Short report: differences in dihydrofolate reductase but not dihydropteroate synthase alleles in Plasmodium falciparum isolates from geographically distinct areas in Malaysia

Drug resistance of Plasmodium falciparum and Plasmodium vivax isolates in Indonesia

This review article aims to investigate the genotypic profiles of Plasmodium falciparum and Plasmodium vivax isolates collected across a wide geographic region and their association with resistance to anti-malarial drugs used in Indonesia. A systematic review was conducted between 1991 and date. Search engines, such as PubMed, Science Direct, and Google Scholar, were used for articles published in English and Indonesian to search the literature. Of the 471 initially identified studies, 61 were selected for 4316 P. falciparum and 1950 P. vivax individual infections. The studies included 23 molecular studies and 38 therapeutic efficacy studies. K76T was the most common pfcrt mutation. K76N (2.1%) was associated with the haplotype CVMNN. By following dihydroartemisinin–piperaquine (DHA–PPQ) therapy, the mutant pfmdr1 alleles 86Y and 1034C were selected. Low prevalence of haplotype N86Y/Y184/D1246Ypfmdr1 reduces susceptibility to AS–AQ. SNP mutation pvmdr1 Y976F reached 96.1% in Papua and East Nusa Tenggara. Polymorphism analysis in the pfdhfr gene revealed 94/111 (84.7%) double mutants S108N/C59R or S108T/A16V in Central Java. The predominant pfdhfr haplotypes (based on alleles 16, 51, 59,108, 164) found in Indonesia were ANCNI, ANCSI, ANRNI, and ANRNL. Some isolates carried A437G (35.3%) or A437G/K540E SNPs (26.5%) in pfdhps. Two novel pfdhps mutant alleles, I588F/G and K540T, were associated with six pfdhps haplotypes. The highest prevalence of pvdhfr quadruple mutation (F57L/S58R/T61M/S117T) (61.8%) was detected in Papua. In pvdhps, the only polymorphism before and after 2008 was 383G mutation with 19% prevalence. There were no mutations in the pfk13 gene reported with validated and candidate or associated k13 mutation. An increased copy number of pfpm2, associated with piperaquine resistance, was found only in cases of reinfection. Meanwhile, mutation of pvk12 and pvpm4 I165V is unlikely associated with ART and PPQ drug resistance. DHA–PPQ is still effective in treating uncomplicated falciparum and vivax malaria. Serious consideration should be given to interrupt local malaria transmission and dynamic patterns of resistance to anti-malarial drugs to modify chemotherapeutic policy treatment strategies. The presence of several changes in pfk13 in the parasite population is of concern and highlights the importance of further evaluation of parasitic ART susceptibility in Indonesia.

Graphical Abstract

Molecular characterization of Plasmodium falciparum antifolate resistance markers in Thailand between 2008 and 2016

BACKGROUND

Resistance to anti-malarials is a major threat to the control and elimination of malaria. Sulfadoxine-pyrimethamine (SP) anti-malarial treatment was used as a national policy for treatment of uncomplicated falciparum malaria in Thailand from 1973 to 1990. In order to determine whether withdrawal of this antifolate drug has led to restoration of SP sensitivity, the prevalence of genetic markers of SP resistance was assessed in historical Thai samples.

METHODS

Plasmodium falciparum DNA was collected from the Thailand-Myanmar, Thailand-Malaysia and Thailand-Cambodia borders during 2008-2016 (N = 233). Semi-nested PCR and nucleotide sequencing were used to assess mutations in Plasmodium falciparum dihydrofolate reductase (pfdhfr), P. falciparum dihydropteroate synthase (pfdhps). Gene amplification of Plasmodium falcipaurm GTP cyclohydrolase-1 (pfgch1) was assessed by quantitative real-time PCR. The association between pfdhfr/pfdhps mutations and pfgch1 copy numbers were evaluated.

