Discovery of Specific Antigens That Can Predict Microfilarial Intensity in Loa loa Infection

Abstract

Antigen-based immunoassays are currently needed for point-of-care quantification of Loa loa microfilariae (mf). Coupling transcriptomic approaches with bioinformatic analysis, we have identified 11 specific putative proteins (coding mRNAs) with potential utility as biomarkers of patent (mf ؉ ) L. loa infection. We successfully developed antigen capture immunoassays to quantify 2 (LOAG_14221 and LOAG_ 15846) of these proteins in individual plasma/serum samples. Of the 2 quantifiable circulating biomarkers, LOAG_14221 showed the highest degree of specificity, particularly with a monoclonal antibody-based immunoassay. Moreover, the levels of LOAG_14221 in L. loa mf ؉ patients were positively correlated to the mf densities in the corresponding blood samples (r ϭ 0.53 and P ϭ 0.008 for polyclonal assay; r ϭ 0.54 and P ϭ 0.004 for monoclonal assay). Thus, LOAG_14221 is a very promising biomarker that will be exploited in a quantitative point-of-care immunoassay for determination of L. loa mf densities.KEYWORDS biomarker, Loa loa, antigen assay, filarial parasite, immunoassays, microfilaria, transcriptomics L oiasis, caused by the filarial parasite Loa loa, affects ϳ14 million people in Central and West Africa (1). Because the majority of infections are clinically asymptomatic and the symptomatic infections are rarely life-threatening, loiasis has been largely neglected (2). However, L. loa infection has gained importance over the past 20 years because of its negative impact on the elimination programs for onchocerciasis and lymphatic filariasis. Indeed, individuals with very high L. loa microfilariae (mf) levels can develop serious adverse events (SAEs), most notably irreversible neurological conditions (mainly encephalopathies) that can lead to coma or even death, following administration of ivermectin (IVM) during mass drug administration (MDA) campaigns (3, 4). As a result, IVM-based MDA campaigns have been interrupted or delayed in areas of Central Africa where L. loa is coendemic with either Wuchereria bancrofti or Onchocerca volvulus (5).Diagnostic methods that can accurately identify individuals that are at high risk of developing SAEs during IVM-based treatment are thus needed to achieve lymphatic filariasis and onchocerciasis elimination goals by 2020/2025 as targeted by the WHO. With the recent findings of an association between very high L. loa mf loads and mortality, independent of the effect of IVM treatment (6), identifying those at risk becomes all the more important.Traditional methods of L. loa mf identification and quantification are based on the microscopic examination of midday blood samples (7), a tedious and sometimes inaccurate process that is neither point of care (POC) nor high throughput (8). Real-time quantitative PCR (qPCR) and loop-mediated isothermal amplification (LAMP) methods are credible alternatives to microscopy since they are high throughput and combine a high degree of sensitivity and specificity with the ability to accurately quantify L. loa mf

Alternative treatment strategies to accelerate the elimination of onchocerciasis

“…While LoaScope performance is excellent, an RDT with similar performance but which is easier to apply is desirable for Loa-first TNT. Promising biomarkers of Loa possibly correlated with microfilarial density have been identified, 80 and RDTs are being developed (). The not-for-profit biotech company Drugs & Diagnostics for Tropical Diseases has developed a Loa antibody detection test that may help further map loiasis distribution.…”

Identification of biomarker candidates for filarial parasite infections by analysis of extracellular vesicles

“…transcriptome data for prioritizing candidates and showed some success in detecting antigen biomarker candidates by ELISA with varying degrees of sensitivity and specificity (Drame et al, 2017).…”

Mining Filarial Genomes for Diagnostic and Therapeutic Targets

“…Among several Loa -derived proteins detected using mass spectrometry and genome-based identification in body fluids of infected patients, we were able to identify LOAG_16297 as a potential biomarker for L. loa microfilarial loads in infected individuals [44]. Likewise, the use of microfilarial RNA-seq data and comparative bioinformatics led to the identification of LOAG_14221 as another quantitative biomarker for Loa -microfilarial density [45].…”