Intestinal protozoa and epithelial cell kinetics, structure and function

Intestinal protozoa are not only common enteric pathogens in the tropics but also the high incidence of infection among immunocompromised patients in northern countries has evoked an increased interest in these parasites. Although enteric protozoa are a major cause of diarrhea and malabsorption in humans and other animals, the pathophysiology of gut disturbances caused by them remains poorly understood. Clinical signs related to enteric protozoan disease commonly involve malabsorption, diarrhea, weight loss or retarded weight gain and anorexua. Since these infections are most prevalent and most severe in the young, this may translate into considerable illness among children and significant loss to the agricultural economy where domestic animals are prone to infection. In this review we describe the effects of intestinal protozoan diseases on the structure, kinetics and function of absorptive intestinal cells and other epithelial cells, and correlate morphological injury with physiological alterations in the parasitized gut. Some of the interactions between immune responses and pathophysiology will be discussed, but in-depth discussion of intestinal immunity has recently been undertaken by other authors.     

Ancylostoma ceylanicum excretory-secretory protein 2 adopts a netrin-like fold and defines a novel family of nematode proteins

Hookworms are human parasites that have devastating effects on global health, particularly in underdeveloped countries. Ancylostoma ceylanicum infects humans and animals, making it a useful model organism to study disease pathogenesis. A. ceylanicum excretory-secretory protein 2 (AceES-2), a highly immunoreactive molecule secreted by adult worms at the site of intestinal attachment, is partially protective when administered as a mucosal vaccine against hookworm anemia. The crystal structure of AceES-2 determined at 1.75 Å resolution shows that it adopts a netrin-like fold similar to that found in tissue inhibitors of matrix metalloproteases (TIMPs) and in complement factors C3 and C5. However, recombinant AceES-2 does not significantly inhibit the 10 most abundant human matrix metalloproteases or complement-mediated cell lysis. The presence of a highly acidic surface on AceES-2 suggests that it may function as a cytokine decoy receptor. Several small nematode proteins that have been annotated as TIMPs or netrin-domain-containing proteins display sequence homology in structurally important regions of AceES-2′s netrin-like fold. Together, our results suggest that AceES-2 defines a novel family of nematode netrin-like proteins, which may function to modulate the host immune response to hookworm and other parasites.     

Parasites as probes for prehistoric human migrations?

Host-specific parasites of humans are used to track ancient migrations. Based on archaeoparasitology, it is clear that humans entered the New World at least twice in ancient times. The archaeoparasitology of some intestinal parasites in the New World points to migration routes other than the Bering Land Bridge. Helminths have been found in mummies and coprolites in North and South America. Hookworms (Necator and Ancylostoma), whipworms (Trichuris trichiura) and other helminths require specific conditions for life-cycle completion. They could not survive in the cold climate of the northern region of the Americas. Therefore, humans would have lost some intestinal parasites while crossing Beringia. Evidence is provided here from published data of pre-Columbian sites for the peopling of the Americas through trans-oceanic or costal migrations.     

Protozoan parasite-specific carbohydrate structures

The carbohydrate moieties displayed by pathogenic protozoan parasites exhibit many unusual structural features and their expression is often developmentally regulated. These unique structures suggest a specific relationship between such carbohydrates and parasite pathogenicity. Studies of infected humans indicate that immune responses to protozoan parasites are elicited by glycan determinants on cell-surface or secreted molecules. Infections by protozoa are a major worldwide health problem, and no vaccines or efficacious treatments exist to date. Recent progress has been made in elucidating the structure and function of carbohydrates displayed by major protozoan parasites that infect man. These structures can be used as prototypes for the chemical or combined chemo-enzymatic synthesis of new compounds for diagnosis and vaccine development, or as inhibitors specifically designed to target parasite glycan biosynthesis.     