RESULTS

Mutations in pfdhfr/pfdhsp and pfgch1 copy number fluctuated overtime through the study period. Altogether, 14 unique pfdhfr-pdfhps haplotypes collectively containing quadruple to octuple mutations were identified. High variation in pfdhfr-pfdhps haplotypes and a high proportion of pfgch1 multiple copy number (51% (73/146)) were observed on the Thailand-Myanmar border compared to other parts of Thailand. Overall, the prevalence of septuple mutations was observed for pfdhfr-pfdhps haplotypes. In particular, the prevalence of pfdhfr-pfdhps, septuple mutation was observed in the Thailand-Myanmar (50%, 73/146) and Thailand-Cambodia (65%, 26/40) border. In Thailand-Malaysia border, majority of the pfdhfr-pfdhps haplotypes transaction from quadruple (90%, 9/10) to quintuple (65%, 24/37) during 2008-2016. Within the pfdhfr-pfdhps haplotypes, during 2008-2013 the pfdhps A/S436F mutation was observed only in Thailand-Myanmar border (9%, 10/107), while it was not identified later. In general, significant correlation was observed between the prevalence of pfdhfr I164L (ϕ = 0.213, p-value = 0.001) or pfdhps K540E/N (ϕ = 0.399, p-value ≤ 0.001) mutations and pfgch1 gene amplification.

CONCLUSIONS

Despite withdrawal of SP as anti-malarial treatment for 17 years, the border regions of Thailand continue to display high prevalence of antifolate and anti-sulfonamide resistance markers in falciparum malaria. Significant association between pfgch1 amplification and pfdhfr (I164L) or pfdhps (K540E) resistance markers were observed, suggesting a compensatory mutation.

Dihydrofolate-Reductase Mutations in Plasmodium knowlesi Appear Unrelated to Selective Drug Pressure from Putative Human-To-Human Transmission in Sabah, Malaysia

Background

Malaria caused by zoonotic Plasmodium knowlesi is an emerging threat in Eastern Malaysia. Despite demonstrated vector competency, it is unknown whether human-to-human (H-H) transmission is occurring naturally. We sought evidence of drug selection pressure from the antimalarial sulfadoxine-pyrimethamine (SP) as a potential marker of H-H transmission.

Methods

The P. knowlesi dihdyrofolate-reductase (pkdhfr) gene was sequenced from 449 P. knowlesi malaria cases from Sabah (Malaysian Borneo) and genotypes evaluated for association with clinical and epidemiological factors. Homology modelling using the pvdhfr template was used to assess the effect of pkdhfr mutations on the pyrimethamine binding pocket.

Results

Fourteen non-synonymous mutations were detected, with the most common being at codon T91P (10.2%) and R34L (10.0%), resulting in 21 different genotypes, including the wild-type, 14 single mutants, and six double mutants. One third of the P. knowlesi infections were with pkdhfr mutants; 145 (32%) patients had single mutants and 14 (3%) had double-mutants. In contrast, among the 47 P. falciparum isolates sequenced, three pfdhfr genotypes were found, with the double mutant 108N+59R being fixed and the triple mutants 108N+59R+51I and 108N+59R+164L occurring with frequencies of 4% and 8%, respectively. Two non-random spatio-temporal clusters were identified with pkdhfr genotypes. There was no association between pkdhfr mutations and hyperparasitaemia or malaria severity, both hypothesized to be indicators of H-H transmission. The orthologous loci associated with resistance in P. falciparum were not mutated in pkdhfr. Subsequent homology modelling of pkdhfr revealed gene loci 13, 53, 120, and 173 as being critical for pyrimethamine binding, however, there were no mutations at these sites among the 449 P. knowlesi isolates.

Conclusion

Although moderate diversity was observed in pkdhfr in Sabah, there was no evidence this reflected selective antifolate drug pressure in humans.

Pharmacokinetics of co-formulated mefloquine and artesunate in pregnant and non-pregnant women with uncomplicated Plasmodium falciparum infection in Burkina Faso

OBJECTIVES

Mefloquine/artesunate has recently been developed as a fixed-dose combination, providing a promising rescue/alternative treatment for malaria during pregnancy. However, limited data are available on the effect of pregnancy on its pharmacokinetic properties. This study was conducted to assess the pharmacokinetic properties of mefloquine/carboxymefloquine and artesunate/dihydroartemisinin in pregnant and non-pregnant women with uncomplicated malaria.

