Nematode Infections:

Comparison of three PCR-based methods to detect Loa loa and Mansonella perstans in long-term frozen storage dried blood spots

OBJECTIVES

Loa loa and Mansonella perstans are two very common filarial species in Africa. Although microscopy is the traditional diagnostic method for human filariasis, several polymerase chain reaction (PCR) methods have emerged as an alternative approach for identifying filarial parasites. The aim of this study is to compare three molecular methods and decide which is the most suitable for diagnosing human loiasis and mansonellosis in non-endemic regions using dried blood spot (DBS) as a medium for sample collection and storage.

METHODS

A total of 100 DBS samples, with their corresponding thin and thick blood smears, were selected for this study. Microscopy was used as the reference method to diagnose and calculate the microfilaraemia. Filarial DNA was extracted using the saponin/Chelex method and the DNA isolated was assayed by Filaria-real time-PCR, filaria-nested PCR, and cytochrome oxidase I PCR. All PCR products were subsequently purified and sequenced. The statistical values for each molecular test were calculated and compared.

RESULTS

Overall, 64 samples were identified as negative by all tests and a further 36 samples were positive by at least one of the methods used. The sensitivity and specificity were similar for the different molecular methods, all of which demonstrated good agreement with microscopy.

CONCLUSIONS

Based on this study, and from a practical point of view (single and short amplification round), the optimal technique for diagnosing filarial infection in non-endemic regions is filaria-real time-PCR, which presents high sensitivity and specificity and is also able to detect a wide range of human filariae.

Characterising co-infections with Plasmodium spp., Mansonella perstans or Loa loa in asymptomatic children, adults and elderly people living on Bioko Island using nucleic acids extracted from malaria rapid diagnostic tests

Background

Regular and comprehensive epidemiological surveys of the filarial nematodes Mansonella perstans and Loa loa in children, adolescents and adults living across Bioko Island, Equatorial Guinea are lacking. We aimed to demonstrate that blood retained on malaria rapid diagnostic tests, commonly deployed for malaria surveys, could be used as a source of nucleic acids for molecular based detection of M. perstans and L. loa. We wanted to determine the positivity rate and distribution of filarial nematodes across different age groups and geographical areas as well as to understand level of co-infections with malaria in an asymptomatic population.

Methodology

M. perstans, L. loa and Plasmodium spp. parasites were monitored by qPCR in a cross-sectional study using DNA extracted from a subset malaria rapid diagnostic tests (mRDTs) collected during the annual malaria indicator survey conducted on Bioko Island in 2018.

Principal findings

We identified DNA specific for the two filarial nematodes investigated among 8.2% (263) of the 3214 RDTs screened. Positivity rates of M. perstans and L. loa were 6.6% and 1.5%, respectively. M. perstans infection were more prominent in male (10.5%) compared to female (3.9%) survey participants. M. perstans parasite density and positivity rate was higher among older people and the population living in rural areas. The socio-economic status of participants strongly influenced the infection rate with people belonging to the lowest socio-economic quintile more than 3 and 5 times more likely to be L. loa and M. perstans infected, respectively. No increased risk of being co-infected with Plasmodium spp. parasites was observed among the different age groups.

Conclusions/Significance

We found otherwise asymptomatic individuals were infected with M. perstans and L. loa. Our study demonstrates that employing mRDTs probed with blood for malaria testing represents a promising, future tool to preserve and ship NAs at room temperature to laboratories for molecular, high-throughput diagnosis and genotyping of blood-dwelling nematode filarial infections. Using this approach, asymptomatic populations can be reached and surveyed for infectious diseases beyond malaria.

Mansonella perstans and Loa loa are filarial nematodes that infect millions of people living in less developed areas, predominantly in sub-Saharan Africa. Both parasites are neglected among other filarial nematodes because both are regarded as causing mainly asymptomatic infections. The aim of this study was to explore the feasibility of using malaria rapid diagnostic tests (mRDTs) deployed during malaria surveys as a convenient sampling strategy for molecular surveillance of blood-dwelling filarial nematode infections. Our findings demonstrate the potential of mRDTs as a source of parasite DNA beyond malaria, providing an opportunity to expand current knowledge on the distribution and populations mostly affected by M. perstans and L. loa infections to Equatorial Guinea, located in Central-West Africa.

