Low sensitivity of nested PCR using Plasmodium DNA extracted from stained thick blood smears: an epidemiological retrospective study among subjects with low parasitaemia in an endemic area of the Brazilian Amazon region

Identification and serological responses to a novel Plasmodium vivax merozoite surface protein 1 (PvMSP-1) derived synthetic peptide: a putative biomarker for malaria exposure

Background

The integration of diagnostic methods holds promise for advancing the surveillance of malaria transmission in both endemic and non-endemic regions. Serological assays emerge as valuable tools to identify and delimit malaria transmission, serving as a complementary method to rapid diagnostic tests (RDT) and thick smear microscopy. Here, we evaluate the potential of antibodies directed against peptides encompassing the entire amino acid sequence of the PvMSP-1 Sal-I strain as viable serological biomarkers for P. vivax exposure.

Methods

We screened peptides encompassing the complete amino acid sequence of the Plasmodium vivax Merozoite Surface Protein 1 (PvMSP-1) Sal-I strain as potential biomarkers for P. vivax exposure. Here, immunodominant peptides specifically recognized by antibodies from individuals infected with P. vivax were identified using the SPOT-synthesis technique followed by immunoblotting. Two 15-mer peptides were selected based on their higher and specific reactivity in immunoblotting assays. Subsequently, peptides p70 and p314 were synthesized in soluble form using SPPS (Solid Phase Peptide Synthesis) and tested by ELISA (IgG, and subclasses).

Results

This study unveils the presence of IgG antibodies against the peptide p314 in most P. vivax-infected individuals from the Brazilian Amazon region. In silico B-cell epitope prediction further supports the utilization of p314 as a potential biomarker for evaluating malaria transmission, strengthened by its amino acid sequence being part of a conserved block of PvMSP-1. Indeed, compared to patients infected with P. falciparum and uninfected individuals never exposed to malaria, P. vivax-infected patients have a notably higher recognition of p314 by IgG1 and IgG3.

Leucocytozoon cariamae n. sp. and Haemoproteus pulcher coinfection in Cariama cristata (Aves: Cariamiformes): first mitochondrial genome analysis and morphological description of a leucocytozoid in Brazil

The distribution of avian haemosporidians of the genus Leucocytozoon in the Neotropics remains poorly understood. Recent studies confirmed their presence in the region using molecular techniques alone, but evidence for gametocytes and data on putative competent hosts for Leucocytozoon are still lacking outside highland areas. We combined morphological and molecular data to characterize a new Leucocytozoon species infecting a non-migratory red-legged seriema (Cariama cristata), the first report of a competent host for Leucocytozoon in Brazil. Leucocytozoon cariamae n. sp. is distinguished from the Leucocytozoon fringillinarum group by its microgametocytes that are not strongly appressed to the host cell nucleus. The bird studied was coinfected with Haemoproteus pulcher, and we present a Bayesian phylogenetic analysis based on nearly complete mitochondrial genomes of these 2 parasites. Leucocytozoon cariamae n. sp. morphology is consistent with our phylogenetic analysis indicating that it does not share a recent common ancestor with the L. fringillinarum group. Haemoproteus pulcher and Haemoproteus catharti form a monophyletic group with Haemocystidium parasites of Reptilia, supporting the polyphyly of the genus Haemoproteus. We also discussed the hypothesis that H. pulcher and H. catharti may be avian Haemocystidium, highlighting the need to study non-passerine parasites to untangle the systematics of Haemosporida.

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?

Limited Polymorphism in Plasmodium falciparum Artemisinin Resistance Kelch13-Propeller Gene Among Clinical Isolates from Bushenyi District, Uganda

INTRODUCTION

Drug resistance remains a major challenge in malaria treatment, especially after the emergence of resistance to artemisinin-based combined therapies. Plasmodium falciparum Kelch13 gene mutations are implicated in conferring artemisinin resistance. Thus, this study was aimed at determining the occurrence of Kelch13 (K13) propeller resistance gene polymorphism mutations in Bushenyi district, Uganda.

METHODS

Participants suspected to have malaria were recruited. P. falciparum was confirmed using antigen histidine-rich protein 2 (HRP2) (Pf) (Access Bio, Inc, USA) and microscopy. Malaria-positive patients were treated with artemeter-lumefantrine (AL). Blood was withdrawn from participants who tested positive for parasites after day 3 and kept in blood filter papers (ET31CHR; Whatman Limited, Kent, UK). DNA was extracted using chelex-suspension method. Nested polymerase chain reaction (PCR) was conducted and the second-round products sequenced using Sanger's method. Sequenced products were analyzed using DNAsp 5.10.01 software and then blasted on to the NCBI for K13-propeller gene sequence identity using the Basic Local Alignment Search Tool (BLAST).

RESULTS

Out of 283 enrolled participants, 194 completed the follow-up schedule. A total of 134 (69%) had no parasites on day 3, while 60 (31%) had parasites on that day. Out of the 60 samples, 40 (62%) were positively amplified as P. falciparum, with polymorphisms in the K13-propeller gene detected in 3 (7.5%) out of the 40 amplicons. Polymorphisms at codon 1929, 1788 and 1801 were detected separately in one sample each. Sequences have been deposited in NCBI with accession numbers PRJNA720348 and PRJNA720800.

CONCLUSION

Polymorphisms in the K13-propeller gene previously reported to be associated with artemisinin resistance were not detected in the P. falciparum isolates from Bushenyi district, Uganda. More studies need to be conducted on the new mutations detected so as to understand their association, if any, with ACT resistance.

Performance evaluation of the highly sensitive histidine-rich protein 2 rapid test for plasmodium falciparum malaria in North-West Tanzania

Background

Precise detection of Plasmodium infections in community surveys is essential for effective malaria control. Microscopy and rapid diagnostic tests (RDTs) are the major techniques used to identify malaria infections in the field-based surveys. Although microscopy is still considered as the gold standard, RDTs are increasingly becoming versatile due to their rapid and adequate performance characteristics.

Methods

A malaria prevalence cross-sectional survey was carried out in north-western Tanzania in 2016, aimed at appraising the performance of high sensitivity Plasmodium falciparum (HSPf) tests compared to SD Bioline Pf and microscopy in detecting P. falciparum infections. A total of 397 individuals aged five years and above were tested for P. falciparum infections. The sensitivity, specificity, positive, and negative predictive values (PPV and NPV) of microscopy, Pf RDT and HSPf RDT was determined using PCR as the gold standard method.

Results

The prevalence of P. falciparum infections determined by microscopy, SD Bioline Pf, HSPf and PCR was 21.9, 27.7, 33.3 and 43.2%, respectively. The new HSPf RDT had significantly higher sensitivity (98.2%) and specificity (91.6%) compared to the routinely used SD Bioline Pf RDT(P < 0.001). The positive predictive value (PPV) was 81.8% and the negative predictive value (NPV) was 99.2% for the routinely used SD Bioline Pf RDT. Moreover, HSPf RDT had sensitivity of 69% and specificity of 76.8% compared to microscopy. The PPV was 45.5% and the NPV was 89.8% for microscopy. Furthermore, the analytical sensitivity test indicated that the newly developed HSPf RDT had lower detection limits compared to routinely used SD Bioline RDT.

Conclusions

HSPf RDT had better performance when compared to both microscopy and the currently used malaria RDTs. The false negativity could be associated with the low parasite density of the samples. False positivity may be related to the limitations of the expertise of microscopists or persistent antigenicity from previous infections in the case of RDTs. Nevertheless, HS PfRDT performed better compared to routinely used Pf RDT, and microscopy in detecting malaria infections. Therefore, HS Pf RDT presents the best alternative to the existing commercial/regularly available RDTs due to its sensitivity and specificity, and reliability in diagnosing malaria infections.

Detecting Plasmodium falciparum in community surveys: a comparison of Paracheck Pf® Test and ICT Malaria Pf® Cassette Test to polymerase chain reaction in Mutasa District, Zimbabwe

BACKGROUND

Microscopy and rapid diagnostic tests (RDTs) are the main techniques used to diagnose malaria. While microscopy is considered the gold standard, RDTs have established popularity as they allow for rapid diagnosis with minimal technical skills. This study aimed to compare the diagnostic performance of two Plasmodium falciparum histidine-rich protein 2 (PfHRP2)-based RDTs (Paracheck Pf® Test (Paracheck) and Malaria Pf™ ICT (ICT)) to polymerase chain reaction (PCR) in a community survey.

