Failure to detect Plasmodium vivax in West and Central Africa by PCR species typing

Linkages between blood groups and malaria susceptibility

Blood typing has revolutionized the field of medical science since its discovery about a century ago. Besides its established role in life-saving blood transfusions, researchers have always been curious about the relationship between blood groups and human ailments. The effect of blood groups on disease outcomes, susceptibility, and mortality has been widely explored. According to a particular school of thought, the endemicity of diseases shapes the distribution of blood group frequency in human populations and exert selection pressure favoring one blood type over another. Here we discuss the scope and association of different blood groups in the context of malaria.

Prevalence of non-Plasmodium falciparum species in southern districts of Brazzaville in The Republic of the Congo

BACKGROUND

Although Plasmodium falciparum infection is largely documented and this parasite is the main target for malaria eradication, other Plasmodium species persist, and these require more attention in Africa. Information on the epidemiological situation of non-P. falciparum species infections is scarce in many countries, including in the Democratic Republic of the Congo (hereafter Republic of the Congo) where malaria is highly endemic. The aim of this study was to determine the prevalence and distribution of non-P. falciparum species infections in the region south of Brazzaville.

METHODS

A cross-sectional survey was conducted in volunteers living in rural and urban settings during the dry and rainy seasons in 2021. Socio-demographic and clinical parameters were recorded. Plasmodium infection in blood samples was detected by microscopic analysis and nested PCR (sub-microscopic analysis).

RESULTS

Of the 773 participants enrolled in the study, 93.7% were from the rural area, of whom 97% were afebrile. The prevalence of microscopic and sub-microscopic Plasmodium spp. infection was 31.2% and 63.7%, respectively. Microscopic Plasmodium malariae infection was found in 1.3% of participants, while sub-microscopic studies detected a prevalence of 14.9% for P. malariae and 5.3% for Plasmodium ovale. The rate of co-infection of P. malariae or P. ovale with P. falciparum was 8.3% and 2.6%, respectively. Higher rates of sub-microscopic infection were reported for the urban area without seasonal fluctuation. In contrast, non-P. falciparum species infection was more pronounced in the rural area, with the associated risk of the prevalence of sub-microscopic P. malariae infection increasing during the dry season.

CONCLUSION

There is a need to include non-P. falciparum species in malaria control programs, surveillance measures and eradication strategies in the Republic of the Congo.

African Plasmodium vivax malaria improbably rare or benign

The overwhelming dominance of Duffy blood group negativity among most people living in sub-Saharan Africa has been considered the basis of their protection from endemic Plasmodium vivax malaria. New evidence demonstrates widespread transmission of P. vivax in Duffy-negative Africa, though currently of unknown distribution, magnitude, or consequences. Other new evidence from outside of Africa demonstrates marked tropisms of P. vivax for extravascular tissues of bone marrow and spleen. Those establish states of proliferative infection with low-grade or undetectable parasitemia of peripheral blood causing acute and chronic disease. This review examines the plausibility of those infectious processes also operating in Duffy-negative Africans and causing harm of unrecognized origin.

The primate malaria parasites Plasmodium malariae, Plasmodium brasilianum and Plasmodium ovale spp.: genomic insights into distribution, dispersal and host transitions

During the twentieth century, there was an explosion in understanding of the malaria parasites infecting humans and wild primates. This was built on three main data sources: from detailed descriptive morphology, from observational histories of induced infections in captive primates, syphilis patients, prison inmates and volunteers, and from clinical and epidemiological studies in the field. All three were wholly dependent on parasitological information from blood-film microscopy, and The Primate Malarias” by Coatney and colleagues (1971) provides an overview of this knowledge available at that time. Here, 50 years on, a perspective from the third decade of the twenty-first century is presented on two pairs of primate malaria parasite species. Included is a near-exhaustive summary of the recent and current geographical distribution for each of these four species, and of the underlying molecular and genomic evidence for each. The important role of host transitions in the radiation of Plasmodium spp. is discussed, as are any implications for the desired elimination of all malaria species in human populations. Two important questions are posed, requiring further work on these often ignored taxa. Is Plasmodium brasilianum, circulating among wild simian hosts in the Americas, a distinct species from Plasmodium malariae? Can new insights into the genomic differences between Plasmodium ovale curtisi and Plasmodium ovale wallikeri be linked to any important differences in parasite morphology, cell biology or clinical and epidemiological features?

Nationwide molecular surveillance of three Plasmodium species harboured by symptomatic malaria patients living in Ghana

BACKGROUND

Clinical presentations of malaria in Ghana are primarily caused by infections containing microscopic densities of Plasmodium falciparum, with a minor contribution from Plasmodium malariae and Plasmodium ovale. However, infections containing submicroscopic parasite densities can result in clinical disease. In this study, we used PCR to determine the prevalence of three human malaria parasite species harboured by suspected malaria patients attending healthcare facilities across the country.

METHODS

Archived dried blood spots on filter paper that had been prepared from whole blood collected from 5260 patients with suspected malaria attending healthcare facilities across the country in 2018 were used as experimental material. Plasmodium species-specific PCR was performed on DNA extracted from the dried blood spots. Demographic data and microscopy data for the subset of samples tested were available from the original study on these specimens.

RESULTS

The overall frequency of P. falciparum, P. malariae and P. ovale detected by PCR was 74.9, 1.4 and 0.9%, respectively. Of the suspected symptomatic P. falciparum malaria cases, 33.5% contained submicroscopic densities of parasites. For all regions, molecular diagnosis of P. falciparum, P. malariae and P. ovale was significantly higher than diagnosis using microscopy: up to 98.7% (75/76) of P. malariae and 97.8% (45/46) of P. ovale infections detected by PCR were missed by microscopy.

CONCLUSION

Plasmodium malariae and P. ovale contributed to clinical malaria infections, with children aged between 5 and 15 years harbouring a higher frequency of P. falciparum and P. ovale, whilst P. malariae was more predominant in individuals aged between 10 and 20 years. More sensitive point-of-care tools are needed to detect the presence of low-density (submicroscopic) Plasmodium infections, which may be responsible for symptomatic infections.

Sequence analysis of Plasmodium vivax Duffy binding proteins reveals the presence of unique haplotypes and diversifying selection in Ethiopian isolates

BACKGROUND

Red blood cell invasion by the Plasmodium vivax merozoite requires interaction between the Duffy antigen receptor for chemokines (DARC) and the P. vivax Duffy-binding protein II (PvDBPII). Given that the disruption of this interaction prevents P. vivax blood-stage infection, a PvDBP-based vaccine development has been well recognized. However, the polymorphic nature of PvDBPII prevents a strain transcending immune response and complicates attempts to design a vaccine.

METHODS

Twenty-three P. vivax clinical isolates collected from three areas of Ethiopia were sequenced at the pvdbpII locus. A total of 392 global pvdbpII sequences from seven P. vivax endemic countries were also retrieved from the NCBI archive for comparative analysis of genetic diversity, departure from neutrality, linkage disequilibrium, genetic differentiation, PvDBP polymorphisms, recombination and population structure of the parasite population. To establish a haplotype relationship a network was constructed using the median joining algorithm.

RESULTS

A total of 110 variable sites were found, of which 44 were parsimony informative. For Ethiopian isolates there were 12 variable sites of which 10 were parsimony informative. These parsimony informative variants resulted in 10 nonsynonymous mutations. The overall haplotype diversity for global isolates was 0.9596; however, the haplotype diversity was 0.874 for Ethiopia. Fst values for genetic revealed Ethiopian isolates were closest to Indian isolates as well as to Sri Lankan and Sudanese isolates but further away from Mexican, Papua New Guinean and South Korean isolates. There was a total of 136 haplotypes from the 415 global isolates included for this study. Haplotype prevalence ranged from 36.76% to 0.7%, from this 74.2% were represented by single parasite isolates. None of the Ethiopian isolates grouped with the Sal I reference haplotype. From the total observed nonsynonymous mutations 13 mapped to experimentally verified epitope sequences. Including 10 non-synonymous mutations from Ethiopia. However, all the polymorphic regions in Ethiopian isolates were located away from DARC, responsible for junction formation.

