Poor gametocytocidal activity of 45 mg primaquine in chloroquine-treated patients with acute, uncomplicated, Plasmodium falciparum malaria in Mumbai (Bombay): an issue of public-health importance

In the city of Mumbai (formerly Bombay), chloroquine (CQ) continues to be recommended as the drug of first choice for the treatment of Plasmodium vivax and P. falciparum infections, even though > 50% of local isolates of P. falciparum are resistant to it. Primaquine, an 8-aminoquinoline is also given to patients with falciparum malaria, in a single, 45-mg dose, to kill the gametocytes and so reduce transmission. The gametocytocidal activity of supervised primaquine (45 mg given on day 8) was investigated in 90 patients who had been treated with CQ. Of these, 15 were found to be CQ-sensitive patients, 61 were resistant (49, eight and four considered RI, RII and RIII, respectively) and 14 were lost before completion of the follow-up. The mean (S.D.) baseline gametocytaemias in the CQ-sensitive and RI-resistant cases were 665.1 (411.3) and 1537.4 (1045.5)/microliter, respectively. Despite supervised primaquine treatment, four of the 15 CQ-sensitive patients and 32 of the 49 patients found to be RI-resistant had gametocytes on day 29. There therefore appears to be a need to review the current, gametocytocidal, primaquine-dosage schedule and to re-treat patients who remain gametocytaemic with higher doses of primaquine, as an important, transmission-blocking strategy.     

伯氏疟原虫氯喹结合蛋白的分离与定量

目的： 分离伯氏疟原虫敏感株（ Ｃ Ｓ） 与抗氯喹株的氯喹（ｃｈｌｏｒｏｑｕｉｎｅ Ｃ Ｑ） 结合蛋白。方法： 给两株感染鼠ｉｇ Ｃ Ｑ４００ ｍｇ／ｋｇ , ３ ｈ 后, 收集伯氏疟原虫用（ Ｕｌｔｒｏｇｅｌ Ｒ） Ａｃ Ａ３４ 凝胶柱分离蛋白, 按 Ｂｅｒｇｑｖｉｓｔ 法抽提与蛋白结合的 Ｃ Ｑ, 然后用 Ｈ Ｐ Ｌ Ｃ （ 外标法） 定量。结果： Ｃ Ｓ 有５８ 个蛋白峰, 均与 Ｃ Ｑ 结合, 其中以 Ｎｏ６４ ～８６部分（ 峰９） 结合的 Ｃ Ｑ 量最多, 占总结合量的１６４ ％ 。抗氯喹伯氏疟原虫（ Ｃ Ｒ） 有４０ 个蛋白峰, 除８ 个峰外,均与 Ｃ Ｑ 结合, 结合量最多的蛋白部分与 Ｃ Ｓ相同, 在 Ｎｏ６０ ～８３ 部分（ 峰６ 及峰７） , 但是它与 Ｃ Ｑ 的结合能力（ Ｃ Ｑｎｍｏｌ／ ｍｇ 蛋白） 显著高于 Ｃ Ｓ。结论： 分离与测定了 Ｃ Ｓ和 Ｃ Ｒ 两株疟原虫各个蛋白峰的分布与定量, 及其与 Ｃ Ｑ 结合的能力。在同一株疟原虫中, 各蛋白与 Ｃ Ｑ 的结合能力存有差异, 在 Ｃ Ｓ与 Ｃ Ｒ 间此差异更大。     

Evidence for different mechanisms of chloroquine resistance in 2 Plasmodium species that cause human malaria

Chloroquine (CQ)-resistant Plasmodium vivax malaria was first reported 12 years ago, nearly 30 years after the recognition of CQ-resistant P. falciparum. Loss of CQ efficacy now poses a severe problem for the prevention and treatment of both diseases. Mutations in a digestive vacuole protein encoded by a 13-exon gene, pfcrt, were shown recently to have a central role in the CQ resistance (CQR) of P. falciparum. Whether mutations in pfcrt orthologues of other Plasmodium species are involved in CQR remains an open question. This report describes pfcrt homologues from P. vivax, P. knowlesi, P. berghei, and Dictyostelium discoideum. Synteny between the P. falciparum and P. vivax genes is demonstrated. However, a survey of patient isolates and monkey-adapted lines has shown no association between in vivo CQR and codon mutations in the P. vivax gene. This is evidence that the molecular events underlying P. vivax CQR differ from those in P. falciparum.     