Cryptosporidium sp. skunk genotype in wild raccoons (Procyon lotor) naturally infected with Baylisascaris procyonis from Central Germany

Cryptosporidium spp. are apicomplexan parasites of public health concern. They are one of the main causes of intestinal diseases in humans and animals. Contaminated water is among the main sources of infection for humans and mammals. Raccoons are an introduced species in Germany. They are anthropogenic adapters with a natural affinity for water bodies. We collected samples from wild raccoons in the Federal States of Saxony and Thuringia, Central Germany. Through molecular genotyping, we found Cryptosporidium sp. skunk genotype in one raccoon from Saxony (1/24) and in one animal from Thuringia (1/27). Both raccoons were also infected with the zoonotic nematode Baylisascaris procyonis. This is the first report of co-infection with these two parasites in raccoons from Germany. Our study highlights the potential of these animals as carriers of zoonotic pathogens. Since raccoons can thrive in human settlements, this study provides data that can be used as a baseline for preventive programs.     

Helminths as heirlooms and souvenirs: a review of new world paleoparasitology

Evidence from studies on ancient human feces, intestinal contents and organs of preserved bodies has established that Enterobius vermicularis, Trichuris trichiura, Diphyllobothrium spp and probably Trichinella spiralis infected humans in the pre-Columbian New World. These species, and perhaps other common human helminths for which there is not yet convincing evidence, probably accompanied transberingeal immigrants and their dogs, and thus can be seen as heirloom parasites. Early humans on the American continents were affected by helminths of native animals such as Paragonimus and Cryptocotyle, and these have also been found in precontact human remains. Michael Kliks considers that the indigenous parasites infecting early Americans may be viewed as zoonotic souvenirs of some 50 millennia of migrations from Alaska to Patagonia. Among the most serious zoonoses would have been infection by cystic hydatid larvae of echinococcid tapeworms, the many enzootic filarial worms, and a variety of larval trematodes and nematodes.     

Diethylcarbamazine Increases Activation of Voltage-Activated Potassium (SLO-1) Currents in Ascaris suum and Potentiates Effects of Emodepside

Diethylcarbamazine is a drug that is used for the treatment of filariasis in humans and animals; it also has effects on intestinal nematodes, but its mechanism of action remains unclear. Emodepside is a resistance-busting anthelmintic approved for treating intestinal parasitic nematodes in animals. The novel mode of action and resistance-breaking properties of emodepside has led to its use against intestinal nematodes of animals, and as a candidate drug for treating filarial parasites. We have previously demonstrated effects of emodepside on SLO-1 K⁺-like currents in Ascaris suum. Here, we demonstrate that diethylcarbamazine, which has been proposed to work through host mediated effects, has direct effects on a nematode parasite, Ascaris suum. It increases activation of SLO-1 K⁺ currents and potentiates effects of emodepside. Our results suggest consideration of the combination of emodepside and diethylcarbamazine for therapy, which is predicted to be synergistic. The mode of action of diethylcarbamazine may involve effects on parasite signaling pathways (including nitric oxide) as well as effects mediated by host inflammatory mediators.     

Characterization of two cysteine proteases secreted by Blastocystis ST7, a human intestinal parasite

Blastocystis spp. are unicellular anaerobic intestinal parasites of both humans and animals and the most prevalent ones found in human stool samples. Their association with various gastrointestinal disorders raises the questions of its pathogenicity and of the molecular mechanisms involved. Since secreted proteases are well-known to be implicated in intestinal parasite virulence, we intended to determine whether Blastocystis spp. possess such pathogenic factors. In silico analysis of the Blastocystis subtype 7 (ST7) genome sequence highlighted 22 genes coding proteases which were predicted to be secreted. We characterized the proteolytic activities in the secretory products of Blastocystis ST7 using specific protease inhibitors. Two cysteine proteases, a cathepsin B and a legumain, were identified in the parasite culture supernatant by gelatin zymographic SDS-PAGE gel and MS/MS analysis. These proteases might act on intestinal cells and disturb gut function. This work provides serious molecular candidates to link Blastocystis spp. and intestinal disorders.     

