Human Nematode Infections Research Articles

Identification of Small Molecules of the Infective Stage of Human Hookworm Using LCMS-Based Metabolomics and Lipidomics Protocols.

Hookworm infections affect millions of people worldwide and are responsible for impaired mental and physical growth in children, and anemias. There is no vaccine, and increasing anthelmintic drug resistance in nematodes of domestic animals, and reduced drug cure rates in nematode infections of humans is alarming. Despite this looming health problem, there is a significant knowledge gap in terms of nonproteinaceous "excretory/secretory products" (ESPs) and how they orchestrate a parasitic existence. In the current study, we have conducted the first metabolomic and lipidomic analysis of the infective third-stage filariform larvae (L3) of the predominant human hookworm Necator americanus using liquid chromatography-mass spectrometry. Altogether, we have identified a total of 645 small molecules that were mainly produced through amino acid and glycerophospholipid metabolism. Putatively, 495 metabolites were unique to the somatic tissue extract, and 34 metabolites were present only in the ESP component. More than 21 novel mass features with nitrogen and sulfur functional groups were detected in the ESP component for the first time from helminths. While this study could not establish the biological functions of the metabolites identified, literature searches revealed that these metabolites possess various biological properties, including anti-inflammatory activities. These metabolites are likely used by the parasite upon exposure to a host to facilitate skin penetration, passage through different tissues, and immune regulation in the small bowel. Overall, the results presented herein offer significant insight into the metabolome of N.americanus L3 and have the potential to instigate future work to establish biomarkers of infection. This area urgently needs attention, given the lack of sensitive point-of-care diagnostic tools.

Identification of three immunodominant motifs with atypical isotype profile scattered over the Onchocerca volvulus proteome.

Understanding the immune response upon infection with the filarial nematode Onchocerca volvulus and the mechanisms that evolved in this parasite to evade immune mediated elimination is essential to expand the toolbox available for diagnostics, therapeutics and vaccines development. Using high-density peptide microarrays we scanned the proteome-wide linear epitope repertoire in Cameroonian onchocerciasis patients and healthy controls from Southern Africa which led to the identification of 249 immunodominant antigenic peptides. Motif analysis learned that 3 immunodominant motifs, encompassing 3 linear epitopes, are present in 70, 43, and 31 of these peptides, respectively and appear to be scattered over the entire proteome in seemingly non-related proteins. These linear epitopes are shown to have an atypical isotype profile dominated by IgG1, IgG3, IgE and IgM, in contrast to the commonly observed IgG4 response in chronic active helminth infections. The identification of these linear epitope motifs may lead to novel diagnostic development but further evaluation of cross-reactivity against common co-infecting human nematode infections will be needed.

Ascariasis: Public Health Importance and its Status in Ethiopia

Waterborne diseases are a major public health problem in many countries of the world including Ethiopia. Waterborne diseases are caused by viruses, bacteria, protozoa, helminthes, and fungi. Currently, about 1.1 billion people in the world drink unsafe water, which is responsible for millions of cases of waterborne diseases. Ascariasis is among the several parasites which is widely prevalent helminthic disease of public health significance. It is commonly found in warm tropical and sub-tropical climates in Sub-Saharan Africa and Southeast Asia. It flourishes in areas with poor sanitation and crop irrigation by improperly treated wastewater. Severe ascariasis infections cause approximately, 60,000 deaths annually, mainly in children. It is transmitted through accidental ingestion of Ascaris eggs from contaminated water, food or soil. Among the Ascaris species, Ascaris lumbricoides and Ascaris suum are the parasitic nematode infections of humans and pigs with serious outcomes, respectively. Ascariasis is found in association with low personal hygiene, poor sanitation, and in places where human faeces are used as fertilizer. Clinical spectrum of disease varies from asymptomatic to nausea, vomiting, abdominal pain, pneumonia, and intestinal obstruction. Laboratory help is imperative to assist the clinical diagnosis. Treatment of adult worms can be done with albendazole, mebendazole, and pyrantel pamote. Public health department should improve the safety of the drinking water. Health education to the community, mainly the school children about the personal hygiene and environmental sanitation will be important in preventing the infection. Ascariasis caused by A. lumbricoides is found among children and adults in Ethiopia. Considering the importance of ascariasis from public health and economic perspective, further research on the development of safe, potent and cheap vaccine is emphasized. Moreover, comprehensive studies on zoonotic importance of A. suum should be planned particularly, in pig rearing countries