Plasmodium falciparum gametocytaemia in Nigerian children: before,during and after treatment with antimalarial drugs

We evaluated gametocyte carriage and intensities of gametocytaemia in 710 children presenting with acute, symptomatic, uncomplicated Plasmodium falciparum malaria who were treated with various antimalarial drug regimens: chloroquine (CQ); chloroquine plus chlorpheniramine, a histamine H1 receptor antagonist that reverses CQ resistance in P. falciparum in vitro and in vivo (CQCP); chloroquine plus ketotifen, a histamine H1 receptor antagonist that reverses CQ resistance in P. falciparum in vitro but not in vivo in the present study (CQK); chloroquine plus pyrimethamine-sulphadoxine (CQPS); amodiaquine (AQ); amodiaquine plus pyrimethamine-sulphadoxine (AQPS); and pyrimethamine-sulphadoxine (PS). On presentation, gametocyte carriage was significantly higher in CQ-resistant (CQ-R) than in CQ-sensitive (CQ-S) infections. Following CQ treatment, gametocyte carriage was significantly higher at all times after treatment and gametocyte density significantly higher on day 7 of follow-up in children with CQ-R than CQ-S infections. CQ treatment of CQ-R infections resulted in significantly higher density of gametocytaemia on day 7 compared with pre-treatment (day 0), but similar treatment of CQ-S infections resulted in significantly lower density of gametocytaemia on day 14 compared with day 0. Among children with CQ-R infections, those with mild (RI) resistance carried gametocytes significantly more often than those with moderate (RII) resistance on days 5 and 7 of follow-up (P = 0.04 and 0.01, respectively). Disposition kinetics of gametocytaemia using a non-compartmental method showed that the half life of gametocytaemia was longer and the clearance slower in children with CQ-R than in those with CQ-S infections. PS treatment was associated with significantly higher gametocyte carriage at all times between days 1 and 14, and significantly higher gametocytaemias on days 7 and 14 than in the other treatment regimens. Combination of AQ with PS significantly decreased gametocyte carriage at all times between days 1 and 14 of follow-up. Continuing use of CQ in CQ-R infections may encourage transmission of CQ-R infections; SP monotherapy is associated with significant gametocyte carriage and gametocytaemia and may encourage transmission of SP resistant infections as resistance to the drug increases.     

Chloroquine and desethylchloroquine concentrations in blood cells and plasma from Indian patients infected with sensitive or resistant Plasmodium falciparum

The sensitivities of 61 Indian cases of Plasmodium falciparum malaria to chloroquine (CQ) were investigated using in-vitro and in-vivo methods. Concentrations of CQ and desethylchloroquine (DCQ) in blood cells and plasma from CQ-sensitive and -resistant cases were determined 2 and 7 days after initiation of treatment, by HPLC. On day 2, the mean CQ concentrations in the samples collected from the sensitive cases were higher than those in the samples from the resistant patients, in plasma (0.47 v. 0.32 microgram/ml; P < 0.02) and particularly in the blood cells (1.51 v. 0.46 micrograms/ml; P < 0.001). By day 7, however, the CQ concentrations in the two groups were similar. Although, on day 2, the mean ratio of the CQ to DCQ concentrations was significantly higher in the blood cells from the sensitive group than in those from the resistant cases (P < 0.01), the CQ/DCQ ratios for the plasma were similar for the two groups. Similarly, the mean ratio between the blood-cell concentration of CQ on day 2 and the concurrent plasma concentration (BPr) was also relatively high in the sensitive group (P < 0.001).     

Anti-malarial efficacy of pyronaridine and artesunate in combination in vitro and in vivo

Pyronaridine is a Mannich base anti-malarial with demonstrated efficacy against drug resistant Plasmodium falciparum, P. vivax, P. ovale and P. malariae. However, resistance to pyronaridine can develop quickly when it is used alone but can be considerably delayed when it is administered with artesunate in rodent malaria models. The aim of this study was to evaluate the efficacy of pyronaridine in combination with artesunate against P. falciparum in vitro and in rodent malaria models in vivo to support its clinical application. Pyronaridine showed consistently high levels of in vitro activity against a panel of six P. falciparum drug-sensitive and resistant strains (Geometric Mean IC50=2.24 nM, 95% CI=1.20-3.27). In vitro interactions between pyronaridine and artesunate showed a slight antagonistic trend, but in vivo compared to pyronaridine and artesunate administered alone, the 3:1 ratio of the combination, reduced the ED90 of artesunate by approximately 15.6-fold in a pyronaridine-resistant P. berghei line and by approximately 200-fold in an artesunate-resistant line of P. berghei. Complete cure rates were achieved with doses of the combination above or equal to 8 mg/kg per day against P. chabaudi AS. These results indicate that the combination had an enhanced effect over monotherapy and lower daily doses of artesunate could be used to obtain a curative effect. The data suggest that the combination of pyronaridine and artesunate should have potential in areas of multi-drug resistant malaria.     