METHODS

A cross-sectional study was conducted between October 2012 and December 2014 in Mutasa District, Manicaland Province, eastern Zimbabwe. Households were randomly selected using satellite imagery, and 224 households were visited. Residents present in the household on the date of the visit were recruited for the study. Participants of all age groups from the selected households were screened with Paracheck and ICT RDTs in parallel. Dried blood spots (DBS) and thin and thick smears were collected. Parasite DNA extracted from the DBS was subjected to nested PCR targeting the Plasmodium cytochrome b mitochondrial gene. Data analysis was performed using the Cohen's Kappa test to determine the interrater agreement and the sensitivity and specificity of the diagnostic test were reported.

RESULTS

Results from a total of 702 participants were analysed. Most were females, 397 (57%), and the median age of participants was 21 years with an interquartile range of 9-39 years. Of those who were screened, 8 (1.1%), 35 (5.0%), and 21 (2.9%) were malaria parasite positive by microscopy, RDT and PCR, respectively. Paracheck and ICT RDTs had a 100% agreement. Comparing RDT and PCR results, 34 participants (4.8%) had discordant results. Most of the discordant cases were RDT positive but PCR negative (n = 24). Half of those RDT positive, but PCR negative individuals reported anti-malarials to use in the past month, which is significantly higher than reported anti-malarial drug use in the population (p < 0.001). The participant was febrile on the day of the visit, but relying on PfHRP2-based RDT would miss this case. Among the diagnostic methods evaluated, with reference to PCR, the sensitivity was higher with the RDT (52.4%) while specificity was higher with the microscopy (99.9%). The positive predictive value (PPV) was higher with the microscopy (87.5%), while the negative predictive values were similar for both microscopy and RDTs (98%). Overall, a strong correlated agreement with PCR was observed for the microscopy (97.9%) and the RDTs (95.2%).

CONCLUSIONS

Paracheck and ICT RDTs showed 100% agreement and can be used interchangeably. As malaria transmission declines and Zimbabwe aims to reach malaria elimination, management of infected individuals with low parasitaemia as well as non-P. falciparum infection can be critical.

Genetic diversity of Plasmodium falciparum and genetic profile in children affected by uncomplicated malaria in Cameroon

BACKGROUND

Malaria is a major public health problem in Cameroon. The study of the genetic diversity within parasite population is essential for understanding the mechanism underlying malaria pathology and to determine parasite clones profile in an infection, for proper malaria control strategies. The objective of this study was to perform a molecular characterization of highly polymorphic genetic markers of Plasmodium falciparum, and to determine allelic distribution with their influencing factors valuable to investigate malaria transmission dynamics in Cameroon.

METHODS

A total of 350 P. falciparum clinical isolates were characterized by genotyping block 2 of msp-1, block 3 of msp-2, and region II of glurp gene using nested PCR and DNA sequencing between 2012 and 2013.

RESULTS

A total of 5 different genotypes with fragment sizes ranging from 597 to 817 bp were recorded for GLURP. Overall, 16 MSP-1 genotypes, including K1, MAD20 and RO33 were identified, ranging from 153 to 335 bp. A peculiarity about this study is the RO33 monomorphic pattern revealed among the Pfmsp-1 allelic type. Again, this study identified 27 different Pfmsp-2 genotypes, ranging from 140 to 568 bp in size, including 15 belonging to the 3D7-type and 12 to the FC27 allelic families. The analysis of the MSP-1 and MSP-2 peptides indicates that the region of the alignment corresponding K1 polymorphism had the highest similarity in the MSP1and MSP2 clade followed by MAD20 with 93% to 100% homology. Therefore, population structure of P. falciparum isolates is identical to that of other areas in Africa, suggesting that vaccine developed with K1 and MAD20 of Pfmsp1 allelic variant could be protective for Africa children but these findings requires further genetic and immunological investigations. The multiplicity of infection (MOI) was significantly higher (P < 0.05) for Pfmsp-2 loci (3.82), as compare with Pfmsp-1 (2.51) and heterozygotes ranged from 0.55 for Pfmsp-1 to 0.96 for Pfmsp-2.

CONCLUSION

High genetic diversity and allelic frequencies in P. falciparum isolates indicate a persisting high level of transmission. This study advocate for an intensification of the malaria control strategies in Cameroon. Trial registration This study was approved by Cameroon National Ethics Committee. It is a randomized controlled trial retrospectively registered in NIH U.S. National Library of Medicine, ClinicalTrials.gov on the 28/11/2016 at https://clinicaltrials.gov/ct2/show/NCT02974348 with the registration number NCT02974348.

Effects of IgG and IgM autoantibodies on non-infected erythrocytes is related to ABO blood group in Plasmodium vivax malaria and is associated with anemia

Autoantibodies play an important role in the destruction of non-infected red blood cells (nRBCs) during malaria. However, the relationship between this clearance and ABO blood groups is yet to be fully enlightened, especially for Plasmodium vivax infections. Here we show that anti-RBC IgG and IgM are increased in anemic patients with acute vivax malaria. Furthermore, both antibodies are able to decrease the deformability of nRBCs, but only IgG can induce in vitro erythrophagocytosis. Such effects are enhanced in type O erythrocytes, suggesting that individuals from this blood group infected with P. vivax malaria may be more susceptible to develop anemia.

DNA recovery from archived RDTs for genetic characterization of Plasmodium falciparum in a routine setting in Lambaréné, Gabon

Background

Rapid diagnostic tests (RDTs) have been described as a source of genetic material to analyse malaria parasites in proof-of-concept studies. The increasing use of RDTs (e.g., in focal or mass screening and treatment campaigns) makes this approach particularly attractive for large-scale investigations of parasite populations. In this study, the complexity of Plasmodium falciparum infections, parasite load and chloroquine resistance transporter gene mutations were investigated in DNA samples extracted from positive RDTs, obtained in a routine setting and archived at ambient temperature.

Methods

A total of 669 archived RDTs collected from malaria cases in urban, semi-urban and rural areas of central Gabon were used for P. falciparum DNA extraction. Performance of RDTs as a source of DNA for PCR was determined using: (i) amplification of a single copy merozoite surface protein 1 (msp1) gene followed by highly sensitive and automated capillary electrophoresis; (ii) genotyping of the pfcrt gene locus 72–76 using haplotype-specific-probe-based real-time PCR to characterize chloroquine resistance; and, (iii) real-time PCR targeting 18S genes to detect and quantify Plasmodium parasites.

Results

Out of the 669 archived RDTs, amplification of P. falciparum nucleic materials had a success rate of 97% for 18S real-time PCR, and 88% for the msp1 gene. The multiplicity of infections (MOI) of the whole population was 2.6 (95% CI 2.5–2.8). The highest number of alleles detected in one infection was 11. The MOI decreased with increasing age (β = − 0.0046, p = 0.02) and residence in Lambaréné was associated with smaller MOIs (p < 0.001). The overall prevalence of mutations associated with chloroquine resistance was 78.5% and was not associated with age. In Lambaréné, prevalence of chloroquine resistance was lower compared to rural Moyen-Ogooué (β = − 0.809, p-value = 0.011).

Conclusion

RDT is a reliable source of DNA for P. falciparum detection and genotyping assays. Furthermore, the increasing use of RDTs allows them to be an alternative source of DNA for large-scale genetic epidemiological studies. Parasite populations in the study area are highly diverse and prevalence of chloroquine-resistant P. falciparum remains high, especially in rural areas.

First Report of a Novel Hepatozoon sp. in Giant Pandas (Ailuropoda melanoleuca)

The first report of giant pandas (Ailuropoda melanoleuca) infected with a novel Hepatozoon species is presented. An intraleukocytic parasite was detected via routine blood smear from a zoo-housed giant panda at the National Zoological Park. Ribosomal DNA sequences indicated a previously undescribed Hepatozoon species. Phylogenetic and distance analyses of the sequences placed it within its own branch, clustered with Old World species with carnivore (primarily ursid and mustelid) hosts. Retrospective and opportunistic testing of other individuals produced additional positive detections (17/23, 73.9%), demonstrating 100% prevalence (14/14) across five institutions. All animals were asymptomatic at time of sampling, and health implications for giant pandas remain unknown.