CONCLUSION

The results of this study are concurrent with the multivalent vaccine approach to design an effective treatment. However, the presence of novel haplotypes in Ethiopian isolates that were not shared by other global sequences warrant further investigation.

The epidemiology of Plasmodium vivax among adults in the Democratic Republic of the Congo

Reports of P. vivax infections among Duffy-negative hosts have accumulated throughout sub-Saharan Africa. Despite this growing body of evidence, no nationally representative epidemiological surveys of P. vivax in sub-Saharan Africa have been performed. To overcome this gap in knowledge, we screened over 17,000 adults in the Democratic Republic of the Congo (DRC) for P. vivax using samples from the 2013-2014 Demographic Health Survey. Overall, we found a 2.97% (95% CI: 2.28%, 3.65%) prevalence of P. vivax infections across the DRC. Infections were associated with few risk-factors and demonstrated a relatively flat distribution of prevalence across space with focal regions of relatively higher prevalence in the north and northeast. Mitochondrial genomes suggested that DRC P. vivax were distinct from circulating non-human ape strains and an ancestral European P. vivax strain, and instead may be part of a separate contemporary clade. Our findings suggest P. vivax is diffusely spread across the DRC at a low prevalence, which may be associated with long-term carriage of low parasitemia, frequent relapses, or a general pool of infections with limited forward propagation.

High frequency of the Duffy-negative genotype and absence of Plasmodium vivax infections in Ghana

Background

Recent studies from different malaria-endemic regions including western Africa have now shown that Plasmodium vivax can infect red blood cells (RBCs) and cause clinical disease in Duffy-negative people, though the Duffy-negative phenotype was thought to confer complete refractoriness against blood invasion with P. vivax. The actual prevalence of P. vivax in local populations in Ghana is unknown and little information is available about the distribution of Duffy genotypes. The aim of this study was to assess the prevalence of P. vivax in both asymptomatic and symptomatic outpatients and the distribution of Duffy genotypes in Ghana.

Methods

DNA was extracted from dried blood spots (DBS) collected from 952 subjects (845 malaria patients and 107 asymptomatic persons) from nine locations in Ghana. Plasmodium species identification was carried out by nested polymerase chain reaction (PCR) amplification of the small-subunit (SSU) rRNA genes. For P. vivax detection, a second PCR of the central region of the Pvcsp gene was carried out. Duffy blood group genotyping was performed by allele-specific PCR to detect the presence of the FY^ES allele.

Results

No cases of P. vivax were detected in any of the samples by both PCR methods used. Majority of infections (542, 94.8%) in the malaria patient samples were due to P. falciparum with only 1 infection (0.0017%) due to Plasmodium malariae, and 2 infections (0.0034%) due to Plasmodium ovale. No case of mixed infection was identified. Of the samples tested for the FY^ES allele from all the sites, 90.5% (862/952) had the FY^ES allele. All positive samples were genotyped as FY*B-33/FY*B-33 (Duffy-negative homozygous) and therefore classified as Fy(a−b−).

Conclusions

No cases of P. vivax were detected by both PCRs and majority of the subjects tested carried the FY^ES allele. The lack of P. vivax infections observed can be attributed to the high frequency of the FY^ES allele that silences erythroid expression of the Duffy. These results provide insights on the host susceptibility for P. vivax infections that had not been investigated in Ghana before.

Profiles of Plasmodium falciparum infections detected by microscopy through the first year of life in Kintampo a high transmission area of Ghana

Although malaria mortality among children under five years of age is high, the characteristics of their infection patterns are not well described. The aim of this study was to examine the longitudinal sequence pattern of Plasmodium falciparum infections in the first year of life within a birth cohort in Kintampo, Ghana (N = 1855). Infants were monitored at home with monthly sampling and also at the clinic for any febrile illness between 2008 and 2011. Light microscopy was performed on monthly scheduled visits and febrile ill visits over twelve months of follow-ups (n = 19231). Microscopy-positive visits accompanied with or without symptoms were rare during the first five months of life but were common from six to twelve months of age. Among 1264 infants with microscopy data over a minimum of eight monthly visits and also throughout in sick visits, some were microscopy negative (36%), and others positive: only-symptomatic (35%), alternating (22%) and only-asymptomatic (7%). The median age of microscopic infection was seven months for the alternating group and eight months for both the only-symptomatic and only-asymptomatic groups. The alternating group had the highest cumulative incidence of microscopic infections, the lowest age at first infection and 87 different infection patterns. Parasite densities detected by microscopy were significantly higher for symptomatic versus asymptomatic infection. We conclude that infants in malaria endemic areas experience diverse infection profiles throughout their first year of life. Further investigations should include submicroscopic reservoir and may shed more light on the factors that determine susceptibility to malaria during infancy.

Bisphosphoglycerate Mutase Deficiency Protects against Cerebral Malaria and Severe Malaria-Induced Anemia

The replication cycle and pathogenesis of the Plasmodium malarial parasite involves rapid expansion in red blood cells (RBCs), and variants of certain RBC-specific proteins protect against malaria in humans. In RBCs, bisphosphoglycerate mutase (BPGM) acts as a key allosteric regulator of hemoglobin/oxyhemoglobin. We demonstrate here that a loss-of-function mutation in the murine Bpgm (Bpgm^L166P) gene confers protection against both Plasmodium-induced cerebral malaria and blood-stage malaria. The malaria protection seen in Bpgm^L166P mutant mice is associated with reduced blood parasitemia levels, milder clinical symptoms, and increased survival. The protective effect of Bpgm^L166P involves a dual mechanism that enhances the host's stress erythroid response to Plasmodium-driven RBC loss and simultaneously alters the intracellular milieu of the RBCs, including increased oxyhemoglobin and reduced energy metabolism, reducing Plasmodium maturation, and replication. Overall, our study highlights the importance of BPGM as a regulator of hemoglobin/oxyhemoglobin in malaria pathogenesis and suggests a new potential malaria therapeutic target.

Under the Radar: Epidemiology of Plasmodium ovale in the Democratic Republic of the Congo

BACKGROUND

Plasmodium ovale is an understudied malaria species prevalent throughout much of sub-Saharan Africa. Little is known about the distribution of ovale malaria and risk factors for infection in areas of high malaria endemicity.

METHODS

Using the 2013 Democratic Republic of the Congo (DRC) Demographic and Health Survey, we conducted a risk factor analysis for P. ovale infections. We evaluated geographic clustering of infections and speciated to P. ovale curtisi and P. ovale wallikeri through deep sequencing.

RESULTS

Of 18 149 adults tested, we detected 143 prevalent P. ovale infections (prevalence estimate 0.8%; 95% confidence interval [CI], .59%-.98%). Prevalence ratios (PR) for significant risk factors were: male sex PR = 2.12 (95% CI, 1.38-3.26), coprevalent P. falciparum PR = 3.52 (95% CI, 2.06-5.99), and rural residence PR = 2.19 (95% CI, 1.31-3.66). P. ovale was broadly distributed throughout the DRC; an elevated cluster of infections was detected in the south-central region. Speciation revealed P. ovale curtisi and P. ovale wallikeri circulating throughout the country.

CONCLUSIONS

P. ovale persists broadly in the DRC, a high malaria burden country. For successful elimination of all malaria species, P. ovale needs to be on the radar of malaria control programs.

Global prevalence and mortality of severe Plasmodium malariae infection: a systematic review and meta-analysis

Background

Severe complications among patients with Plasmodium malariae infection are rare. This is the first systematic review and meta-analysis demonstrating the global prevalence and mortality of severe P. malariae infection in humans.

Methods

The systematic review and meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. All research articles published on the severity and mortality of P. malariae infection cases in humans were retrieved from three public databases: PubMed, Scopus, and ISI Web of Science. The pooled prevalence estimate and 95% confidence interval (CI) of complications in patients with P. malariae malaria was analysed using the random-effects model provided in Stata software. The pooled odds ratio (OR) and 95% CI of severe malaria for P. malariae infection and Plasmodium falciparum infection were analysed using Review Manager software.