Malaria studies in vitro. IV: Chloroquine resistance and the intracellular pH of erythrocytes parasitised with Plasmodium berghei.

The erythrocytic stages of strains of plasmodia sensitive to chloroquine (CQ) concentrate some three to six times more drug than CQ-resistant strains. A simple, but so far untested hypothesis is that the intracellular pH of drug resistant strains is higher than that for sensitive strains. This would result in a reduced accumulation of any weakly basic drug molecule (e.g. CQ) which is capable of passive diffusion through the cellular membran. The mean intracellular pH of erythrocytes parasitised with either CQ-sensitive or CQ-resistant strains of P. berghei was determined, therefore, from the distribution of 14C-5, 5-dimethyloxazolidine-2,4-dione between intra- and extracellular aqueous phases. The results obtained showed that over the range 6-8--7-2 the intracellular pH is governed directly by the extracellular pH and that the intracellular pH of CQ-sensitive parasites is slightly above that for resistant ones, neither being greatly different from that for uninfected erythrocytes. There was no evidence, therefore, to support, the suggested hypothesis. Elimination of this possibility adds weight to the opinion that changes in drug sensitivity of these plasmodia are the result of changes in the properties of drug-binding sites.     

Rifampicin antagonizes the effect of choloroquine on chloroquine-resistant Plasmodium berghei in mice

Chloroquine (CQ)-resistant Plasmodium falciparum appears to decrease CQ accumulation in its food vacuole by enhancing its efflux via an active membrane pump, which has been reported to be a P-glycoprotein-like transporter. Rifampicin (RIF) is a P-glycoprotein inhibitor and also has some antimalarial activity. It is hoped that a combination of choloroquine-rifampicin (CQ + RIF) would be advantageous in the treatment of CQ-resistant malaria. Swiss albino mice were inoculated with CQ-resistant P. berghei intraperitoneally, and studied for the effect of CQ versus the combination of CQ + RIF at various doses on the clearance of parasitemia, the survival of the mice, and the recrudescence of malaria. Paradoxically, RIF decreased the survival rate and rate of clearance of parasitemia and increased the rate of recrudescence significantly when combined with various doses of CQ. Our results indicated that RIF worsened the course of the disease, and we concluded that RIF should not be combined with CQ in the treatment of malaria.     

Randomized, controlled, double-blind trial of daily oral azithromycin in adults for the prophylaxis of Plasmodium vivax malaria in Western Thailand

We assessed the prophylactic efficacy of azithromycin (250 mg/day) against malaria in 276 adults in western Thailand in a randomized, double-blind, placebo-controlled trial. After antimalarial suppressive treatment, volunteers were randomized in a 2:1 ratio to either the azithromycin or placebo, respectively. Study medication was given for an average of 74 days. The azithromycin group (n = 179) had five endpoint parasitemias (1 Plasmodium vivax and 4 P. falciparum), and the placebo group (n = 97) had 28 endpoint parasitemias (21 P. vivax, 5 P. falciparum, and 2 mixed infections). Adverse events and compliance and withdrawal rates were similar in both groups. The protective efficacy (PE) of azithromycin was 98% for P. vivax (95% confidence interval [CI] = 88-100%). There were too few cases to reliably estimate the efficacy of azithromycin for P. falciparum (PE =71%, 95% C =-14-94%). We conclude that daily azithromycin was safe, well-tolerated, and had a high efficacy for the prevention of P. vivax malaria.     

In vivo responses to antimalarials by Plasmodium falciparum and Plasmodium vivax from isolated Gag Island off northwest Irian Jaya, Indonesia.

