Artemisinin or chloroquine for blood stage Plasmodium vivax malaria in Vietnam

Chloroquine-resistant Plasmodium vivax has not yet occurred in Vietnam. The efficacy of artemisinin for P. vivax was not established. We conducted a double-blind randomized study involving 240 inpatients with P. vivax malaria who received artemisinin (40 mg/kg over 3 days) plus placebo chloroquine (Art) or chloroquine (25 mg/kg over 3 days) plus placebo artemisinin (Chl). Patients were followed up with weekly blood smears for 28 days. In each group 113 cases were analysed. All patients recovered rapidly. The median (range) parasite clearance time of regimen Art was 24 h (8-72) and of Chl 24 h (8-64; P = 0.3). Parasites reappeared in two cases in each group on day 14, in eight cases in each group (7%) on day 16 and in 25 (23%) and 18 (16%) cases, respectively, at the end of 4-week follow-up (P = 0.3). The population parasite clearance curve followed a mono-exponential decline. The parasite reduction ratio per 48 h reproduction cycle was 2.3 x 104 for both regimens. We conclude that artemisinin and chloroquine are equally effective in the treatment of P. vivax infections in Vietnam. Reappearance of parasites before day 16 (7%) suggests the emergence of chloroquine resistance. Three days of artemisinin monotherapy does not prevent recrudescence.     

Treatment of children with Plasmodium falciparum malaria with chloroquine in Guinea-Bissau

Children with symptomatic malaria in Bissau, Guinea-Bissau were randomly assigned to treatment with a 25 mg/kg total dose of chloroquine as recommended by the National Malaria Program or with a higher total dose of 50 mg/kg. Sixty-seven and 62 children, respectively, completed the treatment and were then followed once a week for five weeks. Treatment with a dose of 50 mg/kg was significantly more effective than treatment with 25 mg/kg in preventing recrudescence. The cumulative relative risk (95% confidence interval) of having parasitemia in the low-dose group during follow-up was 0.20 (0.08-0.52) on day 21, 0.38 (0.17-0.86) on day 28, and 0.48 (0.23-0.98) on day 35. Few adverse events were reported, although more children complained of vomiting and diarrhea on day 2 in the high-dose group compared with those in the low-dose group. However, this difference was not statistically significant. We conclude that a dose of 50 mg/kg of chloroquine could be recommended for treatment of Plasmodium falciparum malaria in Bissau. To minimize the risk of side effects, this higher dose should be given divided into two daily doses over a three-day period.     

Role of Plasmodium falciparum chloroquine resistance transporter and multidrug resistance 1 genes on in vitro chloroquine resistance in isolates of Plasmodium falciparum from Thailand

Resistance to chloroquine is a public health problem worldwide. Polymorphisms of the Plasmodium falciparum chloroquine resistance transporter (pfcrt) and P. falciparum multidrug resistance 1 (pfmdr1) genes have been linked to chloroquine resistance. Although the K76T mutation in the pfcrt gene has been shown to be a key determinant in chloroquine resistance, evidence suggests that the pfmdr1 gene could modulate the level of chloroquine resistance. However, few studies of field isolates could identify the interactive role of these two genes in chloroquine resistance. Thus, we evaluated the influence of pfcrt and pfmdr1 polymorphisms on in vitro chloroquine sensitivity in 89 adapted isolates of P. falciparum from Thailand. We found that 87 of 89 isolates contained the CVIET haplotype of the pfcrt gene. Two additional mutations in the pfcrt gene were identified, i.e., K6Q and H97L. For the pfmdr1 polymorphisms, the 184F allele was common in the parasites isolated along the Thailand-Cambodia border, and those isolated along the Thailand-Myanmar border contained higher copy numbers. Our results indicate that the additional mutations, in particular H97L in the pfcrt gene and Y184F in the pfmdr1 gene and its copy number, influence the level of chloroquine resistance.     

Drug resistance in Plasmodium falciparum malaria

Four classes of drugs are reviewed: blood schizontocides acting only on the hemoglobin-digesting blood stages, the antifolates which attack tetrahydrofolate synthesis in all the growing stages, antimitochondrials affecting synthesis and electron transport, and 8-aminoquinolines which interfere with redox processes. Drug efflux via a multidrug resistance membrane protein, and the production of a protein competing with the drug for the target hemin are thought to be responsible for resistance to blood schizontocides. Structural changes in target enzymes are responsible for easily-developed resistance to antifolates and antimitochondrials. The judicious use of drug combinations can help to avoid development of resistance and combat resistant infections, but new drugs are urgently needed.     

