Analysis of circulating populations of Plasmodium falciparum in mild and severe malaria in two different epidemiological patterns in Madagascar

OBJECTIVE

To investigate whether the severity of Plasmodium falciparum attack in endemic areas was associated with the multiplicity of infection (MOI) and/or with a particular genotype(s).

METHOD

In two areas of different malaria transmission pattern in Madagascar (Sainte-Marie - mesoendemic and Tsiroanomandidy - hypoendemic) the number and the proportions of msp-2 genotypes within isolates were determined for each patient using a capillary electrophoresis genotyping method. DNA sequencing was performed to identify the msp-2 allelic family of dominant clones.

RESULTS

Eighty six uncomplicated and 33 severe cases were included in Sainte-Marie and 48 uncomplicated and 69 severe cases were included in Tsiroanomandidy. We found no association between the MOI and severity of malaria as the same mean number of msp-2 genotypes was found in isolates from uncomplicated and from severe malaria cases (3.72 and 3.73, respectively, P>0.05). The study of the association of dominant clones with clinical status showed no particular genotype or allelic family associated with malaria severity.

CONCLUSIONS

Severity of malaria was not associated with higher MOI in our study. Severity did not appear restricted to some particular genotypes either. On the contrary, severe malaria appeared to be caused by very common genotypes in the studied areas. More comprehensive explorations including immunity and genetic factors of the host are needed to acquire new information about this complex condition.

Prolonged Plasmodium falciparum infection in immigrants, Paris

Few immigrant travelers have Plasmodium falciparum infections >2 months after leaving malaria-endemic areas. We conducted a case-control study to identify factors associated with prolonged P. falciparum infection in immigrant travelers. Results suggest that P. falciparum infection should be systematically suspected, even months after travel, especially in pregnant women and first-arrival immigrants.

Plasmodium falciparum malaria and atovaquone-proguanil treatment failure

We noticed overrepresentation of atovaquone-proguanil therapeutic failures among Plasmodium falciparum-infected travelers weighing >100 kg. We report here 1 of these cases, which was not due to resistant parasites or impaired drug bioavailability. The follow-up of such patients should be strengthened.

Sulphadoxine/pyrimethamine versus amodiaquine for treating uncomplicated childhood malaria in Gabon: a randomized trial to guide national policy

BACKGROUND

In Gabon, following the adoption of amodiaquine/artesunate combination (AQ/AS) as first-line treatment of malaria and of sulphadoxine/pyrimethamine (SP) for preventive intermittent treatment of pregnant women, a clinical trial of SP versus AQ was conducted in a sub-urban area. This is the first study carried out in Gabon following the WHO guidelines.

METHODS

A random comparison of the efficacy of AQ (10 mg/kg/day x 3 d) and a single dose of SP (25 mg/kg of sulphadoxine/1.25 mg/kg of pyrimethamine) was performed in children under five years of age, with uncomplicated falciparum malaria, using the 28-day WHO therapeutic efficacy test. In addition, molecular genotyping was performed to distinguish recrudescence from reinfection and to determine the frequency of the dhps K540E mutation, as a molecular marker to predict SP-treatment failure.

RESULTS

The day-28 PCR-adjusted treatment failures for SP and AQ were 11.6% (8/69; 95% IC: 5.5-22.1) and 28.2% (20/71; 95% CI: 17.7-38.7), respectively This indicated that SP was significantly superior to AQ (P = 0.019) in the treatment of uncomplicated childhood malaria and for preventing recurrent infections. Both treatments were safe and well-tolerated, with no serious adverse reactions recorded. The dhps K540E mutation was not found among the 76 parasite isolates tested.

CONCLUSION

The level of AQ-resistance observed in the present study may compromise efficacy and duration of use of the AQ/AS combination, the new first-line malaria treatment. Gabonese policy-makers need to plan country-wide and close surveillance of AQ/AS efficacy to determine whether, and for how long, these new recommendations for the treatment of uncomplicated malaria remain valid.

Evaluation of the intra- and inter-specific genetic variability of Plasmodium lactate dehydrogenase

BACKGROUND

Malaria diagnosis is vital to efficient control programmes and the recent advent of malaria rapid diagnostic tests (RDTs) provides a reliable and simple diagnostic method. However a characterization of the efficiency of these tests and the proteins they detect is needed to maximize RDT sensitivity.

