Plasmodium vivax and Plasmodium falciparum ex vivo susceptibility to anti-malarials and gene characterization in Rondônia, West Amazon, Brazil

Abstract

BackgroundChloroquine (CQ), a cost effective antimalarial drug with a relatively good safety profile and therapeutic index, is no longer used by itself to treat patients with Plasmodium falciparum due to CQ-resistant strains. P. vivax, representing over 90% of malaria cases in Brazil, despite reported resistance, is treated with CQ as well as with primaquine to block malaria transmission and avoid late P. vivax malaria relapses. Resistance to CQ and other antimalarial drugs influences malaria control, thus monitoring resistance phenotype by parasite genotyping is helpful in endemic areas.MethodsA total of 47 P. vivax and nine P. falciparum fresh isolates were genetically characterized and tested for CQ, mefloquine (MQ) and artesunate (ART) susceptibility in vitro. The genes mdr1 and pfcrt, likely related to CQ resistance, were analyzed in all isolates. Drug susceptibility was determined using short-term parasite cultures of ring stages for 48 to 72 hour and thick blood smears counts. Each parasite isolate was tested with the antimalarials to measure the geometric mean of 50% inhibitory concentration.ResultsThe low numbers of P. falciparum isolates reflect the species prevalence in Brazil; most displayed low sensitivity to CQ (IC50 70 nM). However, CQ resistance was rare among P. vivax isolates (IC50 of 32 nM). The majority of P. vivax and P. falciparum isolates were sensitive to ART and MQ. One hundred percent of P. falciparum isolates carried non-synonymous mutations in the pfmdr1 gene in codons 184, 1042 and 1246, 84% in codons 1034 and none in codon 86, a well-known resistance mutation. For the pfcrt gene, mutations were observed in codons 72 and 76 in all P. falciparum isolates. One P. falciparum isolate from Angola, Africa, showing sensitivity to the antimalarials, presented no mutations. In P. vivax, mutations of pvmdr1 and the multidrug resistance gene 1 marker at codon F976 were absent.ConclusionAll P. falciparum Brazilian isolates showed CQ resistance and presented non-synonymous mutations in pfmdr1 and pfcrt. CQ resistant genotypes were not present among P. vivax isolates and the IC50 values were low in all samples of the Brazilian West Amazon.

Assessment of copy number variation in genes related to drug resistance in Plasmodium vivax and Plasmodium falciparum isolates from the Brazilian Amazon and a systematic review of the literature

“…1). The fixation of the 76T allele is in agreement with other studies in Brazil [43, 55, 56], despite the withdrawal of CQ from national treatment guidelines in the mid-1980s [57]. The presence of the 76Y allele is in accordance with the description of isolates resistant to CQ in the same regions analysed here [43, 55].…”

K13 Propeller Alleles, mdr1 Polymorphism, and Drug Effectiveness at Day 3 after Artemether-Lumefantrine Treatment for Plasmodium falciparum Malaria in Colombia, 2014-2015

“…These findings are similar to the 100% S1034 and 93.3% 1042D prevalences reported for Colombian isolates (20,32) and to the 84% 1034C and 100% 1042D prevalences reported for Brazilian isolates (38). Although SNPs at positions 1034 and 1042 have not been adequately evaluated, the 1042D mutation has been associated with increased in vitro susceptibility to LF in Thailand in 1999 to 2002, when AS-MQ was being used to treat falciparum malaria (42).…”

“…It is not known whether this is because LF is selecting the N86 allele or because CQ-which has limited use in the treatment of vivax malaria-is failing to select the 86Y allele, which is found at increased levels in some regions following CQ use and is associated with decreased CQ susceptibility in vitro in Asia (39). We also found that 98.3% of our samples carried the 184F mutation, similarly to the 92.8% and 100% prevalences reported for Colombian Pacific Coast samples (32) and Brazilian samples (38). The relationship between the 184F mutation and antimalarial drug responses is unclear, as it has been associated with decreased in vitro susceptibility to MQ, HF, and quinine (QN) in some studies (37,40) but not in others (37,41).…”

“…In Benin, however, the wild-type N86 allele was selected for in recurrent infections after AL treatment and was associated with decreased LF and MQ susceptibility ex vivo (37). Remarkably, 100% of our Colombian isolates carried the wild-type N86 allele, as did 100% of Brazilian isolates in 2012 to 2013 (38). It is not known whether this is because LF is selecting the N86 allele or because CQ-which has limited use in the treatment of vivax malaria-is failing to select the 86Y allele, which is found at increased levels in some regions following CQ use and is associated with decreased CQ susceptibility in vitro in Asia (39).…”

In Vitro Susceptibility of Plasmodium vivax to Antimalarials in Colombia

“…Such results suggest that derivatives of artemisinins have been effective against this type of parasite. However, an IC 50 of 32.6 nM was found for artesunate in Thailand in 2011 and an IC 50 of 21.0 nM was found for this antimalarial in a Brazilian region in 2014, which suggests a susceptibility loss of P. vivax to this antimalarial in two different geographic regions (Table 5) (9,19,21,22,36,38). In this study, when the isolates were classified according to the initial parasitic stages, IC 50 s of 0.3 nM for AS in group 1 and 1.4 nM in group 2 were found (Table 3).…”