Results

Six studies were used to estimate the pooled prevalence of severe P. malariae malaria. Out of 10,520 patients infected with P. malariae, the pooled prevalence estimate of severe P. malariae infection was 3% (95% CI 2–5%), with high heterogeneity (I²: 90.7%). Severe anaemia (3.32%), pulmonary complications (0.46%), and renal impairments (0.24%) were the most common severe complications found in patients with P. malariae infection. The pooled proportion of severe anaemia for P. malariae infection and P. falciparum infection was comparable among the four included studies (OR: 0.74, 95% CI 0.22–2.45, I² = 98%). The pooled proportion of pulmonary complications was comparable between patients with P. malariae infection and those with P. falciparum infection among the four included studies (OR: 1.44; 95% CI 0.17–12.31, I²: 92%). For renal complications, the funnel plot showed that the pooled proportion of renal complications for P. malariae infection and P. falciparum infection was comparable among the four included studies (OR: 0.94, 95% CI 0.18–4.93, I²: 91%). The mortality rate of patients with P. malariae infection was 0.17% (18/10,502 cases).

Conclusions

This systematic review demonstrated that approximately two percent of patients with P. malariae infection developed severe complications, with a low mortality rate. Severe anaemia, pulmonary involvement, and renal impairment were the most common complications found in patients with P. malariae infection. Although a low prevalence and low mortality of P. malariae infection have been reported, patients with P. malariae infection need to be investigated for severe anaemia and, if present, treated aggressively to prevent anaemia-related death.

Clinical Sequelae Associated with Unresolved Tropical Splenomegaly in a Cohort of Recently Resettled Congolese Refugees in the United States-Multiple States, 2015-2018

Tropical splenomegaly is often associated with malaria and schistosomiasis. In 2014 and 2015, 145 Congolese refugees in western Uganda diagnosed with splenomegaly during predeparture medical examinations underwent enhanced screening for various etiologies. After anecdotal reports of unresolved splenomegaly and complications after U.S. arrival, patients were reassessed to describe long-term clinical progression after arrival in the United States. Post-arrival medical information was obtained through medical chart abstraction in collaboration with state health partners in nine participating states. We evaluated observed splenomegaly duration and associated clinical sequelae between 130 case patients from eastern Congo and 102 controls through adjusted hierarchical Poisson models, accounting for familial clustering. Of the 130 case patients, 95 (73.1%) had detectable splenomegaly after arrival. Of the 85 patients with records beyond 6 months, 45 (52.9%) had persistent splenomegaly, with a median persistence of 14.7 months (range 6.0-27.9 months). Of the 112 patients with available results, 65 (58.0%) patients had evidence of malaria infection, and the mean splenomegaly duration did not differ by Plasmodium species. Refugees with splenomegaly on arrival were 43% more likely to have anemia (adjusted relative risk [aRR]: 1.43, 95% CI: 1.04-1.97). Those with persistent splenomegaly were 60% more likely (adjusted relative risk [aRR]: 1.60, 95% CI: 1.15-2.23) to have a hematologic abnormality, particularly thrombocytopenia (aRR: 5.53, 95% CI: 1.73-17.62), and elevated alkaline phosphatase (aRR: 1.57, 95% CI: 1.03-2.40). Many patients experienced persistent splenomegaly, contradicting literature describing resolution after treatment and removal from an endemic setting. Other possible etiologies should be investigated and effective treatment, beyond treatment for malaria and schistosomiasis, explored.

The enigmatic mechanisms by which Plasmodium vivax infects Duffy-negative individuals

The absence of the Duffy protein at the surface of erythrocytes was considered for decades to confer full protection against Plasmodium vivax as this blood group is the receptor for the key parasite ligand P. vivax Duffy binding protein (PvDBP). However, it is now clear that the parasite is able to break through this protection and induce clinical malaria in Duffy-negative people, although the underlying mechanisms are still not understood. Here, we briefly review the evidence of Duffy-negative infections by P. vivax and summarize the current hypothesis at the basis of this invasion process. We discuss those in the perspective of malaria-elimination challenges, notably in African countries.

Impact of the Microbiome on the Human Genome

Humans live in a microbial world that includes pathogenic bacteria, viruses, and fungi that cause lethal infections. In addition, a large number of microbial communities inhabit mucosal surfaces where they provide key metabolic activities, facilitating adaptation to changing environments. New genome technologies enable both sequencing of the human genome and sequence-based cataloging of microbial communities inhabiting human mucosal surfaces. These have revealed intricate two-way relationships between the microbiome and the genome, including strong effects of human genotypes on the composition and activity of the microbiome. Likewise, the microbiome plays an important role in training and regulating the immune system, and acts to modify expression of human genetic risk for debilitating chronic inflammatory and immune conditions. These studies are suggesting a new role of the microbiome in human health and disease.

Structural basis for inhibition of Plasmodium vivax invasion by a broadly neutralizing vaccine-induced human antibody

The most widespread form of malaria is caused by Plasmodium vivax. To replicate, this parasite must invade immature red blood cells, through a process which requires interaction of the Plasmodium vivax Duffy binding protein, PvDBP with its human receptor, the Duffy antigen receptor for chemokines, DARC. Naturally acquired antibodies that inhibit this interaction associate with clinical immunity, suggesting PvDBP as a leading candidate for inclusion in a vaccine to prevent malaria due to Plasmodium vivax. Here, we isolated a panel of monoclonal antibodies from human volunteers immunised in a clinical vaccine trial of PvDBP. We screened their ability to prevent PvDBP from binding to DARC, and their capacity to block red blood cell invasion by a transgenic Plasmodium knowlesi parasite genetically modified to express PvDBP and to prevent reticulocyte invasion by multiple clinical isolates of Plasmodium vivax. This identified a broadly neutralising human monoclonal antibody which inhibited invasion of all tested strains of Plasmodium vivax. Finally, we determined the structure of a complex of this antibody bound to PvDBP, indicating the molecular basis for inhibition. These findings will guide future vaccine design strategies and open up possibilities for testing the prophylactic use of such an antibody.

The Molecular Basis of Erythrocyte Invasion by Malaria Parasites

Plasmodium species cause malaria by proliferating in human erythrocytes. Invasion of immunologically privileged erythrocytes provides a relatively protective niche as well as access to a rich source of nutrients. Plasmodium spp. target erythrocytes of different ages, but share a common mechanism of invasion. Specific engagement of erythrocyte receptors defines target cell tropism, activating downstream events and resulting in the physical penetration of the erythrocyte, powered by the parasite's actinomyosin-based motor. Here we review the latest in our understanding of the molecular composition of this highly complex and fascinating biological process.

Unexpected high circulation of Plasmodium vivax in asymptomatic children from Kédougou, southeastern Senegal

Background

Malaria in Senegal is due essentially to infections by Plasmodium falciparum and, to a lesser extent to Plasmodium malariae and Plasmodium ovale. By the use of molecular methods, detection of Plasmodium vivax has been recently reported in the region of Kedougou, raising the question of appraisal of its potential prevalence in this setting.

Methods

A retrospective serological study was carried out using 188 samples taken from 2010 to 2011 in a longitudinal school survey during which 48 asymptomatic children (9–11 years) were recruited. Four collections of samples collected during two successive dry and rainy seasons were analysed for antibody responses to P. vivax and P. falciparum. Recombinant P. falciparum and P. vivax MSP1 antigens and total P. falciparum schizont lysate from African 07/03 strain (adapted to culture) were used for ELISA. Nested PCR amplification was used for molecular detection of P. vivax.

Results

A surprising high prevalence of IgG responses against P. vivax MSP1 was evidenced with 53% of positive samples and 58% of the individuals that were found positive to this antigen. There was 77% of responders to P. falciparum outlined by 63% of positive samples. Prevalence of responders did not differ as function of seasons. Levels of antibodies to P. falciparum fluctuated with significant increasing between dry and rainy season (P < 0.05), contrary to responses to P. vivax. There was a significant reciprocal relationship (P < 10⁻³) between antibody responses to the different antigens, but with weak coefficient of correlation (Rho around 0.3) underlining a variable profile at the individual level. Clear molecular signature was found in positive IgG to P. vivax msp1 samples by PCR.

