Mosquito bites and stage-specific antibody responses against Plasmodium falciparum in southern Ghana

BACKGROUND

The human host elicits specific immune responses after exposure to various life stages of the malaria parasite as well as components of mosquito saliva injected into the host during a mosquito bite. This study describes differences in IgG responses against antigens derived from the sporozoite (PfCSP), asexual stage parasite (PfEBA175) and the gametocyte (Pfs230), in addition to an Anopheles gambiae salivary gland antigen (gSG6-P1), in two communities in Ghana with similar blood stage malaria parasite prevalence.

METHODS

This study used archived plasma samples collected from an earlier cross-sectional study that enrolled volunteers aged from 6 months to 70 years from Simiw, peri-urban community (N = 347) and Obom, rural community (N = 291). An archived thick and thin blood smear for microscopy was used for the estimation of Plasmodium parasite density and species and DNA extraction from blood spots and P. falciparum confirmation was performed using PCR. This study used the stored plasma samples to determine IgG antibody levels to P. falciparum and Anopheles salivary antigens using indirect ELISA.

RESULTS

Individuals from Simiw had significantly higher levels of IgG against mosquito gSG6-P1 [median (95%CI)] [2.590 (2.452-2.783) ng/mL] compared to those from Obom [2.119 (1.957-2.345) ng/mL], p < 0.0001. Both IgG responses against Pfs230proC (p = 0.0006), and PfCSP (p = 0.002) were significantly lower in volunteers from Simiw compared to the participants from Obom. The seroprevalence of PfEBA-175.5R (p = 0.8613), gSG6-P1 (p = 0.0704), PfCSP (p = 0.7798) IgG were all similar in Obom and Simiw. However, Pfs230 seroprevalence was significantly higher at Obom compared to Simiw (p = 0.0006). Spearman correlation analysis showed no significant association between IgG responses against gSG6-P1, PfCSP, Pfs230proC and PfEBA-175.5R and parasite density at both Obom and Simiw (p > 0.05).

CONCLUSION

In conclusion, the study showed that participants from Simiw had higher concentrations of circulating gSG6-P1 IgG antibodies but lower concentrations of P. falciparum antibodies, PfCSP IgG and Pfs230proC IgG compared to participants from Obom.

High Plasma Levels of Neopterin Are Associated with Increased Mortality among Children with Severe Malaria in Benin

Among the barriers to accessing adequate treatment and high-level monitoring for malaria febrile patients is the lack of effective prognostic markers. Neopterin, which is a marker of monocyte/macrophage activation, was found have increased during severe malaria. In this study, we used quantitative ELISA in order to assess the levels of plasma soluble neopterin in 151 patients from a cohort of Beninese children with severe malaria. We evaluated the prognostic accuracy of this molecule in order to predict the outcome of the disease. Our results show that neopterin levels were not significantly different between patients with different forms of severe malaria, including severe non-cerebral malaria (SNCM) and cerebral malaria (CM). However, the levels of this molecule were found to be higher in patients with severe malarial anemia (SMA) among both CM and SNCM cases (p-value = 0.02). Additionally, the levels of this molecule were found to be higher in patients who died from these pathologies compared to those who survived among the two clinical groups (p-value < 0.0001) and within the same group (p-value < 0.0001 for the CM group, p-value = 0.0046 for the SNCM group). The AUC-ROC for fatality among all the severe cases was 0.77 with a 95%CI of (0.69-0.85). These results suggest that plasma neopterin levels constitute a potential biomarker for predicting fatality among severe falciparum malaria patients.

Association of Endothelial Protein C Receptor (EPCR) rs867186 Gene Polymorphism With Increased Levels of Soluble EPCR and High Risk of Severe Malaria and Fatality in Beninese Children

The endothelial protein C receptor (EPCR)-rs867186 G allele has been linked to high plasma levels of soluble EPCR (sEPCR) and controversially associated with either susceptibility or resistance to severe and cerebral malaria. In this study, quantitative enzyme-linked immunosorbent assay and sequencing were used to assess sEPCR levels and EPCR-rs867186 polymorphism in blood samples from Beninese children with different clinical presentations of malaria. Our findings show that sEPCR levels were higher at hospital admission than during convalescence and that EPCR-rs867186 G allele was associated with increased sEPCR plasma levels, malaria severity, and mortality rate (P < .001, P = .03, and P = .04, respectively), suggesting a role of sEPCR in the pathogenesis of severe malaria.

Population-based sero-epidemiological investigation of the dynamics of SARS-CoV-2 infections in the Greater Accra Region of Ghana

The coronavirus disease 2019 (COVID-19) pandemic devastated countries worldwide, and resulted in a global shutdown. Not all infections are symptomatic and hence the extent of SARS-CoV-2 infection in the community is unknown. The paper presents the dynamics of the SARS-CoV-2 epidemic in the Greater Accra Metropolis, describing the evolution of seroprevalence through time and by age group. Three repeated independent population-based surveys at 6-week intervals were conducted in from November 2020 to July 2021. The global and by age-groups weighted seroprevalences were estimated and the risk factors for SARS-CoV-2 antibody seropositivity were assessed using logistic regression. The overall age-standardized SARS-CoV-2 antibody seroprevalence for both spike and nucleocapsid increased from 13.8% (95% CI 11.9, 16.1) in November 2020 to 39.6% (95% CI 34.8, 44.6) in July 2021. After controlling for gender, marital status, education level, and occupation, the older age group over 40 years had a higher odds of seropositivity than the younger age group (OR 3.0 [95% CI 1.1-8.5]) in the final survey. Pupils or students had 3.3-fold increased odds of seropositivity (OR 3.2 [95% CI 1.1-8.5]) compared to the unemployed. This study reinforces that, SARS-CoV-2 infections have been significantly higher than reported.

ICAM-1-binding Plasmodium falciparum erythrocyte membrane protein 1 variants elicits opsonic-phagocytosis IgG responses in Beninese children

Members of the highly polymorphic Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family expressed on the surface of infected erythrocytes (IEs) are important virulence factors, which mediate vascular adhesion of IEs via endothelial host receptors and are targets of naturally acquired immunity. The PfEMP1 family can be divided into clinically relevant subgroups, of which some bind intercellular adhesion molecule 1 (ICAM-1). While the acquisition of IgG specific for ICAM-1-binding DBLβ domains is known to differ between PfEMP1 groups, its ability to induce antibody-dependent cellular phagocytosis (ADCP) is unclear. We therefore measured plasma levels of DBLβ-specific IgG, the ability of such IgG to inhibit PfEMP1-binding to ICAM-1, and its ability to opsonize IEs for ADCP, using plasma from Beninese children with severe (SM) or uncomplicated malaria (UM). IgG specific for DBLβ from group A and B ICAM-1-binding PfEMP1 were dominated by IgG1 and IgG3, and were similar in SM and UM. However, levels of plasma IgG inhibiting ICAM-1-binding of group A DBLβ of PFD1235w was significantly higher in children with UM than SM, and acute UM plasma induced a higher ADCP response than acute SM plasma.

ICAM-1 Kilifi variant is not associated with cerebral and severe malaria pathogenesis in Beninese children

Background

Cytoadhesion and sequestration of Plasmodium falciparum infected red blood cells (iRBC) in the microvasculature of vital organs are a major cause of malaria pathology. Several studies have provided evidence on the implication of the human host intercellular adhesion molecule-1 (ICAM-1) as a major receptor for iRBCs binding to P. falciparum erythrocyte membrane protein 1 (PfEMP1) in the development of severe and cerebral malaria. The genetic polymorphism K29M in the immunoglobulin-like domain of ICAM-1, known as ICAM-1Kilifi, has been associated with either increased or decreased risk of developing cerebral malaria.

Methods

To provide more conclusive results, the genetic polymorphism of ICAM-1Kilifi was assessed by PCR and sequencing in blood samples from 215 Beninese children who presented with either mild or severe malaria including cerebral malaria.

Results and conclusions

The results showed that in this cohort of Beninese children, the ICAM-1kilifi variant is present at the frequencies of 0.27, similar to the frequency observed in other African countries. This ICAM-1kilifi variant was not associated with disease severity in agreement with other findings from the Gambia, Tanzania, Malawi, Gabon, and Thailand, suggesting no evidence of a direct link between this polymorphism and the pathogenesis of severe and cerebral malaria.