METHODS

Plasmodial lactate dehydrogenase (pLDH) gene of wild isolates of the four human species of Plasmodium from a variety of malaria endemic settings were sequenced and analysed.

RESULTS

No variation in nucleotide was found within Plasmodium falciparum, synonymous mutations were found for Plasmodium malariae and Plasmodium. vivax; and three different types of amino acid sequence were found for Plasmodium ovale. Conserved and variable regions were identified within each species.

CONCLUSION

The results indicate that antigen variability is unlikely to explain variability in performance of RDTs detecting pLDH from cases of P. falciparum, P. vivax or P. malariae malaria, but may contribute to poor detection of P. ovale.

World Antimalarial Resistance Network (WARN) II: in vitro antimalarial drug susceptibility

Intrinsic resistance of Plasmodium falciparum is clearly a major determinant of the clinical failure of antimalarial drugs. However, complex interactions between the host, the parasite and the drug obscure the ability to define parasite drug resistance in vivo. The in vitro antimalarial drug susceptibility assay determines ex-vivo growth of parasite in the presence of serial drug concentrations and, thus, eliminates host effects, such as drug metabolism and immunity. Although the sensitivity of the parasite to various antimalarials provided by such a test provides an important indicator of intrinsic parasite susceptibility, there are fundamental methodological issues that undermine comparison of in vitro susceptibility both between laboratories and within a single laboratory over time. A network of laboratories is proposed that will agree on the basic parameters of the in vitro test and associated measures of quality control. The aim of the network would be to establish baseline values of sensitivity to commonly used antimalarial agents from key regions of the world, and create a global database, linked to clinical, molecular and pharmacology databases, to support active surveillance to monitor temporal trends in parasite susceptibility. Such a network would facilitate the rapid detection of strains with novel antimalarial resistance profiles and investigate suitable alternative treatments with retained efficacy.

Hospitalization criteria in imported falciparum malaria

BACKGROUND

Controversy exists about the management of patients with imported Plasmodium falciparum malaria. We postulated that rapid parasite clearance supports ambulatory care, or, conversely, that factors associated with longer parasite clearance time (PCT) could be used as hospitalization criteria.

METHODS

Hospitalized patients with imported falciparum malaria recruited through one single travel clinic between 1993 and 2000. We used a linear regression to identify factors independently associated with PCT defined as the time in hours from antimalarial drug administration until the first negative malaria smear.

RESULTS

Among 400 patients hospitalized with falciparum malaria, mean (range) PCT was 58 (1-189) hours. In multivariate analysis, severe malaria, gastrointestinal signs, initial temperature greater than or equal to 40 degrees C, parasitemia greater than or equal to 1%, and platelet counts less than 50,000/microL were associated with longer PCT. Offering ambulatory care to patients aged 15 to 64 years with none of the factors associated with longer PCT in the study would have resulted in 147 (37%) patients receiving outpatient care.

CONCLUSION

Factors identified in this model may help physicians determine which P falciparum malaria patients can be treated on an ambulatory basis, and contribute to revisions of national guidelines for imported malaria management.

Risk factors for imported fatal Plasmodium falciparum malaria, France, 1996-2003

Plasmodium falciparum malaria is a serious health hazard for travelers to malaria-endemic areas and is often diagnosed on return to the country of residence. We conducted a retrospective study of imported falciparum malaria among travelers returning to France from malaria-endemic areas from 1996 through 2003. Epidemiologic, clinical, and parasitologic data were collected by a network of 120 laboratories. Factors associated with fatal malaria were identified by logistic regression analysis. During the study period, 21,888 falciparum malaria cases were reported. There were 96 deaths, for a case-fatality rate of 4.4 per 1,000 cases of falciparum malaria. In multivariate analysis, risk factors independently associated with death from imported malaria were older age, European origin, travel to East Africa, and absence of chemoprophylaxis. Fatal imported malaria remains rare and preventable. Pretravel advice and malaria management should take into account these risk factors, particularly for senior travelers.