Conclusion

This cross-sectional longitudinal study highlights the unexpected high circulation of P. vivax in this endemic area. Sero-immunology and molecular methods are powerful additive tools to identify endemic sites where relevant control measures have to be settled and monitored.

QTL mapping of a natural genetic polymorphism for long-term parasite persistence in Daphnia populations

Knowing the determinants of the geographic ranges of parasites is important for understanding their evolutionary ecology, epidemiology and their potential to expand their range. Here we explore the determinants of geographic range in the peculiar case of a parasite species – the microsporidian Hamiltosporidium tvaerminnensis – that has a limited geographic distribution in a wide-spread host – Daphnia magna. We conducted a quantitative trait loci (QTLs) analysis with monoclonal F2D. magna populations originating from a cross between a susceptible northern European genotype and a resistant central European genotype. Contrary to our expectations, long-term persistence turned out to be a quantitative trait across the F2 offspring. Evidence for two QTLs, one epistatic interaction and for further minor QTL was found. This finding contrasts markedly with the previously described bimodal pattern for long-term parasite persistence in natural host genotypes across Europe and leaves open the question of how a quantitative genetic trait could determine the disjunct geographic distribution of the parasite across Europe.

Antibodies elicited during natural infection in a predominantly Plasmodium falciparum transmission area cross-react with sexual stage-specific antigen in P. vivax

Infections caused by Plasmodium falciparum and P. vivax account for more than 90% of global malaria burden. Exposure to malaria parasite elicits immune responses during natural infection and it is generally believed that the immunity is not only stage specific but also species specific. However, partial genomic similarity for various antigens in different Plasmodium spp. raises the possibility of immunological cross-reactivity at the level of specific antigens. Serum samples collected from children who were permanent residents of a P. falciparum transmission area in Zimbabwe were screened for antibody reactivity against Pfs48/45, a P. falciparum gametocyte antigen and Pvs48/45, a P. vivax homolog of Pfs48/45 using ELISA. Western blotting was used to further confirm identity of the specific antibody reactivity to the Pfs48/45 and Pvs48/45 proteins. Pan Plasmodium PCR and nested PCR were used to confirm infection with the Plasmodium species. Twenty-seven percent (49/181) of the participants were found to be sero-positive for Pfs48/45 and 73% (n=36) of these Pfs48/45 positive sera also showed reactivity with Pvs48/45. Immune cross-reactivity revealed by ELISA was also confirmed by Western blot analysis using a panel of randomly selected 23 Pfs48/45 and Pvs48/45 ELISA positive samples. Nested PCR analysis of 27 blood samples randomly selected from the 36 that showed positive ELISA reactivity to both Pfs48/45 and Pvs48/45 antigens confirmed infection with P. falciparum and generalized absence of P. vivax except for a single sample which revealed PCR positivity for both P. vivax and P. falciparum. Our studies with sera samples from a predominantly P. falciparum transmission area in Zimbabwe suggest immunological cross-reactivity with Pvs48/45, thus raising the possibility of partial species cross-reactive immunity and possible cross-boosting of immunity during co-infection with P. falciparum and P. vivax.

Wild African great apes as natural hosts of malaria parasites: current knowledge and research perspectives

Humans and African great apes (AGAs) are naturally infected with several species of closely related malaria parasites. The need to understand the origins of human malaria as well as the risk of zoonotic transmissions and emergence of new malaria strains in human populations has markedly encouraged research on great ape Plasmodium parasites. Progress in the use of non-invasive methods has rendered investigations into wild ape populations possible. Present knowledge is mainly focused on parasite diversity and phylogeny, with still large gaps to fill on malaria parasite ecology. Understanding what malaria infection means in terms of great ape health is also an important, but challenging avenue of research and has been subject to relatively few research efforts so far. This paper reviews current knowledge on African great ape malaria and identifies gaps and future research perspectives.

Malaria epidemiological research in the Republic of Congo

BACKGROUND

Reliable and comprehensive information on the burden of malaria is critical for guiding national and international efforts in malaria control. The purpose of this review is to provide an overview of published data and available information on malaria resulting from field studies/investigations conducted in the Republic of Congo (RoC) from 1992 to 2015, as baseline for assisting public health authorities and researchers to define future research priorities as well as interventions.

METHODS

This review considers data from peer-reviewed articles and information from the National Malaria Control Programme reports, based on field investigations or samples collected from 1992 to 2015. Peer-reviewed papers were searched throughout online bibliographic databases PubMed, HINARI and Google Scholar using the following terms: "malaria", "Congo", "Brazzaville", "prevalence", "antimalarial", "efficacy", "falciparum", "genetic", "diversity". Original articles and reviews were included and selection of relevant papers was made.

RESULTS

Twenty-eight published articles were included in this review and two additional records from the National Malaria Control Programme were also considered. The majority of studies were conducted in Brazzaville and Pointe-Noire.

CONCLUSION

The present systematic review reveals that number of studies have been conducted in the RoC with regard to malaria. However, their results cannot formally be generalized at the country level. This suggests a need for implementing regular multisite investigations and surveys that may be representative of the country, calling for the support and lead of the Ministry of Health.

Non-human primate malaria parasites: out of the forest and into the laboratory

The study of malaria in the laboratory relies on either thein vitroculture of human parasites, or the use of non-human malaria parasites in laboratory animals. In this review, we address the use of non-human primate malaria parasite species (NHPMPs) in laboratory research. We describe the features of the most commonly used NHPMPs, review their contribution to our understanding of malaria to date, and discuss their potential contribution to future studies.

Key Knowledge Gaps for Plasmodium vivax Control and Elimination

There is inadequate understanding of the biology, pathology, transmission, and control of Plasmodium vivax, the geographically most widespread cause of human malaria. During the last decades, study of this species was neglected, in part due to the erroneous belief that it is intrinsically benign. In addition, many technical challenges in culturing the parasite also hampered understanding its fundamental biology and molecular and cellular responses to chemotherapeutics. Research on vivax malaria needs to be substantially expanded over the next decade to accelerate its elimination and eradication. This article summarizes key knowledge gaps identified by researchers, national malaria control programs, and other stakeholders assembled by the World Health Organization to develop strategies for controlling and eliminating vivax malaria. The priorities presented in this article emerged in these technical discussions, and were adopted by expert consensus of the authors. All involved understood the priority placed upon pragmatism in this research agenda, that is, focus upon tools delivering better prevention, diagnosis, treatment, and surveillance of P. vivax.

Widespread distribution of Plasmodium vivax malaria in Mauritania on the interface of the Maghreb and West Africa

BACKGROUND

Plasmodium vivax is very rarely seen in West Africa, although specific detection methods are not widely applied in the region, and it is now considered to be absent from North Africa. However, this parasite species has recently been reported to account for most malaria cases in Nouakchott, the capital of Mauritania, which is a large country at the interface of sub-Saharan West Africa and the Maghreb region in northwest Africa.

METHODS

To determine the distribution of malaria parasite species throughout Mauritania, malaria cases were sampled in 2012 and 2013 from health facilities in 12 different areas. These sampling sites were located in eight major administrative regions of the country, within different parts of the Sahara and Sahel zones. Blood spots from finger-prick samples of malaria cases were processed to identify parasite DNA by species-specific PCR.

RESULTS

Out of 472 malaria cases examined, 163 (34.5 %) had P. vivax alone, 296 (62.7 %) Plasmodium falciparum alone, and 13 (2.8 %) had mixed P. falciparum and P. vivax infection. All cases were negative for Plasmodium malariae and Plasmodium ovale. The parasite species distribution showed a broad spectrum, P. vivax being detected at six of the different sites, in five of the country's major administrative regions (Tiris Zemmour, Tagant, Brakna, Assaba, and the capital Nouakchott). Most cases in Nouakchott were due to P. vivax, although proportions vary significantly among different health facilities in the city. In the northern town of Zouérat, all cases were due to P. vivax, whereas almost all cases in the south of the country were due to P. falciparum. All P. vivax cases tested were Duffy blood group positive.