Specific Combinations of Inflammatory, Angiogenesis and Vascular Integrity Biomarkers Are Associated with Clinical Severity, Coma and Mortality in Beninese Children with Plasmodium Falciparum Malaria

Malaria-related deaths could be prevented if powerful diagnostic and reliable prognostic biomarkers were available to allow rapid prediction of the clinical severity allowing adequate treatment. Using quantitative ELISA, we assessed the plasma concentrations of Procalcitonin, Pentraxine-3, Ang-2, sTie-2, suPAR, sEPCR and sICAM-1 in a cohort of Beninese children with malaria to investigate their potential association with clinical manifestations of malaria. We found that all molecules showed higher levels in children with severe or cerebral malaria compared to those with uncomplicated malaria (p-value < 0.005). Plasma concentrations of Pentraxine-3, Procalcitonin, Ang-2 and the soluble receptors were significantly higher in children with coma as defined by a Blantyre Coma Score < 3 (p < 0.001 for Pentraxine-3, suPAR, and sTie-2, p = 0.004 for PCT, p = 0.005 for sICAM-1, p = 0.04 for Ang-2). Moreover, except for the PCT level, the concentrations of Pentraxine-3, suPAR, sEPCR, sICAM-1, sTie-2 and Ang-2 were higher among children who died from severe malaria compared to those who survived (p = 0.037, p = 0.035, p < 0.0001, p= 0.0008, p = 0.01 and p = 0.02, respectively). These findings indicate the ability of these molecules to accurately discriminate among clinical manifestations of malaria, thus, they might be potentially useful for the early prognostic of severe and fatal malaria, and to improve management of severe cases.

IgG acquisition against PfEMP1 PF11_0521 domain cassette DC13, DBLβ3_D4 domain, and peptides located within these constructs in children with cerebral malaria

The Plasmodium falciparum erythrocyte-membrane-protein-1 (PF3D7_1150400/PF11_0521) contains both domain cassette DC13 and DBLβ3 domain binding to EPCR and ICAM-1 receptors, respectively. This type of PfEMP1 proteins with dual binding specificity mediate specific interactions with brain micro-vessels endothelium leading to the development of cerebral malaria (CM). Using plasma collected from children at time of hospital admission and after 30 days, we study an acquisition of IgG response to PF3D7_1150400/PF11_0521 DC13 and DBLβ3_D4 recombinant constructs, and five peptides located within these constructs, specifically in DBLα1.7_D2 and DBLβ3_D4 domains. We found significant IgG responses against the entire DC13, PF11_0521_DBLβ3_D4 domain, and peptides. The responses varied against different peptides and depended on the clinical status of children. The response was stronger at day 30, and mostly did not differ between CM and uncomplicated malaria (UM) groups. Specifically, the DBLβ3 B3-34 peptide that contains essential residues involved in the interaction between PF11_0521 DBLβ3_D4 domain and ICAM-1 receptor demonstrated significant increase in reactivity to IgG1 and IgG3 antibodies at convalescence. Further, IgG reactivity in CM group at time of admission against functionally active (ICAM-1-binding) PF11_0521 DBLβ3_D4 domain was associated with protection against severe anemia. These results support development of vaccine based on the PF3D7_1150400/PF11_0521 structures to prevent CM.

Assessment of glucose-6-phosphate dehydrogenase activity using CareStart G6PD rapid diagnostic test and associated genetic variants in Plasmodium vivax malaria endemic setting in Mauritania

Background

Primaquine is recommended by the World Health Organization (WHO) for radical treatment of Plasmodium vivax malaria. This drug is known to provoke acute hemolytic anemia in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Due to lack of data on G6PD deficiency, the use of primaquine has been limited in Africa. In the present study, G6PD deficiency was investigated in blood donors of various ethnic groups living in Nouakchott, a P. vivax endemic area in Mauritania.

Methodology/Principal findings

Venous blood samples from 443 healthy blood donors recruited at the National Transfusion Center in Nouakchott were screened for G6PD activity using the CareStart G6PD deficiency rapid diagnostic test. G6PD allelic variants were investigated using DiaPlexC G6PD genotyping kit that detects African (A^-) and Mediterranean (B^-) variants. Overall, 50 of 443 (11.3%) individuals (49 [11.8%] men and 1 [3.7%] woman) were phenotypically deficient. Amongst men, Black Africans had the highest prevalence of G6PD deficiency (15 of 100 [15%]) and White Moors the lowest (10 of 168, [5.9%]). The most commonly observed G6PD allelic variants among 44 tested G6PD-deficient men were the African variant A^- (202A/376G) in 14 (31.8%), the Mediterranean variant B^- (563T) in 13 (29.5%), and the Betica-Selma A^- (376G/968C) allelic variant in 6 (13.6%). The Santamaria A^- variant (376G/542T) and A variant (376G) were observed in only one and two individuals, respectively. None of the expected variants was observed in 8 (18.2%) of the tested phenotypically G6PD-deficient men.

Conclusion

This is the first published data on G6PD deficiency in Mauritanians. The prevalence of phenotypic G6PD deficiency was relatively high (11.3%). It was mostly associated with either African or Mediterranean variants, in agreement with diverse Arab and Black African origins of the Mauritanian population.

Oasis Malaria, Northern Mauritania1

A malaria survey was conducted in Atar, the northernmost oasis city in Mauritania, during 2015–2016. All febrile patients in whom malaria was suspected were screened for malaria by using rapid diagnostic testing and microscopic examination of blood smears and later confirmed by PCR. Of 453 suspected malaria cases, 108 (23.8%) were positive by rapid diagnostic testing, 154 (34.0%) by microscopic examination, and 162 (35.7%) by PCR. Malaria cases were observed throughout the year and among all age groups. Plasmodium vivax was present in 120/162 (74.1%) cases, P. falciparum in 4/162 (2.4%), and mixed P. falciparum–P. vivax in 38/162 (23.4%). Malaria is endemic in northern Mauritania and could be spreading farther north in the Sahara, possibly because of human-driven environmental changes. Further entomologic and parasitologic studies and monitoring are needed to relate these findings to major Anopheles mosquito vectors and to design and implement strategies for malaria prevention and control.

High-level artemisinin-resistance with quinine co-resistance emerges in P. falciparum malaria under in vivo artesunate pressure

BACKGROUND

Humanity has become largely dependent on artemisinin derivatives for both the treatment and control of malaria, with few alternatives available. A Plasmodium falciparum phenotype with delayed parasite clearance during artemisinin-based combination therapy has established in Southeast Asia, and is emerging elsewhere. Therefore, we must know how fast, and by how much, artemisinin-resistance can strengthen.

METHODS

P. falciparum was subjected to discontinuous in vivo artemisinin drug pressure by capitalizing on a novel model that allows for long-lasting, high-parasite loads. Intravenous artesunate was administered, using either single flash-doses or a 2-day regimen, to P. falciparum-infected humanized NOD/SCID IL-2Rγ^-/-immunocompromised mice, with progressive dose increments as parasites recovered. The parasite's response to artemisinins and other available anti-malarial compounds was characterized in vivo and in vitro.

RESULTS

Artemisinin resistance evolved very rapidly up to extreme, near-lethal doses of artesunate (240 mg/kg), an increase of > 3000-fold in the effective in vivo dose, far above resistance levels reported from the field. Artemisinin resistance selection was reproducible, occurring in 80% and 41% of mice treated with flash-dose and 2-day regimens, respectively, and the resistance phenotype was stable. Measuring in vitro sensitivity proved inappropriate as an early marker of resistance, as IC₅₀ remained stable despite in vivo resistance up to 30 mg/kg (ART-S: 10.7 nM (95% CI 10.2-11.2) vs. ART-R₃₀: 11.5 nM (6.6-16.9), F = 0.525, p = 0.47). However, when in vivo resistance strengthened further, IC₅₀ increased 10-fold (ART-R₂₄₀ 100.3 nM (92.9-118.4), F = 304.8, p < 0.0001), reaching a level much higher than ever seen in clinical samples. Artemisinin resistance in this African P. falciparum strain was not associated with mutations in kelch-13, casting doubt over the universality of this genetic marker for resistance screening. Remarkably, despite exclusive exposure to artesunate, full resistance to quinine, the only other drug sufficiently fast-acting to deal with severe malaria, evolved independently in two parasite lines exposed to different artesunate regimens in vivo, and was confirmed in vitro.

CONCLUSION

P. falciparum has the potential to evolve extreme artemisinin resistance and more complex patterns of multidrug resistance than anticipated. If resistance in the field continues to advance along this trajectory, we will be left with a limited choice of suboptimal treatments for acute malaria, and no satisfactory option for severe malaria.