A Shared Asian Origin of the Triple‐MutantdhfrAllele inPlasmodium falciparumfrom Sites across Africa

BACKGROUND

Usefulness of sulfadoxine-pyrimethamine as first-line therapy for uncomplicated Plasmodium falciparum malaria and intermittent preventive treatment in pregnancy throughout sub-Saharan Africa is compromised by the spread of dhfr alleles associated with pyrimethamine resistance. A predominant haplotype associated with the N51I+C59R+S108N triple-mutant dhfr allele has been reported recently in 4 African countries. A more comprehensive picture of the evolution of this mutant allele in Africa is lacking.

METHODS

Seventy-five P. falciparum isolates carrying the wild-type dhfr allele and 204 carrying the triple-mutant dhfr allele from 11 African countries were selected. The genetic diversity of the chromosomes bearing these alleles was analyzed with 4 microsatellite markers closely linked to the dhfr gene.

RESULTS

Seventy-three different 4-locus haplotypes carrying the wild-type dhfr allele were found. By contrast, 175 (85%) of 204 isolates carrying the triple-mutant dhfr allele shared a unique haplotype, identical to the one identified in Thailand. For the remaining triple-mutant isolates and one isolate with the quadruple-mutant dhfr allele (N51I+C59R+S108N+I164L), haplotypes were closely related to the predominant haplotype by mutation or recombination.

CONCLUSIONS

Migration of parasites carrying an ancestral triple-mutant dhfr allele drives the spread of dhfr alleles associated with pyrimethamine resistance throughout West and Central Africa.

Shelf life of predosed plates containing mefloquine, artemisinin, dihydroartemisinin, and artesunate as used for in vitro Plasmodium falciparum susceptibility assessment

The shelf lives of preserved antimalarial agent-predosed plates according to the type of wrapping and the temperature of storage were studied by measuring the 50% inhibitory concentrations of drug for Plasmodium falciparum 3D7. The shelf life of mefloquine was 8 weeks at 25 degrees C; and those of artesunate, artemisinin, and dihydroartemisinin were a minimum of 24, 12, and 8 weeks, respectively, at 4 degrees C.

Parallel evolution of adaptive mutations in Plasmodium falciparum mitochondrial DNA during atovaquone-proguanil treatment

Here we provide direct evidence that two adaptive nucleotide changes in the same codon (268) of the cytochrome b gene (pfcytb) each occurred repeatedly in independent Plasmodium falciparum lineages exposed to the antimalarial drug atovaquone-proguanil (AP). We analyzed the history of 7 AP resistance alleles from clinical isolates by sequencing the mitochondrial (mt) genome that encodes the pfcytb gene and found that a distinct mt haplotype was associated with each AP resistance allele. By comparing mt sequences and microsatellite genotypes of the isolates both before treatment initiation and at the day of failure for each uncured patient, we observed that the AP resistance alleles occurred and spread within the patients. These data demonstrate that identical AP resistance alleles have multiple independent origins and provide an example of parallel evolution driven by drug treatment selection in P. falciparum.

[New drugs against parasitic diseases]

The gap in the antiparasitic armamentarium is still not filled in 2006 and few original and useful drugs were marketed in the last decade. Against malaria, artemether combined with lumefantrine is adopted as first line therapy in a majority of endemic countries but still not available in France and several european countries. As its tolerance and efficacy are satisfactory, atovaquone-proguanil, is taking a major place for prevention and treatment in travellers. Liposomal amphothericin B and miltefosine extended the treatment of visceral leishmaniasis. Nitazoxanide and triclabendazole may be usefull in cryptosoridiosis or giardiasis and fasciolasis, respectively.

Rapid dissemination of Plasmodium falciparum drug resistance despite strictly controlled antimalarial use

BACKGROUND

Inadequate treatment practices with antimalarials are considered major contributors to Plasmodium falciparum resistance to chloroquine, pyrimethamine and sulfadoxine. The longitudinal survey conducted in Dielmo, a rural Senegalese community, offers a unique frame to explore the impact of strictly controlled and quantified antimalarial use for diagnosed malaria on drug resistance.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted on a yearly basis a retrospective survey over a ten-year period that included two successive treatment policies, namely quinine during 1990-1994, and chloroquine (CQ) and sulfadoxine/pyrimethamine (SP) as first and second line treatments, respectively, during 1995-1999. Molecular beacon-based genotyping, gene sequencing and microsatellite analysis showed a low prevalence of Pfcrt and Pfdhfr-ts resistance alleles of Southeast Asian origin by the end of 1994 and their effective dissemination within one year of CQ and SP implementation. The Pfcrt resistant allele rose from 9% to 46% prevalence during the first year of CQ reintroduction, i.e., after a mean of 1.66 CQ treatment courses/person/year. The Pfdhfr-ts triple mutant rose from 0% to 20% by end 1996, after a mean of 0.35 SP treatment courses/person in a 16-month period. Both resistance alleles were observed at a younger age than all other alleles. Their spreading was associated with enhanced in vitro resistance and rapidly translated in an increased incidence of clinical malaria episodes during the early post-treatment period.