CONCLUSIONS

It is important that P. vivax is recognized to be a widespread cause of malaria in Mauritania, occurring in diverse regions. This should be noted by the World Health Organization, as it has significant implications for diagnosis, treatment and control of malaria in the northwestern part of Africa.

The role of folate in malaria - implications for home fortification programmes among children aged 6-59 months

Folic acid and iron supplementation has historically been recommended as the preferred anaemia control strategy among preschoolers in sub-Saharan Africa and other resource-poor settings, but home fortification of complementary foods with multiple micronutrient powders (MNPs) can now be considered the preferred approach. The World Health Organization endorses home fortification with MNPs containing at least iron, vitamin A and zinc to control childhood anaemia, and calls for concomitant malaria control strategies in malaria endemic regions. Among other micronutrients, current MNP formulations generally include 88 μg folic acid (corresponding to 100% of the Recommended Nutrient Intake). The risks and benefits of providing supplemental folic acid at these levels are unclear. The limited data available indicate that folate deficiency may not be a major public health problem among children living in sub-Saharan Africa and supplemental folic acid may therefore not have any benefits. Furthermore, supraphysiological, and possibly even physiological, folic acid dosages may favour Plasmodium falciparum growth, inhibit parasite clearance of sulphadoxine-pyrimethamine (SP)-treated malaria and increase subsequent recrudescence. Even though programmatic options to limit prophylactic SP use or to promote the use of insecticide treated bed nets may render the use of folic acid safer, programmatic barriers to these approaches are likely to persist. Research is needed to characterise the prevalence of folate deficiency among young children worldwide and to design safe MNP and other types of fortification approaches in sub-Sahara Africa. In parallel, updated global guidance is needed for MNP programmes in these regions.

RC, Battle KE, Longbottom J, Mappin B, Ordanovich D, Tatem AJ, Drakeley C, Gething PW, Zimmerman PA, Smith DL, Hay SI. Plasmodium vivax Transmission in Africa

Malaria in sub-Saharan Africa has historically been almost exclusively attributed to Plasmodium falciparum (Pf). Current diagnostic and surveillance systems in much of sub-Saharan Africa are not designed to identify or report non-Pf human malaria infections accurately, resulting in a dearth of routine epidemiological data about their significance. The high prevalence of Duffy negativity provided a rationale for excluding the possibility of Plasmodium vivax (Pv) transmission. However, review of varied evidence sources including traveller infections, community prevalence surveys, local clinical case reports, entomological and serological studies contradicts this viewpoint. Here, these data reports are weighted in a unified framework to reflect the strength of evidence of indigenous Pv transmission in terms of diagnostic specificity, size of individual reports and corroboration between evidence sources. Direct evidence was reported from 21 of the 47 malaria-endemic countries studied, while 42 countries were attributed with infections of visiting travellers. Overall, moderate to conclusive evidence of transmission was available from 18 countries, distributed across all parts of the continent. Approximately 86.6 million Duffy positive hosts were at risk of infection in Africa in 2015. Analysis of the mechanisms sustaining Pv transmission across this continent of low frequency of susceptible hosts found that reports of Pv prevalence were consistent with transmission being potentially limited to Duffy positive populations. Finally, reports of apparent Duffy-independent transmission are discussed. While Pv is evidently not a major malaria parasite across most of sub-Saharan Africa, the evidence presented here highlights its widespread low-level endemicity. An increased awareness of Pv as a potential malaria parasite, coupled with policy shifts towards species-specific diagnostics and reporting, will allow a robust assessment of the public health significance of Pv, as well as the other neglected non-Pf parasites, which are currently invisible to most public health authorities in Africa, but which can cause severe clinical illness and require specific control interventions.

The influence of host genetics on erythrocytes and malaria infection: is there therapeutic potential?

As parasites, Plasmodium species depend upon their host for survival. During the blood stage of their life-cycle parasites invade and reside within erythrocytes, commandeering host proteins and resources towards their own ends, and dramatically transforming the host cell. Parasites aptly avoid immune detection by minimizing the exposure of parasite proteins and removing themselves from circulation through cytoadherence. Erythrocytic disorders brought on by host genetic mutations can interfere with one or more of these processes, thereby providing a measure of protection against malaria to the host. This review summarizes recent findings regarding the mechanistic aspects of this protection, as mediated through the parasites interaction with abnormal erythrocytes. These novel findings include the reliance of the parasite on the host enzyme ferrochelatase, and the discovery of basigin and CD55 as obligate erythrocyte receptors for parasite invasion. The elucidation of these naturally occurring malaria resistance mechanisms is increasing the understanding of the host-parasite interaction, and as discussed below, is providing new insights into the development of therapies to prevent this disease.

Assessment of antibody responses in local and immigrant residents of areas with autochthonous malaria transmission in Greece

Greece has been officially malaria free since 1974. However, from 2009 to 2012, several locally acquired, cases of Plasmodium vivax malaria were detected, in immigrants and in Greek citizens. In this study, the antibody (Ab) response of Greeks and immigrants with documented malaria was initially assessed, followed by an Ab screening of Greeks and immigrant residents of local transmission areas. Of the 38 patients tested, 10.5% of Greeks and 15.7% of immigrants were positive 5-7 months after infection. Of the 1,019 individuals from various areas of Greece, including those of autochthonous transmission, 85 of the 721 (11.8%) immigrants were positive, whereas all 298 Greeks were negative. The rapid Ab titer decline observed is reasonable, given the non-endemic epidemiological setting. The seroepidemiological findings indicate that the local Greek population remains malaria naive and that at this point Greeks are unlikely to serve as reservoir for the infection of local mosquitoes.

Evaluation of the diagnostic accuracy of CareStart G6PD deficiency Rapid Diagnostic Test (RDT) in a malaria endemic area in Ghana, Africa

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most widespread enzyme defect that can result in red cell breakdown under oxidative stress when exposed to certain medicines including antimalarials. We evaluated the diagnostic accuracy of CareStart G6PD deficiency Rapid Diagnostic Test (RDT) as a point-of-care tool for screening G6PD deficiency.

METHODS

A cross-sectional study was conducted among 206 randomly selected and consented participants from a group with known G6PD deficiency status between February 2013 and June 2013. A maximum of 1.6ml of capillary blood samples were used for G6PD deficiency screening using CareStart G6PD RDT and Trinity qualitative with Trinity quantitative methods as the "gold standard". Samples were also screened for the presence of malaria parasites. Data entry and analysis were done using Microsoft Access 2010 and Stata Software version 12. Kintampo Health Research Centre Institutional Ethics Committee granted ethical approval.

RESULTS

The sensitivity (SE) and specificity (SP) of CareStart G6PD deficiency RDT was 100% and 72.1% compared to Trinity quantitative method respectively and was 98.9% and 96.2% compared to Trinity qualitative method. Malaria infection status had no significant (P=0.199) change on the performance of the G6PD RDT test kit compared to the "gold standard".

CONCLUSIONS

The outcome of this study suggests that the diagnostic performance of the CareStart G6PD deficiency RDT kit was high and it is acceptable at determining the G6PD deficiency status in a high malaria endemic area in Ghana. The RDT kit presents as an attractive tool for point-of-care G6PD deficiency for rapid testing in areas with high temperatures and less expertise. The CareStart G6PD deficiency RDT kit could be used to screen malaria patients before administration of the fixed dose primaquine with artemisinin-based combination therapy.

Does malaria epidemiology project Cameroon as 'Africa in miniature'?