Parasites Causing Cerebral Falciparum Malaria Bind Multiple Endothelial Receptors and Express EPCR and ICAM-1-Binding PfEMP1

Background

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) mediates the binding and accumulation of infected erythrocytes (IE) to blood vessels and tissues. Specific interactions have been described between PfEMP1 and human endothelial proteins CD36, intercellular adhesion molecule-1 (ICAM-1), and endothelial protein C receptor (EPCR); however, cytoadhesion patterns typical for pediatric malaria syndromes and the associated PfEMP1 members are still undefined.

Methods

In a cohort of 94 hospitalized children with malaria, we characterized the binding properties of IE collected on admission, and var gene transcription using quantitative polymerase chain reaction.

Results

IE from patients with cerebral malaria were more likely to bind EPCR and ICAM-1 than IE from children with uncomplicated malaria (P = .007). The level of transcripts encoding CIDRα1.4 and CIDRα1.5 domain subclasses was higher in patients with severe disease (P < .05). IE populations exhibiting binding to all 3 receptors had higher levels of transcripts encoding PfEMP1 with CIDRα1.4 and Duffy binding-like (DBL)-β3 domains than parasites, which only bound CD36.

Conclusions

These results underpin the significance of EPCR binding in pediatric malaria patients that require hospital admission, and support the notion that complementary receptor interactions of EPCR binding PfEMP1with ICAM-1 amplifies development of severe malaria symptoms.

Comparison of anti-malarial drugs efficacy in the treatment of uncomplicated malaria in African children and adults using network meta-analysis

Background

Artemisinin-based combination therapy (ACT) and novel drug combinations are available and used in African countries to treat uncomplicated malaria. Network meta-analysis methods are rarely and poorly applied for the comparison of their efficacies. This method was applied on a set of randomized controlled trials to illustrate its usefulness.

Methods

A literature review available in Pubmed was conducted in July 2016. Eligible studies, conducted in sub-Saharan Africa, published between 2002 and 2016, focused on randomized controlled trials of at least two artemisinin-based combinations to treat uncomplicated malaria in children and adults. Agglomerate data were: the number of PCR-corrected adequate clinical and parasitological response (ACPR) on day 28, used as the primary endpoint in all interventions, the number of participants and the list of treatments. A Bayesian random effect meta-analysis using a binary outcome was the method to compare the efficacy. Ranking measure was used to obtain a hierarchy of the competing interventions.

Results

In total, 76 articles were included; 13 treatment regimens were involved and tested in 36,001 patients. Using artemether–lumefantrine (AL) as the common comparator for the entire network, 12 relative treatment effects were estimated and indirect comparisons were obtained. Dihydroartemisinin–piperaquine (DHAP) was shown to be more effective than AL (odds ratio [OR] = 1.92; 95% CI 1.30–2.82; 19,163 patients), ASAQ (OR = 1.70; 95% CI 1.10–2.64; 14,433 patients), and amodiaquine–sulfadoxine–pyrimethamine (AQSP): OR = 2.20; 95% CI 1.21–3.96; 8863 patients. Artesunate–amodiaquine (ASAQ) was comparable to AL (OR = 1.11; 95% CI 0.84–1.45; 21,235 patients). No significant difference was found between artesunate and mefloquine (ASMQ) and AL (OR = 1.20; 95% CI = 0.52-2.8; 13,824 participants). According to treatment ranking, among the WHO-recommended ACT medicines, DHAP was shown to be the most efficacious.

Conclusions

Based on the available evidence, this study demonstrated the superiority of DHAP among currently recommended artemisinin-based combinations. The application of the methods described here may be helpful to gain better understanding of treatment efficacy and improve future decisions. However, more data are needed to allow robust conclusions about the results in comparison with novel drugs. Further surveillance of the efficacy of anti-malarial drugs and clinical trials are needed to closely follow the evolution of the epidemiology of drug-resistant malaria in Africa.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1963-0) contains supplementary material, which is available to authorized users.

Molecular Epidemiology of Malaria in Cameroon and Côte d'Ivoire. XXXI. Kelch 13 Propeller Sequences in Plasmodium falciparum Isolates before and after Implementation of Artemisinin-Based Combination Therapy

Artemisinin-resistant malaria has not been reported from Africa, but resistance can possibly spread from Asia or arise independently in Africa. The emergence of artemisinin resistance in Africa can be monitored by molecular assay of Kelch 13 (K13) propeller sequences. A total of 251 archived DNA samples of Plasmodium falciparum isolates collected in 2002, 2003, and 2006 in Yaounde, Cameroon, and 47 samples collected in 2006 and 2013 in Abidjan, Côte d'Ivoire, were analyzed for K13-propeller sequence polymorphism. Only one isolate carried a mutant K13-propeller allele (E602D). None of the isolates carried the key mutant alleles (Y493H, R539T, I543T, and C580Y) associated with artemisinin resistance in Cambodia. The presence of the mutant allele was not correlated with in vitro response to dihydroartemisinin determined by the classical hypoxanthine incorporation assay. There was no evidence of K13 mutations associated with artemisinin resistance before and soon after the introduction of artemisinin-based combination therapies in Cameroon and Côte d'Ivoire.

Reemergence of chloroquine-sensitive pfcrt K76 Plasmodium falciparum genotype in southeastern Cameroon

BACKGROUND

Chloroquine had been used extensively during the last five decades in Cameroon. Its decreasing clinical effectiveness, supported by high proportions of clinical isolates carrying the mutant pfcrt haplotype (CVIET), led the health authorities to resort to amodiaquine monotherapy in 2002 and artemisinin-based combination therapy (ACT) in 2004 (artesunate-amodiaquine, with artemether-lumefantrine as an alternative since 2006) as the first-line treatment of uncomplicated malaria. The aim of the present study was to investigate whether the withdrawal of chloroquine was associated with a reduction in pfcrt mutant parasite population and reemergence of chloroquine-sensitive parasites in southeastern Cameroon between 2003 and 2012.

METHODS

The frequency of pfcrt haplotypes at positions 72-76 in Plasmodium falciparum isolates collected from individuals in 2003 and 2012 in southeastern Cameroon was determined by sequence specific oligonucleotide probes-enzyme linked immunosorbent assay (SSOP-ELISA).

RESULTS

The proportions of parasites carrying the mutant haplotype CVIET and the wild-type CVMNK were 53.0 and 28.0% in 2003, respectively. The proportion of the mutant haplotype in samples collected 9 years later decreased to 25.3% whereas the proportion of parasites carrying the wild-type CVMNK haplotype was 53.7%.

CONCLUSIONS

Even though the proportion of chloroquine-sensitive parasites seems to be increasing in southeastern Cameroon, a reintroduction of chloroquine cannot be recommended at present in Cameroon. The current national anti-malarial drug policy should be implemented and reinforced to combat drug-resistant malaria.

Plasma levels of eight different mediators and their potential as biomarkers of various clinical malaria conditions in African children

BACKGROUND

Plasmodium falciparum infection can lead to several clinical manifestations ranging from asymptomatic infections (AM) and uncomplicated malaria (UM) to potentially fatal severe malaria (SM), including cerebral malaria (CM). Factors implicated in the progression towards severe disease are not fully understood.

METHODS

In the present study, an enzyme-linked immunosorbent assay (ELISA) method was used to investigate the plasma content of several biomarkers of the immune response, namely Neopterin, sCD163, suPAR, Pentraxin 3 (PTX3), sCD14, Fractalkine (CX3CL1), sTREM-1 and MIG (CXCL9), in patients with distinct clinical manifestations of malaria. The goal of this study was to determine the relative involvement of these inflammatory mediators in the pathogenesis of malaria and test their relevance as biomarkers of disease severity.

RESULTS

ROC curve analysis show that children with AM were characterized by high levels of Fractalkine and sCD163 whereas children with UM were distinguishable by the presence of PTX3 in their plasma. Furthermore, principal component analysis indicated that the combination of Fractalkine, MIG, and Neopterin was the best predictor of AM condition, while suPAR, PTX3 and sTREM-1 combination was the best indicator of UM when compared to AM. The association of Neopterin, suPAR and Fractalkine was strongly predictive of SM or CM compared to UM.

CONCLUSIONS

The results indicate that the simultaneous evaluation of these bioactive molecules as quantifiable blood parameters may be helpful to get a better insight into the clinical syndromes in children with malaria.