CONCLUSION/SIGNIFICANCE

In such a highly endemic setting, selection of drug-resistant parasites took a single year after drug implementation, resulting in a rapid progression of the incidence of clinical malaria during the early post-treatment period. Controlled antimalarial use at the community level did not prevent dissemination of resistance haplotypes. This data pleads against reintroduction of CQ in places where resistant allele frequency has dropped to a very low level after CQ use has been discontinued, unless drastic measures are put in place to prevent selection and spreading of mutants during the post-treatment period.

Assessment of the drug susceptibility of Plasmodium falciparum clinical isolates from africa by using a Plasmodium lactate dehydrogenase immunodetection assay and an inhibitory maximum effect model for precise measurement of the 50-percent inhibitory concentration

The extension of drug resistance among malaria-causing Plasmodium falciparum parasites in Africa necessitates implementation of new combined therapeutic strategies. Drug susceptibility phenotyping requires precise measurements. Until recently, schizont maturation and isotopic in vitro assays were the only methods available, but their use was limited by technical constraints. This explains the revived interest in the development of replacement methods, such as the Plasmodium lactate dehydrogenase (pLDH) immunodetection assay. We evaluated a commercially controlled pLDH enzyme-linked immunosorbent assay (ELISA; the ELISA-Malaria antigen test; DiaMed AG, Cressier s/Morat, Switzerland) to assess drug susceptibility in a standard in vitro assay using fairly basic laboratory equipment to study the in vitro resistance of malaria parasites to major antimalarials. Five Plasmodium falciparum clones and 121 clinical African isolates collected during 2003 and 2004 were studied by the pLDH ELISA and the [8-(3)H]hypoxanthine isotopic assay as a reference with four antimalarials. Nonlinear regression with a maximum effect model was used to estimate the 50% inhibitory concentration (IC(50)) and its confidence intervals. The two methods were observed to have similar reproducibilities, but the pLDH ELISA demonstrated a higher sensitivity. The high correlation (r = 0.98) and the high phenotypic agreement (kappa = 0.88) between the two methods allowed comparison by determination of the IC(50)s. Recently collected Plasmodium falciparum African isolates were tested by pLDH ELISA and showed drug resistance or decreased susceptibilities of 62% to chloroquine and 11.5% to the active metabolite of amodiaquine. No decreased susceptibility to lumefantrine or the active metabolite of artemisinin was detected. The availability of this simple and highly sensitive pLDH immunodetection assay will provide an easier method for drug susceptibility testing of malaria parasites.

Invasion of Africa by a single pfcrt allele of South East Asian type

BACKGROUND

Because of its dramatic public health impact, Plasmodium falciparum resistance to chloroquine (CQ) has been documented early on. Chloroquine-resistance (CQR) emerged in the late 1950's independently in South East Asia and South America and progressively spread over all malaria areas. CQR was reported in East Africa in the 1970's, and has since invaded the African continent. Many questions remain about the actual selection and spreading process of CQR parasites, and about the evolution of the ancestral mutant gene(s) during spreading.

METHODS

Eleven clinical isolates of P. falciparum from Cambodia and 238 from Africa (Senegal, Ivory Coast, Bukina Faso, Mali, Guinea, Togo, Benin, Niger, Congo, Madagascar, Comoros Islands, Tanzania, Kenya, Mozambique, Cameroun, Gabon) were collected during active case detection surveys carried out between 1996 and 2001. Parasite DNA was extracted from frozen blood aliquots and amplification of the gene pfcrt exon 2 (codon 72-76), exon 4 and intron 4 (codon 220 and microsatellite marker) were performed. All fragments were sequenced.