Anti-band 3 and anti-spectrin antibodies are increased in Plasmodium vivax infection and are associated with anemia

Clearance of non-infected red blood cells (nRBCs) is one of the main components of anemia associated with Plasmodium vivax malaria. Recently, we have shown that anemic patients with P. vivax infection had elevated levels of anti-RBCs antibodies, which could enhance in vitro phagocytosis of nRBCs and decrease their deformability. Using immunoproteomics, here we characterized erythrocytic antigens that are differentially recognized by autoantibodies from anemic and non-anemic patients with acute vivax malaria. Protein spots exclusively recognized by anemic P. vivax-infected patients were identified by mass spectrometry revealing band 3 and spectrin as the main targets. To confirm this finding, antibody responses against these specific proteins were assessed by ELISA. In addition, an inverse association between hemoglobin and anti-band 3 or anti-spectrin antibodies levels was found. Anemic patients had higher levels of IgG against both band 3 and spectrin than the non-anemic ones. To determine if these autoantibodies were elicited because of molecular mimicry, we used in silico analysis and identified P. vivax proteins that share homology with human RBC proteins such as spectrin, suggesting that infection drives autoimmune responses. These findings suggest that band 3 and spectrin are potential targets of autoantibodies that may be relevant for P. vivax malaria-associated anemia.

Detection of Plasmodium Species by High-Resolution Melt Analysis of DNA from Blood Smears Acquired in Southwestern Uganda

Microscopic diagnosis of malaria using Giemsa-stained blood smears is the standard of care in resource-limited settings. These smears represent a potential source of DNA for PCR testing to confirm Plasmodium infections or for epidemiological studies of archived samples. Therefore, we assessed the use of DNA extracts from stained blood smears for the detection of Plasmodium species using real-time PCR. We extracted DNA from archived blood smears and corresponding red blood cell pellets collected from asymptomatic children in southwestern Uganda in 2010. We then performed real-time PCR followed by high-resolution melting (HRM) to identify Plasmodium species, and we compared our results to those of microscopy. We analyzed a total of 367 blood smears and corresponding red blood cell pellets, including 185 smears (50.4%) that were positive by microscopy. Compared to microscopy, PCR-HRM analysis of smear DNA had a sensitivity of 93.0% (95% confidence interval [CI], 88.2 to 96.2%) and a specificity of 96.7% (95% CI, 93.0 to 98.8%), and PCR-HRM analysis of pellet DNA had a sensitivity of 100.0% (95% CI, 98.0 to 100.0%) and a specificity of 94.0% (95% CI, 89.4 to 96.9%). Identification of positive PCR-HRM results to the species level revealed Plasmodium falciparum (92.0%), Plasmodium ovale (5.6%), and Plasmodium malariae (2.4%). PCR-HRM analysis of DNA extracts from Giemsa-stained thick blood smears or corresponding blood pellets had high sensitivity and specificity for malaria diagnosis, compared to microscopy. Therefore, blood smears can provide an adequate source of DNA for confirmation of Plasmodium species infections and can be used for retrospective genetic studies.

Identification of Plasmodium spp. in Neotropical primates of Maranhense Amazon in Northeast Brazil

In the Brazilian Amazon region, malaria caused by Plasmodium malariae is considered to be a zoonosis because of cross-transfer of the parasite between humans and Neotropical primates. To contribute information on this issue, we investigated occurrences of natural infection with Plasmodium sp. among Neotropical primates in the Maranhense Amazon (Amazon region of the state of Maranhão), in the northeastern region of Brazil. Blood samples were collected from 161 Neotropical primates of six species that were caught in an environmental reserve (Sítio Aguahy) and from captive primates (CETAS-Wildlife Screening Center, municipality of São Luís), in Maranhão. Plasmodium sp. was diagnosed based on light microscopy, PCR, qPCR and LAMP for amplification of the 18S rRNA gene. Serum samples were also assayed by means of indirect immunofluorescence for IgG antibodies against P. malariae/P. brasilianum, P. falciparum and P. berghei. Parasites were detected through light microscopy on five slides from captive primates (four Sapajus spp. and one Callithrix jacchus). In the molecular tests, 34.16% (55/161) and 29.81% (48/161) of the animals sampled were positive in the qPCR and PCR assays, respectively. In the PCR, 47/48 animals were positive for P. malariae/P. brasilianum; of these, eight were free-living primates and 39 from CETAS, São Luís. One sample showed a band in the genus-specific reaction, but not in the second PCR reaction. Anti-P. malariae/P. brasilianum IgG antibodies were detected in four serum samples from Sapajus spp. in captivity. In this study, circulation of P. malariae/P. brasilianum in Neotropical primates was confirmed, with low levels of parasitemia and low levels of antibodies. The importance of these animals as reservoirs of human malaria in the region studied is still unknown. This scenario has an impact on control and elimination of malaria in this region.

Anti-erythrocyte antibodies may contribute to anaemia in Plasmodium vivax malaria by decreasing red blood cell deformability and increasing erythrophagocytosis

Background

Plasmodium vivax accounts for the majority of human malaria infections outside Africa and is being increasingly associated in fatal outcomes with anaemia as one of the major complications. One of the causes of malarial anaemia is the augmented removal of circulating non-infected red blood cells (nRBCs), an issue not yet fully understood. High levels of auto-antibodies against RBCs have been associated with severe anaemia and reduced survival of nRBCs in patients with falciparum malaria. Since there are no substantial data about the role of those antibodies in vivax malaria, this study was designed to determine whether or not auto-antibodies against erythrocytes are involved in nRBC clearance. Moreover, the possible immune mechanisms elicited by them that may be associated to induce anaemia in P. vivax infection was investigated.

Methods

Concentrations of total IgG were determined by sandwich ELISA in sera from clinically well-defined groups of P. vivax-infected patients with or without anaemia and in healthy controls never exposed to malaria, whereas the levels of specific IgG to nRBCs were determined by cell-ELISA. Erythrophagocytosis assay was used to investigate the ability of IgGs purified from each studied pooled sera in enhancing nRBC in vitro clearance by THP-1 macrophages. Defocusing microscopy was employed to measure the biomechanical modifications of individual nRBCs opsonized by IgGs purified from each group.

Results

Anaemic patients had higher levels of total and specific anti-RBC antibodies in comparison to the non-anaemic ones. Opsonization with purified IgG from anaemic patients significantly enhanced RBCs in vitro phagocytosis by THP-1 macrophages. Auto-antibodies purified from anaemic patients decreased the nRBC dynamic membrane fluctuations suggesting a possible participation of such antibodies in the perturbation of erythrocyte flexibility and morphology integrity maintenance.

Conclusions

These findings revealed that vivax-infected patients with anaemia have increased levels of IgG auto-antibodies against nRBCs and that their deposition on the surface of non-infected erythrocytes decreases their deformability, which, in turn, may enhance nRBC clearance by phagocytes, contributing to the anaemic outcome. These data provide insights into the immune mechanisms associated with vivax malaria anaemia and may be important to the development of new therapy and vaccine strategies.

Detection of Plasmodium using filter paper and nested PCR for patients with malaria in Sanliurfa, in Turkey

Background

The objective of this study to detect Plasmodium and a subspecies of Plasmodium using filter paper in malaria endemic province, Sanliurfa, in Turkey, compare the results of nested PCR (nPCR) with microscopy for the diagnosis of malaria and present the epidemiological data of malaria.

Methods

This study was carried out in malaria-endemic Sanliurfa between 2008 and 2011. Finger prick blood samples, thick and thin Giemsa-stained blood smears, were collected from 153 malaria-suspected farmworkers. The Giemsa-stained blood smears were examined microscopically. The obtained DNA products, extracted from blood-spotted filter papers or from the thick blood smears, were analysed by nPCR to amplify the 18S ssrRNA Plasmodium gene with genus and specific primers. The results of the microscopy were compared to the nPCR results.