Evaluation of LAMP for the diagnosis of Loa loa infection in dried blood spots compared to PCR-based assays and microscopy

BACKGROUND

Loa loa is a filarial species found exclusively in West and Central Africa. Microscopy is the traditional diagnosis method for human loiasis. Several molecular methods have developed as an alternative approach for identification of L. loa filarial parasites.

OBJECTIVES

The aim of this study was to evaluate a Loa-Loop-mediated isothermal amplification (LAMP) assay to diagnose loiasis disease on dried blood spots (DBS) samples, compared to microscopy, filaria-real time-polymerase chain reaction (PCR) and nested-Loa PCR.

METHODS

A total of 100 DBS samples and 100 blood smears were used for this study. DNA was extracted using saponin/Chelex method. DNA isolated was assayed by a Loa-LAMP assay in parallel to microscopy, filaria-real time PCR and nested-Loa PCR. The sensitivities and specificities of Loa-LAMP assay was computed comparing to each one of the reference methods.

FINDINGS

Loa-LAMP’s sensitivity was more than 90% and specificity was nearly 100% when compared to molecular methods. On the other hand, sensitivity was decreased a bit when Loa-LAMP faced microscopy, but keeping the other statistical values high.

MAIN CONCLUSIONS

Loa-LAMP is an appropriate method for loiasis diagnosis in endemic areas. Though, it has disadvantages like the reagents’ high price at the moment and not to be able to detect more filarial species at once.

Filariasis an Unusual Cause of Retroperitoneal Fibrosis, Hydronephrosis, and Infertility in a Young Adult Male

Background: Filariasis is a tropical disease caused by infection with nematode parasites of the Filarioidea family. Filariasis is an endemic disease in parts of India, Sub-Saharan Africa, and Southeast Asia. Filariasis is a progressive disease predominantly affecting the lymphoreticular system, which can result in genitourinary complications (hydrocele, scrotal pain, and infertility), lymphedema, and elephantitis. Retroperitoneal fibrosis has a broad etiology, including secondary to chronic infection. Currently an estimated 25 million men are suffering from lymphatic filariasis with urogenital involvement worldwide. Case Presentation: We present a rare case of a 40-year-old man presenting with fever, groin lymphadenopathy, and a history of infertility. Imaging confirmed significant hydronephrosis and retroperitoneal fibrosis. Filariasis serology was positive. Prior bilateral testicular biopsy demonstrated chronic inflammation and atrophy. Disease course was not improved by empirical eradication and supportive retrograde ureteral stenting. The patient developed elephantitis and progressive retroperitoneal fibrosis leading to a solitary functioning right kidney with nephrostomy. Conclusion: Urologists should be aware of index presentations of filariasis and its associated urological complications, particularly in the travelling adult population in whom the etiology of renal impairment and infertility remains unclear.

Evidence of stage progression in a novel, validated fluorescence-navigated and microsurgical-assisted secondary lymphedema rodent model

Secondary lymphedema (SL)is a frequent and devastating complication of modern oncological therapy and filarial infections. A lack of a reliable preclinical model to investigate the underlying mechanism of clinical stage progression has limited the development of new therapeutic strategies. Current first line treatment has shown to be merely symptomatic and relies on lifetime use of compression garments and decongestive physiotherapy. In this study, we present the development of a secondary lymphedema model in 35 rats using pre- and intraoperative fluorescence-guided mapping of the lymphatics and microsurgical induction. In contrast to the few models reported so far, we decided to avoid the use of radiation for lymphedema induction. It turned out, that the model is nearly free of complications and capable of generating a statistically significant limb volume increase by water displacement measurements, sustained for at least 48 days. A translational, accurate lymphatic dysfunction was visualized by a novel VIS-NIR X-ray ICG-Clearance-Capacity imaging technology. For the first-time SL stage progression was validated by characteristic histological alterations, such as subdermal mast cell infiltration, adipose tissue deposition, and fibrosis by increased skin collagen content. Immunofluorescence confocal microscopy analysis suggested that stage progression is related to the presence of a characteristic α SMA+/HSP-47+/vimentin+ fibroblast subpopulation phenotype. These findings demonstrate that the in-vivo model is a reliable and clinically relevant SL model for the development of further secondary lymphedema therapeutic strategies and the analysis of the veiled molecular mechanisms of lymphatic dysfunction.

