New research into efficacy of repeated mass drug administration
In a study involving primary school children in Uganda, praziquantel was found to have reduced efficacy against Schistosoma mansoni infection after multiple rounds of mass drug administration (MDA).
The mass distribution of praziquantel as a means of controlling schistosomiasis has been widely adopted across sub-Saharan Africa. This approach is dependent on the continued high efficacy of praziquantel, however drug efficacy is rarely monitored using appropriate statistical approaches that can detect early signs of wane.
The research team conducted a cross-sectional study of six schools in eastern Uganda. Students at the schools had received between one and nine rounds of praziquantel MDA for S. mansoni control during an 11-year period. The researchers gauged drug efficacy by collecting and measuring student egg reduction rates (ERR).
The study included 414 children (50.84% female) aged 6 to 12 years showed that S. mansoni and soil-transmitted helminths (STH) were present in 34% of the students, the majority of infections being hookworm.
Analysis showed the mean ERR among children in the schools that had received eight or nine rounds of MDA (91.49%) was significantly lower compared with those of students at schools that had received five rounds (98.04%) or one round (97.81%).
The researchers estimated that 16.42% of the children whose schools received eight to nine rounds of praziquantel MDA had ERRs below the 90% threshold set by WHO for optimal efficacy vs. those exposed to one round (5.11%) and eight or nine rounds (4.55%).
Researchers found that reduced praziquantel efficacy is caused by drug-tolerant genetic variants within the S. mansoni population in highly treated areas.The effect of this reduction in efficacy poses a potential threat to the effectiveness of schistosomiasis control programmes. In response to these findings, WHO has revised its strategic plan from disease control to the interruption of transmission in selected African countries, including Uganda, by 2025.