There is renewed interest in the rich nickel and cobalt deposits of Pulau Gag, an isolated but malarious island off the northwest coast of Irian Jaya. In preparation for an expanded workforce, an environmental assessment of malaria risk was made, focusing upon malaria prevalence in the small indigenous population, and the in vivo sensitivity of Plasmodium falciparum and P. vivax to chloroquine (CQ) and sulfadoxine/pyrimethamine (S/P), the respective first- and second-line drugs for uncomplicated malaria in Indonesia. During April-June 1997, mildly symptomatic or asymptomatic malaria infections were found in 24% of 456 native residents. Infections by P. falciparum accounted for 60% of the cases. Respective day 28 cure rates for CQ (10 mg base/kg on days 0 and 1; 5 mg/kg on day 2) in children and adults were 14% and 55% (P < 0.005). Type RII and RIII resistance characterized only 5% of the CQ failures. Re-treatment of 36 P. falciparum CQ treatment failures with S/P (25 mg/kg and 1.25 mg/kg, respectively) demonstrated rapid clearance and complete sensitivity during the 28-day follow-up period. More than 97% of the P. vivax malaria cases treated with CQ cleared parasitemia within 48 hr. Three cases of P. vivax malaria recurred between days 21 and 28, but against low drug levels in the blood. The low frequency of RII and RIII P. falciparum resistance to CQ, the complete sensitivity of this species to S/P, and the absence of CQ resistance by P. vivax are in contrast to in vivo and in vitro test results from sites on mainland Irian Jaya.     

Therapeutic responses of Plasmodium vivax and P. falciparum to chloroquine, in an area of western India where P. vivax predominates

In 2003-2005, following an increase in the local incidence of human malaria, the therapeutic efficacy of chloroquine (CQ) in the treatment of Plasmodium vivax and P. falciparum malaria was evaluated in the Anand district of Gujarat state, in western India. After oral administration of CQ, clinical and parasitological responses were measured over a follow-up period of 28 days, following the standard protocol of the World Health Organization. Most of the recurrent infections were checked, by genotyping, to see whether they were the result of treatment failure or re-infection during the follow-up. At the primary health centre (PHC) in Deva, all 57 P. vivax cases included in the study responded to CQ within 3 days. At the Pansora PHC, however, only 59 [90.8%, with a 95% confidence interval (CI) of 83.7%-97.8%] of the 65 P. vivax cases appeared to respond completely, recurrent infections being observed in the other six cases (9.2%; CI=2.2%-16.3%). Of the four recurrent infections checked by genotyping, however, only two appeared to be the result of true treatment failure. Twenty-seven (81.8%; CI=67.2%-94.4%) of the 33 P. falciparum cases who were enrolled in the study, all from Pansora PHC also showed apparent treatment failure, with one early failure, 17 late clinical failures and nine late parasitological failures. All 23 P. falciparum cases that showed apparent treatment failure and were investigated by genotyping appeared to be true cases of failure, none showing any evidence of re-infection during follow-up. The mean parasite-clearance times for those infected with P. falciparum, both those considered CQ-sensitive and the treatment failures, exceeded 2 days. These results indicate the presence of CQ-resistant P. vivax and P. falciparum in Anand district. The high frequency of CQ failure against P. falciparum observed in this study led to a change in the drug policy at the Pansora PHC, with artemisinin-based combination therapy now being used for the first-line treatment of P. falciparum malaria. Chloroquine remains the recommended first-line treatment for P. vivax infections in the area but the treatment failure seen in at least two P. vivax cases indicates a need for further monitoring of the therapeutic efficacy of CQ against such infections, in central Gujarat and elsewhere.     

Antimalarial activity of Carica papaya (Family: Caricaceae) leaf extract against Plasmodium falciparum