旋毛虫感染与肠黏膜免疫应答作用的研究进展

旋毛虫病是一种常见的人兽共患寄生虫病,也是一种重要的食源性寄生虫病,严重危害着人类的健康。肠黏膜是肠道寄生虫（包括旋毛虫等）进入宿主的重要门户,即机体非特异性抗感染的第一道防线,也是宿主抵御肠道寄生虫入侵的重要固有屏障,后者发挥着固有性免疫和适应性免疫功能的作用。宿主的肠黏膜免疫应答反应决定旋毛虫与宿主相互作用和适应关系。本研究就目前国内外学者研究旋毛虫感染与宿主免疫的现状,分别从肠道黏膜组织学结构、免疫细胞、细胞因子和小肠上皮细胞4个方面,综述一下肠黏膜对旋毛虫感染的免疫应答作用,目的在于揭示宿主肠黏膜对旋毛虫感染的免疫应答机制。     

捕食风险对越冬根田鼠肠道寄生物易感性的影响

在自然生态系统中,不同营养级物种可通过特征介导间接效应对生态系统的稳定及种群产生深刻的影响。但目前有关特征介导间接效应的实验研究多见于无脊椎动物、鱼类和两爬类。本研究以根田鼠为对象,在野外围栏内建立预防捕食者和未预防捕食者两种实验处理种群,并通过采用麦克马斯特法测定两种处理种群实验个体肠道寄生物感染种类及感染率和感染强度,采用PHA（phytohemagglutinin）反应和白细胞分类计数测定不同处理种群实验个体免疫能力,以分析捕食风险对根田鼠肠道寄生物的感染效应。结果表明,未预防捕食者处理组根田鼠PHA反应、白细胞计数和淋巴细胞计数较预防捕食者处理组实验个体显著降低,而球虫 E. wenrichi 的感染率和感染强度则显著增加,但绦虫和线虫以及其他3种球虫的感染率和感染强度无显著差异。结果表明,捕食者可通过介导猎物免疫力特征而间接影响猎物肠道寄生物的感染,验证了本项提出的捕食风险可通过降低根田鼠的免疫能力而增加其肠道寄生物感染的假设。     

Dogs and intestinal parasites: a public health problem.

The stools of 239 stray dogs were examined for intestinal parasites. Of the helminths found, Toxocara canis (43.5%), tapeworms (25.5%), Ascaris species (21.3%) and hookworms (12.5%) were the commonest. Of the protozoans found, Isospora species and Entamoeba coli were the most prevalent. An unusual feature of the present study was the finding of Ascaris species. The importance of the high prevalence of intestinal parasites in dogs, the close contact of humans with dogs'' excreta and the possible role of this environmental pollution in the spread of human disease are discussed.     

Parasites: Small Players with Crucial Roles in the Ecological Theater

Effective management of our natural resources requires an understanding of ecosystem structure and function; effectively, an ecosystem-based approach to management. Parasites occur, albeit cryptically, in almost all ecosystems, yet they are usually neglected in studies on populations and communties of organisms. Parasites can have pronounced or subtle effects on hosts affecting host behavior, growth, fecundity, and mortality. Furthermore, parasites may regulate host population dynamics and influence community structure. Many parasites have complex life cycles and depend for transmission on the presence of a variety of invertebrate and vertebrate intermediate hosts. Often transmission involves predator–prey interactions. Thus, parasites reflect the hosts position in the food web and are indicative of changes in ecosystem structure and function. Parasites can provide information on population structure, evolutionary hypotheses, environmental stressors, trophic interactions, biodiversity, and climatic conditions. I use examples from diverse freshwater and marine systems to demonstrate that parasites should be incorporated into research and monitoring programs to maximize information gathered in ecosystem-based studies and resource management.Supplementary Tables 3, 4, 5, 6 and additional references for this article are available for viewing by subscribers only at     

