Rapid increase of Plasmodium falciparum dhfr/dhps resistant haplotypes, after the adoption of sulphadoxine-pyrimethamine as first line treatment in 2002, in southern Mozambique.

BACKGROUND: In late 2002, the health authorities of Mozambique implemented sulphadoxine-pyrimethamine (SP)/amodiaquine (AQ) as first-line treatment against uncomplicated falciparum malaria. In 2004, this has been altered to SP/artesunate in line with WHO recommendations of using Artemisinin Combination Therapies (ACTs), despite the fact that all the neighbouring countries have abandoned SP-drug combinations due to high levels of SP drug resistance. In the study area, one year prior to the change to SP/AQ, SP alone was used to treat uncomplicated malaria cases. The study described here investigated the immediate impact of the change to SP on the frequency of SP and CQ resistance-related haplotypes in the Plasmodium falciparum genes Pfdhfr, Pfdhps and Pfcrt before and a year after the introduction of SP. METHODS: Samples were collected during two cross sectional surveys in early 2002 and 2003 involving 796 and 692 children one year or older and adults randomly selected living in Maciana, an area located in Manhiça district, Southern Mozambique. Out of these, 171 and 173 P. falciparum positive samples were randomly selected to measure the frequency of resistance- related haplotypes in Pfdhfr, Pfdhps and Pfcrt based on results obtained by nested PCR followed by sequence-specific oligonucleotide probe (SSOP)-ELISA. RESULTS: The frequency of the SP-resistance associated Pfdhps double mutant (SGEAA) haplotype increased significantly from 14% to 35% (P < 0.001), while the triple mutant Pfdhfr haplotype (CIRNI) remained high and only changed marginally from 46% to 53% (P = 0.405) after one year with SP as first-line treatment in the study area. Conversely, the combined Pfdhfr/Pfdhps quintuple mutant haplotype increased from 8% to 26% (P = 0.005). The frequency of the chloroquine resistance associated Pfcrt-CVIET haplotype was above 90% in both years. CONCLUSION: These retrospective findings add to the general concern on the lifespan of the combination of SP/artesunate in Mozambique. The high frequency of quintuple Pfdhfr/Pfdhps haplotypes found here as early as 2002 most likely cause ideal conditions for the development of artesunate tolerance in the P. falciparum populations and may even endanger the sensitivity to the second-line drug, Coartem.

Laboratory indicators of the diagnosis and course of imported malaria.

When travellers return from malaria-endemic areas and present to hospital with fever, microscopy of blood smears remains the leading method to verify a suspected diagnosis of malaria. Additional laboratory abnormalities may, however, also be indicative of acute malaria infection. We monitored prospectively a group of patients with imported Plasmodium falciparum (n=28) or P. vivax/P. ovale (n=12) infection, respectively, and assessed haemoglobin, leucocytes, thrombocytes, C-reactive protein, coagulation factor II-VII-X, lactate dehydrogenase and bilirubin during 7 d of admission and weekly until d 28. For comparison, admission values of a group of febrile patients with suspected malaria, but with negative blood slides, were also assessed (n=66). The thrombocyte, leucocyte counts and coagulation factor II-VII-X were significantly lower in the malaria group compared to the non-malaria group, whereas the C-reactive protein, lactate dehydrogenase and bilirubin were significantly higher in the malaria group. The differences were particularly strong with falciparum malaria. By contrast, haemoglobin levels were not affected. In conclusion, our study emphasizes the role of a few commonly analysed laboratory parameters, in particular thrombocyte counts, in guiding the clinician managing a returning traveller with fever.

High reinfection rate and treatment failures in children treated with amodiaquine for falciparum malaria in Muheza villages, Northeastern Tanzania.

In May 2003, we studied amodiaquine (AQ) efficacy in children < 5 years of age with uncomplicated falciparum malaria in Magoda and Mpapayu (with insecticide treated nets [ITNs]) and Mgome (without ITNs) in Muheza, Tanzania. The trial involved 28 days of follow-up, and data were adjusted by polymerase chain reaction (PCR) genotyping of msp1 and msp2 genes. Additionally, Pfcrt codon 72-76 polymorphisms were studied by PCR and sequence-specific oligonucleotide probe (SSOP) ELISA. In 54 cases with complete follow-up, a significant difference in late treatment failure (LTF) rates was seen (60.7% in ITN versus 88.5% in non-ITN villages, P = 0.02) before PCR correction. However, after PCR correction, 23 cases (60.5%) were confirmed as reinfections, giving a true LTF rate of 21.4% (6/28) and 34.6% (9/26) in the above settings, respectively. Frequency of Pfcrt CVIET haplotype mutation pretreatment was high (97.0%); the remaining samples were CVMNK. We conclude that AQ alone is no longer effective in the study area.

