Chloroquine-resistant Infections Research Articles

No Association between the Plasmodium vivax crt-o MS334 or In9pvcrt Polymorphisms and Chloroquine Failure in a Pre-Elimination Clinical Cohort from Malaysia with a Large Clonal Expansion.

Increasing reports of resistance to a frontline malaria blood-stage treatment, chloroquine (CQ), raises concerns for the elimination of Plasmodium vivax. The absence of an effective molecular marker of CQ resistance in P. vivax greatly constrains surveillance of this emerging threat. A recent genetic cross between CQ sensitive (CQS) and CQ resistant (CQR) NIH-1993 strains of P. vivax linked a moderate CQR phenotype with two candidate markers in P. vivax CQ resistance transporter gene (pvcrt-o): MS334 and In9pvcrt. Longer TGAAGH motif lengths at MS334 were associated with CQ resistance, as were shorter motifs at the In9pvcrt locus. In this study, high-grade CQR clinical isolates of P. vivax from a low endemic setting in Malaysia were used to investigate the association between the MS334 and In9pvcrt variants and treatment efficacy. Among a total of 49 independent monoclonal P. vivax isolates assessed, high-quality MS334 and In9pvcrt sequences could be derived from 30 (61%) and 23 (47%), respectively. Five MS334 and six In9pvcrt alleles were observed, with allele frequencies ranging from 2 to 76% and 3 to 71%, respectively. None of the clinical isolates had the same variant as the NIH-1993 CQR strain, and none of the variants were associated with CQ treatment failure (all P > 0.05). Multi-locus genotypes (MLGs) at 9 neutral microsatellites revealed a predominant P. vivax strain (MLG6) accounting for 52% of Day 0 infections. The MLG6 strain comprised equal proportions of CQS and CQR infections. Our study reveals complexity in the genetic basis of CQ resistance in the Malaysian P. vivax pre-elimination setting and suggests that the proposed pvcrt-o MS334 and In9pvcrt markers are not reliable markers of CQ treatment efficacy in this setting. Further studies are needed in other endemic settings, applying hypothesis-free genome-wide approaches, and functional approaches to understand the biological impact of the TGAAGH repeats linked to CQ response in a cross are warranted to comprehend and track CQR P. vivax.

Human genetic variation influences Plasmodium falciparum drug resistance selection

Here we address the issue of the possible interplay between host genetic variation and the risk of acquiring Plasmodium falciparum drug-resistant strains. The involvement of human genetic variation as a possible co-factor in the selection and spread of P. falciparum drug resistance is a new tool in the study of malaria and possibly of other infectious diseases. The driving hypothesis of this approach is that parasite drug resistance could be affected both by ethnicity and human variability in the genes encoding for enzymes that metabolise antimalarials (cytochrome P450 liver enzymes). Understanding if parasite drug sensitivity is influenced and possibly modulated by human diversity can contribute to a better knowledge and control of the spread of drug resistance. So far, few studies have addressed this strategic issue. To explore this hypothesis we carried out an association analysis on 506 human/P. falciparum DNA samples from adult asymptomatic subjects belonging to three sympatric ethnic groups of Burkina Faso, an area of hyperendemic malaria in West Africa. Here we report that the prevalence of chloroquine-resistant infections (pfcrt 76T and/or pfmdr1 86Y) differs among sympatric ethnic groups, being higher in Mossi and Rimaibe compared to Fulani (OR: 2.24; 1.27-3.92; P = 0.007). Moreover, the human CYP2C8*2 variant, known to determine a poor drug metaboliser phenotype, is associated with P. falciparum chloroquine-resistant infections (OR: 1.66; 1.13-2.43; P = 0.008). The results strongly suggest that human genetic variation affects the dynamics of selection of parasite drug-resistance. We strongly believe that these observations are of general interest and may have important implications in public health.

Human Genetic Variation Is Associated With Plasmodium falciparum Drug Resistance

One approach to investigate if human genetic variation influences the selection of Plasmodium falciparum drug resistance is to compare the frequency of resistant infections among human populations differing in their genetic background and living in the same epidemiological context. A further complementary approach consists in comparing drug resistance among subjects differing for genes involved in drug metabolism. Here we report, from malariological surveys performed in Burkina Faso, that the prevalence of P. falciparum chloroquine-resistant infections (pfcrt 76T and/or pfmdr1 86Y alleles) differs among sympatric ethnic groups, being higher in the Mossi and Rimaibé groups than in the Fulani group (odds ratio [OR], 2.24; 95% confidence interval [CI], 1.27-3.92; P = .007). The association analysis revealed that the human CYP2C8*2 variant, known to determine a poor drug metabolizer phenotype, was associated with P. falciparum chloroquine-resistant infections (OR, 1.66; 95% CI, 1.13-2.43; P = .008). This variant is more frequent in the Mossi-Rimaibé group (23.7% ± 1.4%) than in the Fulani group (9.9% ± 2.5%; P = .0003). This study provides an example of how host genetic variation may influence the selection dynamics of a pathogen's drug resistance.