A Worldwide Map of Plasmodium falciparum K13-Propeller Polymorphisms

BACKGROUND

Recent gains in reducing the global burden of malaria are threatened by the emergence of Plasmodium falciparum resistance to artemisinins. The discovery that mutations in portions of a P. falciparum gene encoding kelch (K13)-propeller domains are the major determinant of resistance has provided opportunities for monitoring such resistance on a global scale.

METHODS

We analyzed the K13-propeller sequence polymorphism in 14,037 samples collected in 59 countries in which malaria is endemic. Most of the samples (84.5%) were obtained from patients who were treated at sentinel sites used for nationwide surveillance of antimalarial resistance. We evaluated the emergence and dissemination of mutations by haplotyping neighboring loci.

RESULTS

We identified 108 nonsynonymous K13 mutations, which showed marked geographic disparity in their frequency and distribution. In Asia, 36.5% of the K13 mutations were distributed within two areas--one in Cambodia, Vietnam, and Laos and the other in western Thailand, Myanmar, and China--with no overlap. In Africa, we observed a broad array of rare nonsynonymous mutations that were not associated with delayed parasite clearance. The gene-edited Dd2 transgenic line with the A578S mutation, which expresses the most frequently observed African allele, was found to be susceptible to artemisinin in vitro on a ring-stage survival assay.

CONCLUSIONS

No evidence of artemisinin resistance was found outside Southeast Asia and China, where resistance-associated K13 mutations were confined. The common African A578S allele was not associated with clinical or in vitro resistance to artemisinin, and many African mutations appear to be neutral. (Funded by Institut Pasteur Paris and others.).

Evolution of the levels of human leukocyte antigen G (HLA-G) in Beninese infant during the first year of life in a malaria endemic area: using latent class analysis

Background

HLA-G, a non-classical HLA class I antigen, is of crucial interest during pregnancy by inhibiting maternal immune response. Its role during infections is discussed, and it has been described that high levels of soluble HLA-G during childhood increase the risk of malaria. To explore more precisely interactions between soluble HLA-G and malaria, latent class analysis was used to test whether distinct sub-populations of children, each with distinctive soluble HLA-G evolutions may suggest the existence of groups presenting variable malaria susceptibility.

Method

A study was conducted in Benin from 2010 to 2013 and 165 children were followed from birth to 12 months. Evolution of soluble HLA-G was studied by the latent class method.

Results

Three groups of children were identified: one with consistently low levels of soluble HLA-G during follow-up, a second with very high levels and a last intermediate group. In all groups, low birth weight, high number of malaria infections and high exposure to malaria transmission were associated with high level of soluble HLA-G. Placental malaria was not. Presence of soluble HLA-G in cord blood increased the probability of belonging to the highest trajectory.

Conclusion

These results, together with previous ones, confirm the important role of HLA-G in the individual susceptibility to malaria. Assaying soluble HLA-G at birth could be a good indicator of newborns more fragile and at risk of infections during childhood.

Molecular epidemiology of drug-resistant Plasmodium falciparum in Benguela province, Angola

Background

The malaria situation has been worsening in Angola, partly due to armed conflict until the recent past and drug-resistant Plasmodium falciparum. Malaria transmission is heterogeneous within the country, and data on drug-resistant malaria in different parts of the country are incomplete. The aim of the present study was to evaluate resistance to 4-aminoquinolines and antifolate drugs in P. falciparum isolates collected in Benguela province, central Angola, using molecular markers.

Methods

Fingerprick capillary blood was collected from asymptomatic children aged less than 15 years old during a household survey in and around Balombo town in 2010–2011. Samples were screened for P. falciparum by nested PCR. Molecular markers (P. falciparum dihydrofolate reductase [pfdhfr], P. falciparum dihydropteroate synthase [pfdhps], P. falciparum chloroquine resistance transporter [pfcrt], and P. falciparum multidrug-resistance gene 1 [pfmdr1]) were sequenced to determine the key codons associated with drug resistance.

Results

A total of 60 blood samples were positive for P. falciparum. Most isolates with successful PCR amplification had mutant pfdhfr alleles, with either double mutant AICNI (69%) or triple mutant AIRNI (21%) haplotypes. A16V, S108T, and I164L substitutions were not found. Many of the isolates were carriers of either SGKAA (60%) or AGKAA (27%) pfdhps haplotype. K540E substitution was absent. There were only two pfcrt haplotypes: wild-type CVMNK (11%) and mutant CVIET (89%). Wild-type pfmdr1 NYSND haplotype was found in 19% of the isolates, whereas single mutant pfmdr1 YYSND and NFSND haplotypes occurred in 48% and 11%, respectively. Double mutant pfmdr1 haplotypes (YFSND and YYSNY) occurred rarely.

Conclusions

The results suggest that the high prevalence of mutant pfcrt CVIET haplotype is in agreement with low clinical efficacy of chloroquine observed in earlier studies and that the double pfdhfr mutant AICNI and single pfdhps mutant SGKAA are currently the predominant haplotypes associated with antifolate resistance in Benguela province. The hallmark of clinical resistance observed in East Africa, i.e. triple pfdhfr mutant haplotype (AIRNI) and double pfdhps mutant haplotype (SGEAA), was absent. These molecular findings need to be further evaluated in parallel with clinical studies, in particular with the efficacy of intermittent preventive treatment using sulphadoxine-pyrimethamine in pregnant women and artesunate-amodiaquine for uncomplicated malaria.

Differences in gene transcriptomic pattern of Plasmodium falciparum in children with cerebral malaria and asymptomatic carriers

The mechanisms underlying the heterogeneity of clinical malaria remain largely unknown. We hypothesized that differential gene expression contributes to phenotypic variation of parasites which results in a specific interaction with the host, leading to different clinical features of malaria. In this study, we analyzed the transcriptomes of isolates obtained from asymptomatic carriers and patients with uncomplicated or cerebral malaria. We also investigated the transcriptomes of 3D7 clone and 3D7-Lib that expresses severe malaria associated-variant surface antigen. Our findings revealed a specific up-regulation of genes involved in pathogenesis, adhesion to host cell, and erythrocyte aggregation in parasites from patients with cerebral malaria and 3D7-Lib, compared to parasites from asymptomatic carriers and 3D7, respectively. However, we did not find any significant difference between the transcriptomes of parasites from cerebral malaria and uncomplicated malaria, suggesting similar transcriptomic pattern in these two parasite populations. The difference between isolates from asymptomatic children and cerebral malaria concerned genes coding for exported proteins, Maurer's cleft proteins, transcriptional factor proteins, proteins implicated in protein transport, as well as Plasmodium conserved and hypothetical proteins. Interestingly, UPs A1, A2, A3 and UPs B1 of var genes were predominantly found in cerebral malaria-associated isolates and those containing architectural domains of DC4, DC5, DC13 and their neighboring rif genes in 3D7-lib. Therefore, more investigations are needed to analyze the effective role of these genes during malaria infection to provide with new knowledge on malaria pathology. In addition, concomitant regulation of genes within the chromosomal neighborhood suggests a common mechanism of gene regulation in P. falciparum.

High plasma levels of soluble endothelial protein C receptor are associated with increased mortality among children with cerebral malaria in Benin

Loss of endothelial protein C receptor (EPCR) occurs at the sites of Plasmodium falciparum-infected erythrocyte sequestration in patients with or who died from cerebral malaria. In children presenting with different clinical syndromes of malaria, we assessed the relationships between endogenous plasma soluble EPCR (sEPCR) levels and clinical presentation or mortality. After adjustment for age, for treatment before admission, and for a known genetic factor, sEPCR level at admission was positively associated with cerebral malaria (P = .011) and with malaria-related mortality (P = .0003). Measuring sEPCR levels at admission could provide an early biological marker of the outcome of cerebral malaria.

Cytoadherence phenotype of Plasmodium falciparum-infected erythrocytes is associated with specific pfemp-1 expression in parasites from children with cerebral malaria

Background

Cytoadherence of Plasmodium falciparum-infected erythrocytes (IEs) in deep microvasculature endothelia plays a major role in the pathogenesis of cerebral malaria (CM). This biological process is thought to be mediated by P. falciparum erythrocyte membrane protein-1 (PfEMP-1) and human receptors such as CD36 and ICAM-1. The relationship between the expression of PfEMP-1 variants and cytoadherence phenotype in the pathology of malaria is not well established.