Cameroon, a west-central African country with a ~ 20 million population, is commonly regarded as 'Africa in miniature' due to the extensive biological and cultural diversities of whole Africa being present in a single-country setting. This country is inhabited by ancestral human lineages in unique eco-climatic conditions and diverse topography. Over 90 percent Cameroonians are at risk of malaria infection, and ~ 41 percent have at least one episode of malaria each year. Historically, the rate of malaria infection in Cameroon has fluctuated over the years; the number of cases was about 2 million in 2010 and 2011. The Cameroonian malaria control programme faces an uphill task due to high prevalence of multidrug-resistant parasites and insecticide-resistant malaria vectors. Above all, continued human migration from the rural to urban areas as well as population exchange with adjoining countries, high rate of ecological instabilities caused by deforestation, poor housing, lack of proper sanitation and drainage system might have resulted in the recent increase in incidences of malaria and other vector-borne diseases in Cameroon. The available data on eco-environmental variability and intricate malaria epidemiology in Cameroon reflect the situation in the whole of Africa, and warrant the need for in-depth study by using modern surveillance tools for meaningful basic understanding of the malaria triangle (host-parasite-vector-environment).

The Plasmodium vivax in China: decreased in local cases but increased imported cases from Southeast Asia and Africa

Currently the local P. vivax was sharply decreased while the imported vivax malaria increased in China. Despite Southeast Asia was still the main import source of vivax malaria, the trend of Africa become serious, especially for west and central Africa. Herein we have clarified the trend of P. vivax in China from 2004–2012, and made some analysis for the differences of imported vivax back from different regions. There are significantly different of P. vivax between Southeast Asia and Africa, also the difference was observed for different regions in Africa. Additionally, we have explored the possibility for the difference of the P. vivax between migrant workers back from west and central Africa and the prevalence of local population. This reminds us that surveillance and training should be strengthened by medical staffs on the imported P. vivax cases reported especially from west and central Africa, in order to reduce the risk of malaria reintroduction and, specific tools should be developed, as well as the epidemiological study to avoid the misdiagnosis such as P. ovale and P. vivax.

Genetics of Sub-Saharan African Human Population: Implications for HIV/AIDS, Tuberculosis, and Malaria

Sub-Saharan Africa has continued leading in prevalence and incidence of major infectious disease killers such as HIV/AIDS, tuberculosis, and malaria. Epidemiological triad of infectious diseases includes susceptible host, pathogen, and environment. It is imperative that all aspects of vertices of the infectious disease triad are analysed to better understand why this is so. Studies done to address this intriguing reality though have mainly addressed pathogen and environmental components of the triad. Africa is the most genetically diverse region of the world as well as being the origin of modern humans. Malaria is relatively an ancient infection in this region as compared to TB and HIV/AIDS; from the evolutionary perspective, we would draw lessons that this ancestrally unique population now under three important infectious diseases both ancient and exotic will be skewed into increased genetic diversity; moreover, other evolutionary forces are also still at play. Host genetic diversity resulting from many years of malaria infection has been well documented in this population; we are yet to account for genetic diversity from the trio of these infections. Effect of host genetics on treatment outcome has been documented. Host genetics of sub-Saharan African population and its implication to infectious diseases are an important aspect that this review seeks to address.

Molecular evidence of Plasmodium vivax mono and mixed malaria parasite infections in Duffy-negative native Cameroonians

The malaria parasite Plasmodium vivax is known to be majorly endemic to Asian and Latin American countries with no or very few reports of Africans infected with this parasite. Since the human Duffy antigens act as receptors for P. vivax to invade human RBCs and Africans are generally Duffy-negative, non-endemicity of P. vivax in Africa has been attributed to this fact. However, recent reports describing P. vivax infections in Duffy-negative Africans from West and Central parts of Africa have been surfaced including a recent report on P. vivax infection in native Cameroonians. In order to know if Cameroonians living in the southern regions are also susceptible to P. vivax infection, we collected finger-prick blood samples from 485 malarial symptomatic patients in five locations and followed PCR diagnostic assays with DNA sequencing of the 18S ribosomal RNA gene. Out of the 201 malaria positive cases detected, 193 were pure P. falciparum, six pure P. vivax and two mixed parasite infections (P. falciparum + P. vivax). The eight P. vivax infected samples (six single + two mixed) were further subjected to DNA sequencing of the P. vivax multidrug resistance 1 (pvmdr1) and the P.vivax circumsporozoite (pvcsp) genes. Alignment of the eight Cameroonian pvmdr1 sequences with the reference sequence showed high sequence similarities, reconfirming P. vivax infection in all the eight patients. DNA sequencing of the pvcsp gene indicated all the eight P. vivax to be of VK247 type. Interestingly, DNA sequencing of a part of the human Duffy gene covering the promoter region in the eight P. vivax-infected Cameroonians to identify the T-33C mutation revealed all these patients as Duffy-negative. The results provide evidence of single P. vivax as well as mixed malaria parasite infection in native Cameroonians and add knowledge to the growing evidences of P. vivax infection in Duffy-negative Africans.

Molecular typing reveals substantial Plasmodium vivax infection in asymptomatic adults in a rural area of Cameroon

BACKGROUND

Malaria in Cameroon is due to infections by Plasmodium falciparum and, to a lesser extent, Plasmodium malariae and Plasmodium ovale, but rarely Plasmodium vivax. A recent report suggested "Plasmodium vivax-like" infections around the study area that remained unconfirmed. Therefore, molecular and antigenic typing was used to investigate the prevalence of P. vivax and Duffy in asymptomatic adults resident in Bolifamba.

METHODS

A cross-sectional study was conducted from July 2008 to October 2009. The status of all parasite species was determined by nested PCR in 269 blood samples collected. The P. falciparum and P. vivax anti-MSP/CSP antibody status of each subject was also determined qualitatively by a rapid card assay. Parasite DNA was extracted from a sample infected with three parasite species, purified and sequenced. The Duffy antigen status of 12 subjects infected with P. vivax was also determined by sequencing. In silico web-based tools were used to analyse sequence data for similarities and matches to reference sequences in public DNA databases.

RESULTS

The overall malaria parasite prevalence in 269 individuals was 32.3% (87) as determined by PCR. Remarkably, 14.9% (13/87) of infections were caused either exclusively or concomitantly by P. vivax, established both by PCR and microscopic examination of blood smears, in individuals both positive (50%, 6/12) and negative (50%, 6/12) for the Duffy receptor. A triple infection by P. falciparum, P. vivax and P. malariae, was detected in one infected individual. Anti-MSP/CSP antibodies were detected in 72.1% (194/269) of samples, indicating high and continuous exposure to infection through mosquito bites.

DISCUSSION

These data provide the first molecular evidence of P. vivax in Duffy positive and negative Cameroonians and suggest that there may be a significant prevalence of P. vivax infection than expected in the study area. Whether the P. vivax cases were imported or due to expansion of a founder effect was not investigated. Notwithstanding, the presence of P. vivax may complicate control efforts if these parasites become hypnozoitic or latent as the liver stage.

CONCLUSIONS

These data strongly suggest that P. vivax is endemic to the south-west region of Cameroon and should be taken into account when designing malaria control strategies.

External quality assessment of reading and interpretation of malaria rapid diagnostic tests among 1849 end-users in the Democratic Republic of the Congo through Short Message Service (SMS)

Background

Although malaria rapid diagnostic tests (RDT) are simple to perform, they remain subject to errors, mainly related to the post-analytical phase. We organized the first large scale SMS based external quality assessment (EQA) on correct reading and interpretation of photographs of a three-band malaria RDT among laboratory health workers in the Democratic Republic of the Congo (DR Congo).

Methods and Findings

High resolution EQA photographs of 10 RDT results together with a questionnaire were distributed to health facilities in 9 out of 11 provinces in DR Congo. Each laboratory health worker answered the EQA by Short Message Service (SMS). Filled-in questionnaires from each health facility were sent back to Kinshasa. A total of 1849 laboratory health workers in 1014 health facilities participated. Most frequent errors in RDT reading were i) failure to recognize invalid (13.2–32.5% ) or negative test results (9.8–12.8%), (ii) overlooking faint test lines (4.1–31.2%) and (iii) incorrect identification of the malaria species (12.1–17.4%). No uniform strategy for diagnosis of malaria at the health facility was present. Stock outs of RDTs occurred frequently. Half of the health facilities had not received an RDT training. Only two thirds used the RDT recommended by the National Malaria Control Program. Performance of RDT reading was positively associated with training and the technical level of health facility. Facilities with RDT positivity rates >50% and located in Eastern DR Congo performed worse.