An update on non-invasive urine diagnostics for human-infecting parasitic helminths: what more could be done and how?

Reliable diagnosis of human helminth infection(s) is essential for ongoing disease surveillance and disease elimination. Current WHO-recommended diagnostic assays are unreliable in low-endemic near-elimination settings and typically involve the invasive, onerous and potentially hazardous sampling of bodily fluids such as stool and blood, as well as tissue via biopsy. In contrast, diagnosis by use of non-invasive urine sampling is generally painless, more convenient and low risk. It negates the need for specialist staff, can usually be obtained immediately upon request and is better accepted by patients. In some instances, urine-based diagnostic assays have also been shown to provide a more reliable diagnosis of infection when compared to traditional methods that require alternative and more invasive bodily samples, particularly in low-endemicity settings. Given these relative benefits, we identify and review current research literature to evaluate whether non-invasive urine sampling is currently exploited to its full potential in the development of diagnostic tools for human helminthiases. Though further development, assessment and validation are needed before their routine use in control programmes, low-cost, rapid and reliable assays capable of detecting transrenal helminth-derived antigens and cell-free DNA show excellent promise for future use at the point-of-care in high-, medium- and even low-endemicity elimination settings.

Emerging role of circulating microRNA in the diagnosis of human infectious diseases

The endogenic microRNAs (miRNA) are evolutionary, conserved, and belong to a group of small noncoding RNAs with a stretch of 19-24 nucleotides. The miRNAs play an indispensable role in gene modulation at the posttranscriptional level, inclusive of stem-cell differentiation, embryogenesis, hematopoiesis, metabolism, immune responses, or infections. The miRNAs secreted from the cells and their presence in the biological fluids signifies the regulatory role of circulating miRNAs in the pathogenesis. The phenomenal expression levels of circulating miRNAs in serum or plasma during infection makes them the potential therapeutic biomarkers for the diagnosis of assorted human infectious diseases. In this article, we have accentuated the methods for the profiling of circulating miRNA as well as the importance of miRNA as biomarkers for the diagnosis of human infectious diseases. To date, numerous biomarkers have been identified for the diagnostic or prognostic purpose; for instance, miR-182, miR-486, and miR15a in sepsis; miR-320 and miR505 in inflammatory bowel disease; miR-155 and miR-1260 in influenza; miR-12, miRVP-3p, and miR-184 in arboviruses; and miR-29b and miR-125 in hepatitis infection. Nevertheless, the noninvasive diagnostic approach, with the aid of biomarkers, currently plays a decisive role in the untimely diagnosis of human infections. So, in the near future, the exploitation of circulating miRNAs as therapeutic biomarkers for the diagnosis of human infections will help us to cure the associated diseases promptly and effectively.

Identification, Characterization, and Structure of Tm16 from Trichuris muris

Trichuriasis is a disease of poverty for which excretory and secretory (ES) products that induce the protective immunity are being investigated as candidate vaccines antigens. In this study, ES products of T. muris and immune sera were produced. The immune sera recognized more than 20 proteins on a 2D-gel of ES products of T. muris adult worms. Tm16 was one of the proteins identified by mass spectrometry. Tm16 shares 57% sequence identity with Ov16, an immunodominant diagnostic antigen from Onchocerca volvulus. Recombinant Tm16 with a carboxyl terminal hexahistidine was produced using Pichia pastoris. Polyclonal antibodies against rTm16 were generated by one-prime and two-boost immunization of three female Balb/c mice with 25 μg of recombinant Tm16 emulsified with ISA720 adjuvant. These polyclonal antibodies confirmed that Tm16 is localized to the ES products and the soluble fraction of the adult worm. Additionally, the high-resolution crystal structure of Tm16 was solved by molecular replacement. Tm16 belongs to the phosphatidylethanolamine-binding-like protein (PEBP1) family and this is the first structure of a PEBP1 from a parasite.