Strongylid Nematode Infections of Humans, Ruminants and Pigs in Kumasi, Ashanti Region of Ghana

Strongylid Nematode Infections of Humans, Ruminants and Pigs in Kumasi, Ashanti Region of Ghana

Nitazoxanide: Nematicidal mode of action and drug combination studies

Intestinal nematodes or roundworms (aka soil-transmitted helminths or STHs) cause great disease. They infect upwards of two billion people, leading to high morbidity and a range of health problems, especially in infected children and pregnant women. Development of resistance to the two main classes of drugs used to treat intestinal nematode infections of humans has been reported. To fight STH infections, we need new and more effective drugs and ways to improve the efficacy of the old drugs. One promising alternative drug is nitazoxanide (NTZ). NTZ, approved for treating human protozoan infections, was serendipitously shown to have therapeutic activity against STHs. However, its mechanism of action against nematodes is not known. Using the laboratory nematode Caenorhabditis elegans, we show that NTZ acts on the nematodes through avr-14, an alpha-type subunit of a glutamate-gated chloride ion channel known for its role in ivermectin susceptibility. In addition, a forward genetic screen to select C. elegans mutants resistant to NTZ resulted in isolation of two NTZ resistant mutants that are not in avr-14, suggesting that additional mechanisms are involved in resistance to NTZ. We found that NTZ combines synergistically with other classes of anthelmintic drugs, i.e. albendazole and pyrantel, making it a good candidate for further studies on its use in drug combination therapy of STH infections. Given NTZ acts against a wide range of nematode parasites, our findings also validate avr-14 as an excellent target for pan-STH therapy.

In silico approach to screen compounds active against parasitic nematodes of major socio-economic importance

BackgroundInfections due to parasitic nematodes are common causes of morbidity and fatality around the world especially in developing nations. At present however, there are only three major classes of drugs for treating human nematode infections. Additionally the scientific knowledge on the mechanism of action and the reason for the resistance to these drugs is poorly understood. Commercial incentives to design drugs that are endemic to developing countries are limited therefore, virtual screening in academic settings can play a vital role is discovering novel drugs useful against neglected diseases. In this study we propose to build robust machine learning model to classify and screen compounds active against parasitic nematodes.ResultsA set of compounds active against parasitic nematodes were collated from various literature sources including PubChem while the inactive set was derived from DrugBank database. The support vector machine (SVM) algorithm was used for model development, and stratified ten-fold cross validation was used to evaluate the performance of each classifier. The best results were obtained using the radial basis function kernel. The SVM method achieved an accuracy of 81.79% on an independent test set. Using the model developed above, we were able to indentify novel compounds with potential anthelmintic activity.ConclusionIn this study, we successfully present the SVM approach for predicting compounds active against parasitic nematodes which suggests the effectiveness of computational approaches for antiparasitic drug discovery. Although, the accuracy obtained is lower than the previously reported in a similar study but we believe that our model is more robust because we intentionally employed stringent criteria to select inactive dataset thus making it difficult for the model to classify compounds. The method presents an alternative approach to the existing traditional methods and may be useful for predicting hitherto novel anthelmintic compounds.

Pharmacotherapy of helminth infection

Background: In the first decade of the 21st century, worm infections are still very common, especially – but not exclusively – in the developing world. Objective: To review the current pharmacotherapy of the major trematode, cestode and nematode infections of humans. Methods: A systematic search of the Cochrane Databank of Controlled Trials and PubMed with MeSH terms (anthelmint* or treatment or therapy) and (cestoda or trematoda or nematoda or specific helminth species or specific medication). Further references were obtained from article biobliographies. Results: Three hundred and twenty-six publications were selected for further review. Conclusion: Albendazole, praziquantel and ivermectin are the most important anthelmintics available, easy to use and active against most helminths. Diethylcarbamazine is used in loasis and lymphatic filariasis. Doxycycline can eliminate endosymbiotic bacteria of certain filariae, but its place in therapy needs to be further defined. In the treatment of cystic hydatid disease, a better, non-caustic protoscolicidal drug would diminish the complication rate of current puncture–aspiration–injection–reaspiration treatment. The reliance on so few drugs creates a dangerous situation for development of resistance. Triclabendazole is a welcome addition for fascioliasis. Tribendimidine, artemisinine derivatives and nitazoxanide are promising products, but their therapeutic place needs to be further defined.