Efficacy of chloroquine in the treatment of Plasmodium vivax malaria in Turkey

In most regions of the world, chloroquine (CQ) has been the standard treatment for Plasmodium vivax malaria for more than 40 years. Recently, however, CQ-resistant P. vivax has been reported from Oceania, several parts of Asia, and South America. The therapeutic efficacy of CQ in the treatment of acute, P. vivax malaria has now been assessed in two areas of the Turkish province of Sanliurfa: the towns of Karacadag and Sekerli. On admission and on days 2, 3, 7, 14, 21, and 28, all 112 patients investigated were examined clinically and blood samples were collected and smeared. Treatment consisted of 10 mg CQ/kg on day 0, the same dose on day 1, and 5 mg CQ/mg on day 2, each dose being supervised. Worryingly, 14.7% of the patients from Karacadag and 10.3% of those from Sekerli showed apparent treatment failure between days 3 and 28. In Sanliurfa province, in south-eastern Turkey, there therefore seems to be a high risk of therapeutic failure in patients given CQ to cure P. vivax malaria, probably because of CQ resistance.     

Changes in genotypes of Plasmodium falciparum human malaria parasite following withdrawal of chloroquine in Tiwi, Kenya

Chloroquine (CQ) drug was withdrawn in 1998 as a first-line treatment of uncomplicated malaria in Kenya. This was in response to resistance to the drug in Plasmodium falciparum malaria parasite. Investigations were conducted to determine prevalence of CQ resistance genotypes in the parasites in Tiwi, a malaria endemic town in Kenya, before and about a decade after the withdrawal of the drug. Blood samples were collected and spotted on filter papers in 1999 and 2008 from 75 and 77 out-patients respectively with uncomplicated malaria. The sampling was conducted using finger pricking technique. DNA was extracted from individual spots in the papers and screened for the presence of P. falciparum chloroquine resistance transporter (Pfcrt) and multi drug resistance (Pfmdr-1) markers using nested PCR. Nature of mutations (haplotypes) in the Pfcrt and Pfmdr-1 markers in the samples were confirmed using dot blot hybridization technique. Changes in pattern of CQ resistance in the parasite samples in 1999 and 2008 were assessed by Chi Square test. There was a significant (P<0.05) reduction in CQ resistant genotypes of the parasite between 1999 and 2008. Pfmdr and Pfcrt CQ resistant genotypes in 2008 reduced to 54.10 and 63.64% respectively, from 75.39 and 88.0% respectively in 1999. This reduction was accompanied by emergence of Pfcrt specific CQ sensitive (IEK) and intermediate/partially CQ resistant (MET) haplotypes. Results suggest significant reversal of the phenotype of the parasite from chloroquine resistant to wild/sensitive type. The novel haplotypes indicates transitional phase of the parasite to the wild type. Current prevalence of chloroquine resistant genotype is definitely above the threshold for efficacious re-introduction of chloroquine for treatment of malaria in Tiwi.     

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.     

恶性疟原虫氯喹抗性的研究进展

恶性疟原虫氯喹抗药性的产生是一个多基因、多因素作用的复杂过程。该文通过对恶性疟原虫氯喹抗性产生机制以及与抗性相关的pfmdr1基因、pfcrt基因和cg2基因等的研究进展进行综述。探讨氯喹抗性产生的机制，为恶性疟原虫氯喹抗性机制的研究及新药设计提供参考。     

停用氯喹12年抗氯喹恶性疟原虫对氯喹抗性...