METHODS

Twenty-four women in their second and third trimesters of pregnancy and 24 paired non-pregnant women were enrolled. All patients were treated for uncomplicated Plasmodium falciparum malaria with a standard fixed-dose combination of oral mefloquine and artesunate one daily over 3 days. Frequent blood samples were collected before treatment and at scheduled times post-dose for the drug measurements and pharmacokinetic analyses. The study was registered at www.clinicaltrials.gov (identifier: NCT00701961).

RESULTS

The total median exposure to mefloquine and dihydroartemisinin was not significantly different between the pregnant and non-pregnant women (P>0.05). There was a trend of higher exposure to mefloquine in the pregnant women, but this difference did not reach statistical significance (656700 versus 542400 h × ng/mL; P=0.059). However, the total exposure to carboxymefloquine was 49% lower during pregnancy (735600 versus 1499000 h × ng/mL; P<0.001) and the total drug exposure to artesunate was 42% higher during pregnancy (89.0 versus 62.9 h × ng/mL; P=0.039) compared with non-pregnant controls.

CONCLUSIONS

The plasma levels of mefloquine and dihydroartemisinin appeared to be similar in both pregnant and non-pregnant women, but there were significant differences in carboxymefloquine and artesunate exposure. The data presented here do not warrant a dose adjustment in pregnant patients, but an extensive analysis of the data could provide a better understanding of these findings.

Mutational analysis of Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase genes in the interior division of Sabah, Malaysia

Background

The sulphadoxine/pyrimethamine (SDX/PYR) combination had been chosen to treat uncomplicated falciparum malaria in Malaysia for more than 30 years. Non-silent mutations in dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes are responsible for the resistance to pyrimethamine and sulphadoxine, respectively. This study reports the mutational analysis of pfdhfr and pfdhps in single Plasmodium falciparum infection isolates from the interior division of Sabah, Malaysian Borneo.

Methods

A total of 22 P. falciparum single infection isolates collected from two districts of the interior division of Sabah from February to November 2010 were recruited for the mutational study of pfdhfr and pfdhps. Both genes were amplified by nested PCR prior to DNA sequencing and mutational analysis.

Results

A total of three pfdhfr and four pfdhps alleles were identified. The most prevalent pfdhfr allele is ANRNL (86%) involving triple mutation at position 108(S to N), 59(C to R) and 164(I to L). In pfdhps, two novel alleles, SGTGA (73%) and AAKAA (5%) were identified. Alleles involving triple mutation in both pfdhfr (ANRNL) and pfdhps (SGTGA), which were absent in Sabah in a study conducted about 15 years ago, are now prevalent.

Conclusions

High prevalence of mutations in SDX/PYR associated drug resistance genes are reported in this study. This mutational study of pfdhps and pfdhfr indicating that SDX/PYR should be discontinued in this region.

Prevalence of malaria and use of malaria risk reduction measures among resettled pregnant women in South Sudan

BACKGROUND

The study assessed aspects of malaria infection, prevention and treatment in a population of resettled pregnant women in South Sudan.

METHODS

During April and May 2008, a cross-sectional study was carried out to estimate malaria prevalence and to assess the use of malaria risk reduction measures and their associations with selected background characteristics. Two hundred and twenty women were tested for malaria parasitaemia and questioned about their malaria prevention and treatment practices.

RESULTS

The results showed a prevalence of Plasmodium falciparum parasitaemia of 9.1%. No statistically significant associations were observed between selected background characteristics and malaria infection status. However, school attendance was significantly associated with insecticide-treated net ownership (OR = 6.52, 95% CI 2.37-17.94; p = 0.001) and access to malaria diagnosis and treatment (OR = 3.20, 95% CI 1.26-8.16; p = 0.015).

