Reduced efficacy of albendazole against Ascaris lumbricoides in Rwandan schoolchildren

Abstract

Control of human soil-transmitted helminths (STHs) relies on preventive chemotherapy of schoolchildren applying the benzimidazoles (BZ) albendazole or mebendazole. Anthelmintic resistance (AR) is a common problem in nematodes of veterinary importance but for human STHs, information on drug efficacy is limited and routine monitoring is rarely implemented. Herein, the efficacy of single dose albendazole (400 mg) was evaluated in 12 schools in the Huye district of Rwanda where Ascaris is the predominant STH. Ascaris eggs were detected by wet mount microscopy and the Mini-FLOTAC method to assess cure rate (CR) and faecal egg count reduction (FECR). Blood and faecal samples were analysed for co-infections with Plasmodium sp. and Giardia duodenalis, respectively. Ascaris positive samples collected before and after treatment were analysed for putatively BZ-resistance associated β-tubulin gene single nucleotide polymorphisms. The overall CR was 69.9% by Mini-FLOTAC and 88.6% by wet mount microscopy. The FECR was 75.4% and the 95% calculated confidence intervals were 50.4-87.8% using sample variance, 55.4-88.8% by bootstrapping, and 75.0-75.7% applying a Markov Chain Monte Carlo Bayesian approach. FECR varied widely between 0 and 96.8% for individual schools. No putative BZ-resistance associated polymorphisms were found in the four Ascaris β-tubulin isotype genes examined. Since FECRs <95% indicate reduced efficacy, these findings raise the suspicion of BZ resistance. In the absence of respective molecular evidence, heritable AR in the local Ascaris populations cannot be formally proven. However, since FECRs <95% indicate reduced efficacy, BZ resistance may be suspected which would be alarming and calls for further analyses and routine monitoring in preventive chemotherapy programs.

Keywords: Albendazole; Ascaris; Benzimidazole; Deworming; Resistance; Soil-transmitted helminth; Tubulin.

Graphical abstract

Fig. 1

Statistical analyses of treatment effects. Three schools for which only very few positive samples were found before treatment (between 1 and 4) are not shown here. (A) Cure rates for all samples from all 12 schools (Total) and for 9 individual schools (also presented in Fig. 1 or Fig. S1) are shown. Vertical lines indicate for comparison in red mean cure rate (continuous) and lower 95% CI (broken line) as determined in a meta-analysis by Keiser and Utzinger (2008) and in blue the mean (continuous) and lower range (broken line) of a recent study from 7 South American, African and Asian countries published by Vercruysse et al. (2011b). Feacal egg count reductions (FECR) were calculated as arithmetic means and 95% CI were calculated according to the approximate method postulated by Coles et al. (1992) (B) or using parametric bootstrapping with 10,000 iterations as described by Torgerson et al. (2005) (C). Alternatively, FECR and 95% credibile intervals were obtained as mode and highest posterior density intervals (95% HPD) after sampling from a Markow Chain Monte Carlo approach (D). In (B–D), the region between 95 and 100% FECR corresponding to full efficacy is highlighted by grey shading. Estimates of the FECR are shown in red and the 95% CI/HPD in black. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Effects of treatment on eggs per gram faeces. Faecal egg counts are shown for all paired samples from 12 schools (All schools) or for selected schools (Sholi, Mbazi, Karama, Sovu, Kigoma). In order to improve the legibility of the diagrams, data for the remaining schools are shown in Fig. S1. N, number of paired samples; n, number of samples negative before and after treatment.

Fig. s1

Effects of treatment on eggs per gram stool (faeces) in 2014. Feacal egg counts are shown for those schools not shown in Fig. 1. N, number of paired samples; n, number of samples negative before and after treatment or number of samples with an increase in FEC as specified in brackets.

Fig. s2

Individual faecal egg count reduction and Plasmodium prevalence in different schools. (A) Box plots show distribution of individual faecal egg count reductions (FECR) in different schools with wiskers indicating the 10 and 90% percentile. Schools with only a few number of sample pairs (≤5) were excluded. The minimal number of pairs per included school was 8. Except for Kigoma, the mean of all datasets was 100%. (B) Prevalence of Plasmodium for the same schools included in (A). Error bars indicate 95% confidence intervals. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Fig. s3

Effects of treatment on eggs per gram stool (faeces) in 2015 for additional schools. N, number of paired samples; n, number of samples negative before and after treatment or number of samples with an increase in FEC as specified in brackets.