In view of the fact the resistance of Plasmodium falciparum to chloroquine occurred extensively in Hainan, a decision was made in 1979 that the use of chloroquine should be quit in the whole province. A longitudinal survey on chloroquine-sensitivity of P. falciparum was carried out during 1981-1991 to observe the variation in resistance of the parasite after the cessation of the chloroquine medication for every 2-3 years. A tendency of progressive decline of resistance was revealed. By using in vitro test, the rate of chloroquine-resistant P. falciparum dropped from 97.9% in 1981 to 60.9% in 1991 (P < 0.001). The mean dosage of chloroquine for complete inhibition of schizont formation declined from 10.46 pmol/microliters in 1981 to 3.02 pmol/microliters in 1991 (P < 0.001). The percentage of population requiring larger dosage (6.4 pmol/microliters to completely inhibit schizont formation declined from 83.3% in 1981 to 17.4% in 1991 (P < 0.001); whereas those requiring small dosage (1.6 pmol/microliters), increased from 4.2% in 1981 to 60.8% in 1991 (P < 0.001). In in vivo test, the rate of chloroquine-resistant P. falciparum decreased from 84.2% in 1981 to 40% in 1991 (P < 0.001). The proportion of RII plus RIII cases of the total resistant cases dropped from 59.4% in 1981 to 37.5% in 1991 (0.02 > P > 0.01).     

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.     

Frequency of pruritus in Plasmodium vivax malaria patients treated with chloroquine in Thailand

Chloroquine-induced itch in black-skinned African malaria patients is common and frequently leads to poor compliance or treatment defaulting.To assess the frequency and severity of chloroquine-induced pruritus in an Asian population, we reviewed case records of 1189 Plasmodium vivax malaria patients treated with chloroquine (25 mg/kg over 3 days) at the Bangkok Hospital for Tropical Diseases from 1992 through 1997.The majority of patients were Thais or ethnic Burmese (light brown skin), referred from the western border of Thailand. Overall, there were 23 patients (1.9%) with complaints of pruritus during chloroquine therapy. Of these, 12 (52%) had palm and sole involvement, eight (35%) had generalized pruritus including the palms and soles, and three (13%) had palm itching only. One patient developed pruritus on the palms and soles on two consecutive admissions.The pruritus did not interfere with daily activity, was reduced in intensity by anti-histamine therapy, and did not affect the patient's willingness to complete the chloroquine regimen. Therapeutic responses in the 23 patients with chloroquine itch was similar to those without itch. Among the itch patients, there was no association with gender or level of parasitaemias. Our findings indicate that the frequency of chloroquine-induced pruritus in Asian patients treated with chloroquine for P. vivax malaria is low in comparison with black-skinned Africans.This may be related to pharmacogenetic factors, the infective Plasmodium species, drug metabolism or drug-parasite interactions, or a lower affinity of chloroquine for less pigmented skin.     

Reemergence of chloroquine-sensitive Plasmodium falciparum malaria after cessation of chloroquine use in Malawi

In 1993, Malawi became the first African country to replace chloroquine with sulfadoxine-pyrimethamine nationwide in response to high rates of chloroquine-resistant falciparum malaria. To determine whether withdrawal of chloroquine can lead to the reemergence of chloroquine sensitivity, the prevalence of the pfcrt 76T molecular marker for chloroquine-resistant Plasmodium falciparum malaria was retrospectively measured in Blantyre, Malawi. The prevalence of the chloroquine-resistant pfcrt genotype decreased from 85% in 1992 to 13% in 2000. In 2001, chloroquine cleared 100% of 63 asymptomatic P. falciparum infections, no isolates were resistant to chloroquine in vitro, and no infections with the chloroquine-resistant pfcrt genotype were detected. A concerted national effort to withdraw chloroquine from use has been followed by a return of chloroquine-sensitive falciparum malaria in Malawi. The reintroduction of chloroquine, ideally in combination with another antimalarial drug, should be considered in areas where chloroquine resistance has declined and safe and affordable alternatives remain unavailable.     