CONCLUSIONS

The results suggest that educational attainment need not be very advanced to affect practices of malaria prevention and treatment. Primary school attendance was a stronger predictor for use of malaria risk reduction measures than any of the other selected background characteristics. Educational attainment, information and communication about malaria prevention and control play a pivotal role in increasing and improving use of malaria risk reduction measures.

Effectiveness of intermittent preventive treatment with sulfadoxine-pyrimethamine during pregnancy on maternal and birth outcomes in Machinga district, Malawi

BACKGROUND

Malaria during pregnancy is associated with low birth weight and increased perinatal mortality, especially among primigravidae. Despite increasing prevalence of malarial parasite resistance to sulfadoxine-pyrimethamine (SP), SP continues to be recommended for intermittent preventive treatment in pregnancy (IPTp).

METHODS

Women without human immunodeficiency virus infection were enrolled upon delivery. Data on the number of SP doses received during pregnancy were recorded. The primary outcome was placental infection demonstrated by histologic analysis. Secondary outcomes included malaria parasitemia (in peripheral, placental, cord blood specimens) at delivery and composite birth outcome (small for gestational age, preterm delivery, or low birth weight). RESULTS.: Of 703 women enrolled, 22% received <2 SP doses. Receipt of ≥ 2 SP doses had no impact on histologically confirmed placental infection. IPTp-SP was associated with a dose-dependent protective effect on composite birth outcome in primigravidae, with an adjusted prevalence ratio of 0.50 (95% confidence interval [CI], .30-.82), 0.30 (95% CI, .19-.48), and 0.18 (95% CI, .05-.61) for 1, 2, and ≥ 3 doses, respectively, compared with 0 doses.

CONCLUSIONS

IPTp-SP did not reduce the frequency of placental infection but was associated with improved birth outcomes. Few women received no SP, so the true effect of IPTp-SP may be underestimated. Malawian pregnant women should continue to receive IPTp-SP, but alternative strategies and antimalarials for preventing malaria during pregnancy should be investigated.

High prevalence of mutation in the Plasmodium falciparum dhfr and dhps genes in field isolates from Sabah, Northern Borneo

Background

Sulphadoxine-pyrimethamine (SP) has been in use for the treatment of uncomplicated falciparum malaria in Malaysia since the 1970s and is still widely employed in spite of widespread clinical resistance. Resistance to SP is known to be mediated by mutations in the pfdhfr and pfdhps genes. The aim of the present study was to investigate the distribution of pfdhfr and pfdhps gene polymorphism in Plasmodium falciparum field isolates from Kalabakan, Sabah, in northern Borneo.

Methods

A total number of 619 individuals were screened from 23 study sites of which 31 were positive for P. falciparum. Analysis of restriction fragment length polymorphisms (RFLP) was used to identify polymorphism in the pfdhfr and pfdhps genes at positions 16, 51, 59, 108, 164 and 437, 540, 581, respectively.

Results

All samples had at least one mutation in each of the genes associated with drug resistance. The prevalence of pfdhfr 59arg, 164leu and 108asn were 100%, 80.65% and 58.06%, respectively. Pfdhps mutants 437gly and 581gly accounted for 100% and 74.19% respectively. In pfdhfr, the most common mutant genotypes were combination 59arg + 164leu (22.58%) and 59arg + 108asn + 164leu (51.61%). In pfdhps the most common genotype was 437gly + 581gly (74.19%). One individual (3.22%) harboured parasites with four pfdhfr (16 val + 59arg + 108asn + 164leu) and two pfdhps (437gly + 581gly) mutations. The highest quintuple pfdhfr/pfdhps (41.94%) was three pfdhfr (59arg + 108asn + 164gly) and two pfdhps (437gly + 581gly).

Conclusion

The data suggest a high prevalence of genetic variations conferring resistance to SP which can predict treatment failure before becoming clinically evident. In areas like this, the use of SP may no longer be indicated.