Patterns of chloroquine use and resistance in sub-Saharan Africa: a systematic review of household survey and molecular data

BackgroundAs a result of widespread chloroquine and sulphadoxine-pyrimethamine (SP) resistance, 90% of sub-Saharan African countries had adopted policies of artemisinin-based combination therapy (ACT) for treatment of uncomplicated malaria by 2007. In Malawi, cessation of chloroquine use was followed by the re-emergence of chloroquine-susceptible malaria. It was expected that introduction of ACT would lead to a return in chloroquine susceptibility throughout Africa, but this has not yet widely occurred. This observation suggests that there is continuing use of ineffective anti-malarials in Africa and that persistent chloroquine-resistant malaria is due to ongoing drug pressure despite national policy changes.MethodsTo estimate drug use on a national level, 2006-2007 Demographic Health Survey and Multiple Indicator Cluster Survey data from 21 African countries were analysed. Resistance data were compiled by systematic review of the published literature on the prevalence of the Plasmodium falciparum chloroquine resistance transporter polymorphism at codon 76, which causes chloroquine resistance.ResultsChloroquine was the most common anti-malarial used according to surveys from 14 of 21 countries analysed, predominantly in West Africa. SP was most commonly reported in two of 21 countries. Among eight countries with longitudinal molecular resistance data, the four countries where the highest proportion of children treated for fever received chloroquine (Uganda, Burkina Faso, Guinea Bissau, and Mali) also showed no significant declines in the prevalence of chloroquine-resistant infections. The three countries with low or decreasing chloroquine use among children who reported fever treatment (Malawi, Kenya, and Tanzania) had statistically significant declines in the prevalence of chloroquine resistance.ConclusionsThis study demonstrates that in 2006-2007, chloroquine and SP continued to be used at high rates in many African countries. In countries reporting sustained chloroquine use, chloroquine-resistant malaria persists. In contrast, a low level of estimated chloroquine use is associated with a declining prevalence of chloroquine resistance.

CHLOROQUINE-RESISTANT PLASMODIUM VIVAX MALARIA IN PERU

Reports from several sites in South America suggest the presence of isolated cases of chloroquine-resistant Plasmodium vivax malaria. To investigate the possibility of chloroquine-resistant P. vivax in Peru, we conducted 28-day in vivo drug efficacy trials at three sites in the Amazon region and one site on the northern Pacific Coast between 1998 and 2001. A total of 242 patients between the ages of 2 and 60 years were enrolled (177 from the Amazon region and 65 from the northern coast). All subjects received directly observed therapy with chloroquine, 25 mg/kg, over a three-day period. On enrollment, 49% had a documented fever and 96% had a history of fever; their geometric mean parasite density was 5,129 parasites/microL. A total of 212 (88%) of the 242 subjects completed their 28-day follow-up. Four of the 177 patients from the Amazon region had a recurrence of P. vivax parasitemia on days 21 and 28 after treatment was initiated. Two of these patients had chloroquine-resistant infections, based on polymerase chain reaction-single-stranded conformational polymorphism genotyping and chloroquine-desethylchloroquine blood levels, which were > or = 97 ng/mL at the time of the reappearance of parasitemia. None of the subjects studied on the northern Pacific Coast had recurrent parasitemia.

Polyamine metabolism in various tissues during pathogenesis of chloroquine-susceptible and resistant malaria.

The pathophysiological impact of infections with chloroquine-susceptible (CQS) and chloroquine-resistant (CQR) strains of Plasmodium berghei in Mastomys natalensis was studied with respect to changes in polyamine profiles in various tissues. Both CQS and CQR infections produced similar changes in polyamine profiles of various tissues. Maximum increase was recorded in spleen followed by liver and lungs. Renal, cardiac and cerebral tissues did not register significant changes. An increase in spermidine level was more prominent as compared to putrescine and spermine, leading to an overall increase in spermidine/spermine ratio. This ratio is an important index of cellular proliferation. Liver did not show considerable change in the activities of ornithine decarboxylase and S-adenosyl methionine decarboxylase, the regulatory enzymes of the polyamine biosynthetic pathway. Spleen however, registered marked induction of both the enzymes which was more prominent in the CQS infection than CQR. Normal erythrocytes contained traces of polyamine while the erythrocytes loaded with P. berghei parasites exhibited appreciably higher polyamine levels. Spermidine was detected in about five-fold higher concentrations than putrescine and spermine which were detected in equimolar levels. Again, CQS as well as CQR P. berghei, exhibited qualitatively and quantitatively similar polyamine profiles thus ruling out a role of polyamines in CQ-resistance in malaria.