Occurrence of the Southeast Asian/South American SVMNT haplotype of the chloroquine-resistance transporter gene in Plasmodium falciparum in Tanzania.

Two main haplotypes, CVIET and SVMNT, of the Plasmodium falciparum chloroquine-resistance transporter gene (Pfcrt) are linked to 4-aminoquinoline resistance. The CVIET haplotype has been reported in most malaria-endemic regions, whereas the SVMNT haplotype has only been found outside Africa. We investigated Pfcrt haplotype frequencies in Korogwe District, Tanzania, in 2003 and 2004. The SVMNT haplotype was not detected in 2003 but was found in 19% of infected individuals in 2004. Amodiaquine use has increased in the region. The introduction and high prevalence of the SVMNT haplotype may reflect this and may raise concern regarding the use of amodiaquine in artemisinin-based combination therapies in Africa.

Response of Plasmodium falciparum to cotrimoxazole therapy: relationship with plasma drug concentrations and dihydrofolate reductase and dihydropteroate synthase genotypes.

We assessed the efficacy of trimethoprim/sulfamethoxazole (TRM/SMX) in vivo in relation to the frequency of dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) alleles in 45 Sudanese malaria patients. Plasma levels of TRM, SMX, and acetylsulfamethoxazole (AcSMX) were measured before treatment and at days 3, 7, and 14 or upon recrudescence to ascertain drug absorption. Forty patients (89%) had an adequate clinical response, one patient (2%) had an early treatment failure response, while four patients (8%) showed late treatment failure responses. Genotyping of merozoite surface protein 1, MSP-1, MSP-2, and glutamate-rich protein before treatment and upon recrudescence showed that all recurring parasites were recrudescences. The plasma levels of TRM, AcSMX, and SMX indicated adequate drug absorption in all patients. This suggests parasite resistance as a cause of treatment failure. The presence of dhfr Ile 51 and Asn 108 alone or coupled with dhps Ala-436 among parasites that were cleared after treatment indicates that these alleles alone are insufficient to cause in vivo resistance. However, the presence of the triple mutant dhfr (Ile-51/Arg-59/Asn-108) with the dhps Gly-437 genotype in all recurring infections, suggests the importance of codon 59 and 437 alleles in susceptibility to TRM/SMX. However, the number is too little to make firm conclusions.

A simple, high-throughput method to detect Plasmodium falciparum single nucleotide polymorphisms in the dihydrofolate reductase, dihydropteroate synthase, and P. falciparum chloroquine resistance transporter genes using polymerase chain reaction- and enzyme-linked immunosorbent assay-based technology.

Single nucleotide polymorphisms (SNPs) in the Plasmodium falciparum dihydrofolate reductase (dhfr), and dihydropteroate synthetase (dhps), and chloroquine resistance transporter (Pfcrt) genes are used as molecular markers of P. falciparum resistance to sulfadoxine/pyrimethamine and chloroquine. However, to be a practical tool in the surveillance of drug resistance, simpler methods for high-throughput haplotyping are warranted. Here we describe a quick and simple technique that detects dhfr, dhps, and Pfcrt SNPs using polymerase chain reaction (PCR)- and enzyme-linked immunosorbent assay (ELISA)-based technology. Biotinylated PCR products of dhfr, dhps, or Pfcrt were captured on streptavidin-coated microtiter plates and sequence-specific oligonucleotide probes (SSOPs) were hybridized with the PCR products. A stringent washing procedure enabled detection of remaining bound SSOPs and distinguished between the SNPs of dhfr, dhps, and Pfcrt with high specificity. The SSOP-ELISA compared well with a standard PCR-restriction fragment length polymorphism procedure, and gave identical positive results in more than 90% of the P. falciparum slide-positive samples tested. The SSOP-ELISA of all dhfr, dhps, or Pfcrt SNPs on 88 samples can be performed in a single day and provides quick and reproducible results. The system can potentially be modified to detect SNPs in other genes.

Atovaquone-proguanil (malarone): an effective treatment for uncomplicated Plasmodium falciparum malaria in travelers from Denmark.

BACKGROUND: Previous experience with unacceptable adverse effects with mefloquine as treatment for uncomplicated Plasmodium falciparum malaria prompted an evaluation of the effectiveness and side effects of atovaquone-proguanil (Malarone) in a hospital setting. METHODS: Atovaquone-proguanil was given as standard treatment (1,000/400 mgq.d. for 3 days) to 50 adults who had traveled in Africa and returned with uncomplicated Plasmodium falciparum malaria. Half of the treated patients were African and had lived outside Africa for varying periods of time; the other half were Danish-born persons without any previous immunity towards malaria. RESULTS: All patients treated with Malarone were cured without complications. The mean fever clearance times differed among the groups and according to various degrees of prior exposure to malaria and ranged from 1.3 to 2.2 days. Adverse effects during treatment were mild, and were likely to be due to the malaria itself. Fourteen people who had acquired falciparum malaria in spite of taking proguanil-chloroquine prophylaxis were also cured uneventfully without recrudescence. CONCLUSIONS: Malarone appears to be an effective, safe and acceptable oral treatment for uncomplicated malaria.