ObjectiveTo determine the antimalarial activity of the ethanol leaf extract of Carica papaya (C. papaya), blood stages of CQ-sensitive and CQ resistant strains against Plasmodium falciparum (P. falciparum) as target species.MethodsC. papaya leaf was collected in and around Kalveerampalyam village, Coimbatore, Tamil Nadu, India. C. papaya leaf was washed with tap water and shade dried at room temperature. An electrical blender powdered the dried plant materials (leaves). The powder 500g of the leaf was extracted with 1.5 L of organic solvents of ethanol for 8 h using a Soxhlet apparatus. The crude plant extracts were evaporated to dryness in rotary vacuum evaporator. One gram of the plant residue was dissolved in 100 mL of acetone (stock solution) and considered as 1% stock solution. From this stock solution, different concentrations were prepared ranging from 2%, 4%, 6%, 8% and 10%, respectively.ResultsThe highest larval mortality in the ethanol leaf extract of C. papaya against the 1st to 4th instars larvae and pupae values of LC₅₀= 3.65%, 4.28%, 5.41%, 6.70%, and 7.50%, respectively. The LC₉₀values of 9.61%, 11.75%, 13.53%, 16.36%, and 16.92%, respectively. Plant extracts showed moderate to good antiparasitic effects. These four concentrations (25, 50,100 and 150 μg/mL) of ethanol leaf extracts exhibited promising inhibitory activity against the CQ sensitive strain with (IC₅₀) values 40.75%, 36.54%, 25.30%, and 18.0% and in CQ resistant 50.23%, 32.50%, 21.45%, and 23.12% against P. falciparum.ConclusionsIn conclusion, the results indicate the effective plant extracts have the potential to be used as an ideal eco-friendly approaches for the control of vector mosquitoes.     

Inhibitory activity of ferroquine, versus chloroquine, against western Kenya Plasmodium falciparum field isolates determined by a SYBR Green I in vitro assay

Ferroquine (FQ), a chloroquine (CQ) analog, is being developed to treat persons with Plasmodium falciparum malaria. In 146 P. falciparum field isolates from western Kenya, we measured 50% inhibitory concentrations (IC(50); nM) of CQ and FQ by a SYBR Green I in vitro assay. Reference clones included W2 (CQ resistant) and D6 (CQ sensitive). Mutation analysis was done for P. falciparum CQ-resistance transporter gene (Pfcrt K76T). Median IC(50) values for FQ were lower than CQ for field isolates and the W2 clone (both P < 0.05). The Pfcrt mutation (76T), which was detected in > 80% of isolates, conferred higher CQ IC(50) values (P < 0.05) and modestly lower FQ IC(50) values (P < 0.05), versus Pfcrt wild type (K76). FQ is more potent than CQ against CQ-resistant P. falciparum field isolates and the W2 clone, and is less affected by Pfcrt 76T. These findings support the notion that FQ could be useful in treating persons with P. falciparum malaria.     

Gametocytemia and infectivity to mosquitoes of patients with uncomplicated Plasmodium falciparum malaria attacks treated with chloroquine or sulfadoxine plus pyrimethamine

Plasmodium falciparum gametocytemia and its related infectivity for mosquitoes was studied in 115 patients (median age = 18 years, range = 4-45) with simple malaria attacks who lived in the hypoendemic area of Dakar, Senegal. Patients were included in a 28-day in vivo sensitivity test after treatment with chloroquine (CQ, n = 82) or sulfadoxine plus pyrimethamine (SP, n = 33). The prevalence of resistant infections was 58.5% in those treated with CQ and 0% in those treated with SP. The gametocytemia peaked at day 7 after treatment. The maximal gametocyte prevalence was 38.2% in the CQ-sensitive infection group, 89.6% in the CQ-resistant group, and 97.0% in those treated with SP The maximal geometric mean gametocytemia was 2.19/microl in the CQ-sensitive infection group, 29.12/microl in the CQ-resistant group and 85.55/microl in those treated with SP. The period between appearance of the first clinical symptom and treatment was positively related to gametocyte prevalence at days 0 and 2. Experimental infection of wild Anopheles arabiensis using membrane feeders was performed at days 0 and 7, and mosquito infectivity was measured by oocyst detection on the midgut. At day 0, 14.1% of the patients had infected at least 1 mosquito, and at day 7, this value was 38.5%. The mean percentage of infected mosquitoes was 3.2% at day 0 and 12.6% at day 7. At day 7 after treatment with CQ, the relative risk for patients with resistant infections of infecting anophelines was 4.07 higher than in those with sensitive infections. No difference was observed in infectivity for mosquitoes between RI-type resistance and the RII + RIII-type resistance. A sporonticidal effect of SP was observed at day 7 after treatment. These data show that P. falciparum gametocytes and their infectivity for mosquitoes were differentiated according to the drug used, its efficacy, and the duration of symptoms before treatment; they were not dependent on the density of asexual stages. Prompt treatment of malaria cases performed at the beginning of symptoms could limit the spread of resistant parasites.     