Results

Of the specimens, 7.2 % were determined as Plasmodium-positive by microscopy, whereas 9.8 % were determined as Plasmodium-positive by nPCR. Of the positive Plasmodium specimens, 93.33 % were identified as P. vivax. Four out of the 15 specimens that were microscopically diagnosed as negative were Plasmodium-positive with nPCR. When compared to the microscopy, the sensitivity, specificity, and positive predictive values of the nPCR were determined as 100, 97.2 and 73.3 %, respectively. nPCR was determined to be more sensitive and specific than microscopy.

Conclusions

This study revealed that the accurate diagnosis of malaria by nPCR was compulsory in malaria-endemic Sanliurfa and nPCR should be applied routinely in laboratory studies.

Seroepidemiology of Plasmodium species infections in Zimbabwean population

BACKGROUND

Individuals living in malaria-endemic regions may be exposed to more than one Plasmodium species; there is paucity of data on the distribution of the different species of Plasmodium in affected populations, in part due to the diagnostic method of microscopy, which cannot easily differentiate between the species. Sero-epidemiological data can overcome some of the shortcomings of microscopy.

METHODS

The specificity of IgG antibodies to recombinant merozoite surface protein 1 (MSP-119) derived from four human Plasmodium species (Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, Plasmodium ovale) was investigated using competition enzyme-linked immunosorbent assay. Subsequently, these antigens were used to determine the exposure prevalence to the different Plasmodium species in serum samples of participants. One-hundred individuals, aged five-18 years, from each of the three Plasmodium meso-endemic Zimbabwean villages (Burma Valley, Mutoko, Chiredzi) were recruited in the study.

RESULTS

The study demonstrated that the host serum reactivity to MSP-119 antigens was species-specific and that no cross-reactivity occurred. The overall prevalence of antibody response to MSP-119 antigens was 61 % in Burma Valley, 31 % in Mutoko and 32 % in Chiredzi. Single species IgG responses to MSP-119 were most frequent against P. falciparum, followed by P. malariae and P. ovale, with responses to P. vivax being the least prevalent. Interestingly, 78-87 and 50 % of sera with IgG responses to P. malariae and P. ovale MSP-119, respectively, also had IgG specific response for P. falciparum MSP-119 antigens, indicating that exposure to these species is a common occurrence in these populations. Single species IgG responses to the non-falciparum species were at a very low frequency, ranging between 0 and 13 % for P. malariae.

CONCLUSIONS

There is evidence of a higher exposure to the non-falciparum parasite species than previously reported in Zimbabwe. The recombinant MSP-119 antigens could be used as additional diagnostic tools in antibody assays for the detection of exposure to the different Plasmodium species. The results also introduce an interesting concept of the co-infection of non-falciparum Plasmodium almost always with P. falciparum, which requires further validation and mechanistic studies.

Use of Blood Smears and Dried Blood Spots for Polymerase Chain Reaction-Based Detection and Quantification of Bacterial Infection and Plasmodium falciparum in Severely Ill Febrile African Children

Molecular approaches offer a means of testing archived samples stored as dried blood spots in settings where standard blood cultures are not possible. Peripheral blood films are one suggested source of material, although the sensitivity of this approach has not been well defined. Thin blood smears and dried blood spots from a severe pediatric malaria study were assessed using specific polymerase chain reaction (PCR) primers to detect non-typhoidal Salmonella (NTS; MisL gene), Streptococcus pneumoniae (lytA), and Plasmodium falciparum (18S rRNA). Of 16 cases of NTS and S. pneumoniae confirmed on blood culture, none were positive by PCR using DNA extracts from blood films or dried blood spots. In contrast, four of 36 dried blood spots and two of 178 plasma samples were PCR positive for S. pneumoniae, despite negative bacterial blood cultures, suggesting false positives. Quantitative assessment revealed that the effective concentration of P. falciparum DNA in blood films was three log orders of magnitude lower than for dried blood spots. The P. falciparum kelch13 gene could not be amplified from blood films. These findings question the value of blood PCR-based approaches for detection of NTS and S. pneumoniae, and show that stored blood films are an inefficient method of studying P. falciparum.

Frequency and distribution of mixed Plasmodium falciparum-vivax infections in French Guiana between 2000 and 2008

Background

The two main plasmodial species in French Guiana are Plasmodium vivax and Plasmodium falciparum whose respective prevalence influences the frequency of mixed plasmodial infections. The accuracy of their diagnosis is influenced by the sensitivity of the method used, whereas neither microscopy nor rapid diagnostic tests allow a satisfactory evaluation of mixed plasmodial infections.

Methods

In the present study, the frequency of mixed infections in different part of French Guiana was determined using real time PCR, a sensitive and specific technique.

Results

From 400 cases of malaria initially diagnosed by microscopy, real time PCR showed that 10.75 % of the cases were mixed infections. Their prevalence varied considerably between geographical areas. The presence, in equivalent proportions, of the two plasmodial species in eastern French Guiana was associated with a much higher prevalence of mixed plasmodial infections than in western French Guiana, where the majority of the population was Duffy negative and thus resistant to vivax malaria.

Conclusion

Clinicians must be more vigilant regarding mixed infections in co-endemic P. falciparum/P. vivax areas, in order to deliver optimal care for patients suffering from malaria. This may involve the use of rapid diagnostic tests capable of detecting mixed infections or low density single infections. This is important as French Guiana moves towards malaria elimination.

Systematic revision of the adeleid haemogregarines, with creation of Bartazoon n. g., reassignment of Hepatozoon argantis Garnham, 1954 to Hemolivia, and molecular data on Hemolivia stellata

Life cycles and molecular data for terrestrial haemogregarines are reviewed in this article. Collection material was re-examined: Hepatozoon argantis Garnham, 1954 in Argas brumpti was reassigned to Hemolivia as Hemolivia argantis (Garnham, 1954) n. comb.; parasite DNA was extracted from a tick crush on smear of an archived slide of Hemolivia stellata in Amblyomma rotondatum, then the 18S ssrRNA gene was amplified by PCR. A systematic revision of the group is proposed, based on biological life cycles and phylogenetic reconstruction. Four types of life cycles, based on parasite vector, vertebrate host and the characteristics of their development, are defined. We propose combining species, based on their biology, into four groups (types I, II, III and IV). The characters of each type are defined and associated with a type genus and a type species. The biological characters of each type are associated with a different genus and a type species. The phylogenetic reconstruction with sequences deposited in the databases and our own new sequence of Hemolivia stellata is consistent with this classification. The classification is as follows: Type I, Hepatozoon Miller, 1908, type species H. perniciosum Miller, 1908; Type II, Karyolysus Labbé, 1894, type species K. lacertae (Danilewsky, 1886) Reichenow, 1913; Type III Hemolivia Petit et al., 1990, type species H. stellata, Petit et al., 1990; and Type IV: Bartazoon n. g., type species B. breinli (Mackerras, 1960).

Characterization of Hepatozoon spp. in Leptodactylus chaquensis and Leptodactylus podicipinus from two regions of the Pantanal, state of Mato Grosso do Sul, Brazil

Hepatozoon sp. are parasites that commonly infect frogs and arthropod vectors. This species has variability in the morphological and morphometric characteristics. Due to these variations, the naming of the species is thus impaired and only by visualizing the sporogonic cycle in vector and by molecular studies this problem can be solved. Recently, the use of molecular genetics has helped the species denomination. In this work, we collected 145 frogs (68 Leptodactylus chaquensis and 77 Leptodactylus podicipinus) in different sampling sites, where were found 18 (26.47%) L. chaquensis and 24 (31.17%) L. podicipinus parasitized; besides of gamonts, schizogonic forms were also seen in animals organs. The positivity difference between the collection sites for both frog species was not significant (p = 0.958). Comparing gamonts found in each species of anuran, we observed differences in morphology. The comparison in the molecular level for L. podicipinus was not possible due to small amount of blood obtained, just L. chaquensis had their parasites DNA sequenced. The amplified and sequenced samples, named HEP1 to HEP10, are presented in the phylogenetic tree as a different branch from other haemogregarines described on other hosts. Therefore, we have seen that, although the morphology and morphometry of the collected parasites at each site showed differences, the sequencing of these samples revealed identical species of Hepatozoon, and different compared to those from GenBank, thereby demonstrating that the species of Hepatozoon in L. chaquensis observed in this study probably represent a new species.

