High Chloroquine Resistance Research Articles

Genomic analysis of Plasmodium vivax describes patterns of connectivity and putative drivers of adaptation in Ethiopia

Ethiopia has the greatest burden of Plasmodium vivax in Africa, but little is known about the epidemiological landscape of parasites across the country. We analysed the genomic diversity of 137 P. vivax isolates collected nine Ethiopian districts from 2012 to 2016. Signatures of selection were detected by cross-country comparisons with isolates from Thailand (n = 104) and Indonesia (n = 111), representing regions with low and high chloroquine resistance respectively. 26% (35/137) of Ethiopian infections were polyclonal, and 48.5% (17/35) of these comprised highly related clones (within-host identity-by-descent > 25%), indicating frequent co-transmission and superinfection. Parasite gene flow between districts could not be explained entirely by geographic distance, with economic and cultural factors hypothesised to have an impact on connectivity. Amplification of the duffy binding protein gene (pvdbp1) was prevalent across all districts (16–75%). Cross-population haplotype homozygosity revealed positive selection in a region proximal to the putative chloroquine resistance transporter gene (pvcrt-o). An S25P variant in amino acid transporter 1 (pvaat1), whose homologue has recently been implicated in P. falciparum chloroquine resistance evolution, was prevalent in Ethiopia (96%) but not Thailand or Indonesia (35–53%). The genomic architecture in Ethiopia highlights circulating variants of potential public health concern in an endemic setting with evidence of stable transmission.

High chloroquine treatment failure rates and predominance of mutant genotypes associated with chloroquine and antifolate resistance among falciparum malaria patients from the island of Car Nicobar, India

An in vivo chloroquine efficacy study was undertaken on the island of Car Nicobar because a temporal rise in the Plasmodium falciparum parasite population containing mutations in the chloroquine resistance transporter (PfCRT) protein has been reported there. A WHO protocol with a 28 day follow-up schedule was used for chloroquine efficacy studies. Finger-prick blood from P. falciparum malaria patients was used for sequencing the genes encoding PfCRT (exon 2), dihydrofolate reductase (PfDHFR) and dihydropteroate synthetase (PfDHPS). The majority of patients showed chloroquine treatment failure (60.42%, n=48). A higher early treatment failure (ETF) rate was recorded among non-responders (23 of 29, 79.31%). Each patient, irrespective of their chloroquine response, was infected with P. falciparum that contained mutated PfCRT (predominantly genotype C72V73I74E75T76) associated with high chloroquine resistance and none with the wild-type pfcrt gene. Therefore, mutated PfCRT was also present in the P. falciparum isolates of all the chloroquine responders. The majority of individuals from both groups also contained parasites with a high number of two-locus PfDHFR-PfDHPS mutations, associated with a high level of antifolate resistance. There is a predominance of chloroquine- and antifolate-resistant P. falciparum malaria in Car Nicobar, requiring an alternative antimalarial drug treatment policy, such as implementation of artesunate combination therapy (ACT), for this island.

In‐vivo efficacy of amodiaquine‐artesunate in children with uncomplicated Plasmodium falciparum malaria in western Kenya

To assess the efficacy of amodiaquine-artesunate in an area with high chloroquine resistance in western Kenya. Twenty-eight day in-vivo efficacy trial of amodiaquine-artesunate in 103 children aged 6-59 months in western Kenya with smear-confirmed uncomplicated Plasmodium falciparum malaria. The 28-day uncorrected adequate clinical and parasitological response (ACPR) was 69.0%, with 15.5% Late Clinical Failure and 15.5% Late Parasitologic Failure rates. The PCR-corrected 28-day ACPR was 90.2%. Clinical risk factors for recurrent infection (recrudescences and reinfections) were lower axillary temperature at enrollment and low weight-for-age Z-score. The presence of single nucleotide polymorphisms pfcrt 76T and pfmdr1 86Y at baseline was associated with increased risk of recurrent infections, both reinfections and recrudescences. Although artemether-lumefantrine (Coartem) is the first line ACT in Kenya, amodiaquine-artesunate is registered as an option for treatment of uncomplicated P. falciparum and remains an effective alternative to Coartem in western Kenya. Continued amodiaquine monotherapy in the private sector may jeopardize the future use of amodiaquine-artesunate as an alternative artemisinin-based combination therapy.