Protein Translation Enzyme lysyl-tRNA Synthetase Presents a New Target for Drug Development against Causative Agents of Loiasis and Schistosomiasis

Helminth parasites are an assemblage of two major phyla of nematodes (also known as roundworms) and platyhelminths (also called flatworms). These parasites are a major human health burden, and infections caused by helminths are considered under neglected tropical diseases (NTDs). These infections are typified by limited clinical treatment options and threat of drug resistance. Aminoacyl-tRNA synthetases (aaRSs) are vital enzymes that decode genetic information and enable protein translation. The specific inhibition of pathogen aaRSs bores well for development of next generation anti-parasitics. Here, we have identified and annotated aaRSs and accessory proteins from Loa loa (nematode) and Schistosoma mansoni (flatworm) to provide a glimpse of these protein translation enzymes within these parasites. Using purified parasitic lysyl-tRNA synthetases (KRSs), we developed series of assays that address KRS enzymatic activity, oligomeric states, crystal structure and inhibition profiles. We show that L. loa and S. mansoni KRSs are potently inhibited by the fungal metabolite cladosporin. Our co-crystal structure of Loa loa KRS-cladosporin complex reveals key interacting residues and provides a platform for structure-based drug development. This work hence provides a new direction for both novel target discovery and inhibitor development against eukaryotic pathogens that include L. loa and S. mansoni.

Honoring antiparasitics: The 2015 Nobel Prize in Physiology or Medicine

Protozoa and helminths are the two main groups that cause parasitic diseases with a broad spectrum of clinical symptoms. Protozoa are unicellular organisms like the malaria parasite Plasmodium, which is responsible for the majority of deaths associated with parasitic infections. Helminths are alternative parasites that can produce debilitating diseases in hosts, some of which result in chronic infections. The discovery of effective therapeutic drugs is the key to improving health in regions of poverty and poor sanitation where these parasites usually occur. It is very encouraging that the 2015 Nobel Prize in Physiology or Medicine was awarded to Youyou Tu as well as William C. Campbell and Satoshi Õmura for their considerable contributions in discovering artemisinin and avermectin, respectively. Both drugs revolutionized therapies for filariasis and malaria, significantly reducing by large percentages their morbidity and mortality.

Extracellular Onchocerca-derived small RNAs in host nodules and blood

Background

microRNAs (miRNAs), a class of short, non-coding RNA can be found in a highly stable, cell-free form in mammalian body fluids. Specific miRNAs are secreted by parasitic nematodes in exosomes and have been detected in the serum of murine and dog hosts infected with the filarial nematodes Litomosoides sigmodontis and Dirofilaria immitis, respectively. Here we identify extracellular, parasite-derived small RNAs associated with Onchocerca species infecting cattle and humans.

Methods

Small RNA libraries were prepared from total RNA extracted from the nodule fluid of cattle infected with Onchocerca ochengi as well as serum and plasma from humans infected with Onchocerca volvulus in Cameroon and Ghana. Parasite-derived miRNAs were identified based on the criteria that sequences unambiguously map to hairpin structures in Onchocerca genomes, do not align to the human genome and are not present in European control serum.

Results

A total of 62 mature miRNAs from 52 distinct pre-miRNA candidates were identified in nodule fluid from cattle infected with O. ochengi of which 59 are identical in the genome of the human parasite O. volvulus. Six of the extracellular miRNAs were also identified in sequencing analyses of serum and plasma from humans infected with O. volvulus. Based on sequencing analysis the abundance levels of the parasite miRNAs in serum or plasma range from 5 to 127 reads/per million total host miRNA reads identified, comparable to our previous analyses of Schistosoma mansoni and L. sigmodontis miRNAs in serum. All six of the O. volvulus miRNAs identified have orthologs in other filarial nematodes and four were identified in the serum of mice infected with L. sigmodontis.

Conclusions

We have identified parasite-derived miRNAs associated with onchocerciasis in cattle and humans. Our results confirm the conserved nature of RNA secretion by diverse nematodes. Additional species-specific small RNAs from O. volvulus may be present in serum based on the novel miRNA sequences identified in the nodule fluid. In our analyses comparison to European control serum illuminates the scope for false-positives, warranting caution in criteria that should be applied to identification of biomarkers of infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-0656-1) contains supplementary material, which is available to authorized users.

Repurposing drugs for the treatment and control of helminth infections

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Drug repurposing continues to be the central drug discovery strategy for helminths.

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Most repurposed drugs come from veterinary medicine and known drug classes.