Plasmodium vivax resistance to chloroquine in Dawei, southern Myanmar

Objective  To assess the efficacy of chloroquine in the treatment of Plasmodium vivax malaria in in Dawei District, southern Myanmar.
Methods  Enrolled patients at Sonsinphya clinic >6 months of age were assessed clinically and parasitologically every week for 28 days. To differentiate new infections from recrudescence, we genotyped pre- and post-treatment parasitaemia. Blood chloroquine was measured to confirm resistant strains.
Results  Between December 2002 and April 2003, 2661 patients were screened, of whom 252 were included and 235 analysed. Thirty-four per cent (95% CI: 28.1–40.6) of patients had recurrent parasitaemia and were considered treatment failures. 59.4% of these recurrences were with a different parasite strain. Two (0.8%) patients with recurrences on day 14 had chloroquine concentrations above the threshold of 100 ng/ml and were considered infected with chloroquine resistant parasites. 21% of failures occurred during the first 3 weeks of follow-up: early recurrence and median levels of blood chloroquine comparable to those of controls suggested P. vivax resistance.
Conclusions  Plasmodium vivax resistance to chloroquine seems to be emerging in Dawei, near the Thai-Burmese border. While chloroquine remains the first-line drug for P. vivax infections in this area of Myanmar, regular monitoring is needed to detect further development of parasite resistance.     

巢式PCR法在疟疾检测及虫种鉴别中的应用

根据疟原虫小亚单位核糖体核糖核酸(SSU rRNA)基因序列设计疟原虫通用型和种特异性的引物,对60份血样进行巢式PCR检测及虫种鉴定,并与血样的吉氏染色镜检结果进行比较。巢式PCR检出40份疟原虫阳性血样,其中22份为恶性疟原虫(Plasmodium falciparum)阳性、13份为间日疟原虫(P.vivax)阳性、3份为恶性疟原虫和间日疟原虫混合感染、1份为卵形疟原虫阳性(P.ovale)、1份未能分型。与镜检结果一致的血样为46份,占76.7%(46/60),其中恶性疟原虫阳性18份、间日疟原虫阳性11份和阴性17份。将两种检测结果不一致的血样进行扩增片段序列测定和实时荧光PCR分析,检测结果均与巢式PCR结果一致。卵形疟原虫阳性血样扩增片段的序列分析结果显示,该序列与卵形疟原虫SSU rRNA基因序列(GenBank登录号DQ845247)的对应部分同源性为100%,证实该病例为输入性卵形疟原虫感染病例。     

海南省乐东县恶性疟原虫对氯喹抗性的变化

目的：监测海南省停用氯喹后抗氯喹恶性疟原虫对氯喹抗性的消长。方法：选择恶性疟原虫对氯喹有高度抗性且恶性疟发病率较高的海南省乐东县为观察点,采用ＷＨＯ标准体外微量法和体内四周法,间隔一定时间检测一次。结果：停用氯喹１８年,体外法,抗性率由１９８１年的９７．９％下降至１９９７年的２６．７％（Ｐ＜０．００１）,完全抑制裂殖体形成的平均药浓度由１０．４６±７．１４ｐｍｏｌ／μｌ血降至１．６３±１．４７ｐｍｏｌ／μｌ血（Ｐ＜０．００１）;体内法,抗性率由１９８１年的８４．２％降为１９９７年的１８．４％（Ｐ＜０．００１）,ＲⅢ占抗性病例的比例由５３．１％降为１４．３％。结论：海南省停用氯喹后恶性疟原虫对氯喹逐渐恢复了敏感性     

Molecular epidemiology of malaria in Cameroon. XIV. Plasmodium falciparum chloroquine resistance transporter (PFCRT) gene sequences of isolates before and after chloroquine treatment

Laboratory studies have strongly suggested that the gene coding for Plasmodium falciparum chloroquine resistance transporter (PFCRT) may play a determinant role in chloroquine resistance. A clinical study in Mali also found evidence for selection of the key PFCRT amino acid substitution, Lys76Thr, in patients who fail to respond to chloroquine treatment. To test the hypothesis that in vivo selection of mutant PFCRT alleles occurs after chloroquine treatment, PFCRT and merozoite surface antigen 2 (msa-2) polymorphisms were compared between 61 pretreatment and posttreatment paired samples from children with either clinical or parasitologic failure. There were six wild-type PFCRT alleles, 44 mutant alleles, and 11 mixed alleles among pretreatment isolates. All posttreatment parasites had mutant PFCRT alleles. Recrudescence accounted for 42 of 61 posttreatment infections, while 19 posttreatment infections were due to new infection (including all isolates with Lys-76 before treatment and Thr-76 after treatment). Seven pretreatment isolates with mixed PFCRT alleles had only Thr-76 on recrudescence, providing a direct evidence for in vivo selection for mutant PFCRT. Although the presence of mutant PFCRT alleles in pretreatment isolates is not predictive of chloroquine treatment failure, our data support the hypothesis that in vivo selection for recrudescent parasites carrying mutant PFCRT alleles occurs. These results may have important implications for the future surveillance of chloroquine resistance by the use of molecular markers.     