Homology building as a means to define antigenic epitopes on dihydrofolate reductase (DHFR) from Plasmodium falciparum.

BACKGROUND: The aim of this study was to develop site-specific antibodies as a tool to capture Plasmodium falciparum-dihydrofolate reductase (Pf-DHFR) from blood samples from P. falciparum infected individuals in order to detect, in a sandwich ELISA, structural alterations due to point mutations in the gene coding for Pf-DHFR. Furthermore, we wanted to study the potential use of homology models in general and of Pf-DHFR in particular in predicting antigenic malarial surface epitopes. METHODS: A homology model of Pf-DHFR domain was employed to define an epitope for the development of site-specific antibodies against Pf-DHFR. The homology model suggested an exposed loop encompassing amino acid residues 64-100. A synthetic peptide of 37-mers whose sequence corresponded to the sequence of amino acid residues 64-100 of Pf-DHFR was synthesized and used to immunize mice for antibodies. Additionally, polyclonal antibodies recognizing a recombinant DHFR enzyme were produced in rabbits. RESULTS AND CONCLUSIONS: Serum from mice immunized with the 37-mer showed strong reactivity against both the immunizing peptide, recombinant DHFR and a preparation of crude antigen from P. falciparum infected red blood cells. Five monoclonal antibodies were obtained, one of which showed reactivity towards crude antigen prepared from P. falciparum infected red cells. Western blot analysis revealed that both the polyclonal and monoclonal antibodies recognized Pf-DHFR. Our study provides insight into the potential use of homology models in general and of Pf-DHFR in particular in predicting antigenic malarial surface epitopes.

Increasing prevalence of wildtypes in the dihydrofolate reductase gene of Plasmodium falciparum in an area with high levels of sulfadoxine/pyrimethamine resistance after introduction of treated bed nets.

In Magoda and Mpapayu villages in Tanzania, we have previously found comparable high prevalence of Plasmodium falciparum resistance to sulfadoxine/pyrimethamine (S/P) in vivo and of mutations in the dihydrofolate reductase (dhfr) and dihydropteroate synthetase (dhps) genes of P. falciparum responsible for resistance to S/P. In December 1998, Magoda received insecticide-treated nets (ITNs), whereas ITNs were introduced in Mpapayu in March 2001. We have studied the effect of ITNs on P. falciparum resistance genes by monitoring the prevalence of dhfr and dhps genotypes in children less than five years old living in the villages from 1998 to 2000. In 2000, after two years of bed net use, the prevalence of wild types in codon 51, 59, and 108 of dhfr increased significantly in Magoda compared with previous years. Furthermore, the prevalence of dhfr wild types was significantly higher in Magoda than in Mpapayu in 2000. The impact of ITNs on the transmission intensity seems not only to affect the overall malaria morbidity, but may even facilitate restoration of susceptibility to antimalarial drugs.

Dihydrofolate reductase and dihydropteroate synthase genotypes associated with in vitro resistance of Plasmodium falciparum to pyrimethamine, trimethoprim, sulfadoxine, and sulfamethoxazole.

A total of 70 Plasmodium falciparum isolates were tested in vitro against pyrimethamine (PYR), trimethoprim (TRM), sulfadoxine (SDX), and sulfamethoxazole (SMX), and their dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genotypes were determined. dhfr genotypes correlated with PYR and TRM drug responses (r = 0.93 and 0.85). Isolates with wild-type alleles showed mean half inhibitory concentrations (IC50 +/- SD) of 0.10 +/- 0.10 and 0.15 +/- 0.06 microg/100 microl for PYR and TRM. Parasites with mutations at codons 108 and 51 alone or combined with codon 59 have IC50 of 11.46 +/- 0.86 (PYR) and 2.90 +/- 0.59 microg/100 microl (TRM). For both drugs, the differences in the mean IC50 between wild and mutant parasites were statistically significant (P < 0.001). Isolates with mixed wild and mutant alleles showed an intermediate level of susceptibility. Our data show partial cross-resistance between PYR/TRM and SDX/SMX (r = 0.85 and 0.65). Correlation was not observed between different dhps genotypes and the in vitro outcome to SDX and SMX (r = 0.30 and 0.34). The lack of correlation could be due to folates and para-aminobenzoic acid in the RPMI medium and the serum used to supplement the cultures.

Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania: a randomised placebo-controlled trial.

BACKGROUND: Malaria is a major cause of infant morbidity and mortality in sub-Saharan Africa, and is often complicated by severe anaemia. Resistance of Plasmodium falciparum to most affordable antimalarial drugs is an impediment to intermittent chemotherapy. We investigated the effect of presumptive intermittent treatment with amodiaquine and daily iron supplementation in infants on malarial fevers and anaemia, in a holoendemic area of Tanzania where malaria is largely resistant to chloroquine and sulfadoxine/ pyrimethamine. METHODS: 291 infants aged 12-16 weeks who attended three clinics were randomised to receive amodiaquine, iron supplementation, amodiaquine plus iron supplementation, or placebo. Over 6 months, we gave amodiaquine three times with intervals of 60 days; oral iron supplementation was given daily. Malarial fevers and anaemia were monitored at bimonthly treatment visits and by self-reporting to health centres. FINDINGS: The protective efficacy of intermittent amodiaquine treatment in prevention of malarial fevers and anaemia was 64.7% (95% CI, 42.4-77.2) and 67.0% (95% CI, 34.5-83.4), respectively. Protective efficacy was similar in the group receiving amodiaquine plus iron supplementation. Infants receiving iron supplementation only were partly protected against anaemia (protective efficacy 59.8%; 95% CI, 23.4-78.9), but not against malarial fevers. 4 months' follow-up did not show rebound morbidity. We noted no haematological or clinical adverse effects. INTERPRETATION: Presumptive intermittent treatment for malaria with amodiaquine reduced malarial fevers and anaemia in infants, in an area with high resistance to other antimalarials. Intermittent treatment strategies for malaria in highly endemic areas could be of great benefit to public health.

Prediction of Plasmodium falciparum resistance to sulfadoxine/pyrimethamine in vivo by mutations in the dihydrofolate reductase and dihydropteroate synthetase genes: a comparative study between sites of differing endemicity.

Plasmodium falciparum resistance to sulfadoxine/pyrimethamine (S/P) is due to mutations in the dihydrofolate reductase (dhfr) and dihydropteroate synthetase (dhfr) genes. Large-scale screening of the prevalence of these mutations could facilitate the surveillance of the level of S/P resistance in vivo. The prevalence of mutations in dhfr and dhps in relation to S/P efficacy was studied in four sites of differing endemicity in Sudan, Mozambique, and Tanzania. The sites were organized in order of increasing resistance and a significant increase in the prevalence of triple mutations in codons c51, c59, and c108 of dhfr was observed. A similar trend was observed when dhfr genotypes were combined with c437 of dhps. Since the differences in S/P resistance between the sites were minor, but nevertheless revealed major differences in dhfr genotype prevalence, the role of dhfr as a general molecular marker seems debatable. The differences may reflect variation in the duration and magnitude of S/P usage (or other antifolate drugs) between the sites. Thus, triple dhfr mutations may prove suitable only as a general guideline for detecting emerging S/P resistance in areas where S/P has been introduced recently. However, changes in susceptibility within the same area with moderate levels of resistance may be possible by longitudinal surveillance of a subset of dhfr/dhps mutations that has been associated with S/P resistance in vivo in a defined location.

Pyrimethamine/sulfadoxine combination in the treatment of uncomplicated falciparum malaria: relation between dihydropteroate synthase/dihydrofolate reductase genotypes, sulfadoxine plasma levels, and treatment outcome.

Several in vitro studies have shown the correlation between mutations in dhfr and dhps genes and resistance to pyrimethamine/sulfadoxine (PYR/SDX) combination, but the in vivo correlates of these mutations with PYR/ SDX efficacy have not been investigated fully. We assessed PYR/SDX efficacy in relation to the frequency of dhfr and dhps mutations in 37 Plasmodium falciparum isolates sampled before treatment. Plasma levels of SDX measured at days 0, 3, 7, and 14 ascertained drug absorption. Point mutations were detected only at codons 51 and 108 of dhfr and codon 436 of dhps. The frequency of dhfr 51/108 and dhps 436 mutations was 79% and 8%. The plasma levels of SDX indicated adequate drug absorption by all patients. The presence of Ile 51 and Asn 108 mutations among parasites that cleared after treatment indicates that these mutations alone are insufficient to cause in vivo resistance. In all recrudescent parasites, however, the presence of Ile 51/Asn 108 dhfr mutations was coupled with the dhps Ala 436. The findings suggest that the presence of Ile 51/Asn 108 dhfr mutations and Ala 436 dhps confers decreased susceptibility of P. falciparum to PYR/SDX in areas of low endemicity.