Sensitive real-time PCR detection of Plasmodium falciparum parasites in whole blood by erythrocyte membrane protein 1 gene amplification

Background

Malaria remains a global public health problem responsible for 445,000 deaths in 2016. While microscopy remains the mainstay of malaria diagnosis, highly sensitive molecular methods for detection of low-grade sub-microscopic infections are needed for surveillance studies and identifying asymptomatic reservoirs of malaria transmission.

Methods

The Plasmodium falciparum genome sequence was analysed to identify high copy number genes that improve P. falciparum parasite detection in blood by RT-PCR. Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1)-specific primers were evaluated for P. falciparum detection in hospital-based microscopically positive dried blood spots and field-acquired whole blood from asymptomatic individuals from Ghana.

Results

PfEMP1 outperformed the Pf18S sequence for amplification-based P. falciparum detection. PfEMP1 primers exhibited sevenfold higher sensitivity compared to Pf18S primers for parasite genomic DNA. Probit analysis established a 95% detection threshold of 9.3 parasites/mL for PfEMP1 compared to 98.2 parasites/mL for Pf18S primers. The PfEMP1 primers also demonstrated superior clinical sensitivity, identifying 100% (20/20) of dried blood spot samples and 70% (69/98) of asymptomatic individuals as positive versus 55% (11/20) and 54% (53/98), respectively, for Pf18S amplification.

Conclusions

These results establish PfEMP1 as a novel amplification target for highly sensitive detection of both acute infections from filter paper samples and submicroscopic asymptomatic low-grade infections.

Superior real-time polymerase chain reaction detection of Babesia microti parasites in whole blood utilizing high-copy BMN antigens as amplification targets

BACKGROUND

Babesiosis is a zoonotic disease transmitted to humans by the bite of infected ticks and caused by apicomplexan parasites, most commonly Babesia microti. Additionally, blood and blood products collected from asymptomatically infected blood donors may cause transfusion-transmitted infections in recipients. Highly sensitive molecular assays that detect parasite nucleic acid are needed for laboratory diagnosis and to identify and defer clinically silent but parasitemic blood donors.

STUDY DESIGN AND METHODS

Here we report the development and analytical and clinical characterization of a real-time polymerase chain reaction (RT-PCR)-based assay for the detection of B. microti genomic DNA in whole blood. We evaluate the detection of Babesia parasites using two separate targets, the traditional18S ribosomal subunit gene (Bm18S) and members of the abundant BMN family of seroreactive antigens (BmBMN).

RESULTS

Analytical sensitivity determination using a probit analysis demonstrated an analytical sensitivity of 30.9 parasites/mL for 18S amplification and 10.0 parasites/mL for BMN amplification The BMN primer set also demonstrates superior sensitivity for serial dilution panels prepared from clinically diagnosed Babesia-infected blood samples, generally detecting 10-fold more dilute nucleic acid.

CONCLUSIONS

Cumulatively, our data demonstrate that RT-PCR detection of the BMN family of seroreactive antigens reflects a sensitive and superior assay for the detection of B. microti in whole blood samples.

A Novel Gametocyte Biomarker for Superior Molecular Detection of the Plasmodium falciparum Infectious Reservoirs

Background

Complete malaria eradication and optimal use of transmission-reducing interventions require knowledge of submicroscopic infectious reservoirs among asymptomatic individuals. Even submicroscopic levels of Plasmodium falciparum gametocytes can infect mosquitoes and promote onward transmission. Most efforts to identify gametocyte carriers use polymerase chain reaction amplification of the gametocyte-specific transcript Pfs25.

Methods

To expand the repertoire of biomarkers available for superior gametocyte detection, we compared the gene expression profiles of gametocytes and asynchronous blood-stage P. falciparum parasites by microarray technology. This allowed the identification of 56 molecules abundantly expressed in the gametocyte stage of the parasite. The analytical sensitivity for gametocyte detection was evaluated for 25 genes with the highest expression levels.

Results

One candidate, Pfg17, exhibited superior analytical sensitivity against a panel of gametocyte-spiked whole blood, detecting 10 gametocytes/mL; in comparison, Pfs25 detected only 25.3 gametocytes/mL. Pfg17 also exhibited superior clinical sensitivity, identifying 19.1% more samples from blood-film microscopy-negative Ghanaian children and 40% more samples from asymptomatic adults as gametocyte positive.

Conclusions

Cumulatively, our results suggest Pfg17 is an excellent biomarker for detecting asymptomatic infectious reservoirs otherwise missed by the most sensitive molecular method available. Our study has also improved the repertoire of transmission-stage antigens available for evaluation as candidate vaccines.

Adverse neuropsychiatric effects of antimalarial drugs

INTRODUCTION

Antimalarial drugs are the primary weapon to treat parasite infection, save lives, and curtail further transmission. Accumulating data have indicated that at least some antimalarial drugs may contribute to severe neurological and/or psychiatric side effects which further complicates their use and limits the pool of available medications.

AREAS COVERED

In this review article, we summarize published scientific studies in search of evidence of the neuropsychiatric effects that may be attributed to the commonly used antimalarial drugs administered alone or in combination. Each individual drug was used as a search term in addition to keywords such as neuropsychiatric, adverse events, and neurotoxicity.