Molecular markers of resistance to sulphadoxine-pyrimethamine during intermittent preventive treatment of pregnant women in Benin

Background

The prevention of malaria faces with the repeated emergence of Plasmodium falciparum resistance to drugs, often involving point mutations of the target gene. In the pregnant woman, currently the WHO recommendation is the administration of an intermittent preventive treatment (IPTp) with sulphadoxine-pyrimethamine. Sulphadoxine-pyrimethamine (SP) resistance has increased for several years in Africa, stressing the need for alternative molecules. In this context, the first randomized clinical trial comparing the efficacy of SP and mefloquine for IPTp has been conducted recently in Benin. Using samples from this trial, the current study evaluated and quantified the prevalence of mutations on the pfdhfr and pfdhps genes as well as the copy number of the pfmdr1 gene in parasites from P. falciparum-infected pregnant women before first and second IPTp administration, and at delivery.

Methods

PCR-restriction fragment length polymorphism of polymorphic codons of the pfdhfr gene (51, 59, 108, and 164) was performed. The identification of mutations in three codons of the pfdhps gene (436, 437 and 540) was achieved by PCR and sequencing. Copy number quantification for pfmdr1 gene was performed using real-time PCR.

Results

Results show a high prevalence rate of mutant parasites in women taking IPTp with sulphadoxine-pyrimethamine or mefloquine. The prevalence of triple and quadruple mutants was high before first drug regimen administration (79/93, 85%), and remained similar until delivery. Infection with mutant parasites was not correlated with low birth weight nor placental infection. In all samples, the copy number of pfmdr1 gene was equal to one.

Conclusions

The clinical trial comparing SP and mefloquine efficacy during IPTp showed SP remained efficacious in preventing low birth weight. The present study shows a high prevalence of triple and quadruple mutations implicated in SP resistance. Although the pfdhfr/pfdhps triple and quadruple mutations were frequent, there was no evidence of correlation between these genotypes and the lack of efficacy of SP in the context of IPTp. Nevertheless, it is now obvious that SP will soon be compromised in whole Africa. Molecular markers have been recommended to monitor SP efficacy for IPTp, but given the current prevalence of mutant parasites their usefulness is questionable.

High prevalence of the 437G mutation associated with sulfadoxine resistance among Plasmodium falciparum clinical isolates from Iran, three years after the introduction of sulfadoxine-pyrimethamine

OBJECTIVE

The objective of this study was to determine the frequency of dhfr and dhps resistance-associated haplotypes in Plasmodium falciparum isolates, three years after the introduction of sulfadoxine-pyrimethamine (SP) as the first-line antimalarial treatment in Iran.

METHODS

Blood samples (N=182) were collected from patients presenting with falciparum malaria from southeastern Iran, and analyzed by nested-PCR/restriction fragment length polymorphism, followed by sequencing analysis.

RESULTS

In pfdhfr, double mutation at positions 59R and 108N was a predominant allele with a prevalence of 95.7%. The pure double mutations of pfdhfr (I(51)N(108)) were detected, and showed an increase from 0.7% to 4.3% after the introduction of SP as first-line drug. Furthermore, a significant decrease in double mutations/wild-type of pfdhfr/pfdhps (R(59)N(108)/A(437)) was observed from 2004 (83.5%) to 2008 (44%) after changes in treatment policy. With regards to pfdhps, the results showed a rapid increase in frequency of the single pure form of pfdhps at position 437G (54.4%) and that of triple pfdhfr/pfdhps (R(59)N(108)/G(437)) mutant haplotype (51.7%) after three years.

CONCLUSIONS

The absence of quintuple mutations in the examined isolates supports the continued use of SP as the treatment of choice for uncomplicated malaria as a partner drug to artemisinin combination therapy in Iran. However, the increase in the triple pfdhfr/pfdhps (R(59)N(108)/G(437)) mutant haplotypes indicates that the P. falciparum parasite populations have the potential to evolve into dhfr/dhps quintuple mutants in the near future. Therefore, monitoring the status of dhps alleles as a predictor of the development of clinical resistance to sulfadoxine should be a high priority in this region.