LIBP-Pred: web server for lipid binding proteins using structural network parameters; PDB mining of human cancer biomarkers and drug targets in parasites and bacteria

Lipid-Binding Proteins (LIBPs) or Fatty Acid-Binding Proteins (FABPs) play an important role in many diseases such as different types of cancer, kidney injury, atherosclerosis, diabetes, intestinal ischemia and parasitic infections. Thus, the computational methods that can predict LIBPs based on 3D structure parameters became a goal of major importance for drug-target discovery, vaccine design and biomarker selection. In addition, the Protein Data Bank (PDB) contains 3000+ protein 3D structures with unknown function. This list, as well as new experimental outcomes in proteomics research, is a very interesting source to discover relevant proteins, including LIBPs. However, to the best of our knowledge, there are no general models to predict new LIBPs based on 3D structures. We developed new Quantitative Structure-Activity Relationship (QSAR) models based on 3D electrostatic parameters of 1801 different proteins, including 801 LIBPs. We calculated these electrostatic parameters with the MARCH-INSIDE software and they correspond to the entire protein or to specific protein regions named core, inner, middle, and surface. We used these parameters as inputs to develop a simple Linear Discriminant Analysis (LDA) classifier to discriminate 3D structure of LIBPs from other proteins. We implemented this predictor in the web server named LIBP-Pred, freely available at , along with other important web servers of the Bio-AIMS portal. The users can carry out an automatic retrieval of protein structures from PDB or upload their custom protein structural models from their disk created with LOMETS server. We demonstrated the PDB mining option performing a predictive study of 2000+ proteins with unknown function. Interesting results regarding the discovery of new Cancer Biomarkers in humans or drug targets in parasites have been discussed here in this sense.     

An efficient method for viable cryopreservation and recovery of hookworms and other gastrointestinal nematodes in the laboratory

Hookworms (genera Ancylostoma and Necator) are amongst the most prevalent and important parasites of humans globally. These intestinal parasites ingest blood, resulting in anemia, growth stunting, malnutrition, and adverse pregnancy outcomes. They are also critical parasites of dogs and other animals. In addition, hookworms and hookworm products are being explored for their use in treatment of autoimmune and inflammatory diseases. There is thus a significant and growing interest in these mammalian host-obligate parasites. Laboratory research is hampered by the lack of good means of cryopreservation and recovery of parasites. Here, we describe a robust method for long-term (≥3 year) cryopreservation and recovery of both Ancylostoma and Necator hookworms that is also applicable to two other intestinal parasites that passage through the infective L3 stage, Strongyloides ratti and Heligmosomoides polygyrus bakeri. The key is a revised recovery method, in which cryopreserved L1s are thawed and raised to the infective L3 stage using activated charcoal mixed with uninfected feces from a permissive host. This technique will greatly facilitate research on and availability of gastrointestinal parasitic nematodes with great importance to global health, companion animal health, and autoimmune/inflammatory disease therapies.     

Recent advances in human protozoan parasites of the gastrointestinal tract

An attempt was made in this report to present an update on the recent development on intestinal protozoan infections in humans. Except for a few historical references the review covers the period from 1980 to the time of writing, mid-1985. The emphasis was on the more important parasites and an effort made to cover the latest developments in their biology, epidemiology and pathogenesis. During preparation of this paper I was impressed with the plethora of papers published on some parasites and the paucity of reports on others. There are an increasing number of papers on Cryptosporidium sp. and the interest in the organisms should continue. Furthermore, it will be of interest to follow the association between Blastocystis hominis and disease. These are essentially new protozoan parasites of man, and one wonders how many more intestinal protozoan parasitosis are still waiting to be found. Like the Cryptosporidium sp., it may be a matter of finding the right diagnostic technique to detect the unknown organism.Giardiasis continues to be a cause of diarrhea among various groups especially campers who are drinking untreated water and G. lamblia as well as E. histolytica are being found more frequently in homosexuals with and without AIDS. The ability to predict virulence in strains of E. histolytica by enzyme patterns is intriguing but some skeptics still prefer the older test for virulence by cecal scoring in animals. New animal models are being evaluated and new techniques applied to the study of pathogenic protozoa. In the future the use of new biotechnological methods will most certainly lead to a better understanding of intestinal protozoa as well as of other parasitic organisms.     