Conclusions

Our study confirmed that errors in reading and interpretation of malaria RDTs are widespread and highlighted the problem of stock outs of RDTs. Adequate training of end-users in the application of malaria RDTs associated with regular EQAs is recommended.

Travellers as sentinels: Assaying the worldwide distribution of polymorphisms associated with artemisinin combination therapy resistance in Plasmodium falciparum using malaria cases imported into Scotland

There is growing evidence that Plasmodium falciparum parasites in southeastern Asia have developed resistance to artemisinin combination therapy. The resistance phenotype has recently been shown to be associated with four single nucleotide polymorphisms in the parasite's genome. We assessed the prevalence of two of these single nucleotide polymorphisms in P. falciparum parasites imported into Scotland between 2009 and 2012, and in additional field samples from six countries in southeastern Asia. We analysed 28 samples from 11 African countries, and 25 samples from nine countries in Asia/southeastern Asia/Oceania. Single nucleotide polymorphisms associated with artemisinin combination therapy resistance were not observed outside Thailand and Cambodia.

Diversity, host switching and evolution of Plasmodium vivax infecting African great apes

Plasmodium vivax is considered to be absent from Central and West Africa because of the protective effect of Duffy negativity. However, there are reports of persons returning from these areas infected with this parasite and observations suggesting the existence of transmission. Among the possible explanations for this apparent paradox, the existence of a zoonotic reservoir has been proposed. May great apes be this reservoir? We analyze the mitochondrial and nuclear genetic diversity of P. vivax parasites isolated from great apes in Africa and compare it to parasites isolated from travelers returning from these regions of Africa, as well as to human isolates distributed all over the world. We show that the P. vivax sequences from parasites of great apes form a clade genetically distinct from the parasites circulating in humans. We show that this clade's parasites can be infectious to humans by describing the case of a traveler returning from the Central African Republic infected with one of them. The relationship between this P. vivax clade in great apes and the human isolates is discussed.

Misclassification of Plasmodium infections by conventional microscopy and the impact of remedial training on the proficiency of laboratory technicians in species identification

BACKGROUND

Malaria diagnosis is largely dependent on the demonstration of parasites in stained blood films by conventional microscopy. Accurate identification of the infecting Plasmodium species relies on detailed examination of parasite morphological characteristics, such as size, shape, pigment granules, besides the size and shape of the parasitized red blood cells and presence of cell inclusions. This work explores misclassifications of four Plasmodium species by conventional microscopy relative to the proficiency of microscopists and morphological characteristics of the parasites on Giemsa-stained blood films.

CASE DESCRIPTION

Ten-day malaria microscopy remedial courses on parasite detection, species identification and parasite counting were conducted for public health and research laboratory personnel. Proficiency in species identification was assessed at the start (pre) and the end (post) of each course using known blood films of Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale and Plasmodium vivax infections with densities ranging from 1,000 to 30,000 parasites/μL. Outcomes were categorized as false negative, positive without speciation, P. falciparum, P. malariae, P. ovale, P. vivax and mixed infections.

DISCUSSION AND EVALUATION

Reported findings are based on 1,878 P. falciparum, 483 P. malariae, 581 P. ovale and 438 P. vivax cumulative results collated from 2008 to 2010 remedial courses. Pre-training false negative and positive misclassifications without speciation were significantly lower on P. falciparum infections compared to non-falciparum infections (p < 0.0001). Post-training misclassifications decreased significantly compared to pre- training misclassifications which in turn led to significant improvements in the identification of the four species. However, P. falciparum infections were highly misclassified as mixed infections, P. ovale misclassified as P. vivax and P. vivax similarly misclassified as P. ovale (p < 0.05).

CONCLUSION

These findings suggest that the misclassification of malaria species could be a common occurrence especially where non-falciparum infections are involved due to lack of requisite skills in microscopic diagnosis and variations in morphological characteristics within and between Plasmodium species. Remedial training might improve reliability of conventional light microscopy with respect to differentiation of Plasmodium infections.

High frequency of the erythroid silent Duffy antigen genotype and lack of Plasmodium vivax infections in Haiti

BACKGROUND

Malaria is a significant public health concern in Haiti where approximately 30,000 cases are reported annually with CDC estimates as high as 200,000. Malaria infections in Haiti are caused almost exclusively by Plasmodium falciparum, while a small number of Plasmodium malariae and an even smaller number of putative Plasmodium vivax infections have been reported. The lack of confirmed P. vivax infections in Haiti could be due to the genetic background of native Haitians. Having descended from West African populations, many Haitians could be Duffy negative due to a single nucleotide polymorphism from thymine to cytosine in the GATA box of the promoter region of the Duffy antigen receptor for chemokines (DARC) gene. This mutation, encoded by the FYES allele, eliminates the expression of the Duffy antigen on erythrocytes, which reduces invasion by P. vivax. This study investigated the frequency of the FYES allele and P. vivax infections in malaria patients with the goal of uncovering factors for the lack of P. vivax infections reported in Haiti.

METHODS

DNA was extracted from dried blood spots collected from malaria patients at four clinic locations in Haiti. The samples were analysed by polymerase chain reaction (PCR) for the presence of the P. vivax small subunit ribosomal RNA gene. PCR, sequencing, and restriction enzyme digestion were used to detect the presence of the FYES allele. Matched samples were examined for both presence of P. vivax and the FYES allele.

RESULTS

No cases of P. vivax were detected in any of the samples (0/136). Of all samples tested for the FYES allele, 99.4% had the FYES allele (163/164). Of the matched samples, 99% had the FYES allele (98/99).

CONCLUSIONS

In this preliminary study, no cases of P. vivax were confirmed by PCR and 99% of the malaria patients tested carried the FYES allele. The high frequency of the FYES allele that silences erythroid expression of the Duffy antigen offers a biologically plausible explanation for the lack of P. vivax infections observed. These results provide insights on the host susceptibility for P. vivax infections that has never before been investigated in Haiti.

Red blood cell polymorphism and susceptibility to Plasmodium vivax

Resistance to Plasmodium vivax blood-stage infection has been widely recognised to result from absence of the Duffy (Fy) blood group from the surface of red blood cells (RBCs) in individuals of African descent. Interestingly, recent studies from different malaria-endemic regions have begun to reveal new perspectives on the association between Duffy gene polymorphism and P. vivax malaria. In Papua New Guinea and the Americas, heterozygous carriers of a Duffy-negative allele are less susceptible to P. vivax infection than Duffy-positive homozygotes. In Brazil, studies show that the Fy(a) antigen, compared to Fy(b), is associated with lower binding to the P. vivax Duffy-binding protein and reduced susceptibility to vivax malaria. Additionally, it is interesting that numerous studies have now shown that P. vivax can infect RBCs and cause clinical disease in Duffy-negative people. This suggests that the relationship between P. vivax and the Duffy antigen is more complex than customarily described. Evidence of P. vivax Duffy-independent red cell invasion indicates that the parasite must be evolving alternative red cell invasion pathways. In this chapter, we review the evidence for P. vivax Duffy-dependent and Duffy-independent red cell invasion. We also consider the influence of further host gene polymorphism associated with malaria endemicity on susceptibility to vivax malaria. The interaction between the parasite and the RBC has significant potential to influence the effectiveness of P. vivax-specific vaccines and drug treatments. Ultimately, the relationships between red cell polymorphisms and P. vivax blood-stage infection will influence our estimates on the population at risk and efforts to eliminate vivax malaria.