Methods

Cytoadherence phenotypes of IEs to CD36, ICAM-1, CSPG and the transcription patterns of A, B, var2csa, var3, var gene groups and domain cassettes DC8 and DC13 were assessed in parasites from children with CM and uncomplicated malaria (UM) to determine if cytoadherence is related to a specific transcription profile of pfemp-1 variants.

Results

Parasites from CM patients bind significantly more to CD36 than those from UM patients, but no difference was observed in their binding ability to ICAM-1 and CSPG. CM isolates highly transcribed groups A, B, var2csa, var3, DC8 and DC13 compared to UM parasites. The high transcription levels of var genes belonging to group B positively correlated with increased binding level to CD36.

Conclusion

CM isolates bind significantly more to CD36 than to ICAM-1, which was correlated with high transcription level of group B var genes, supporting their implication in malaria pathogenesis.

Randomized trial of artesunate-amodiaquine, atovaquone-proguanil, and artesunate-atovaquone-proguanil for the treatment of uncomplicated falciparum malaria in children

BACKGROUND

Artemisinin-based combination therapies (ACTs) are recommended for the treatment of acute uncomplicated falciparum malaria in many malaria-endemic countries. Despite the emergence of artemisinin resistance, few alternative non-ACTs, including atovaquone-proguanil, are currently available.

METHODS

Plasmodium falciparum-infected Cameroonian children ≤5 years old (n = 338) were randomly assigned to artesunate-amodiaquine, atovaquone-proguanil, or artesunate-atovaquone-proguanil treatment groups and followed for 28 days, according to the standard World Health Organization protocol. In vitro response to atovaquone and cytochrome b sequence of clinical isolates were determined.

RESULTS

Eight late failures and 16 failures (8 late and 8 early failures) were observed after artesunate-amodiaquine and atovaquone-proguanil therapies, respectively. Most late failures were due to reinfections. Artesunate-atovaquone-proguanil was not associated with any failure. After correction by genotyping, per-protocol analysis showed no difference in the efficacy of 3 drugs. However, the proportion of atovaquone-proguanil-treated patients with positive smears on day 3 was much higher (36.0%; P < .05) than that of the artesunate-amodiaquine (2.9%) and artesunate-atovaquone-proguanil (1.0%) groups. In vitro response and cytochrome b sequence did not indicate atovaquone resistance.

CONCLUSIONS

Atovaquone-proguanil was characterized by a slow blood schizontocidal action and resulted in early treatment failure in a few patients. Artesunate-atovaquone-proguanil was a highly effective alternative treatment.

CLINICAL TRIALS REGISTRATION

UMIN000003813.

Field evaluation of rapid diagnostic tests for malaria in Yaounde, Cameroon

Rapid diagnostic tests (RDTs) are affordable, alternative diagnostic tools. The present study aimed to evaluate RDTs available in Cameroon and compare their characteristics to follow the parasitological response of patients for 28 days. Malaria diagnosis was assessed in 179 febrile patients using conventional microscopy as the reference method. Parascreen detects both Plasmodium falciparum-specific histidine-rich protein 2 (Pf HRP-2) and Pan-specific plasmodial lactate dehydrogenase (pLDH) in all four human Plasmodium spp. Diaspot is based on the detection of Pf HRP-2. OptiMAL-IT (pLDH specific for P. falciparum and pLDH for all four human Plasmodium spp.) was assessed for comparison. The reliability of RDTs was evaluated by calculating the sensitivity, specificity, positive predictive value, negative predictive value, false-positive rate, false-negative rate, and likelihood ratio. The clinical outcome of 18 children treated with atovaquone-proguanil and followed for 28 days was evaluated using microscopy and RDTs. Of 179 samples, 133 (74.3%) were pure P. falciparum-positive smears, 4 (2.2%) pure P. malariae-positive smears, and 42 (23.5%) negative smears. Parascreen and Diaspot had high sensitivity (>92%) and positive predictive values (>94%). The specificities for Parascreen and Diaspot were 81.0% and 90.5%, respectively. The false-positive rates and the false-negative rates were 19.0% and 4.5% for Parascreen and 9.5% and 8.3% for Diaspot, respectively. Most false-negatives occurred in samples with low parasitaemia (<500 asexual parasites/μL). The performance of RDTs was better at higher parasitaemia (>500 asexual parasites/μL). Four pure P. malariae were only detected by the pan-Plasmodium bands of Parascreen and OptiMAL-IT. In blood samples from patients treated and followed-up for 28 days, HRP2-based RDTs remained positive in most samples until Day 28. Despite negative smears, OptiMAL-IT remained positive in several patients until Day 7 but was negative in all patients from Day 14 onwards. RDTs can improve the management of febrile patients. The validity, ease of use, and cost of HRP2-based tests were comparable. However, one of the current weaknesses of the RDT-based strategy using the tests available in Cameroon is inadequate sensitivity for low parasitaemia. In some cases, RDT results may require correct interpretation based on clinical history, clinical examination, and microscopic diagnosis.

Molecular monitoring of Plasmodium falciparum drug susceptibility at the time of the introduction of artemisinin-based combination therapy in Yaoundé, Cameroon: implications for the future

Background

Regular monitoring of the levels of anti-malarial resistance of Plasmodium falciparum is an essential policy to adapt therapy and improve malaria control. This monitoring can be facilitated by using molecular tools, which are easier to implement than the classical determination of the resistance phenotype. In Cameroon, chloroquine (CQ), previously the first-line therapy for uncomplicated malaria was officially withdrawn in 2002 and replaced initially by amodiaquine (AQ) monotherapy. Then, artemisinin-based combination therapy (ACT), notably artesunate-amodiaquine (AS-AQ) or artemether-lumefantrine (AL), was gradually introduced in 2004. This situation raised the question of the evolution of P. falciparum resistance molecular markers in Yaoundé, a highly urbanized Cameroonian city.

Methods

The genotype of pfcrt 72 and 76 and pfmdr1 86 alleles and pfmdr1 copy number were determined using real-time PCR in 447 P. falciparum samples collected between 2005 and 2009.

Results

This study showed a high prevalence of parasites with mutant pfcrt 76 (83%) and pfmdr1 86 (93%) codons. On the contrary, no mutations in the pfcrt 72 codon and no samples with duplication of the pfmdr1 gene were observed.

Conclusion

The high prevalence of mutant pfcrt 76T and pfmdr1 86Y alleles might be due to the choice of alternative drugs (AQ and AS-AQ) known to select such genotypes. Mutant pfcrt 72 codon was not detected despite the prolonged use of AQ either as monotherapy or combined with artesunate. The absence of pfmdr1 multicopies suggests that AL would still remain efficient. The limited use of mefloquine or the predominance of mutant pfmdr1 86Y codon could explain the lack of pfmdr1 amplification. Indeed, this mutant codon is rarely associated with duplication of pfmdr1 gene. In Cameroon, the changes of therapeutic strategies and the simultaneous use of several formulations of ACT or other anti-malarials that are not officially recommended result in a complex selective pressure, rendering the prediction of the evolution of P. falciparum resistance difficult. This public health problem should lead to increased vigilance and regular monitoring.

Molecular epidemiology of malaria in Cameroon. XXX. sequence analysis of Plasmodium falciparum ATPase 6, dihydrofolate reductase, and dihydropteroate synthase resistance markers in clinical isolates from children treated with an artesunate-sulfadoxine-pyrimethamine combination

Plasmodium falciparum dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes are reliable molecular markers for antifolate resistance. The P. falciparum ATPase 6 (pfatp6) gene has been proposed to be a potential marker for artemisinin resistance. In our previous clinical study, we showed that artesunate-sulfadoxine-pyrimethamine is highly effective against uncomplicated malaria in Yaoundé, Cameroon. In the present study, dhfr, dhps, and pfatp6 mutations in P. falciparum isolates obtained from children treated with artesunate-sulfadoxine-pyrimethamine were determined. All 61 isolates had wild-type Pfatp6 263, 623, and 769 alleles, and 11 (18%) had a single E431K substitution. Three additional mutations, E643Q, E432K, and E641Q, were detected. The results did not indicate any warning signal of serious concern (i.e., no parasites were seen with quintuple dhfr-dhps, DHFR Ile164Leu, or pfatp6 mutations), as confirmed by the high clinical efficacy of artesunate-sulfadoxine-pyrimethamine. Further studies are required to identify a molecular marker that reliably predicts artemisinin resistance.