Evaluation of prevalence's of pfdhfr and pfdhps mutations in Angola

Background

Malaria is the major cause of morbidity and mortality in Angola. The most vulnerable groups to Plasmodium falciparum infection are pregnant women and children under five years of age. The use of an intermittent preventive treatment (IPT) with sulphadoxine/pyrimethamine (SP) in pregnant women was introduced in Angola in 2006 by the National Malaria Control Programme, and currently this strategy has been considered to be used for children malaria control. Considering the previous wide use of SP combination in Angola, together to the reported cases of SP treatment failure it is crucial the evaluation of the prevalence of five mutations in pfdhfr and pfdhps genes associated to P. falciparum resistance to SP before the introduction of S/P IPT in children.

Methods

The study was conducted in five provinces, with different transmission intensities: Huambo, Cabinda, Uíge, Kwanza Norte, and Malanje. The detection of the mutations in pfdhfr and pfdhps genes was carried out in 452 P. falciparum blood samples by PCR RFLP.

Results

For pfdhfr gene, 90,3% of the samples carried the mutation 51I, with 7.5% of mixed infections; 51% carried wild type allele 59C, with 29.2% mixed infections and; 99.1% of isolates harboured the mutant allele 108N. Concerning, pfdhps gene, 83,1% were mutant type 437G with 11% mixed infections , while 87% of the studied isolates were wild type for codon 540.

Discussion

This is the first representative epidemiological study of the whole Angola country on the prevalence of the genotypes associated with SP chemoresistance. A high frequency of individual mutations in both genes (51I and 108N in pfdhfr, and 437G in pfdhps) was found, besides a low prevalence of the quintuple mutation.

Conclusion

The data showed that the implementation IPT using SP in children needs to be reviewed.

Origins and spread of pfdhfr mutant alleles in Plasmodium falciparum

The emergence and spread of Plasmodium falciparum parasite resistant to sulfadoxine and pyrimethamine (SP) poses a serious public health problem. Resistance is caused by point mutations in dihydrofolate reductase (pfdhfr) and dihydropteroate synthase (pfdhps), the two key enzymes in the folate biosynthetic pathway. The use of microsatellite markers flanking pfdhfr has recently shown that the invasion of limited resistant lineages may explain the widespread SP resistance in many endemic regions. In Africa, however, multiple indigenous origins of pfdhfr triple mutants have been demonstrated. More new independent lineages and routes of geographical spread of resistance may be found by further molecular evolutionary analyses using samples from various endemic regions. Here, I review recent studies about the history of SP usage and the evolution and spread of resistant lineages while addressing the technical issue of microsatellite analysis.

Spread and evolution of Plasmodium falciparum drug resistance

Worldwide spread of Plasmodium falciparum drug resistance to conventional antimalarials, chloroquine and sulfadoxine/pyrimethamine, has been imposing a serious public health problem in many endemic regions. Recent discovery of drug resistance-associated genes, pfcrt, pfmdr1, dhfr, and dhps, and applications of microsatellite markers flanking the genes have revealed the evolution of parasite resistance to these antimalarials and the geographical spread of drug resistance. Here, we review our recent knowledge of the evolution and spread of parasite resistance to chloroquine and sulfadoxine/pyrimethamine. In both antimalarials, resistance appears to be largely explained by the invasion of limited resistant lineages to many endemic regions. However, multiple, indigenous evolutionary origins of resistant lineages have also been demonstrated. Further molecular evolutionary and population genetic approaches will greatly facilitate our understanding of the evolution and spread of parasite drug resistance, and will contribute to developing strategies for better control of malaria.

Prevalence of mutations associated with antimalarial drugs in Plasmodium falciparum isolates prior to the introduction of sulphadoxine-pyrimethamine as first-line treatment in Iran

Background

This work was carried out to assess the patterns and prevalence of resistance to chloroquine (CQ) and sulphadoxine-pyrimethamine (SP) in Iran.

Methods

The prevalence of pfcrt K76T, pfmdr1 N86Y, pfdhfr N51I, C59R, S108N/T and I164L and codons S436F/A, A437G, K540E, A581E, and A613S/T in pfdhps genes were genotyped by PCR/RFLP methods in 206 Plasmodium falciparum isolates from Chabahar and Sarbaz districts in Sistan and Baluchistan province, Iran, during 2003–2005.