Antimalarial drug sensitivity profile of western Kenya Plasmodium falciparum field isolates determined by a SYBR Green I in vitro assay and molecular analysis

In vitro drug sensitivity and molecular analyses of Plasmodium falciparum track drug resistance. DNA-binding fluorescent dyes like SYBR Green I may allow field laboratories, proximal to P. falciparum collection sites, to conduct drug assays. In 2007-2008, we assayed 121 P. falciparum field isolates from western Kenya for 50% inhibitory concentrations (IC(50)) against 6 antimalarial drugs using a SYBR Green I in vitro assay: 91 immediate ex vivo (IEV) and 30 culture-adapted, along with P. falciparum reference clones D6 (chloroquine [CQ] sensitive) and W2 (CQ resistant). We also assessed P. falciparum mdr1 (Pfmdr1) copy number and single nucleotide polymorphisms (SNPs) at four codons. The IC(50)s for IEV and culture-adapted P. falciparum isolates were similar, and approximated historical IC(50)s. For Pfmdr1, mean copy number was 1, with SNPs common at codons 86 and 184. The SYBR Green I assay adapted well to our field-based laboratory, for both IEV and culture-adapted P. falciparum, warranting continued use.     

Therapeutic efficacy of chloroquine against uncomplicated, Plasmodium falciparum malaria in south-western Saudi Arabia.

The results of annual random screening indicated that Plasmodium falciparum strains showing chloroquine (CQ) resistance in vitro became increasingly common in the Jazan region of south-western Saudi Arabia between 1986 and 1998 (chi(2) for trend = 50.027; P < 0.001). This worrying trend and the emergence of a micro-epidemic in 1997-1998 prompted an assessment of the therapeutic efficacy of CQ against uncomplicated, P. falciparum malaria in the area. The in-vivo testing of sensitivity to CQ was carried out in 291 clinically manifest, microscopically positive cases of P. falciparum malaria. Most of these patients (88%) were successfully treated with a single standard regimen of CQ therapy. The other 36 patients (12%) showed early treatment failure or a poor response to the CQ, although all of these were then successfully treated with a single standard dose of sulfadoxine-pyrimethamine (Fansidar), as a replacement therapy. Those unsuccessfully treated with CQ were generally younger (t = 2.625; P = 0.01) and tended to have higher body temperatures (t = -2.62; P = 0.012) and higher levels of parasitaemia at initial presentation (P > 0.000) than those who responded well to the drug. Although CQ remains a reasonably effective drug for the treatment of malaria in the Jazan region, and therefore will be kept as the first-line drug for the foreseeable future, failure of CQ efficacy must be carefully monitored in the area.     

Evidence for a reduced effect of chloroquine against Plasmodium falciparum in alpha-thalassaemic children

Alpha-thalassaemia is common in malaria-endemic regions and is considered to confer protection from clinical disease due to infection with Plasmodium falciparum. In vitro, sensitivity to chloroquine (CQ) of P. falciparum infecting alpha-thalassaemic erythrocytes is reduced. We examined, in a cross-sectional study of 405 Nigerian children, associations between alpha-globin genotypes, blood concentrations of CQ, and P. falciparum parasitaemia. Of the children, 44% were alpha+-thalassaemic (36.8% heterozygous, 7.6% homozygous). CQ in blood and P. falciparum-infection were observed in 52 and 80%, respectively. CQ was more frequently found in homozygous alpha+-thalassaemic (71%) than in non-thalassaemic children (50%; odds ratio, 2.42; 95% confidence interval, 1.01-5.8). Among children with CQ in blood and despite similar drug concentrations, alpha+-thalassaemic individuals had fewer infections below the threshold of microscopy which were detectable by PCR only, and they had a higher prevalence of elevated parasitaemia than non-thalassaemic children. No such differences were discernible among drug-free children. CQ displays a lowered efficacy in the suppression of P. falciparum parasitaemia in alpha+-thalassaemic children; hence protection against malaria due to alpha+-thalassaemia may be obscured in areas of intense CQ usage. Moreover, alpha+-thalassaemia may contribute to the expansion of CQ resistance.     