Epidemiology of malaria in endemic areas

Malaria infection is still to be considered a major public health problem in those 106 countries where the risk of contracting the infection with one or more of the Plasmodium species exists. According to estimates from the World Health Organization, over 200 million cases and about 655.000 deaths have occurred in 2010. Estimating the real health and social burden of the disease is a difficult task, because many of the malaria endemic countries have limited diagnostic resources, especially in rural settings where conditions with similar clinical picture may coexist in the same geographical areas. Moreover, asymptomatic parasitaemia may occur in high transmission areas after childhood, when anti-malaria semi-immunity occurs. Malaria endemicity and control activities are very complex issues, that are influenced by factors related to the host, to the parasite, to the vector, to the environment and to the health system capacity to fully implement available anti-malaria weapons such as rapid diagnostic tests, artemisinin-based combination treatment, impregnated bed-nets and insecticide residual spraying while waiting for an effective vaccine to be made available.

African Plasmodium vivax: distribution and origins

There is increasing evidence that the malaria parasite, Plasmodium vivax, is endemic in west and central Africa, a region from which it was previously thought to be almost completely absent due to the very high prevalence of the Duffy negative phenotype in the local human populations. Furthermore, P. vivax, or very closely related parasites, has been identified in both chimpanzees and gorillas from this region. In this review, we discuss the implications of these findings for the current understanding of the origins of P. vivax as a human parasite. With the support of new evidence from mitochondrial genome sequencing, we propose that the evidence is consistent with current, extant P. vivax populations having their origins in Africa.

Modeling Plasmodium vivax: relapses, treatment, seasonality, and G6PD deficiency

Plasmodium vivax (P. vivax) is one of the most important human malaria species that is geographically widely endemic and causes social and economic burden globally. However, its consequences have long been neglected and underestimated as it has been mistakenly considered a benign and inconsequential malaria species as compared to Plasmodium falciparum. One of the important differences between P. falciparum and P. vivax is the formation of P. vivax latent-stage parasites (hypnozoites) that can cause relapses after a course of treatment. In this work, mathematical modeling is employed to investigate how patterns of incubation periods and relapses of P. vivax, variation in treatment, and seasonal abundance of mosquitoes influence the number of humans infected with P. vivax and the mean age at infection of humans in tropical and temperate regions. The model predicts that: (i) the number of humans infected with P. vivax may increase when an incubation period of parasites in humans and a latent period of hypnozoites decrease; (ii) without primaquine, the only licensed drug to prevent relapses, P. vivax may be highly prevalent; (iii) the mean age at infection of humans may increase when a latent period of hypnozoites increases; (iv) the number of infectious humans may peak at a few months before the middle of each dry season and the number of hypnozoite carriers may peak at nearly the middle of each dry season. In addition, glucose-6-phosphate-dehydrogenase (G6PD) deficiency, which is the most common enzyme defect in humans that may provide some protection against P. vivax infection and severity, is taken into account to study its impact on the number of humans infected with P. vivax. Modeling results indicate that the increased number of infected humans may result from a combination of a larger proportion of humans with G6PD deficiency in the population, a lesser protection of G6PD deficiency to P. vivax infection, and a shorter latent period of hypnozoites.

Various pfcrt and pfmdr1 genotypes of Plasmodium falciparum cocirculate with P. malariae, P. ovale spp., and P. vivax in northern Angola

Artemisinin-based combination therapy for malaria has become widely available across Africa. Populations of Plasmodium falciparum that were previously dominated by chloroquine (CQ)-resistant genotypes are now under different drug selection pressures. P. malariae, P. ovale curtisi, and P. ovale wallikeri are sympatric with P. falciparum across the continent and are frequently present as coinfections. The prevalence of human Plasmodium species was determined by PCR using DNA from blood spots collected during a cross-sectional survey in northern Angola. P. falciparum was genotyped at resistance-associated loci in pfcrt and pfmdr1 by real-time PCR or by direct sequencing of amplicons. Of the 3,316 samples collected, 541 (16.3%) contained Plasmodium species infections; 477 (88.2%) of these were P. falciparum alone, 6.5% were P. falciparum and P. malariae together, and 1.1% were P. vivax alone. The majority of the remainder (3.7%) harbored P. ovale curtisi or P. ovale wallikeri alone or in combination with other species. Of 430 P. falciparum isolates genotyped for pfcrt, 61.6% carried the wild-type allele CVMNK at codons 72 to 76, either alone or in combination with the resistant allele CVIET. No other pfcrt allele was found. Wild-type alleles dominated at codons 86, 184, 1034, 1042, and 1246 of the pfmdr1 locus among the sequenced isolates. In contrast to previous studies, P. falciparum in the study area comprises an approximately equal mix of genotypes associated with CQ sensitivity and with CQ resistance, suggesting either lower drug pressure due to poor access to treatment in rural areas or a rapid impact of the policy change away from the use of standard monotherapies.

Effect of seasonality and ecological factors on the prevalence of the four malaria parasite species in northern mali

Background. We performed 2 cross-sectional studies in Ménaka in the Northeastern Mali across 9 sites in different ecological settings: 4 sites have permanent ponds, 4 without ponds, and one (City of Ménaka) has a semipermanent pond. We enrolled 1328 subjects in May 2004 (hot dry season) and 1422 in February 2005 (cold dry season) after the rainy season. Objective. To examine the seasonality of malaria parasite prevalence in this dry northern part of Mali at the edge of the Sahara desert. Results. Slide prevalence was lower in hot dry than cold dry season (4.94 versus 6.85%, P = 0.025). Gametocyte rate increased to 0.91% in February. Four species were identified. Plasmodium falciparum was most prevalent (74.13 and 63.72%). P. malariae increased from 9.38% to 22.54% in February. In contrast, prevalence of P. vivax was higher (10.31%) without seasonal variation. Smear positivity was associated with splenomegaly (P = 0.007). Malaria remained stable in the villages with ponds (P = 0.221); in contrast, prevalence varied between the 2 seasons in the villages without ponds (P = 0.004). Conclusion. Malaria was mesoendemic; 4 species circulates with a seasonal fluctuation for Plasmodium falciparum.

The origins of African Plasmodium vivax; insights from mitochondrial genome sequencing

Plasmodium vivax, the second most prevalent of the human malaria parasites, is estimated to affect 75 million people annually. It is very rare, however, in west and central Africa, due to the high prevalence of the Duffy negative phenotype in the human population. Due to its rarity in Africa, previous studies on the phylogeny of world-wide P. vivax have suffered from insufficient samples of African parasites. Here we compare the mitochondrial sequence diversity of parasites from Africa with those from other areas of the world, in order to investigate the origin of present-day African P. vivax. Mitochondrial genome sequencing revealed relatively little polymorphism within the African population compared to parasites from the rest of the world. This, combined with sequence similarity with parasites from India, suggests that the present day African P. vivax population in humans may have been introduced relatively recently from the Indian subcontinent. Haplotype network analysis also raises the possibility that parasites currently found in Africa and South America may be the closest extant relatives of the ancestors of the current world population. Lines of evidence are adduced that this ancestral population may be from an ancient stock of P. vivax in Africa.

Imported malaria in Scotland--an overview of surveillance, reporting and trends

BACKGROUND

Imported malaria cases continue to occur and are often underreported. This study assessed reporting of malaria cases and their characteristics in Scotland.

METHODS

Cases were identified at the study sites of Aberdeen, Edinburgh, Glasgow and Inverness. The number of cases identified in the period 2003-2008 was compared to surveillance databases from Health Protection Scotland (HPS) and the Malaria Reference Laboratory (MRL). Case characteristics were recorded and analysed.

RESULTS

Of 252 cases of malaria diagnosed and treated, an estimated 235 (93.3%) were reported to the MRL. Between 2006 and 2008, 114 of 126 cases (90.5%) were reported to HPS. Plasmodium falciparum caused 173 cases (68.7%). Business and professional travel accounted for 35.3% of cases (higher in Aberdeen), followed by visiting friends and relatives (33.1%) and holiday makers (25.5%). The majority of infections were imported from West Africa and 65.7% of patients for whom data on prophylaxis was available had taken no or inappropriate prophylaxis.

CONCLUSIONS

Reporting of malaria in Scotland can be improved. There is a continued need to optimise preventive measures and adherence to chemoprophylaxis amongst business travellers, those visiting friends and relatives, and holiday makers in endemic countries in order to reduce imported malaria cases.