CD4+ T cells apoptosis in Plasmodium vivax infection is mediated by activation of both intrinsic and extrinsic pathways

BACKGROUND

Reduction in the number of circulating blood lymphocytes (lymphocytopaenia) has been reported during clinical episodes of malaria and is normalized after treatment with anti-malaria drugs. While this phenomenon is well established in malaria infection, the underlying mechanisms are still not fully elucidated. In the present study, the occurrence of apoptosis and its pathways in CD4+ T cells was investigated in naturally Plasmodium vivax-infected individuals from a Brazilian endemic area (Porto Velho - RO).

METHODS

Blood samples were collected from P. vivax-infected individuals and healthy donors. The apoptosis was characterized by cell staining with Annexin V/FITC and propidium iodide and the apoptosis-associated gene expression profile was carried out using RT2 Profiler PCR Array-Human Apoptosis. The plasma TNF level was determined by ELISA. The unpaired t-test or Mann-Whitney test was applied according to the data distribution.

RESULTS

Plasmodium vivax-infected individuals present low number of leukocytes and lymphocytes with a higher percentage of CD4+ T cells in early and/or late apoptosis. Increased gene expression was observed for TNFRSF1B and Bid, associated with a reduction of Bcl-2, in individuals with P. vivax malaria. Furthermore, these individuals showed increased plasma levels of TNF compared to malaria-naive donors.

CONCLUSIONS

The results of the present study suggest that P. vivax infection induces apoptosis of CD4+ T cells mediated by two types of signaling: by activation of the TNFR1 death receptor (extrinsic pathway), which is amplified by Bid, and by decreased expression of the anti-apoptotic protein Bcl-2 (intrinsic pathway). The T lymphocytes apoptosis could reflect a strategy of immune evasion triggered by the parasite, enabling their persistence but also limiting the occurrence of immunopathology.

High proportion of knowlesi malaria in recent malaria cases in Malaysia

Background

Plasmodium knowlesi is a simian parasite that has been recognized as the fifth species causing human malaria. Naturally-acquired P. knowlesi infection is widespread among human populations in Southeast Asia. The aim of this epidemiological study was to determine the incidence and distribution of malaria parasites, with a particular focus on human P. knowlesi infection in Malaysia.

Methods

A total of 457 microscopically confirmed, malaria-positive blood samples were collected from 22 state and main district hospitals in Malaysia between September 2012 and December 2013. Nested PCR assay targeting the 18S rRNA gene was used to determine the infecting Plasmodium species.

Results

A total of 453 samples were positive for Plasmodium species by using nested PCR assay. Plasmodium knowlesi was identified in 256 (56.5%) samples, followed by 133 (29.4%) cases of Plasmodium vivax, 49 (10.8%) cases of Plasmodium falciparum, two (0.4%) cases of Plasmodium ovale and one (0.2%) case of Plasmodium malariae. Twelve mixed infections were detected, including P. knowlesi/P. vivax (n = 10), P. knowlesi/P. falciparum (n = 1), and P. falciparum/P. vivax (n = 1). Notably, P. knowlesi (Included mixed infections involving P. knowlesi (P. knowlesi/P. vivax and P. knowlesi /P. falciparum)) showed the highest proportion in Sabah (84/115 cases, prevalence of 73.0%), Sarawak (83/120, 69.2%), Kelantan (42/56, 75.0%), Pahang (24/25, 96.0%), Johor (7/9, 77.8%), and Terengganu (4/5, 80.0%,). In contrast, the rates of P. knowlesi infection in Selangor and Negeri Sembilan were found to be 16.2% (18/111 cases) and 50.0% (5/10 cases), respectively. Sample of P. knowlesi was not obtained from Kuala Lumpur, Melaka, Perak, Pulau Pinang, and Perlis during the study period, while a microscopically-positive sample from Kedah was negative by PCR.

Conclusion

In addition to Sabah and Sarawak, which have been known for high prevalence of P. knowlesi infection, the findings from this study highlight the widespread distribution of P. knowlesi in many Peninsular Malaysia states.

Evaluation of three different DNA extraction methods from blood samples collected in dried filter paper in Plasmodium subpatent infections from the Amazon region in Brazil

Asymptomatic Plasmodium infection is a new challenge for public health in the American region. The polymerase chain reaction (PCR) is the best method for diagnosing subpatent parasitemias. In endemic areas, blood collection is hampered by geographical distances and deficient transport and storage conditions of the samples. Because DNA extraction from blood collected on filter paper is an efficient method for molecular studies in high parasitemic individuals, we investigated whether the technique could be an alternative for Plasmodium diagnosis among asymptomatic and pauciparasitemic subjects. In this report we compared three different methods (Chelex®-saponin, methanol and TRIS-EDTA) of DNA extraction from blood collected on filter paper from asymptomatic Plasmodium-infected individuals. Polymerase chain reaction assays for detection of Plasmodium species showed the best results when the Chelex®-saponin method was used. Even though the sensitivity of detection was approximately 66% and 31% for P. falciparum and P. vivax, respectively, this method did not show the effectiveness in DNA extraction required for molecular diagnosis of Plasmodium. The development of better methods for extracting DNA from blood collected on filter paper is important for the diagnosis of subpatent malarial infections in remote areas and would contribute to establishing the epidemiology of this form of infection.

Sequence Diversity of pfmdr1 and Sequence Conserve of pldh in Plasmodium falciparum from Indonesia: Its implications on Designing a Novel Antimalarial Drug with Less Prone to Resistance

BACKGROUND

pfmdr1 and its variants are molecular marker which are responsible for antibiotics resistance in Plasmodium falciparum, a parasitic carrier for malaria disease. A novel strategy to treat malaria disease is by disrupting parasite lactate dehydrogenase (pLDH), a crucial enzyme for Plasmodium survival during their erythrocytic stages. This research was aimed to investigate and characterize the pfmdr1 and pldh genes of P. falciparum isolated from Nusa Tenggara Indonesia.

METHODS

Genomic DNA of P.falciparum was isolated from malaria patients in Nusa Tenggara Indonesia. pfmdr1 was amplified using nested PCR and genotyped using Restriction Fragment Length Polymorphism (RFLP). pldh was amplified, sequenced, and analyzed using NCBI public domain databases and alignment using Clustal W ver. 1.83.

RESULTS

Genotyping of the pfmdr1 revealed that sequence diversity was extremely high among isolates. However, a sequence analysis of pldh indicated that open reading frame of 316 amino acids of the gene showing 100% homology to the P. falciparum 3D7 reference pldh (GeneBank: XM_001349953.1).

CONCLUSION

This is the first report which confirms the heterologous of pfmdr1 and the homologous sequences of P.falciparum pldh isolated from Nusa Tenggara Islands of Indonesia, indicating that the chloroquine could not be used effectively as antimalarial target in the region and the pLDH-targeted antimalarial compound would have higher chance to be successful than using chloroquine for curbing malaria worldwide.

Interleukin-17 producing T helper cells are increased during natural Plasmodium vivax infection

Recent evidences have demonstrated the importance of Th17 cells in host defense against infectious diseases. However, little is known about their role in parasitic infections. Here, we showed that uncomplicated acute vivax malaria induce a significant expansion of IL-17-producing CD4(+) T cells associated to a pro-inflammatory cytokine profile. Furthermore, we demonstrated a correlation between numbers of IL-17(+)CD4(+) T cells and circulating CD4(+) T-cells producing IFN-γ, IL-10 and TGF-β. Finally, correlations between number of these cells and morbidity or parasitemia were not detected. Further studies are underway to investigate whether IL-17-producing CD4(+) T cells are critically involved in the immunity against Plasmodium vivax infection.

Loop-mediated isothermal amplification (LAMP) for malarial parasites of humans: would it come to clinical reality as a point-of-care test?