Indolone-N-oxide derivatives: in vitro activity against fresh clinical isolates of Plasmodium falciparum, stage specificity and in vitro interactions with established antimalarial drugs

OBJECTIVES

Indolone-N-oxides are characterized by the presence of a highly reactive pharmacophore, the nitrone moiety (C=N(+)-O(-)), which undergoes oxidation-reduction reactions. The aims of the present study were to: (i) evaluate the in vitro activity of the parent compound, designated as compound 1, against 34 fresh clinical isolates of Plasmodium falciparum; (ii) compare the activity of compound 1 with that of chloroquine and dihydroartemisinin to assess the potential for cross-resistance; (iii) investigate drug interactions of indolone-N-oxides with standard antimalarials; and (iv) determine the stage-dependent activity of indolone-N-oxides.

METHODS

In vitro antimalarial activity was evaluated against clinical isolates collected from Cameroonian patients by the [(3)H]hypoxanthine incorporation assay. In vitro interactions between compound 1 or another analogue, compound 4, and established antimalarial drugs were assessed by the fixed ratio method. Stage specificity was evaluated by light microscopy using highly synchronized P. falciparum cultures.

RESULTS

The geometric mean 50% inhibitory concentration (IC(50)) of compound 1 was 48.6 nM. Its activity did not differ between the chloroquine-susceptible and the chloroquine-resistant isolates. There was no correlation between chloroquine and compound 1 responses (r = 0.015; P > 0.05), but the in vitro responses of compound 1 and dihydroartemisinin were significantly and positively correlated (r = 0.444; P < 0.05). No significant in vitro interaction was observed between indolone-N-oxide derivatives and established antimalarial drugs (artemisinin and its derivatives, chloroquine, amodiaquine, quinine and mefloquine). Compound 1 and compound 4, as well as artesunate, inhibited parasite maturation at the ring stage.

CONCLUSIONS

These findings suggest that other indolone-N-oxide derivatives with more potent activity than the parent compound may hold promise as antimalarials in the future.

Synthesis and antiplasmodial activity of new indolone N-oxide derivatives

A series of 66 new indolone-N-oxide derivatives was synthesized with three different methods. Compounds were evaluated for in vitro activity against CQ-sensitive (3D7), CQ-resistant (FcB1), and CQ and pyrimethamine cross-resistant (K1) strains of Plasmodium falciparum (P.f.), as well as for cytotoxic concentration (CC(50)) on MCF7 and KB human tumor cell lines. Compound 26 (5-methoxy-indolone-N-oxide analogue) had the most potent antiplasmodial activity in vitro (<3 nM on FcB1 and = 1.7 nM on 3D7) with a very satisfactory selectivity index (CC(50) MCF7/IC(50) FcB1: 14623; CC(50) KB/IC(50) 3D7: 198823). In in vivo experiments, compound 1 (dioxymethylene derivatives of the indolone-N-oxide) showed the best antiplasmodial activity against Plasmodium berghei, 62% inhibition of the parasitaemia at 30 mg/kg/day.

Efficacy of non-artemisinin- and artemisinin-based combination therapies for uncomplicated falciparum malaria in Cameroon

Background

The use of drug combinations, including non-artemisinin-based and artemisinin-based combination therapy (ACT), is a novel strategy that enhances therapeutic efficacy and delays the emergence of multidrug-resistant Plasmodium falciparum. Its use is strongly recommended in most sub-Saharan African countries, namely Cameroon, where resistance to chloroquine is widespread and antifolate resistance is emerging.

Methods

Studies were conducted in Cameroonian children with acute uncomplicated P. falciparum malaria according to the standard World Health Organization protocol at four sentinel sites between 2003 and 2007. A total of 1,401 children were enrolled, of whom 1,337 were assigned to randomized studies and 64 were included in a single non-randomized study. The proportions of adequate clinical and parasitological response (PCR-uncorrected on day 14 and PCR-corrected on day 28) were the primary endpoints to evaluate treatment efficacy on day 14 and day 28. The relative effectiveness of drug combinations was compared by a multi-treatment Bayesian random-effect meta-analysis.

Findings

The results based on the meta-analysis suggested that artesunate-amodiaquine (AS-AQ) is as effective as other drugs (artesunate-sulphadoxine-pyrimethamine [AS-SP], artesunate-chlorproguanil-dapsone [AS-CD], artesunate-mefloquine [AS-MQ], dihydroartemisinin-piperaquine [DH-PP], artemether-lumefantrine [AM-LM], amodiaquine, and amodiaquine-sulphadoxine-pyrimethamine [AQ-SP]). AM-LM appeared to be the most effective with no treatment failure due to recrudescence, closely followed by DH-PP.

Conclusion

Although AM-LM requires six doses, rather than three doses for other artemisinin-based combinations, it has potential advantages over other forms of ACT. Further studies are needed to evaluate the clinical efficacy and tolerance of these combinations in different epidemiological context.

Use of a histidine-rich protein 2-based rapid diagnostic test for malaria by health personnel during routine consultation of febrile outpatients in a peripheral health facility in Yaounde, Cameroon

The role of a rapid diagnostic test (RDT) in the case management of Plasmodium falciparum malaria infections has not been determined in Africa. Our study was conducted during November 2007-January 2008 to assess test accuracy of an RDT in the management of febrile outpatients in a peripheral urban health facility in Cameroon. We found the overall sensitivity to be 71.4% and a specificity of 82.2%; the positive predictive value and negative predictive value were 73.8% and 80.4%, respectively. False-negative and false-positive cases represented 11.8% and 10.5% of all febrile patients. Malaria alone (31.3%) was the first cause of fever; 33.5% of fever cases were of unknown origin. Acute respiratory infections were common among children 0-2 years of age (25.5%) and decreased with age. The risk of having a clinical failure with the presumptive treatment of febrile children was seven times greater than that of the RDT-oriented management (relative risk = 6.8, 95% confidence interval = 0.88-53.4, P = 0.03) because of the delay of appropriate treatment of non-malarial febrile illness. Our results suggest that the RDT may be of limited utility for children greater than five years of age and adults and that diagnosis based on microscopic examination of blood smears should be recommended for these patient populations, as well as in areas of low transmission.

Molecular epidemiology of malaria in Cameroon. XXVIII. In vitro activity of dihydroartemisinin against clinical isolates of Plasmodium falciparum and sequence analysis of the P. falciparum ATPase 6 gene

The Plasmodium falciparum ATPase 6 (Pfatp6), homolog of sarco-endoplasmic reticulum, calcium-dependent ATPase in malaria parasites, has been proposed to be the main target of artemisinins. Four distinct point mutations (L263E, E431K, A623E, and S769N) have been reported to be associated with artemisinin resistance. The Pfatp6 sequence polymorphism was determined to evaluate the prevalence of these mutations in fresh clinical isolates in Yaounde, Cameroon, and compare sequence data with in vitro response to dihydroartemisinin. Two major haplotypes were observed: the wild-type LEAS (n = 60, 62%) and a single mutant LKAS (n = 35, 36%). These amino acid substitutions did not influence the level of in vitro response to dihydroartemisinin (P > 0.05). Plasmodium falciparum isolates from Cameroon are highly sensitive in vitro to artemisinins. However, the relatively high prevalence of E431K may be a warning signal that warrants a regular monitoring of these molecular markers and/or in vitro activity of artemisinin derivatives.

Therapeutic efficacy of sulfadoxine-pyrimethamine and the prevalence of molecular markers of resistance in under 5-year olds in Brazzaville, Congo

OBJECTIVE

To test the efficacy of sulfadoxine-pyremethamine (SP) monotherapy and establish the prevalence of mutations in dhfr and dhps in Brazzaville, Congo.

METHOD

We recruited 97 patients aged 6-59 months with uncomplicated malaria who attended Tenrikyo public health centre. Eighty-three were followed until day 28. SP efficacy was determined by the WHO 28-day test and analysis of mutations in the Plasmodium falciparum dihydrofolate reductase (pfdhfr) and dihydropteroate synthase (pfdhps) genes.