No Genetic Bottleneck in Plasmodium falciparum Wild-Type Pf crt Alleles Reemerging in Hainan Island, China, following High-Level Chloroquine Resistance

Chloroquine-resistant Plasmodium falciparum was highly prevalent in Hainan, China, in the 1970s. Twenty-five years after cessation of chloroquine therapy, the prevalence of P. falciparum wild-type Pfcrt alleles has risen to 36% (95% confidence interval, 22.1 to 52.4%). The diverse origins of wild-type alleles indicate that there was no genetic bottleneck caused by high chloroquine resistance.

In-vitro susceptibility of Plasmodium falciparum to monodesethylamodiaquine, dihydroartemisinin and quinine in an area of high chloroquine resistance in Rwanda

Plasmodium falciparum in-vitro susceptibility to chloroquine (CQ), monodesethylamodiaquine, quinine and dihydroartemisinin was investigated in Rwandan patients with a parasitaemia of at least >or=4000/microl. The study was carried out in November-December 2003. Dihydroartemisinin was the most potent (GM IC(50)=2.6nmol/l, 95% CI 2.2-3.2) among the drugs tested. Resistance to chloroquine was 45% (33/74) and that to monodesethylamodiaquine 7% (5/74). All the tested isolates were susceptible to quinine. The mean IC(50) of monodesethylamodiaquine, quinine and dihydroartemisinin was significantly higher for chloroquine-resistant than for chloroquine-sensitive strains (P<0.05). The IC(50) of each drug was significantly and positively correlated to that of the other three drugs (P<0.005), and this correlation was higher between CQ and monodesethylamodiaquine (r=0.8). In-vitro CQ resistance is linked to that of the other drugs tested. Most worrying is the positive correlation between the IC(50) of dihydroartemisinin and the other drugs, more particularly with CQ, suggesting an increased tolerance of the parasites to all drugs.

Efficacy of chloroquine–proguanil malaria prophylaxis in a non-immune population in Bangui, Central African Republic: a case–control study

A case-control study was conducted to evaluate the efficacy of the combination of chloroquine plus proguanil as malaria prophylaxis in a non-immune population living in the Central African Republic. Cases were patients presenting with a malaria attack confirmed by a positive blood film and/or an HRP2 positive antigen test at the Pasteur Institute of Bangui. Two control subjects were included per case: one was a relative or close friend and the other was matched to the patient with respect to the length of stay. A questionnaire assessing malaria prophylaxis habits and malarial risk factors over the 2-month period prior to inclusion in the study was given to 48 cases and 96 controls. A conditional logistic regression was used to identify risk factors. The efficacy of the chloroquine plus proguanil regimen was found to be high (95.5%, 95% CI 74.0-99.2%) in this country known for high chloroquine resistance. Our data lend some support to the use of chloroquine plus proguanil in Bangui, and the protective efficacy of chloroquine plus proguanil should now be studied prospectively as part of a randomised controlled trial of various prophylactic drugs.

Artemether-lumefantrine for uncomplicated malaria: a systematic review.

The World Health Organization (WHO) is promoting artemether-lumefantrine for treating uncomplicated malaria. The objective of this review is to summarize available evidence of its effects compared with other antimalarial regimens. We sought randomized and quasi-randomized studies comparing artemether-lumefantrine with any other antimalarial drug regimen. Databases searched were MEDLINE (to February 2003), EMBASE (to February 2003), and the Cochrane Controlled Trials Register (issue 1, 2003). Conference proceedings and reference article lists were searched and malaria researchers and the drug manufacturer were contacted. Two reviewers independently applied inclusion criteria and extracted data. Six trials (1698 participants) studied the four-dose regimen. Fever and parasite clearance tended to be shorter with artemether-lumefantrine, but parasitological failure on day 28 was more common with artemether-lumefantrine in comparison with mefloquine (one trial, n = 233), halofantrine (one trial, n = 86) and mefloquine-artesunate (one trial, n = 537); but less common with chloroquine (two trials, n = 378). For the six-dose regimen, two studies compared artemether-lumefantrine with mefloquine-artesunate, but there was insufficient data to demonstrate any meaningful comparative effects for day 28 parasitaemia, and no difference in parasite or fever clearance time was detected. There were 11 parasitological failures with artemether-lumefantrine and none with mefloquine-artesunate. There is no evidence to demonstrate the four-dose regimen of artemether-lumefantrine results in a higher cure rate than other antimalarial regimens against which it has been tested, apart from chloroquine in areas with high chloroquine resistance. Artemether-lumefantrine has potential advantages over non-artemisinin regimens because of the faster clearance time and gametocyte clearance. There is insufficient evidence about the six-dose regimen to know whether it is less or more effective than current antimalarial drug regimens.