Loop-mediated isothermal amplification (LAMP) is a novel molecular method that accelerates and facilitates DNA amplification and detection under isothermal conditions. It represents a revolution in molecular biology by reducing the high cost, turnaround time and technicality of polymerase chain reaction and other amplification methods. It has been applied for the diagnosis of a variety of viral, bacterial, parasitic and other diseases in the biomedical field. LAMP has been involved in studies concerning the diagnosis of malaria which is still a major cause of morbidity and mortality in different parts of the world. For the success attained with this technology to diagnose human malaria, is it time to think that LAMP-based point-of-care diagnostics come to application to support the diagnosis of clinical malaria cases? The present review deals with the use of LAMP in the diagnosis of malaria and related investigations to make a view on what has been investigated and highlights the future perspectives regarding the possible applications of LAMP in diagnosis of the disease.

Naturally acquired antibodies to Plasmodium vivax blood-stage vaccine candidates (PvMSP-1₁₉ and PvMSP-3α₃₅₉₋₇₉₈ and their relationship with hematological features in malaria patients from the Brazilian Amazon

An important step when designing a vaccine is identifying the antigens that function as targets of naturally acquired antibodies. We investigated specific antibody responses against two Plasmodium vivax vaccine candidates, PvMSP-1₁₉ and PvMSP-3α₃₅₉₋₇₉₈. Moreover, we assessed the relationship between these antibodies and morbidity parameters. PvMSP-1₁₉ was the most immunogenic antigen and the frequency of responders to this protein tended to increase in P. vivax patients with higher parasitemia. For both antigens, IgG antibody responses tended to be lower in patients who had experienced their first bout of malaria. Furthermore, anemic patients presented higher IgG antibody responses to PvMSP-3α₃₅₉₋₇₉₈. Since the humoral response involves a number of antibodies acting simultaneously on different targets, we performed a Principal Component Analysis (PCA). Anemic patients had, on average, higher first principal component scores (IgG1/IgG2/IgG3/IgG4 anti-MSP3α), which were negatively correlated with hemoglobin levels. Since antibodies against PfMSP-3 have been strongly associated with clinical protection, we cannot exclude the possibility of a dual role of PvMSP-3 specific antibodies in both immunity and pathogenesis of vivax malaria. Our results confirm the high immunogenicity of the conserved C terminus of PvMSP-1 and points to the considerable immunogenicity of polymorphic PvMSP-3α₃₅₉₋₇₉₈ during natural infection.

A novel synthetic odorant blend for trapping of malaria and other African mosquito species

Estimating the biting fraction of mosquitoes is of critical importance for risk assessment of malaria transmission. Here, we present a novel odor-based tool that has been rigorously assessed in semi-field assays and traditional African villages for estimating the number of mosquitoes that enter houses in search of a blood meal. A standard synthetic blend (SB) consisting of ammonia, (S)-lactic acid, tetradecanoic acid, and carbon dioxide was complemented with isovaleric acid, 4,5 dimethylthiazole, 2-methyl-1-butanol, and 3-methyl-1-butanol in various combinations and concentrations, and tested for attractiveness to the malaria mosquito Anopheles gambiae. Compounds were released through low density polyethylene (LDPE) material or from nylon strips (nylon). Studies were done in a semi-field facility and two traditional villages in western Kenya. The alcohol 3-methyl-1-butanol significantly increased the attraction of SB. The other compounds proved less effective or inhibitory. Tested in a village, 3-methyl-1-butanol, released from LDPE, increased the attraction of SB. Further studies showed a significantly enhanced attraction of adding 3-methyl-1-butanol to SB compared to previously-published attractive blends both under semi-field and village conditions. Other mosquito species with relevance for public health were collected with this blend in significantly higher numbers as well. These results demonstrate the advent of a novel, reliable odor-based sampling tool for the collection of malaria and other mosquitoes. The advantage of this odor-based tool over existing mosquito sampling tools is its reproducibility, objectiveness, and relatively low cost compared to current standards of CDC light traps or the human landing catch.

Genetic diversity of Plasmodium falciparum isolates from Pahang, Malaysia based on MSP-1 and MSP-2 genes

BACKGROUND

Malaria is still a public health problem in Malaysia especially in the interior parts of Peninsular Malaysia and the states of Sabah and Sarawak (East Malaysia). This is the first study on the genetic diversity and genotype multiplicity of Plasmodium falciparum in Malaysia.

METHODS

Seventy-five P. falciparum isolates were genotyped by using nested-PCR of MSP-1 (block 2) and MSP-2 (block 3).

RESULTS

MSP-1 and MSP-2 allelic families were identified in 65 blood samples. RO33 was the predominant MSP-1 allelic family identified in 80.0% (52/65) of the samples while K1 family had the least frequency. Of the MSP-2 allelic families, 3D7 showed higher frequency (76.0%) compared to FC27 (20.0%). The multiplicity of P. falciparum infection (MOI) was 1.37 and 1.20 for MSP-1 and MSP-2, respectively. A total of seven alleles were detected; of which three MSP-1 allelic families (RO33, MAD20 and K1) were monomorphic in terms of size while MSP-2 alleles were polymorphic (two 3D7 and two FC27). Heterozygosity (HE) was 0.57 and 0.55 for MSP-1 and MSP-2, respectively.

CONCLUSIONS

The study showed that the MOI of P. falciparum is low, reflected the low intensity of malaria transmission in Pahang, Malaysia; RO33 and 3D7 were the most predominant circulating allelic families. The findings showed that P. falciparum has low allelic diversity with a high frequency of alleles. As a result, antimalarial drug efficacy trials based on MSP genotyping should be carefully interpreted.

High specificity of semi-nested multiplex PCR using dried blood spots on DNA Banking Card in comparison with frozen liquid blood for detection of Plasmodium falciparum and Plasmodium vivax

BACKGROUND

Venipuncture sampling in test tubes for detecting malaria parasites using PCR assays possesses a number of limitations such as reluctance of patients, some difficulties in transportation of blood samples and freezing them for long time. To overcome the mentioned limitations, some approaches have been employed by a number of authors. This study was proposed to compare between DNA Banking Card (DBC) filter papers containing dried finger-prick blood and venipunctured frozen liquid blood.

METHODS

A total of 75 specimens was prepared from the equal enrolled individuals using three blood storage approaches; making Geimsa-stained thin and thick smears from each individual to determine the malaria-positive or -negative specimens, spotting two to three drops of finger-prick blood onto the DBC filter paper, and collecting a 2-ml venous blood sample into EDTA-contained test tube from each individual. A semi-nested Multiplex PCR technique with DNA extracted from the two latter sets of specimens was used for plasmodia diagnosis.

RESULTS

DNA samples isolated from dried blood spotted on the DBC filter papers resulted in 32 (42.7%) positive and 43 (57.3%) negative cases comparable with the results outcome of frozen liquid blood with 35 (46.7%) positive and 40 (53.3%) negative cases. Statistical analysis revealed higher sensitivity for SnM-PCR using DNA from liquid blood with 100% vs. dried blood spotted on DBC with 97% but higher specificity for the DBC with 100% vs. liquid blood with 95.2%.

CONCLUSIONS

Based on the results obtained from this study to overcome the problems of venipuncture frozen liquid blood sampling, replacement of a reliable filter paper for preserving finger-prick blood samples is a trustable and useful facilitator particularly in remote malaria-endemic areas.

Rapid diagnostic tests as a source of DNA for Plasmodium species-specific real-time PCR

Background

This study describes the use of malaria rapid diagnostic tests (RDTs) as a source of DNA for Plasmodium species-specific real-time PCR.

Methods

First, the best method to recover DNA from RDTs was investigated and then the applicability of this DNA extraction method was assessed on 12 different RDT brands. Finally, two RDT brands (OptiMAL Rapid Malaria Test and SDFK60 malaria Ag Plasmodium falciparum/Pan test) were comprehensively evaluated on a panel of clinical samples submitted for routine malaria diagnosis at ITM. DNA amplification was done with the 18S rRNA real-time PCR targeting the four Plasmodium species. Results of PCR on RDT were compared to those obtained by PCR on whole blood samples.