RESULTS

There were seven (8.4%) early treatment failures, 23 late treatment failures (27.7%), nine (10.8%) late parasitological failures and 44 (53%) adequate clinical and parasitological responses (ACPR). After polymerase chain reaction (PCR) analysis of 64 available samples, the corrected results there were 44 (68.8%) ACPR and 19 recrudescent cases (31.2%). Approximately, 97.5% of samples bore the Asn51Ile mutation, 66.2% the Cys59Arg mutation and 98.8% the Ser108Asn mutation. Mutations of dhps at positions 437 (Ala-Gly) and 436 (Ser-Ala) were found in 85% and 12.5% of samples. Quadruple mutations (pfdhfr triple mutations in codons 51, 59 and 108+ pfdhps mutation in 437) were found in 42 samples (52.5%) and associated with treatment failures.

CONCLUSION

This high level of treatment failures and mutations in both genes calls for the urgent application of the new policy for malaria treatment to delay the spread of SP resistance.

Efficacy of sulfadoxine-pyrimethamine, amodiaquine, and sulfadoxine-pyrimethamine-amodiaquine combination for the treatment of uncomplicated falciparum malaria in the urban and suburban areas of Brazzaville (Congo)

Congo-Brazzaville has recently adopted artesunate-amodiaquine as the first-line antimalarial drug to replace chloroquine. Before the implementation of this new strategy, we conducted several clinical studies to assess the therapeutic efficacy of former, classical first-line antimalarial drugs in the city of Brazzaville, in which reside about 30% of the Congolese population. From 2003 to 2005, non-randomised trials were conducted to evaluate the efficacy of sulfadoxine-pyrimethamine (SP) (n=97 patients), amodiaquine (AQ) (n=62 patients), and the combination of sulfadoxine-pyrimethamine-amodiaquine (n=54 patients) in children aged between 6 months and 5 years with uncomplicated malaria using the 2003 WHO guidelines during the 28-day follow-up period. After excluding new infections by PCR, the proportion of treatment failure on day 28 was 30.2% (95% confidence interval, 19.2-43.0%) for sulfadoxine-pyrimethamine, 34.8% (95% confidence interval, 21.4-50.2%) for amodiaquine, and 14.2% (95% confidence interval, 5.9-27.2%) for sulfadoxine-pyrimethamine+amodiaquine combination. Treatment with sulfadoxine-pyrimethamine was associated with an increase of gametocyte charge. These results suggest that neither sulfadoxine-pyrimethamine nor amodiaquine is efficacious as monotherapy and that their combination may not remain effective in the coming years. Based on our results, the implementation of artemisinin-based combination therapy appears to be urgent in the country.

Molecular epidemiology of malaria in Cameroon. XXV. In vitro activity of fosmidomycin and its derivatives against fresh clinical isolates of Plasmodium falciparum and sequence analysis of 1-deoxy-D-xylulose 5-phosphate reductoisomerase

The in vitro activities of fosmidomycin derivatives, chloroquine, and pyrimethamine were assessed by the radioisotopic assay in clinical isolates of Plasmodium falciparum. In a series of experiments with RPMI 1640 medium-10% fetal bovine serum, the geometric mean 50% inhibitory concentrations (IC(50)s) (n = 34) for fosmidomycin and FR900098 were 301 nM and 118 nM, respectively. In another series of experiments, the geometric mean IC(50)s (n = 33) for fosmidomycin and TH II46 were 413 nM and 249 nM, respectively. The IC(50)s were 2-3 times lower with RPMI-10% fetal bovine serum than the IC(50)s obtained with RPMI-10% human serum. FR900098 and TH II46 were 2.6 and 1.7 times more potent, respectively, than fosmidomycin. There was no correlation between chloroquine or pyrimethamine and fosmidomycin, which suggested the absence of in vitro cross-resistance. Sequence analysis showed five amino acid substitutions, but their possible relationship with the response to fosmidomycin is not clear. Fosmidomycin derivatives are promising candidates for further development.

Molecular epidemiology of malaria in Cameroon. XXVI. Twelve-year in vitro and molecular surveillance of pyrimethamine resistance and experimental studies to modulate pyrimethamine resistance

In vitro pyrimethamine response of Plasmodium falciparum isolates and dihydrofolate reductase (dhfr) gene sequences were analyzed in 2004-2005 and compared with our previous data. Most isolates (n = 103, all dhfr mutants) had 50% inhibitory concentrations (IC(50)s) > or = 119 nM, and six isolates had low IC(50)s (five wild-type or mixed dhfr, 0.04-1.37 nM; one triple mutant, 6.4 nM). Of 194 isolates, only 7 had the wild-type dhfr and 187 were mutants. The results of the two methods were highly concordant and indicated a significant increase (P < 0.05) in the prevalence of mutant, pyrimethamine-resistant P. falciparum between 1994 and 2005. The addition of probenecid or sulfinpyrazone to pyrimethamine resulted in a slight-to-moderate decrease in the level of in vitro pyrimethamine resistance without rendering the parasites susceptible to pyrimethamine. Analysis of molecular markers may be useful for the long-term surveillance of antifolate-resistant malaria.

Molecular epidemiology of malaria in Cameroon. XXVII. Clinical and parasitological response to sulfadoxine-pyrimethamine treatment and Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase alleles in Cameroonian children

The rapidly changing epidemiology of antifolate-resistant Plasmodium falciparum in Africa requires monitoring. The present study was designed to assess the degree of association between the clinical and parasitological response to sulfadoxine-pyrimethamine and allelic combinations of dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes. Of 357 children who completed the 14-day follow-up, an adequate clinical and parasitological response was observed in 316 patients (88.5%) and early and late failures occurred in 18 (5%) and 23 (6.4%, mostly due to recrudescence) patients, respectively. The majority of clinical isolates were characterized as "quadruple" (n=196, 55.2%; N51I-C59R-S108N in DHFR and A437G in DHPS) or "triple" mutants (n=97, 27.3%; N51I-C59R-S108N in DHFR and wild-type DHPS; S108N+N51I or C59R in DHFR and A437G in DHPS). Wild-type, single mutation, and double mutation were observed in 29, 20, and 13 parasites, respectively. The comparison of different sets of mutations and early or late failures did not reveal any molecular marker associated with treatment outcome when the follow-up period was limited to 14 days (P>0.05). In this study, the determination of dhfr-dhps genotypes was of limited value to predict the treatment outcome in individual patients, mostly due to few treatment failures and few wild-type haplotypes. Further monitoring will be required to define the relationship between clinical response to SP therapy and parasite genotypes in our epidemiological setting.

[Molecular surveillance of sulfadoxine-pyrimethamine-resistant Plasmodium falciparum in São Tomé and Príncipe]

The prevalence of point mutations associated with resistance to sulfadoxine and pyrimethamine was determined by sequencing the fragments of genes encoding dihydropteroate synthase (dhps) and dihydrofolate reductase (dhfr), respectively in 59 isolates collected during 2002-2003 in São Tomé and Príncipe to develop an early warning system of drug-resistant P. falciparum. Almost all isolates (57 of 59, 97%) were dhfr mutant. The majority of the isolates (43 of 59, 73%; 16 with mixed alleles) carried the triple dhfr mutations (lle-51/Arg-59/Asn-108). The presence of dhps mutations were only limited to positions 436 and 437. The pure mutant codon Gly-437 was present in 39 out of 59 isolates (66%), in association with Ser-436 (n=34) or Ala-436 (n=5). Mixed isolates displayed different combinations of 436 (Ser, Ala ou Phe) and 437 (Gly with or without Ala) alleles. None of the isolates carried mutant 540, 581 or 613 codons. A total of 39 isolates (66%) were characterized as quadruple mutants (i.e. triple dhfr mutations + Gly-437 dhps mutant allele). Monitoring the possible emergence of isolates carrying multiple dhfr and dhps mutations, in particular codon Glu-540, may be used as an early warning system which indicates a decrease in sulfadoxine-pyrimethamine efficacy.

Carboxypeptidases B of Anopheles gambiae as targets for a Plasmodium falciparum transmission-blocking vaccine

Anopheles gambiae is the major African vector of Plasmodium falciparum, the most deadly species of human malaria parasite and the most prevalent in Africa. Several strategies are being developed to limit the global impact of malaria via reducing transmission rates, among which are transmission-blocking vaccines (TBVs), which induce in the vertebrate host the production of antibodies that inhibit parasite development in the mosquito midgut. So far, the most promising components of a TBV are parasite-derived antigens, although targeting critical mosquito components might also successfully block development of the parasite in its vector. We previously identified A. gambiae genes whose expression was modified in P. falciparum-infected mosquitoes, including one midgut carboxypeptidase gene, cpbAg1. Here we show that P. falciparum up-regulates the expression of cpbAg1 and of a second midgut carboxypeptidase gene, cpbAg2, and that this up-regulation correlates with an increased carboxypeptidase B (CPB) activity at a time when parasites establish infection in the mosquito midgut. The addition of antibodies directed against CPBAg1 to a P. falciparum-containing blood meal inhibited CPB activity and blocked parasite development in the mosquito midgut. Furthermore, the development of the rodent parasite Plasmodium berghei was significantly reduced in mosquitoes fed on infected mice that had been immunized with recombinant CPBAg1. Lastly, mosquitoes fed on anti-CPBAg1 antibodies exhibited reduced reproductive capacity, a secondary effect of a CPB-based TBV that could likely contribute to reducing Plasmodium transmission. These results indicate that A. gambiae CPBs could constitute targets for a TBV that is based upon mosquito molecules.