EXPERT OPINION

Accumulating data based on published reports over several decades have suggested that among the major commonly used antimalarial drugs, only mefloquine exhibited clear indications of serious neurological and/or psychiatric side effects. A more systematic approach to assess the neuropsychiatric adverse effects of new or repurposed antimalarial drugs on their safety, tolerability and efficacy phases of clinical studies and in post-marketing surveillance, is needed to ensure that these life-saving tools remain available and can be prescribed with appropriate caution and medical judgment.

A slot blot immunoassay for quantitative detection of Plasmodium falciparum circumsporozoite protein in mosquito midgut oocyst

There is still a need for sensitive and reproducible immunoassays for quantitative detection of malarial antigens in preclinical and clinical phases of vaccine development and in epidemiology and surveillance studies, particularly in the vector host. Here we report the results of sensitivity and reproducibility studies for a research-grade, quantitative enhanced chemiluminescent-based slot blot assay (ECL-SB) for detection of both recombinant Plasmodium falciparum circumsporozoite protein (rPfCSP) and native PfCSP from Oocysts (Pf Oocyst) developing in the midguts of Anopheles stephensi mosquitoes. The ECL-SB detects as little as 1.25 pg of rPfCSP (linear range of quantitation 2.5-20 pg; R2 = 0.9505). We also find the earliest detectable expression of native PfCSP in Pf Oocyst by ECL-SB occurs on day 7 post feeding with infected blood meal. The ECL-SB was able to detect approximately as few as 0.5 day 8 Pf Oocysts (linear quantitation range 1-4, R2 = 0.9795) and determined that one Pf Oocyst expressed approximately 2.0 pg (0.5-3 pg) of native PfCSP, suggesting a similar range of detection for recombinant and native forms of Pf CSP. The ECL-SB is highly reproducible; the Coefficient of Variation (CV) for inter-assay variability for rPf CSP and native PfCSP were 1.74% and 1.32%, respectively. The CVs for intra-assay variability performed on three days for rPf CSP were 2.41%, 0.82% and 2% and for native Pf CSP 1.52%, 0.57%, and 1.86%, respectively. In addition, the ECL-SB was comparable to microscopy in determining the P. falciparum prevalence in mosquito populations that distinctly contained either high and low midgut Pf Oocyst burden. In whole mosquito samples, estimations of positivity for P. falciparum in the high and low burden groups were 83.3% and 23.3% by ECL-SB and 85.7% and 27.6% by microscopy. Based on its performance characteristics, ECL-SB could be valuable in vaccine development and to measure the parasite prevalence in mosquitoes and transmission-blocking interventions in endemic areas.

A sensitive enhanced chemiluminescent-ELISA for the detection of Plasmodium falciparum circumsporozoite antigen in midguts of Anopheles stephensi mosquitoes

Efforts to develop a successful malaria vaccine are hampered due to lack of assays that are predictive of protective immunity without conducting large clinical studies. The effect of experimental vaccines and drugs on malaria transmission is yet more difficult to measure. Knowledge on the Plasmodium infection rate in mosquito populations will aid the measurement of effects from intervention measures for malaria control. Here, we report the development of a chemiluminescent sandwich ELISA (ECL-ELISA) that can detect Plasmodium falciparum circumsporozoite protein (Pf CSP) produced in recombinant form at concentrations of 4.4pg and in P. falciparum sporozoites (Pf SPZ) derived from mosquito salivary glands at levels corresponding to 5 Pf SPZ. Most importantly, we demonstrate reliable Pf CSP-based detection of 0.056day 8 P. falciparum oocysts developing inside mosquito midguts in whole mosquito lysates. Cumulatively, the ECL-ELISA is 47× more sensitive for the detection of Pf CSP than a colorimetric ELISA while greatly simplifying sample preparation, obviating the need for cumbersome midgut dissections and allowing high throughput screening of Plasmodium infection in mosquito populations. The ECL-ELISA may also have broader application in diagnosis of infectious diseases and the prognostic value in cancer and other diseases such as auto-immunity and genetic disorders based on antigen detection, or quality validation of biological vaccine components.

Loss of giant obscurins promotes breast epithelial cell survival through apoptotic resistance

Obscurins (∼70 - 870 kDa), encoded by the single OBSCN gene, are cytoskeletal proteins originally identified in striated muscles with structural and regulatory roles. Recently, analysis of 13,023 genes in breast and colorectal cancers identified OBSCN as one of the most frequently mutated genes, implicating it in cancer formation. Herein we studied the expression profile of obscurins in breast, colon, and skin cancer cell lines and their involvement in cell survival. Immunoblot analysis demonstrated significant reduction of obscurin proteins [corrected] in cancer cells, resulting from decreased mRNA levels and/or the presence of mutant transcripts. In normal epithelium, obscurins localize in cytoplasmic puncta, the cell membrane, and the nucleus. Accordingly, subcellular fractionation demonstrated the presence of 2 novel nuclear isoforms of ∼110 and ∼120 kDa. Nontumorigenic MCF10A breast epithelial cells stably transduced with shRNAs targeting giant obscurins exhibited increased viability (∼30%) and reduced apoptosis (∼20%) following exposure to the DNA-damaging agent etoposide. Quantitative RT-PCR further indicated that the antiapoptotic genes BAG4 and HAX1 were up-regulated (1.5- and 1.4-fold, respectively), whereas initiator caspase-9 and death caspase-3 transcripts were down-regulated (0.8- and 0.6-fold, respectively). Our findings are the first to pinpoint critical roles for obscurins in cancer development by contributing to the regulation of cell survival.