Monitoring Plasmodium falciparum chloroquine resistance in Yunnan Province, China, 1981-2006

The emergence and spread of drug resistant malaria parasites are an important factor contributing to the global resurgence of malaria, demonstrating the essence of drug resistance surveillance in endemic areas. In the malarious border regions of Yunnan Province, China, we have selected three study sites to monitor in vitro and in vivo resistance of Plasmodium falciparum parasites to chloroquine (CQ) from 1981 to 2006. In vitro studies using the microtest clearly showed high degree of CQ resistance in the early 1980s, when CQ was replaced by artemether monotherapy for falciparum malaria. In subsequent in vitro surveys performed in the early 1990s and 2003-2004, we found reductions in both the concentrations inhibiting 50% parasite growth (IC₅₀s) and the percentage of resistant parasites at all study sites, although the degrees of the reduction varied among sites. Even though amodiaquine has never been used in this area, there were consistently high levels of resistance to this drug, confirming crossresistance between CQ and amodiaquine. In vivo clinical studies were consistent with the results of the in vitro assays. The overall rate of resistant clinical cases decreased from 97% in 1981-1983 to 40% in 2005-2006. Collectively, whereas a general trend of reduction in CQ resistance was observed in Yunnan, variations among sites existed in this relatively small area, probably as the result of both geographical heterogeneity of malaria epidemiology in Yunnan and different levels of CQ resistance in neighboring countries.     

Resistance of Plasmodium falciparum malaria to chloroquine is widespread in eastern Afghanistan

After two decades of war and conflict in Afghanistan, the public-health system is in disarray and malaria has re-emerged as a major disease, with Plasmodium falciparum malaria becoming increasingly common. The limited healthcare services that are available are mainly delivered by non-governmental organizations in collaboration with the Ministry of Health. Although chloroquine (CQ) remains the official first-line treatment against P. falciparum malaria, there is little information on the severity or distribution of resistance to this drug in Afghanistan. In-vivo surveys, co-ordinated by the Malaria Reference Centre in Jalalabad, were therefore performed to determine the frequency and grades of CQ resistance in the three eastern provinces of Kunar, Nangarhar and Laghman. Of the 142 cases enrolled in the study, only 47 (33%) were sensitive. Most of the cases (55%) showed RI resistance but RII/RIII resistance was not uncommon (11%). The prevalence of resistance appeared similar in children and adults, in males and females, and in each of the three provinces investigated. Gametocyte carriage post-treatment was elevated in the resistant cases. As in neighbouring Pakistan, the resurgence of P. falciparum in Afghanistan is probably associated with the transmission and spread of chloroquine-resistant strains. The first-line therapy used against P. falciparum malaria must be changed in order to reverse this trend.     

Randomized comparison of chloroquine and amodiaquine in the treatment of acute, uncomplicated, Plasmodium falciparum malaria in children.

The increasing resistance of Plasmodium falciparum to chloroquine (CQ) has created an urgent need for the evaluation of alternative, effective, safe, cheap, readily available and affordable antimalarial treatments. In the present study, the efficacy of amodiaquine (AQ) in the treatment of acute, symptomatic, uncomplicated, P. falciparum malaria was compared with that of CQ, each drug being given at 10 mg/kg per day for 3 days (days 0, 1 and 2). The 210 subjects (104 given AQ and 106 CQ) were Nigerian children aged 5 months-12 years. Fever-clearance times (FCT), parasite densities on days 1-4 and parasite-clearance times (PCT) were all significantly lower with AQ than with CQ. Mean (S.D.) PCT, for example, were 2.6 (0.8) days with AQ and 3.0 (1.0) days with CQ (P = 0.001). The cure rates obtained on days 14, 21 and 28 - 98.1% v. 79.3% (P =0.000), 97.1% v. 64.2% (P = 0.00001) and 95.2% v. 58.5% (P = 0.0000000) with AQ and CQ, respectively - were all also significantly higher with AQ. All but two of the 20 subjects who were considered CQ-treatment failures by day 14 (i.e. two RIII, two RII and 16 RI) responded to subsequent treatment with AQ, with PCT (but not FCT) significantly shorter than during their initial treatment with CQ. In siblings in whom there was clustering of infections, the cure rates were 100% with AQ (N =12) and 63.6% with CQ (N = 11; P = 0.03). Adverse reactions to CQ and AQ were similar and tolerable: pruritus in 10 and 11 children in the AQ and CQ groups, respectively, and gastro-intestinal disturbances which occurred in three children from each group. Haematological parameters were not adversely affected by either drug. At least in the setting of the present study, AQ appears more effective than CQ, effective against CQ-resistant infections, and well tolerated by children with acute, uncomplicated, P. falciparum malaria. It may therefore be useful as an alternative to CQ in areas of CQ resistance.