RESULTS

124 isolates with a sensitive (c76/c220:CVMNK/A) haplotype and 125 isolates with a resistant c76/c220:CVIET/S haplotype were found. The microsatellite showed 17 different types in the isolates carrying the c76/c220:CVMNK/A haplotype while all 125 isolates with a CVIET/S haplotype but two had a single microsatellite type, namely (TAAA)3(TA)15, whatever the location or time of collection.

CONCLUSION

Those results are consistent with the migration of a single ancestral pfcrt CQR allele from Asia to Africa. This is related to the importance of PFCRT in the fitness of P. falciparum point out this protein as a potential target for developments of new antimalarial drugs.

Low autochtonous urban malaria in Antananarivo (Madagascar)

BACKGROUND

The study of urban malaria is an area undergoing rapid expansion, after many years of neglect. The problem of over-diagnosis of malaria, especially in low transmission settings including urban areas, is also receiving deserved attention. The primary objective of the present study was to assess the frequency of malaria among febrile outpatients seen in private and public primary care facilities of Antananarivo. The second aim was to determine, among the diagnosed malaria cases, the contribution of autochthonous urban malaria.

METHODS

Two cross-sectional surveys in 43 health centres in Antananarivo in February 2003 (rainy season) and in July 2003 (dry season) were conducted. Consenting clinically suspected malaria patients with fever or history of fever in the past 48 hours were included. Malaria rapid diagnostic tests and microscopy were used to diagnose malaria. Basic information was collected from patients to try to identify the origin of the infection: autochthonous or introduced.

RESULTS

In February, among 771 patients, 15 (1.9%) positive cases were detected. Three malaria parasites were implicated: Plasmodium. falciparum (n = 12), Plasmodium vivax (n = 2) and Plasmodium. ovale (n = 1). Only two cases, both P. falciparum, were likely to have been autochthonous (0.26%). In July, among 739 blood smears examined, 11 (1.5%) were positive: P. falciparum (n = 9) and P. vivax (n = 2). Three cases of P. falciparum malaria were considered to be of local origin (0.4%).

CONCLUSION

This study demonstrates that malaria cases among febrile episodes are low in Antananarivo and autochthonous malaria cases exist but are rare.

Lack of association between putative transporter gene polymorphisms in Plasmodium falciparum and chloroquine resistance in imported malaria isolates from Africa

Background

Plasmodium falciparum drug resistance represents a major health problem in malaria endemic countries. The mechanisms of resistance are not fully elucidated. Recently, an association between putative transporter gene polymorphisms and in vitro response to chloroquine (CQ) and quinine has been reported in culture-adapted, cloned isolates from various geographical origins. However, this was not confirmed in another study performed on isolates from a defined region in Thailand.

Methods

This study tried to find an association between putative transporters gene polymorphisms with in vitro response to CQ and pfcrt genotype in isolates originating from various African countries. To avoid biases of parasites adaptation in culture, fresh isolates obtained from symptomatic, malaria-infected travellers returning from Africa to France were used. Monoclonal isolates included in the study were selected using a msp-2 fragment analysis method. In vitro susceptibility to CQ, single nucleotide polymorphisms and microsatellite polymorphisms in pfcrt, pfmdr1 and six putative transporter genes were established in 27 isolates and three reference strains.

Results

Polymorphism of pfcrt at positions 76 and 220 showed a significant association with in vitro chloroquine resistance (P < .02 and P < .05 respectively). Polymorphism of pfmdr1 at position 86 showed an equally significant association with in vitro chloroquine response (P < .05). No association was found between SNPs or microsatellite polymorphisms of putative transporter genes and in vitro CQR or pfcrt genotype in imported malaria isolates from Africa.

Conclusion

The previously described association between putative transporter gene polymorphisms and in vitro response to chloroquine (CQ) was not confirmed in the present study.

Apparent absence of atovaquone/proguanil resistance in 477 Plasmodium falciparum isolates from untreated French travellers

OBJECTIVES

We examined the atovaquone in vitro susceptibility and the cytochrome b (cytb) gene polymorphism of African Plasmodium falciparum isolates during the first years of atovaquone/proguanil use.