Features of recrudescent chloroquine-resistant Plasmodium falciparum infections confer a survival advantage on parasites and have implications for disease control

This paper reports on the features of recrudescent infections of chloroquine-resistant Plasmodium falciparum (CQRPf) malaria from a study in vivo of patients from a malaria endemic ( n = 527) and non-endemic ( n = 129) region of Sri Lanka where the incidence of RI resistance was 30% and 55%, respectively. In both groups of patients, the recrudescent infections which emerged after treatment of the primary infection with chloroquine (CQ) and primaquine had significantly lower peripheral parasitaemia (0·036% and 0·108% in endemic and non-endemic patients, respectively) compared to their primary infections (mean parasitaemia 0·13% and 0·49%; P = 0·021 and 0·002, respectively). The recrudescences of CQ resistant infections also gave rise to clinical disease of markedly reduced severity (average clinical scores of 10·1 and 8·2) compared to their primary infections (average clinical scores of 12·4 and 12·3; P = 0·003 and 0·001, respectively, in endemic and non-endemic patients). CQ resistant recrudescent infections therefore had a lower probability of being diagnosed and treated. In endemic patients, a higher proportion of CQRPf infections (57%) had gametocytaemia compared to the chloroquine sensitive ones (29%) ( P = 0·014, χ 2 = 5·96) and were significantly more infective to mosquitoes ( P = 0·047). These findings imply that, in areas where CQ resistance is prevalent, the continued use of the drug may confer a survival and propagation advantage on resistant parasites and favour the rapid expansion of their reservoir. In support of this, we also present epidemiological evidence showing that, in endemic areas, the proportion of P. falciparum patients carrying gametocytes has increased significantly since the emergence of chloroquine resistance. These findings are relevant to the management of drug resistance and malaria control in countries where P. falciparum is only partially resistant to CQ.

Risk factors of chloroquine resistance in Plasmodium falciparum malaria

Objective: To identify patient-related risk factors of chloroquine resistance. Design: A case control study. Subjects: Plasmodium falciparum infected school children were followed prospectively for 7 days for the detection of chloroquine resistance. Cases were 38 individuals with chloroquine resistant infections. Controls were 125 individuals with chloroquine sensitive infections. Cases were compared with controls with respect to previous or current study factor levels. Subjects were recruited from randomly selected schools which were stratified for area. Study location was in North Guadalcanal, Solomon Islands. Outcome measure: Treatment failure of chloroquine in standard dosage (25 mg/kg). Follow-up period was 7 days. Results: Logistic regression resulted in 5 independent significant predictors of chloroquine resistance, obtained simultaneously with the diagnosis of malarial infection: (i) Young age (odds ratio (OR) for age < 7 years: 7.1; 95% confidence interval (CI): 2.5–25.0; OR per year increase after the age of 5 years: 0.8; 95% CI: 0.6–0.9). (ii) High parasite density (OR for > 1000/ gml: 5.0; 95% CI: 2.0–10.6; OR per 500 parasites/μl increase: 1.3; 95% CI: 1.1–1.7). (iii) Normal spleen size (OR: 4.0; 95% CI: 1.5–10.8). (iv) Malnutrition (OR: 4.9; 95% CI: 1.8–13.2). (v) Presence of gametocytes in the thick smear (OR: 3.0; 95% CI: 1.1–8.0). Conclusion: The identified risk factors are easily measurable without special equipment. They may be useful for health workers in the Solomon Islands, even in remote areas, to identify Plasmodium falciparum infected individuals at high risk for chloroquine resistance before a treatment decision is made.

Studies on a new antimalarial compound: pyronaridine

Pyronaridine, a hydroxyanilino-benzonaphthyridine derivative synthesized in 1970, is a new antimalarial compound which has been in use in China for more than 10 years. The drug is highly effective against Plasmodium falciparum and P. vivax. Furthermore, it is efficacious in combatting chloroquine-resistant strains of falciparum malaria both in vitro and in vivo, in human patients. Extensive field studies involving several thousand cases have shown that pyronaridine has promising therapeutic value in the treatment of malarial infection, including chloroquine-resistant infections. Pyronaridine given orally, intramuscularly or by intravenous drip is not only effective against malaria but also has low toxicity.

In vitro microtechnique for determining the drug susceptibility of cultured parasites of Plasmodium falciparum

1976). Studies were initiated with pyri- methamine and sulphadiazine in order to develop a system for monitoring the susceptibility of parasites to sulphonamide-pyrimethamine combinations, such as Fansidar, which are widely used in the treatment of chloroquine-resistant infections of

Determination of the Drug Sensitivity of Plasmodium falciparum

Chloroquine-resistant infections of malaria are prevalent in many areas of Southeast Asia and South America and their importation into the United States will remain a problem during the foreseeable future. The sensitivity of Plasmodium falciparum to chloroquine and other antimalarial drugs can be determined by a simple in vitro technique. It provides an expedient method for identifying drug-resistant strains and is useful in assessing the blood schizontocidal activity of some antimalarial agents. During studies with the recently solated Vietnam (Marks) strain of P falciparum , parasites showed a marked degree of resistance to chloroquine in vivo and in vitro, but they were significantly more susceptible to amodiaquine. The findings suggest that some P falciparum infections resistant to chloroquine may respond more favorably to treatment with another 4-aminoquinoline.