Results

Best results were obtained by isolating DNA from the proximal part of the nitrocellulose component of the RDT strip with a simple DNA elution method. The PCR on RDT showed a detection limit of 0.02 asexual parasites/μl, which was identical to the same PCR on whole blood. For all 12 RDT brands tested, DNA was detected except for one brand when a low parasite density sample was applied. In RDTs with a plastic seal covering the nitrocellulose strip, DNA extraction was hampered. PCR analysis on clinical RDT samples demonstrated correct identification for single species infections for all RDT samples with asexual parasites of P. falciparum (n = 60), Plasmodium vivax (n = 10), Plasmodium ovale (n = 10) and Plasmodium malariae (n = 10). Samples with only gametocytes were detected in all OptiMAL and in 10 of the 11 SDFK60 tests. None of the negative samples (n = 20) gave a signal by PCR on RDT. With PCR on RDT, higher Ct-values were observed than with PCR on whole blood, with a mean difference of 2.68 for OptiMAL and 3.53 for SDFK60. Mixed infections were correctly identified with PCR on RDT in 4/5 OptiMAL tests and 2/5 SDFK60 tests.

Conclusions

RDTs are a reliable source of DNA for Plasmodium real-time PCR. This study demonstrates the best method of RDT fragment sampling for a wide range of RDT brands in combination with a simple and low cost extraction method, allowing RDT quality control.

Using rapid diagnostic tests as source of malaria parasite DNA for molecular analyses in the era of declining malaria prevalence

Background

Malaria prevalence has recently declined markedly in many parts of Tanzania and other sub-Saharan African countries due to scaling-up of control interventions including more efficient treatment regimens (e.g. artemisinin-based combination therapy) and insecticide-treated bed nets. Although continued molecular surveillance of malaria parasites is important to early identify emerging anti-malarial drug resistance, it is becoming increasingly difficult to obtain parasite samples from ongoing studies, such as routine drug efficacy trials. To explore other sources of parasite DNA, this study was conducted to examine if sufficient DNA could be successfully extracted from malaria rapid diagnostic tests (RDTs), used and collected as part of routine case management services in health facilities, and thus forming the basis for molecular analyses, surveillance and quality control (QC) testing of RDTs.

Methods

One hyper-parasitaemic blood sample (131,260 asexual parasites/μl) was serially diluted in triplicates with whole blood and blotted on RDTs. DNA was extracted from the RDT dilution series, either immediately or after storage for one month at room temperature. The extracted DNA was amplified using a nested PCR method for Plasmodium species detection. Additionally, 165 archived RDTs obtained from ongoing malaria studies were analysed to determine the amplification success and test applicability of RDT for QC testing.

Results

DNA was successfully extracted and amplified from the three sets of RDT dilution series and the minimum detection limit of PCR was <1 asexual parasite/μl. DNA was also successfully amplified from (1) 70/71 (98.6%) archived positive RDTs (RDTs and microscopy positive) (2) 52/63 (82.5%) false negative RDTs (negative by RDTs but positive by microscopy) and (3) 4/24 (16.7%) false positive RDTs (positive by RDTs but negative by microscopy). Finally, 7(100%) negative RDTs (negative by RDTs and microscopy) were also negative by PCR.

Conclusion

This study showed that DNA extracted from archived RDTs can be successfully amplified by PCR and used for detection of malaria parasites. Since Tanzania is planning to introduce RDTs in all health facilities (and possibly also at community level), availability of archived RDTs will provide an alternative source of DNA for genetic studies such as continued surveillance of parasite resistance to anti-malarial drugs. The DNA obtained from RDTs can also be used for QC testing by detecting malaria parasites using PCR in places without facilities for microscopy.

Giemsa-stained thick blood films as a source of DNA for Plasmodium species-specific real-time PCR

Background

This study describes the use of thick blood films (TBF) as specimens for DNA amplification with the Plasmodium species-specific real-time PCR that was recently validated on whole blood samples.

Methods

The panel of 135 Giemsa-stained clinical TBFs represented single infections of the four Plasmodium species with varying parasite densities or only gametocytes, mixed infections, and negative samples and was stored for up to 12 years. Half of the Giemsa-stained TBF was scraped off by a sterile scalpel and collected into phosphate buffered saline. DNA was extracted with the Qiagen DNA mini kit with minor modifications. DNA was amplified with the 18S rRNA real-time PCR targeting the four Plasmodium species with four species-specific primers and probes in combination with one genus-specific reverse primer. Results of the PCR on TBF were compared to those of the PCR on whole blood and to microscopy.

Results

Correct identification for single species infections was obtained for all TBF samples with Plasmodium falciparum (n = 50), Plasmodium vivax (n = 25), Plasmodium ovale (n = 25) and in all but one samples with Plasmodium malariae (n = 10). Compared to whole blood samples, higher Ct-values were observed by PCR on TBF with a mean difference of 5.93. Four out of five mixed infections were correctly identified with PCR on TBF. None of the negative samples (n = 20) gave a PCR signal. PCR on TBF showed a detection limit of 0.2 asexual parasites/μl compared to 0.02/μl for whole blood. Intra-run variation was higher for PCR on TBF (%CV 1.90) compared to PCR on whole blood (%CV 0.54). Compared to microscopy, PCR on TBF generated three more species identifications in samples containing a single species and detected the same four mixed-infections.

Conclusions

Giemsa-stained TBFs are a reliable source of DNA for Plasmodium real-time PCR analysis, allowing applications in reference and research settings in case whole blood samples are not available.

Plasmodium vivax: induction of CD4+CD25+FoxP3+ regulatory T cells during infection are directly associated with level of circulating parasites

Circulation CD4⁺CD25⁺FoxP3⁺ regulatory T cells (Tregs) have been associated with the delicate balancing between control of overwhelming acute malaria infection and prevention of immune pathology due to disproportionate inflammatory responses to erythrocytic stage of the parasite. While the role of Tregs has been well-documented in murine models and P. falciparum infection, the phenotype and function of Tregs in P. vivax infection is still poorly characterized. In the current study, we demonstrated that patients with acute P. vivax infection presented a significant augmentation of circulating Tregs producing anti-inflammatory (IL-10 and TGF-β) as well as pro-inflammatory (IFN-γ, IL-17) cytokines, which was further positively correlated with parasite burden. Surface expression of GITR molecule and intracellular expression of CTLA-4 were significantly upregulated in Tregs from infected donors, presenting also a positive association between either absolute numbers of CD4⁺CD25⁺FoxP3⁺GITR⁺ or CD4⁺CD25⁺FoxP3⁺CTLA-4⁺ and parasite load. Finally, we demonstrate a suppressive effect of Treg cells in specific T cell proliferative responses of P. vivax infected subjects after antigen stimulation with Pv-AMA-1. Our findings indicate that malaria vivax infection lead to an increased number of activated Treg cells that are highly associated with parasite load, which probably exert an important contribution to the modulation of immune responses during P. vivax infection.

Naturally acquired antibodies to Plasmodium vivax Duffy binding protein (DBP) in Brazilian Amazon

Duffy binding protein (DBP), a leading malaria vaccine candidate, plays a critical role in Plasmodium vivax erythrocyte invasion. Sixty-eight of 366 (18.6%) subjects had IgG anti-DBP antibodies by enzyme-linked immunosorbent assay (ELISA) in a community-based cross-sectional survey in the Brazilian Amazon Basin. Despite continuous exposure to low-level malaria transmission, the overall seroprevalence decreased to 9.0% when the population was reexamined 12 months later. Antibodies from 16 of 50 (36.0%) subjects who were ELISA-positive at the baseline were able to inhibit erythrocyte binding to at least one of two DBP variants tested. Most (13 of 16) of these subjects still had inhibitory antibodies when reevaluated 12 months later. Cumulative exposure to malaria was the strongest predictor of DBP seropositivity identified by multiple logistic regression models in this population. The poor antibody recognition of DBP elicited by natural exposure to P. vivax in Amazonian populations represents a challenge to be addressed by vaccine development strategies.