Results

All P. falciparum isolates carried the 108N, while 98.5% parasite isolates carried the 59R mutation. 98.5% of patients carried both 108N and 59R. The prevalence of pfdhps 437G mutation was 17% (Chabahar) and 33% (Sarbaz) isolates. 20.4% of samples presented the pfdhfr 108N, 59R with pfdhps 437G mutations. The frequency of allele pfcrt 76T was 98%, while 41.4% (Chabahar) and 27.7% (Sarbaz) isolates carried pfmdr1 86Y allele. Eight distinct haplotypes were identified in all 206 samples, while the most prevalent haplotype was T_76/N_86/N₅₁R₅₉N_108/A₄₃₇ among both study areas.

Conclusion

Finding the fixed level of CQ resistance polymorphisms (pfcrt 76T) suggests that CQ must be withdrawn from the current treatment strategy in Iran, while SP may remain the treatment of choice for uncomplicated malaria.

Plasmodium falciparum isolates in India exhibit a progressive increase in mutations associated with sulfadoxine-pyrimethamine resistance

The combination of sulfadoxine-pyrimethamine (SP) is used as a second line of therapy for the treatment of uncomplicated chloroquine-resistant Plasmodium falciparum malaria. Resistance to SP arises due to certain point mutations in the genes for the dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS) enzymes of the parasite. We have analyzed these mutations in 312 field isolates of P. falciparum collected from different parts of India to assess the effects of drug pressure. The rate of mutation in the gene for DHFR was found to be higher than that in the gene for DHPS, although the latter had mutations in more alleles. There was a temporal rise in the number of isolates with double dhfr mutations and single dhps mutations, resulting in an increased total number of mutations in the loci for DHFR and DHPS combined over a 5-year period. During these 5 years, the number of isolates with drug-sensitive genotypes decreased and the number of isolates with drug-resistant genotypes (double DHFR mutations and a single DHPS mutation) increased significantly. The number of isolates with the triple mutations in each of the genes for the two enzymes (for a total of six mutations), however, remained very low, coinciding with the very low rate of SP treatment failure in the country. There was a regional bias in the mutation rate, as isolates from the northeastern region (the state of Assam) showed higher rates of mutation and more complex genotypes than isolates from the other regions. It was concluded that even though SP is prescribed as a second line of treatment in India, the mutations associated with SP resistance continue to be progressively increasing.

Application of a multi-faceted approach for the assessment of treatment response in falciparum malaria: a study from Malaysian Borneo

Thirty-two patients reporting to the Lundu District Hospital, Sarawak, Malaysian Borneo, with uncomplicated falciparum malaria were recruited into a multifaceted study to assess treatment response. Following combined chloroquine and sulphadoxine/pyrimethamine treatment the patients were followed for 28 days according to the World Health Organisation in vivo drug response protocol. The in vivo study revealed that 13 (41%) of the patients had a sensitive response to treatment, five (16%) cleared asexual stage parasites but had persistent gametocytes, 11 (34%) had RI type resistance and three (9%) had RII type resistance requiring quinine intervention before day 7 for parasite clearance. Although clinically insignificant, patients with persistent gametocytes, surviving chloroquine and sulphadoxine/pyrimethamine treatment during maturation, were placed in the reduced response to treatment group for analysis. Allelic typing detected 100% prevalence of the pfcrt K76T marker associated with chloroquine resistance and 78% prevalence of the pfdhfr NRNL haplotype associated with sulphadoxine/pyrimethamine treatment failure. High serum chloroquine levels and pfdhfr haplotypes with <or=2 point mutations were independently associated with a sensitive response to treatment. However four patients in the sensitive response group had both low serum chloroquine levels and the pfdhfr NRNL haplotype. A degree of immunity, consistent with malaria endemicity, may account for the apparently paradoxical presence of markers of drug resistance in the sensitive group.

Treatment of uncomplicated falciparum malaria in southern Vietnam: can chloroquine or sulfadoxine-pyrimethamine be reintroduced in combination with artesunate?