Atovaquone-proguanil compared with chloroquine and chloroquine-sulfadoxine-pyrimethamine for treatment of acute Plasmodium falciparum malaria in the Philippines

This randomized, open-label clinical trial compared a fixed-dose combination of atovaquone and proguanil (n=55) with chloroquine (n=23) or a combination of chloroquine, sulfadoxine, and pyrimethamine (n=32) for treatment of acute falciparum malaria in the Philippines. Patients were hospitalized for 28 days to ensure medication compliance and prevent reinfection. Atovaquone-proguanil produced a significantly higher cure rate (100%) compared with that for chloroquine (30.4%; P<.0001) or chloroquine-sulfadoxine-pyrimethamine (87.5%; P<.05). Treatments did not differ significantly with respect to parasite clearance time (mean: 46.7 h for atovaquone-proguanil, 60.0 h for chloroquine, and 42.8 h for chloroquine-sulfadoxine-pyrimethamine) or fever clearance time (mean, 38.8, 46.8, and 34.5 h, respectively). Adverse events were typical of malaria symptoms; the most frequently reported events were vomiting (18% for atovaquone-proguanil, 17% for chloroquine, and 9% for chloroquine-sulfadoxine-pyrimethamine), abdominal pain (15%, 17%, and 3%, respectively), anorexia (11%, 13%, and 0%, respectively), and headache (6%, 17%, and 3%, respectively). Atovaquone-proguanil was well tolerated and more effective than chloroquine or chloroquine-sulfadoxine-pyrimethamine for treatment of multidrug-resistant falciparum malaria in the Philippines.     

Changing trends in prevalence of different Plasmodium species with dominance of Plasmodium falciparum malaria infection in Aligarh (India)

ObjectiveTo determine the prevalence of malaria in Aligarh and analyze species dominance in different years over a decade.MethodsDiagnosis of malaria was done using microscopy as gold standard, rapid antigen detection assays and quantitative buffy coat (QBC) assays. Giemsa stained blood smear examination was done, thick and thin films were examined for presence of different Plasmodium spp. Rapid antigen detection assays employing detection of HRP-2 and parasite lactate dehydrogenase antigen (pLDH) by immunochromatography was done in patients whose blood smear found to be negative by conventional Giemsa slide examination. QBC was done in cases where there is strong clinical suspicion of malaria with blood smear negative, in patients with chronic malaria, splenomegaly, or in those patients who had inadequate treatment and for post-treatment follow up.ResultsPlasmodium vivax and Plasmodium falciparum were only species detected in our hospital. Overall prevalence of malaria in Aligarh was found to be 8.8%. The maximum prevalence of 20.1% was observed in year 2008 and lowest 2.3% in 2002.ConclusionsHigh prevalence of malaria is observed in this part of country with dominance of both species particularly Plasmodium falciparum should be monitored and factors accounting for occurrence should be studied to employ effective control measures.     

Plasmodium falciparum genotypes associated with chloroquine and amodiaquine resistance in Guinea-Bissau

Chloroquine is the most commonly used antimalarial in Guinea-Bissau and high doses are routinely prescribed. Blood from 497 patients treated with different doses of chloroquine or amodiaquine were genotyped. Pfcrt and pfmdr1 polymorphisms were identified. Pfmsp2 analysis identified recrudescent infections. The pfcrt 72-76 haplotypes were CVIET and CVMNK. The pfcrt 76T prevalence was 23% at day 0 and 96%, 83% and 100% at recrudescence following treatment with 25 mg/kg and 50 mg/kg of chloroquine and 15 mg/kg of amodiaquine respectively. When treating pfcrt 76T carrying P. falciparum the efficacy of 50 mg/kg and 25 mg/kg of chloroquine was 78% and 34% respectively (P = 0.007). The genetic basis of chloroquine resistance is probably the same in Guinea-Bissau as in the rest of Africa. The low pfcrt 76T prevalence suggests that resistance to normal dose chloroquine does not confer a major advantage to falciparum in Bissau and could be a result of treatment with high-dose chloroquine.