Plasmodium knowlesi from archival blood films: further evidence that human infections are widely distributed and not newly emergent in Malaysian Borneo

Human infections with Plasmodium knowlesi have been misdiagnosed by microscopy as Plasmodium malariae due to their morphological similarities. Although microscopy-identified P. malariae cases have been reported in the state of Sarawak (Malaysian Borno) as early as 1952, recent epidemiological studies suggest the absence of indigenous P. malariae infections. The present study aimed to determine the past incidence and distribution of P. knowlesi infections in the state of Sarawak based on archival blood films from patients diagnosed by microscopy as having P. malariae infections. Nested PCR assays were used to identify Plasmodium species in DNA extracted from 47 thick blood films collected in 1996 from patients in seven different divisions throughout the state of Sarawak. Plasmodium knowlesi DNA was detected in 35 (97.2%) of 36 blood films that were positive for Plasmodium DNA, with patients originating from all seven divisions. Only one sample was positive for P. malariae DNA. This study provides further evidence of the widespread distribution of human infections with P. knowlesi in Sarawak and its past occurrence. Taken together with data from previous studies, our findings suggest that P. knowlesi malaria is not a newly emergent disease in humans.

Rapid identification of Plasmodium-carrying mosquitoes using loop-mediated isothermal amplification

With an aim to develop a quick and simple method to survey pathogen-transmitting vectors, LAMP (loop-mediated isothermal amplification) was applied to the identification of Plasmodium-carrying mosquitoes, specifically a Plasmodium-transmitting experimental model using rodent malaria parasite (Plasmodium berghei) and anopheline mosquitoes (Anopheles stephensi). The detection sensitivity limit of the LAMP reaction amplifying the SPECT2 gene was determined to be 1 x 10(2) purified Plasmodium parasites, estimated to be sufficient for reliable identification of infectious mosquitoes. The robustness of the LAMP reaction was revealed by its ability to detect both Plasmodium oocysts and sporozoites from an "all-in-one" template using whole mosquito bodies. Moreover, LAMP successfully identified an infectious mosquito carrying just a single oocyst in its midgut, a level that can be easily overlooked in conventional microscopic analysis. These observations suggest that LAMP is more reliable and useful for routine diagnosis of vector mosquitoes in regions where vector-borne diseases such as malaria are endemic.

Inhibitory properties of the antibody response to Plasmodium vivax Duffy binding protein in an area with unstable malaria transmission

The function of the Plasmodium vivax Duffy binding protein (DBP) during the erythrocyte invasion process is critical for successful parasite growth and pathogenesis in human infections. Although DBP is the subject of intensive malaria vaccine research, investigations on the functional proprieties of anti-DBP antibodies in the human population have been limited [Infect Immun68 (2000) 3164]. In the present study, we examined the ability of sera from different populations of the Brazilian Amazon--an area of markedly unstable malaria transmission--to inhibit the erythrocyte-binding function of the DBP ligand domain (region II, DBP(II)). We found that long-term exposure to malaria in the Amazon area elicits DBP-specific antibodies that inhibit the binding of different DBP(II) variants to erythrocytes. Despite the great variability of inhibitory antibody responses observed among study participants, we observed a positive correlation between erythrocyte binding-inhibitory activity and enzyme-linked immunosorbent assay anti-DBP antibodies. Of importance, there was a non-significant tendency towards increased levels of anti-DBP antibodies among individuals with asymptomatic P. vivax infections.

Comparison of PCR and microscopy for the detection of asymptomatic malaria in a Plasmodium falciparum/vivax endemic area in Thailand

OBJECTIVE

The main objective of this study was to compare the performance of nested PCR with expert microscopy as a means of detecting Plasmodium parasites during active malaria surveillance in western Thailand.

METHODS

The study was performed from May 2000 to April 2002 in the village of Kong Mong Tha, located in western Thailand. Plasmodium vivax (PV) and Plasmodium falciparum (PF) are the predominant parasite species in this village, followed by Plasmodium malariae (PM) and Plasmodium ovale (PO). Each month, fingerprick blood samples were taken from each participating individual and used to prepare thick and thin blood films and for PCR analysis.

RESULTS

PCR was sensitive (96%) and specific (98%) for malaria at parasite densities > or = 500/microl; however, only 18% (47/269) of P. falciparum- and 5% (20/390) of P. vivax-positive films had parasite densities this high. Performance of PCR decreased markedly at parasite densities <500/microl, with sensitivity of only 20% for P. falciparum and 24% for P. vivax at densities <100 parasites/microl.

CONCLUSION

Although PCR performance appeared poor when compared to microscopy, data indicated that the discrepancy between the two methods resulted from poor performance of microscopy at low parasite densities rather than poor performance of PCR. These data are not unusual when the diagnostic method being evaluated is more sensitive than the reference method. PCR appears to be a useful method for detecting Plasmodium parasites during active malaria surveillance in Thailand.

Dual role of MyD88 in rapid clearance of relapsing fever Borrelia spp

Relapsing fever Borrelia spp. undergo antigenic variation, achieve high levels in blood, and require rapid production of immunoglobulin M (IgM) for clearance. MyD88-deficient mice display defective clearance of many pathogens; however, the IgM response to persistent infection is essentially normal. Therefore, MyD88(-/-) mice provided a unique opportunity to study the effect of nonantibody, innate host defenses to relapsing fever Borrelia. Infected MyD88(-/-) mice harbored extremely high levels of B. hermsii in the blood compared to wild-type littermates. In the comparison of MyD88(-/-) mice and B- and T-cell-deficient scid mice, two features stood out: (i) bacterial numbers in blood were at least 10-fold greater in MyD88(-/-) mice than scid mice, even though the production of IgM still occurred in MyD88(-/-) mice; and (ii) many of the MyD88(-/-) mice were able to exert partial clearance, although with delayed kinetics relative to wild-type mice, a feature not seen in scid mice. Further analysis revealed a delay in the IgM response to lipoproteins expressed by the original inoculum; however, by 6 days of infection antibodies were produced in MyD88(-/-) mice that could clear spirochetemia in scid mice. While these results indicated that the production of IgM was delayed in MyD88(-/-) mice, they also point to a second, antibody-independent role for MyD88 signaling in host defense to relapsing fever Borrelia. This second defect was apparent only when antibody levels were limiting.

Factors associated with immunoglobulin G subclass polarization in naturally acquired antibodies to Plasmodium falciparum merozoite surface proteins: a cross-sectional survey in Brazilian Amazonia

We investigated immunoglobulin G (IgG) subclass antibody responses to Plasmodium falciparum merozoite surface protein 1 (MSP-1) and MSP-2 in 112 malaria-exposed subjects in Brazil. IgG3 polarization was primarily epitope driven, being little affected by cumulative or current exposure to malaria and not affected by a subject's age and Fcgamma receptor IIA genotype.

Comparison of different PCR protocols for the detection and diagnosis of Plasmodium falciparum

An assessment of differing PCR protocols for the diagnosis of Plasmodium falciparum infection was performed on samples from an area of holoendemic malaria transmission in western Burkina Faso. The PCR protocols had generally high sensitivities (>92%) and specificities (>69%), but the negative predictive values (NPV) were moderate and differed widely among the PCR protocols tested. These PCR protocols that amplified either the P. falciparum pfcrt gene or the small subunit ribosomal DNA were the most reliable diagnostic tools. However, the moderate NPV imply that more than one PCR protocol should be used for diagnosis in holoendemic areas.

IgG isotype to C-terminal 19 kDa of Plasmodium vivax merozoite surface protein 1 among subjects with different levels of exposure to malaria in Brazil

Subclasses of antibodies to the C-terminal 19 kDa fragment of the Plasmodium vivax merozoite surface protein 1 (PvMSP-1(19)) were assessed among subjects with distinct degrees of malaria exposure in the Brazilian endemic area. The PvMSP-1(19) specific IgG1and IgG3 levels were low among subjects with long-term exposure (approximately 19 years) when compared to subjects less and sporadically exposed (<1 year). No statistically difference was observed in IgG subclass distribution of antibodies from symptomatic Plasmodium-infected patients, asymptomatic parasite carriers and non-infected subjects living in a same mesoendemic area. Subjects briefly exposed to a P. vivax outbreak living in a rural community outside the endemic area were also evaluated to measure the persistence of specific antibodies. IgG anti-PvMSP-1(19) antibodies persisted in 40% of the subjects who had had malarial symptoms 8 months before and decreased after 7 years (28%). Specific IgG1 were the predominant isotype. Our study emphasizes the highly immunogenicity of the PvMSP-1(19) and points toward its possible use as a potential malaria vaccine.