The effectiveness of chloroquine or sulfadoxine-pyrimethamine administered with artesunate for treating uncomplicated falciparum malaria was assessed in 2 Vietnamese provinces where the sensitivity of parasites in vitro to conventional therapies had increased with the removal of drug pressure. In the province of Dac Lac, where potential malaria exposure begins at birth, 57 subjects (mean age, 9.6 years) were randomized to receive artesunate-chloroquine (group 1) or artesunate-sulfadoxine-pyrimethamine (group 2). In the province of Binh Phuoc, 66 nonimmune workers and their relatives (mean age, 24.2 years) were similarly randomized. By day 28 of follow-up, >96% of Dac Lac patients and <52% of Binh Phuoc patients in group 1 and group 2 had an in vivo response that demonstrated sensitivity to therapy. PCR-confirmed cure rates paralleled in vivo results among patients in Binh Phuoc, but PCR results identified 9 (15.7%) of the Dac Lac patients as having experienced asymptomatic, submicroscopic recrudescences. In Dac Lac, pfcrt K76T was near fixation, but infection with parasites with this mutation predicted recrudescence among group 1 patients in Binh Phuoc. Common pfdhfr mutations did not predict outcome in group 2. The successful reintroduction of conventional therapies in combination with artesunate depends on epidemiological and/or parasitological factors.

The drug sensitivity and transmission dynamics of human malaria on Nias Island, North Sumatra, Indonesia

Nias Island, off the north-western coast of Sumatra, Indonesia, was one of the first locations in which chloroquine-resistant Plasmodium vivax malaria was reported. This resistance is of particular concern because its ancient megalithic culture and the outstanding surfing conditions make the island a popular tourist destination. International travel to and from the island could rapidly spread chloroquine-resistant strains of P. vivax across the planet. The threat posed by such strains, locally and internationally, has led to the routine and periodic re-assessment of the efficacy of antimalarial drugs and transmission potential on the island. Active case detection identified malaria in 124 (17%) of 710 local residents whereas passive case detection, at the central health clinic, confirmed malaria in 77 (44%) of 173 cases of presumed 'clinical malaria'. Informed consenting volunteers who had malarial parasitaemias were treated, according to the Indonesian Ministry of Health's recommendations, with sulfadoxine-pyrimethamine (SP) on day 0 (for P. falciparum) or with chloroquine (CQ) on days 0, 1 and 2 (for P. vivax). Each volunteer was then monitored for clinical and parasite response until day 28. Recurrent parasitaemia by day 28 treatment was seen in 29 (83%) of the 35 P. falciparum cases given SP (14, 11 and four cases showing RI, RII and RIII resistance, respectively). Recurrent parasitaemia was also observed, between day 11 and day 21, in six (21%) of the 28 P. vivax cases given CQ. Although the results of quantitative analysis confirmed only low prevalences of CQ-resistant P. vivax malaria, the prevalence of SP resistance among the P. falciparum cases was among the highest seen in Indonesia. When the parasites present in the volunteers with P. falciparum infections were genotyped, mutations associated with pyrimethamine resistance were found at high frequency in the dhfr gene but there was no evidence of selection for sulfadoxine resistance in the dhps gene. Night-biting mosquitoes were surveyed by human landing collections and tested for sporozoite infection. Among the five species of human-biting anophelines collected, Anopheles sundaicus was dominant (68%) and the only species found to be infective--two (1.2%) of 167 females being found carrying P. vivax sporozoites. The risk of malarial infection for humans on Nias was considered high because of the abundance of asymptomatic carriers, the reduced effectiveness of the available antimalarial drugs, and the biting and infection 'rates' of the local An. sundaicus.

Parasites that cause problems in Malaysia: soil-transmitted helminths and malaria parasites

Malaysia is a developing country with a range of parasitic infections. Indeed, soil-transmitted helminths and malaria parasites continue to have a significant impact on public health in Malaysia. In this article, the prevalence and distribution of these parasites, the problems associated with parasitic infections, the control measures taken to deal with these parasites and implications for the future will be discussed.