Molecular detection of benzimidazole resistance in Haemonchus contortus using real-time PCR and pyrosequencing

Benzimidazoles (BZ) are widely used to treat parasitic nematode infections of humans and animals, but resistance is widespread in veterinary parasites. Several polymorphisms in beta-tubulin genes have been associated with BZ-resistance. In the present study, we investigated beta-tubulin isotype 1 sequences of 18 Haemonchus contortus isolates with varying levels of resistance to thiabendazole. The only polymorphism whose frequency was significantly increased in the resistant isolates was TTC to TAC at codon 200. Real-time PCR (using DNA from 100 third-stage larvae, L3s) and pyrosequencing (from DNA from 1000-10 000 L3s) were used to measure allele frequencies at codon 200 of these isolates, producing similar results; drug sensitivity decreased with increasing TAC frequency. Pyrosequencing was also used to measure allele frequencies at positions 167 and 198. We showed that such measurements are sufficient to assess the BZ-resistance status of most H. contortus isolates. The concordance between real-time PCR and pyrosequencing results carried out in different laboratories indicated that these tools are suitable for the routine diagnosis of BZ-resistance in H. contortus. The molecular methods were more sensitive than the 'egg hatch test', and less time-consuming than current in vivo- or in vitro-anthelmintic resistance detection methods. Thus, they provide a realistic option for routine molecular resistance testing on farms.

Epithelia Control Gut Inflammation

The intestinal epithelial cells (IECs) provide a crucial barrier function preventing infection. Now these cells also are recognized as key instructors of inflammatory responses. Zaph et al . and Nenci et al . both used IEC-targeted gene knockouts in mice to show that nuclear factor κB (NF-κB) signaling in the IECs was essential for controlling infection and inflammatory responses. Zaph et al . knocked out IKKβ ( Ikkb ΔIEC mice) and Nenci et al . knocked out IKKγ (also known as NEMO) (NEMO IEC-KO mice) or both IKKα and IKKβ (IKK1/2 IEC-KO ); these kinases are involved in NF-κB activation. Zaph et al . studied the mouse response to Trichuris muris infection as a model of human nematode infections. Trichuris infection triggered NF-κB activation in the IECs of wild-type mice, and these mice developed a T helper 2 (T H 2) response; produced interleukin (IL)-4, -5, and -13; and cleared the infection. In contrast, the type 2 immune response of the Ikkb ΔIEC mice was impaired and the mice failed to clear the infection and developed severe intestinal inflammation with infiltration of lymphocytes, ulceration, and ultimately septicemia. This appeared to be due to decreased expression of the RNA of thymic stromal lymphopoietin (TSLP), which is encoded by an NF-κB-regulated gene. TSLP limits dendritic cell proinflammatory cytokine production, limits dendritic cell signals that trigger T H 1 differentiation, and promotes dendritic cell signals that trigger T H 2 cell differentiation. The NEMO IEC-KO and IKK1/2 IEC-KO mice studied by Nenci et al . exhibited a more severe phenotype with spontaneous formation of chronic severe intestinal inflammation. This was due to the complete abrogation of NF-κB signaling in these two knockout mice strains, whereas loss of IKKβ or IKKα function alone impairs but does not eliminate NF-κB signaling. The colitis that the NEMO IEC-KO mice developed was prevented if the mice were also deficient in MyD88, which is an adaptor important for Toll-like receptor (TLR) signaling triggered by pathogens such as intestinal bacteria. Colitis was also prevented in the NEMO IEC-KO if the mice were deficient for tumor necrosis factor-α (TNF-α) receptors. This was consistent with the observation that NEMO-deficient cells are more sensitive to apoptosis caused by TNF-α. Together these two articles clearly show that the NF-κB signaling in IECs plays a crucial role in controlling inflammatory responses and fighting infection in the gut. C. Zaph, A. E. Troy, B. C. Taylor, L. D. Berman-Booty, K. J. Guild, Y. Du, E. A. Yost, A. D. Gruber, M. J. May, F. R. Greten, L. Eckmann, M. Karin, D. Artis, Epithelial-cell-intrinsic IKK-β expression regulates intestinal immune homeostasis. Nature 446 , 552-556 (2007). [PubMed] A. Nenci, C. Becker, A. Wullaert, R. Gareus, G. van Loo, S. Danese, M. Huth, A. Nikolaev, C. Neufert, B. Madison, D. Gumucio, M. F. Neurath, M. Pasparakis, Epithelial NEMO links innate immunity to chronic intestinal inflammation. Nature 446 , 557-561 (2007). [PubMed]

Drug resistance in nematodes: a paper tiger or a real problem?

