug failure, despite 10 years of therapeutic pressure in these villages where there had been resistant infections and worms with decreased response to PZQ.