Molecular epidemiology of malaria in Cameroon. XXII. Geographic mapping and distribution of Plasmodium falciparum dihydrofolate reductase (dhfr) mutant alleles

Sulfadoxine-pyrimethamine (SP) is still a useful drug to combat chloroquine-resistant Plasmodium falciparum malaria in Cameroon. Because of several disadvantages of the in vivo test and in vitro drug sensitivity assays, molecular assays are an alternative laboratory tool to monitor the evolution of antifolate resistance, especially over the entire country that is characterized by several epidemiologic strata and malaria transmission patterns. In this study, 1,430 blood samples from either symptomatic children or asymptomatic carriers were collected from 14 sites throughout the country between 1999 and 2003 for the analysis of dihydrofolate reductase (dhfr) sequence. Of 1,368 samples (95.7%) that were successfully amplified, 1,180 were analyzed by direct sequencing of the polymerase chain reaction product, and 188 were analyzed by restriction enzymes. The prevalences of the wild-type, single Asn-108 mutation, double Arg-59/Asn-108 mutations, double Ile-51/Asn-108 mutations, triple Ile-51/Arg-59/Asn-108 mutations, and mixed alleles were 20.8%, 2.8%, 5.7%, 0.8%, 62.2%, and 7.6%, respectively. The proportions of triple dhfr mutations were > 60% at all study sites, with the exception of the eastern province (42% triple mutants in Bertoua in 1999) and the northern provinces (11-35% triple mutants in Ngaoundere, Garoua, and Maroua). In these two provinces, the proportion of mutant parasites increased significantly (P < 0.05) over the period of 2-4 years. Furthermore, there was a higher proportion (P < 0.05) of wild-type parasites in the northern provinces, compared with the rest of the country. The geographic mapping of molecular markers offers a novel tool for monitoring the epidemiology of drug-resistant malaria.

Genetic variation of the dihydrofolate reductase gene in Plasmodium vivax in Snoul, northeastern Cambodia

In Plasmodium vivax, pyrimethamine resistance is associated with amino acid substitutions Ser117Asn and Ser58Arg in dihydrofolate reductase (DHFR), which correspond to Ser108Asn and Cys59Arg in the Plasmodium falciparum homolog, respectively. Sequence variations within the DHFR domain of 32 P. vivax isolates from Snoul, Cambodia, were analyzed by direct sequencing of polymerase chain reaction (PCR) products. Sequence polymorphisms within the entire DHFR domain were limited to codons 58 and 117 and GGDN tandem repeat units. A large majority (30 of 32) of isolates were characterized to be double mutants (Arg-58 and Asn-117) and associated with the presence of two GGDN repeat units. Only one isolate was of wild-type with three GGDN repeat units, and an additional isolate was of mixed type. Our data suggest that most Cambodian P. vivax isolates display double dhfr mutations associated with pyrimethamine resistance, as in the neighboring countries in Southeast Asia. Further molecular characterization of P. vivax isolates from different endemic areas may be a useful alternative approach to establish the epidemiology of drug-resistant malaria.

Molecular epidemiology of malaria in Cameroon. XVIII. Polymorphisms of the Plasmodium falciparum merozoite surface antigen-2 gene in isolates from symptomatic patients

Merozoite surface antigen-2 (MSA-2) is a polymorphic genetic marker that is highly discriminatory for characterizing Plasmodium falciparum field isolates. Genetic diversity of isolates obtained from symptomatic patients residing in Yaounde, Cameroon was analyzed by an allele-specific polymerase chain reaction and direct sequencing of amplification products. Of 137 isolates, 25 (18%) had only FC27-type alleles, 40 (29%) had only 3D7-type alleles, and 72 (53%) had multiple parasite populations with both alleles. Of 295 fragments, 145 (49.2%) and 150 (50.8%) belonged to FC27 and 3D7 alleles, respectively. There were 23 different MSA-2 alleles (10 FC27-type and 13 3D7-type that yielded 44 different combinations in multiple infections). DNA sequencing showed distinct individual sequences. Sequences belonging to the FC27 allelic family were relatively conserved, with most of the polymorphism arising from differences in the number of repeat units. In contrast, the sequences within the GSA-rich region in 3D7 allelic family were less conserved, but many of the sequences in Cameroonian isolates have been identified in other isolates from geographically distant origins. Our results show an extensive diversity of the central region of MSA-2 in size, allelic family, combinations of these two features in multiple infections, and sequence variations underlying the complex population structure of P. falciparum clinical isolates in Yaounde, Cameroon.

Immune response of Anopheles gambiae to the early sporogonic stages of the human malaria parasite Plasmodium falciparum

Deciphering molecular interactions between the malaria parasite and its mosquito vector is an emerging area of research that will be greatly facilitated by the recent sequencing of the genomes of Anopheles gambiae mosquito and of various Plasmodium species. So far, most such studies have focused on Plasmodium berghei, a parasite species that infects rodents and is more amenable to studies. Here, we analysed the expression pattern of nine An.gambiae genes involved in immune surveillance during development of the human malaria parasite P.falciparum in mosquitoes fed on parasite-containing blood from patients in Cameroon. We found that P.falciparum ingestion triggers a midgut-associated, as well as a systemic, response in the mosquito, with three genes, NOS, defensin and GNBP, being regulated by ingestion of gametocytes, the infectious stage of the parasite. Surprisingly, we found a different pattern of expression of these genes in the An.gambiae-P.berghei model. Therefore, differences in mosquito reaction against various Plasmodium species may exist, which stresses the need to validate the main conclusions suggested by the P.berghei-An.gambiae model in the P.falciparum-An.gambiae system.

Kinetic properties of dihydrofolate reductase from wild-type and mutant Plasmodium vivax expressed in Escherichia coli

Antifolate drugs inhibit malarial dihydrofolate reductase (DHFR). In Plasmodium falciparum, antifolate resistance has been associated with point mutations in the gene encoding DHFR. Recently, mutations at homologous positions have been observed in the P. vivax gene. Since P. vivax cannot be propagated in a continuous in vitro culture for drug sensitivity assays, the kinetic properties of DHFR were studied by expression of the DHFR domain in Escherichia coli. Induced expression yielded a protein product that precipitated as an inclusion body in E. coli. The soluble, active DHFR recovered after denaturation and renaturation was purified to homogeneity by affinity chromatography. Kinetic properties of the recombinant P. vivax DHFR showed that the wild-type DHFR (Ser-58 and Ser-117) and double mutant DHFR (Arg-58 and Asn-117) have similar K(m) values for dihydrofolate and NADPH. Antifolate drugs (pyrimethamine, cycloguanil, trimethoprim, and methotrexate), but not proguanil (parent compound of cycloguanil) inhibit DHFR activity, as expected. The kinetics of enzyme inhibition indicated that point mutations (Ser58Arg and Ser117Asn) are associated with lower affinity between the mutant enzyme and pyrimethamine and cycloguanil, which may be the origin of antifolate resistance.

Informational suppressor alleles of the eEF1A gene, fertility and cell degeneration in Podospora anserina

Mutations that increase readthrough at a UGA stop codon (informational suppressor mutations) were created in the gene (AS4) that encodes translation elongation factor eEF1A in the filamentous fungus Podospora amserina. The results strongly suggest that the net charge of the eEF1A protein controls the accuracy of translation. Physiological analysis of the mutant strains shows that some of the alleles dominantly increase life span, while only one drastically modifies fertility. This exceptional allele (AS4-56) causes a wide array of phenotypes, including a new growth cessation phenomenon that is different from Senescence or Crippled Growth, previously known degenerative syndromes that are both controlled by AS4. The data emphasise the fact that eEF1A exerts a complex control over cellular physiology.