PATIENTS AND METHODS

Between 1999 and 2004, we collected blood samples from French P. falciparum-infected patients returning from African countries. Atovaquone susceptibility was determined using an in vitro isotopic test and cytb genotyping was performed by restriction fragment length polymorphism analysis and sequencing. These results were analysed according to the clinical response to atovaquone/proguanil treatment.

RESULTS

No in vitro atovaquone resistance (IC50 > 1900 nM) and no cytb mutation leading to the Y268S substitution were detected among 477 unexposed African P. falciparum isolates. Eight cytb polymorphisms were found outside the ubiquinone reduction site by sequencing the entire gene of 270 isolates. One atovaquone/proguanil treatment failure was documented; the post-treatment isolate had an atovaquone susceptibility of 8230 nM and the Ser268 Cytb change; the pre-treatment isolate, obtained 4 weeks previously, was Cytb Tyr268 (wild-type).

CONCLUSIONS

No atovaquone/proguanil resistance was detected by phenotyping or genotyping among 477 unexposed African P. falciparum isolates. Atovaquone/proguanil-resistant parasite was detectable only in the post-treatment isolate from a treatment failure.

Epidemiology of drug-resistant malaria in Republic of Congo: using molecular evidence for monitoring antimalarial drug resistance combined with assessment of antimalarial drug use

In Congo, urgent efforts are needed to help with the revision of the national antimalarial drug policy. Despite its high resistance level, chloroquine (CQ) is still extensively used as the first-line treatment for uncomplicated Plasmodium falciparum malaria. The study was conducted in children under 5 years with uncomplicated malaria in Pointe-Noire and Brazzaville, the two largest cities that contain approximately 60% of the population of Congo. We investigated by polymerized chain reaction and sequencing methods the frequency distribution of molecular markers for antimalarial drug resistance, including mutations in P. falciparum chloroquine resistance transporter (pfcrt) gene associated with CQ resistance and mutations in dihydrofolate reductase (dhfr) and dihydropteroate synthetase (dhps) genes conferring resistance to sulphadoxine/pyrimethamine (SP) among pre-treatment P. falciparum isolates, as well as assessing antimalarial drug use in the community. pfcrt (K76T) mutation was present in most isolates (96.4%, n = 138) and high frequency (69.2%, n = 133) of triple-mutant dhfr-S108N, N51I, C59R was observed. The quintuple mutant (dhfr-S108N, N51I, C59R and dhps-A437G or S436A, K540E) considered as molecular marker for SP treatment failure was not found because dhps-K540E mutation was absent in isolates tested; this is a clear evidence for the excellent efficacy of SP that we previously described in the same population. The complete absence of the dhps-K540E mutation is a deterrent component for using this molecular marker as an early warning tool for SP resistance testing in that population. Poor compliance issues related to the antimalarial drug use including inappropriate manufacturing practices reported in this study require intensive attention and should be taken into account when implementing drug policy change. If Congo changes its treatment policy from CQ to SP monotherapy, this will not last long. The strategy of combining SP with other affordable and effective antimalarial drugs such as the artemisinin derivatives to improve efficacy and to delay the development of parasite resistance is essential.

Falciparum malaria acquired by a French tourist in a resort area of the Dominican Republic

Between November 2004 and April 2005, about twenty cases of malaria were reported worldwide in residents from non-endemic regions who had travelled to the Dominican Republic

Efficacy of antimalarial chemoprophylaxis among French residents travelling to Africa

Controversy exists about which antimalarial chemoprophylaxis regimen should be used among travellers to Africa: the WHO and other experts recommend the use of mefloquine throughout sub-Saharan Africa, whereas French experts still support the combination of chloroquine and proguanil in most of West Africa (the so-called zone 2 countries). In this case-control study based at a travel clinic, we examined the compliance with antimalarial chemoprophylaxis and its efficacy among travellers to tropical areas. Cases were patients with Plasmodium falciparum malaria (n = 131). Controls were patients who had a negative malaria film (n = 158). Of all controls, only 36 (22.8%) were adequately protected (i.e. compliant with an adapted regimen of chemoprophylaxis). In zone 2 countries, the efficacy of the combined chloroquine and proguanil was 58% (95% CI 22-78%) for all users, but increased to 100% (95% CI 89-100%) for compliant users. In zone 3 countries, the efficacy of mefloquine was 90% (95% CI 51-98%) and 100% (95% CI 58-100%) for all users and compliant users, respectively.