The purpose of this review is to illustrate where drug resistance in parasitic nematodes has become a major problem. The mechanisms underlying anthelmintic resistance, the possible reasons for the development of anthelmintic resistance, and recommendations to minimize the further development of anthelmintic resistance in humans will be addressed. Resistance has developed to all drugs of the few anthelmintic classes currently available. Drug resistance has become a major threat to sheep production in Australia, New Zealand, Great Britain and South Africa. In addition, the treatment of nematode infections in horses has become insufficient because of anthelmintic resistance, whereas resistance in cattle has recently been found in New Zealand and southern America. In contrast, anthelmintic resistance to human helminths has only been reported anecdotally. The rate of development of anthelmintic resistance is determined by the resistance gene frequency and by selection pressure, as illustrated by the concept of 'worms in refugia' in ovine nematode infections. Although anthelmintic resistance has become a major constraint in livestock production of small ruminants, drug resistance is currently not a major issue in the treatment of human nematode infections. However, if recent community treatment programmes are pursued injudiciously, the inevitable evolutionary consequence of anthelmintic resistance in humans might emerge sooner rather than later.

All you need to know about nematodes

The Biology of Nematodesedited by Donald L. Lee, Taylor & Francis, 2002. £120.00 (hbk) (635 pages)ISBN 0 415 27211 4Nematoda is the second, most diverse animal phylum, after Arthropoda. Free-living nematodes, abundant in the soil, are important as decomposers. Several plant parasitic nematodes cause diseases in economically important crops, and the animal parasitic nematodes are responsible for many animal and human infections worldwide. Because of the medical and veterinary importance of nematodes and their impact on plants, an extensive body of knowledge in the fields of developmental biology, biochemistry, physiology, immunology and molecular biology has emerged.The Biology of Nematodes is well-written and organized to include various aspects of nematode biology, comprising the most recent scientific data. This book has 24 chapters written by scientists with expertise in their subject areas. A detailed literature review in each chapter is useful as a source of reference. The book is a highly coordinated effort to provide reader with the most up-to-date information. There are several strengths in this book. Chapter 1 on systematics, delineates the past and present phylogenetic frameworks, and discusses about how the phylogenies translated into classifications. Chapters 2 and 3 present an excellent review of comparative, general nematode body-structure and life cycles. The inclusion of beautiful electron micrographs and cartoons make it easy to follow these chapters.Several key concepts of developmental biology were understood through studies using Caenorhabditis elegans as a model. Current knowledge on embryology, developmental biology and the hatching process, and pattern differences between different nematodes was described. It was fascinating to learn about the host-stimulated mechanisms that restrict host ranges and hatching behavior to ensure nematode survival. The book also gives a detailed account of the feeding behavior of free-living and parasitic nematodes, metabolism, excretion–secretion mechanisms, neuromuscular organization, locomotion and behavior.Nematode survival involves strategies to synchronize the development of suitable conditions for growth, which are presented in detail. David Gems has elegantly summarized the advances made in the genetics of ageing. Immunology of nematode infections in Chapter 18 covers the specific immune responses against nematode infections. The description of the roles of cytokines, and differences in T helper cell subset expression, specific to nematode infections, helps the non-immunology reader to understand host responses with ease.Basic strategies of biological and chemical control of animal parasitic nematodes and anthelmintic resistance were well described. A succinct reference list of nematicidal drugs, their chemical structures and mechanisms of resistance to several anthelmintics is well documented.Entomopathogenic nematodes kill their insect hosts within 48 h because they possess pathogenic bacteria harmful to insects. Nobuyoshi Ishibashi discusses the use of these nematodes for biological control of insect pests of economically important crops. Novel molecular approaches to crop resistance against nematodes, epidemiology and the control of human nematode infections were covered in the last two chapters.Wolbachia spp. are unique, intracellular symbiotic bacteria in filarial nematodes. Antibiotic treatment of filarial nematodes to clear Wolbachia causes sterility, inhibition of larval development and impacts the viability of adult worms [1xA new approach to the treatment of filariasis. Taylor, M.J. and Hoerauf, A. Curr. Opin. Infect. Dis. 2001; 14: 727–731Crossref | PubMedSee all References][1]. A description of this new control strategy will be valuable in future editions of this book.This book provides ample information for easy reading and understanding of the subject, and the chapters were written for independent reading, but not intended for understanding the detailed parasitism and pathogenic mechanisms of nematodes. It is an excellent reference book, ideally suited for teachers, students of all levels and other academics, who seek knowledge on the nematodes.