活血化瘀法对肠道菌群结构及 肠屏障功能影响的研究

随着人们对于肠道菌群种类以及作用认识的逐渐深入,我们发现作为人体庞大而又复杂的微生态系统,肠道菌群的结构及和菌群分布有紧密联系的肠屏障功能的改变与人体的健康息息相关。中药作为传统医学的一种治疗方法,其对人体的治疗作用是十分显著的,而活血化瘀法是使用具有消散作用及攻逐体内淤血作用的药物来治疗人类各种疾病的一种方法,这种方法对于肠道菌群以及肠屏障功能也产生了深远的影响。本文围绕肠道菌群结构改变及肠黏膜屏障功能的变化,对近十年关于肠道菌群与活血化瘀方药的相关文献进行综述,探究活血化瘀法(中药及中药复方)对于肠道菌群的影响,为临床治疗提供新思路。     

Interplay of parasite-driven immune responses and autoimmunity

As more facts emerge regarding the ways in which parasite-derived molecules modulate the host immune response, it is possible to envisage how a lack of infection by agents that once infected humans commonly might contribute to the rise in autoimmune disease. Through effects on cells of both the innate and adaptive arms of the immune response, parasites can orchestrate a range of outcomes that are beneficial not only to parasites, in terms of facilitating their life cycles, but also to their host, in limiting pathology.     

Functional genetics in Apicomplexa: potentials and limits

The Apicomplexans are obligate intracellular protozoan parasites and the causative agents of severe diseases in humans and animals. Although complete genome sequences are available since many years and for several parasites, they are replete with putative genes of unassigned function. Forward and reverse genetic approaches are limited only to a few Apicomplexans that can either be propagated in vitro or in a convenient animal model. This review will compare and contrast the most recent strategies developed for the genetic manipulation of Plasmodium falciparum, Plasmodium berghei and Toxoplasma gondii that have taken advantage of the intrinsic features of their respective genomes. Efforts towards the improvement of the transfection efficiencies in malaria parasites, the development of approaches to study essential genes and the elaboration of high-throughput methods for the identification of gene function will be discussed.     

The antiparasitic actions of plant jasmonates

Jasmonates are a group of small lipids produced in plants, which function as plant stress hormones. We have previously shown that jasmonates can exert significant cytotoxic effects upon human cancer cells. The purpose of the present study was to determine the effects of jasmonates on parasites. To that end, we chose 2 major human blood parasites, Plasmodium falciparum, a unicellular parasite, and Schistosoma mansoni, a multicellular helminth parasite, and studied the effects of jasmonates on these parasites in vitro. We found that jasmonates are cytotoxic toward both parasites, with P. falciparum being the more susceptible. Jasmonates did not cause any damage to control human erythrocytes at the maximum concentration used in the experiments. This is the first study demonstrating the antiparasitic potential of plant-derived jasmonates.     

肠道病原菌侵袭素在药物纳米载体中的应用

口服给药是药物递送系统中的优选途径。然而,在通过胃肠道时,肠细胞的低渗透性经常会阻碍药物的有效递送。包囊药物能够解决这一问题的关键,取决于其中的细胞侵袭性靶向基团包裹的纳米颗粒系统。这种药物递送系统的侵入特性是由细菌侵袭素的关键成分提供,这些成分具有快速调节药物穿越肠细胞的作用,从而促进宿主细胞对药物的有效吸收。此综述重点阐述细菌侵袭系统,对合适的侵袭素分别从功能和分子结构、作为靶向药物的相对价值以及在使用过程中可能存在的误区依次进行探讨。此外,对口服给药方法的改进和未来前景也进行了讨论。