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Greater MDA reduces praziquantel efficacy against schistosomiasis in Ugandan students
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Children in Ugandan primary schools who were exposed to higher mass drug administration of praziquantel showed reduced resistance to Schistosoma mansoni, according to recently published research.
“Mass drug administration (MDA) began in Uganda in 2003 and 400,000 treatments of praziquantel were distributed that year,” Joanne P. Webster, DPhil, in the department of infectious disease epidemiology at the Imperial College London, and colleagues wrote. “This has since expanded to the treatment of approximately 1.5 million children annually, resulting in significant reductions in S. mansoni prevalence, intensity and associated morbidity.
“Spurred by these results, WHO revised its strategic plan from disease control to the interruption of transmission in certain African countries, including Uganda, by 2025.”
To determine whether the quantity of MDA was linked with the efficacy of praziquantel, Webster and colleagues 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. Parasitic egg counts — collected from Kato-Katz smears before (n = 2,090) and after (n = 2,012) MDA from the students — totaled 4,102. The researchers observed S. mansoni and soil-transmitted helminths in 34% of the students, the majority being hookworm.
Analysis showed the mean ERR among children in the schools that had received eight or nine rounds of MDA (91.49%; 95% Bayesian credible interval [BCI], 88.23-93.64) was significantly lower compared with those of students at schools that had received five rounds (98.04%; 95% BCI, 96.13-99.08) or one round (97.81%; 95% BCI, 95.51-98.96).
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%).
“We are left with the possible explanation that reduced praziquantel efficacy is caused by drug-tolerant genetic variants within the S. mansoni population in highly treated areas,” Webster and colleagues wrote. “We call for the efficacy of anthelmintic drugs used in MDA to be closely monitored.” – by Kate Sherrer
Disclosure: The researchers report no relevant financial disclosures.
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