Role of the pfcrt codon 76 mutation as a molecular marker for population-based surveillance of chloroquine (CQ)-resistant Plasmodium falciparum malaria in Ugandan sentinel sites with high CQ resistance

The mutant genotype at codon 76 of the pfcrt gene (T76) has been proposed as a molecular marker for surveillance of chloroquine (CQ)-resistant Plasmodium falciparum malaria but this proposal has not been validated by population-based surveys. In 1998–1999, in 6 Ugandan sentinel sites, the prevalence of P. falciparum infections with the T76 genotype and the level of CQ use were measured by community surveys, and CQ resistance was determined by in-vivo tests on 6–59-month-old children with clinical malaria. The prevalence of T76 was not related to the overall clinical (early and late treatment failure: ETF+LTF; r = 0 · 14, P = 0 · 78) or parasitological (RI+RII+RIII; r = 0 · 17, P = 0 · 73) CQ resistance. However, the percentage of individuals carrying only infections with the T76 genotype (T76 alone) increased with increasing ETF ( r = 0 · 76, P = 0 · 07) and type RIII parasitological failure ( r = 0 · 69, P = 0 · 12). Similarly, the ratio between T76 and K76 (the wild type) prevalences ( T76 K76 ) was strongly and positively correlated with ETF ( r = 0 · 85, P = 0 · 03) and RIII ( r = 0 · 82, P = 0 · 04). Moreover, T76 alone ( r = 0 · 90, P = 0 · 01) as well as T76 K76 ( r = 0 · 90, P = 0 · 01) significantly increased with increasing community CQ use. T76 alone and T76 K76 can be useful markers to estimate the ETF and RIII prevalence as well as the amount of CQ use in the community.

Amodiaquine, sulfadoxine/pyrimethamine, and combination therapy for treatment of uncomplicated falciparum malaria in Kampala, Uganda: a randomised trial

Increasing Plasmodium falciparum resistance to chloroquine in sub-Saharan Africa necessitates use of alternative antimalarial agents. Affordable alternative treatments include sulfadoxine/pyrimethamine and amodiaquine. Combination of antimalarial agents can increase therapeutic efficacy and delay emergence of drug resistance. We compared the efficacy of sulfadoxine/pyrimethamine, amodiaquine, and an amodiaquine/sulfadoxine/pyrimethamine combination for treatment of uncomplicated malaria in a region of high chloroquine resistance. Patients with symptoms of uncomplicated falciparum malaria and confirmed disease in Kampala, Uganda, were randomly assigned to receive sulfadoxine/pyrimethamine (25 mg/kg sulfadoxine, and 1.25 mg/kg pyrimethamine) plus placebo; amodiaquine (25 mg/kg) plus placebo; or amodiaquine plus sulfadoxine/pyrimethamine. Patients were followed up for 14 days, and clinical and parasitological outcomes were assessed. 90% (400/445) of patients enrolled in the study successfully completed 14 days of follow-up. Treatment failure based on clinical criteria occurred in 13 of 131 (10%) patients on sulfadoxine/ pyrimethamine, nine of 131 (7%) on amodiaquine, and four of 138 (3%) on amodiaquine/sulfadoxine/pyrimethamine. Based on parasitological criteria, treatment failed in 26%, 16%, and 10% of these patients, respectively. Amodiaquine/sulfadoxine/pyrimethamine was significantly more effective than sulfadoxine/pyrimethamine alone in children aged younger than 5 years (clinical failure in 3.5% vs 13.9%, respectively, risk difference 10.4% [95% CI, 1.6-19.3] p=0.021; parasitological failure in 12.8% vs 26.4%, risk difference 13.6% [1.2-26.0] p=0.041). Sulfadoxine/pyrimethamine, amodiaquine, and amodiaquine/sulfadoxine/pyrimethamine were all effective for treatment of uncomplicated falciparum malaria in Uganda. The amodiaquine/sulfadoxine/pyrimethamine combination was the most effective, and could be the optimum low-cost alternative to chloroquine in Africa.