Animal models of intestinal nematode infections of humans.

In this paper we discuss several established and potential animal models for human parasitic infection, with a focus on rodent, pig and primate models and the nematodes Ascaris, Trichuris and Toxocara spp. Firstly, we discuss the relevance of choosing a suitable animal host to fit the particular study hypothesis, and the interaction between mathematical modelling and animal models. Secondly, we review the use of animal models for the study of nutrition-parasite interaction, evaluation of treatment and control strategies, and bacteria-parasite interactions. We show that rodent, pig and primate models are all very useful in parasitological research, and that each model has its limitations. However, based on recent experience with the pig-Ascaris and pig-Trichuris models, a more extensive use of the pig-parasite model is advocated, especially for the study of the interaction between human malnutrition and helminth infection, and congenital helminth infection.

Heligmosomoides polygyrus: CD4 + but not CD8 + T cells regulate the IgE response and protective immunity in mice

Oral inoculation of BALB/c mice with infective larvae of Heligmosomoides polygyrus resulted in chronic infection characterized by the release of parasite eggs in the feces for several months. The actual number of eggs per gram of feces was dependent on the dose of the inoculum. Serum IgE in infected mice peaked at a level of >70 μg/ml during Weeks 3 through 6 following inoculation, and high levels of IgE (>40 μg/ml) persisted for over 14 weeks. Protective immune responses resulted in reduced egg production and the development of markedly fewer adult worms in the small intestines following a challenge inoculation. The role of CD4 + and CD8 + T cells in these responses was examined by depletion in vivo of either T cell subpopulation with rat mAb specific for the appropriate determinants. Mice treated with anti-CD4 during a primary infection had increased EPG which was due primarily to an increase in worm fecundity (eggs produced per adult female). A challenge inoculation of mice that had been cleared of the primary infection with an anthelmintic drug induced a protective response that reduced development of new adult worms by 70–80% and their fecundity by >90%. This protective response was abrogated by injection of mice with anti-CD4. Serum IgE diminished when adult worms were removed after anthelmintic treatment. A more precipitous drop in serum IgE followed successive treatments of mice with an anthelmintic and anti-CD4. In addition, the anamnestic serum IgE response to a challenge inoculation was reduced by over 80% in anti-CD4-treated mice. Anti-CD8 treatment had no appreciable effect on the immunological or parasitological parameters measured following a challenge inoculation with H. polygyrus. Thus, CD4 + T cells regulate host protective immunity, worm fecundity, and IgE levels in an H. polygyrus infection. This experimental system may be particularly suitable for analysis of chronic nematode infections of humans and livestock because of the responsiveness of the parasite in vivo to changes in host immune function.

Surface antigens of male worms and microfilariae of Onchocerca gibsoni

Living adult males and microfilariae of the cattle filarial parasite Onchocerca gibsoni were externally labelled with radioactive iodine using the iodogen and Bolton-Hunter procedures. Characterization of labelled surface proteins by sodium dodecyi sulphate (SDS)-polyaerylamide gel electrophoresis revealed clear cut differences in the two life cycle stages. In addition, the two radiolabelling procedures yielded some differences in the profiles of radiolabelied surface proteins for both adults and microfilariae. Immunoprecipitation analysis revealed a number of labelled antigens recognized by antibodies in human onchocerciasis serum pools, thereby demonstrating the usefulness of O. gibsoni as a model in Onchocerca volvulus vaccine studies. The reactivity ofmicrofilarial antigens extended to antibodies from other human nematode infections, whereas male surface antigens, particularly those of low molecular weight, were Onchocerca specific. This indicates that O. gibsoni can provide a convenient source of specific diagnostic antigen.

Evasion of Immunity by Nematode Parasites Causing Chronic Infections

This chapter discusses the evasion of immunity by nematode parasites causing chronic infections. Human nematode infections are long-lasting (chronic), and people living in endemic areas may become infected in early childhood and carry worms for the remainder of their lives. This chapter considers those aspects of the immunological relationship between host and parasite, in field and laboratory studies, that are pertinent to an understanding of the mechanisms by which immunity is avoided and thus, chronicity of infection achieved. Human parasite epidemiologists, veterinary parasitologists, parasite biologists, and immunologists all have an interest in the strategies employed by parasites to evade host immune responses and also in control measures aimed at breaking the transmission of these important pathogens. Much remains to be accomplished in this challenging area of parasite immunology, and a closer liaison between all research groups interested in chronic nematode parasites ensures rapid progress in the near future.