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Only a handful of drugs have advanced clinically.

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More collaborations and funding are needed to advance discoveries to the market.

Helminth infections are responsible for a considerable public health burden, yet the current drug armamentarium is small. Given the high cost of drug discovery and development, the high failure rates and the long duration to develop novel treatments, drug repurposing circumvents these obstacles by finding new uses for compounds other than those they were initially intended to treat. In the present review, we summarize in vivo and clinical trial findings testing clinical candidates and marketed drugs against schistosomes, food-borne trematodes, soil-transmitted helminths, Strongyloides stercoralis, the major human filariases lymphatic filariasis and onchocerciasis, taeniasis, neurocysticercosis and echinococcosis. While expanding the applications of broad-spectrum or veterinary anthelmintics continues to fuel alternative treatment options, antimalarials, antibiotics, antiprotozoals and anticancer agents appear to be producing fruitful results as well. The trematodes and nematodes continue to be most investigated, while cestodal drug discovery will need to be accelerated. The most clinically advanced drug candidates include the artemisinins and mefloquine against schistosomiasis, tribendimidine against liver flukes, oxantel pamoate against trichuriasis, and doxycycline against filariasis. Preclinical studies indicate a handful of promising future candidates, and are beginning to elucidate the broad-spectrum activity of some currently used anthelmintics. Challenges and opportunities are further discussed.

Detection of circulating parasite-derived microRNAs in filarial infections

Filarial nematodes cause chronic and profoundly debilitating diseases in both humans and animals. Applications of novel technology are providing unprecedented opportunities to improve diagnosis and our understanding of the molecular basis for host-parasite interactions. As a first step, we investigated the presence of circulating miRNAs released by filarial nematodes into the host bloodstream. miRNA deep-sequencing combined with bioinformatics revealed over 200 mature miRNA sequences of potential nematode origin in Dirofilaria immitis-infected dog plasma in two independent analyses, and 21 in Onchocerca volvulus-infected human serum. Total RNA obtained from D. immitis-infected dog plasma was subjected to stem-loop RT-qPCR assays targeting two detected miRNA candidates, miR-71 and miR-34. Additionally, Brugia pahangi-infected dog samples were included in the analysis, as these miRNAs were previously detected in extracts prepared from this species. The presence of miR-71 and miR-34 discriminated infected samples (both species) from uninfected samples, in which no specific miRNA amplification occurred. However, absolute miRNA copy numbers were not significantly correlated with microfilaraemia for either parasite. This may be due to the imprecision of mf counts to estimate infection intensity or to miRNA contributions from the unknown number of adult worms present. Nonetheless, parasite-derived circulating miRNAs are found in plasma or serum even for those species that do not live in the bloodstream.

Filarial parasites commonly infect humans and animals, especially in tropical settings. The strongly debilitating panel of diseases they cause in humans contributes to an entrenched cycle of poverty. For efficient treatment strategies, reliable diagnostic tests are necessary. We investigated the potential of parasite-derived microRNAs (miRNAs; short non-coding RNA molecules present in eukaryotes) as biomarkers of infection. Using deep-sequencing technologies and bioinformatics, we identified over two-hundred mature miRNA candidates of nematode origin in plasma from Dirofilaria immitis-infected dogs. Similarly, we discovered twenty-one miRNA candidates predicted to be released by Onchocerca volvulus in infected human sera. We developed two RT-qPCR assays for the detection of D. immitis miR-71 and miR-34 in dog plasma that discriminated infected from uninfected samples. We demonstrated the presence of filarial miRNAs in host blood, regardless of localization in their respective hosts, and suggest that they are suitable targets for detection by RT-qPCR.

An Extremely Rare Situation - Subcutaneously Filariasis Presented at ED Craiova

A 32 year old male patient presented to the ED Craiova with migratory, burning pain, to the right cervical and left upper eyelid. Sudden, transient, bilateral knee swelling six months ago. An inflammatory trace and a renitent cord can feel at this level, with spontaneous mobility. A microfilaraemic parasite was surgically extracted from upper eyelid. Mobility of the parasite was the key element of an extremely quick and easy diagnosis for a very rare disease but the specific circumstances of the contamination remains unclear. Even uncommon, multiple determinations are possible requiring systematic and long term investigation and medical surveillance.