Melarsoprol Sensitivity Profile of Trypanosoma brucei gambiense Isolates from Cured and Relapsed Sleeping Sickness Patients from the Democratic Republic of the Congo

Abstract

BackgroundSleeping sickness caused by Trypanosoma brucei (T.b.) gambiense constitutes a serious health problem in sub-Sahara Africa. In some foci, alarmingly high relapse rates were observed in patients treated with melarsoprol, which used to be the first line treatment for patients in the neurological disease stage. Particularly problematic was the situation in Mbuji-Mayi, East Kasai Province in the Democratic Republic of the Congo with a 57% relapse rate compared to a 5% relapse rate in Masi-Manimba, Bandundu Province. The present study aimed at investigating the mechanisms underlying the high relapse rate in Mbuji-Mayi using an extended collection of recently isolated T.b. gambiense strains from Mbuji-Mayi and from Masi-Manimba.Methodology/Principal FindingsForty five T.b. gambiense strains were used. Forty one were isolated from patients that were cured or relapsed after melarsoprol treatment in Mbuji-Mayi. In vivo drug sensitivity tests provide evidence of reduced melarsoprol sensitivity in these strains. This reduced melarsoprol sensitivity was not attributable to mutations in TbAT1. However, in all these strains, irrespective of the patient treatment outcome, the two aquaglyceroporin (AQP) 2 and 3 genes are replaced by chimeric AQP2/3 genes that may be associated with resistance to pentamidine and melarsoprol. The 4 T.b. gambiense strains isolated in Masi-Manimba contain both wild-type AQP2 and a different chimeric AQP2/3. These findings suggest that the reduced in vivo melarsoprol sensitivity of the Mbuji-Mayi strains and the high relapse rates in that sleeping sickness focus are caused by mutations in the AQP2/AQP3 locus and not by mutations in TbAT1.Conclusions/SignificanceWe conclude that mutations in the TbAQP2/3 locus of the local T.b. gambiense strains may explain the high melarsoprol relapse rates in the Mbuji-Mayi focus but other factors must also be involved in the treatment outcome of individual patients.

Whole genome sequencing shows sleeping sickness relapse is due to parasite regrowth and not reinfection

“…However, no single genotype appears to confer resistance to all strains. Consistent with this observation, each of the 19 Tbg isolates in our study, regardless of patient treatment outcome, contain a chimeric TbAQP2/3 gene, which is associated with increased pentamidine and melarsoprol cross-resistance Pyana Pati et al 2014).…”

“…As reported in Pyana Pati et al. (), these isolates contain a chimeric gene, TbAQP2/3 , in place of the TbAQP2 and TbAQP3 loci, and are wild type at the TbAT1 locus. Our results support this finding.…”

“…; Pyana Pati et al. ). Many potential targets of mutation appear to exist that can alter a strain's sensitivity, increasing the likelihood an infection will persist through treatment.…”

“…Variation in genes previously shown to affect melarsoprol resistance Table 2 summarizes variation found in 14 genes known to be associated with melarsoprol resistance from previous studies (Maser et al 1999;Shahi et al 2002;Alsford et al 2012;Baker et al 2012). As reported in Pyana Pati et al (2014), these isolates contain a chimeric gene, TbAQP2/3, in place of the TbAQP2 and TbAQP3 loci, and are wild type at the TbAT1 locus. Our results support this finding.…”

“…Furthermore, strains isolated from a region in Sudan with high melarsoprol treatment failure rate did not appear to have resistant TbAT1 alleles (Maina et al 2007). Similar to TbAT1, mutations in aquaglyceroporins occur in natural populations, but are not sufficient to predict relapse after melarsoprol treatment (Graf et al 2013;Pyana Pati et al 2014). Many potential targets of mutation appear to exist that can alter a strain's sensitivity, increasing the likelihood an infection will persist through treatment.…”