Behind the smile: cell biology and disease mechanisms of Giardia species

Machine learning and explainable artificial intelligence for the prevention of waterborne cryptosporidiosis and giardiosis

Cryptosporidium and Giardia are important parasitic protozoa due to their zoonotic potential and impact on human health, and have often caused waterborne outbreaks of disease. Detection of (oo)cysts in water matrices is challenging and extremely costly, thus only few countries have legislated for regular monitoring of drinking water for their presence. Several attempts have been made trying to investigate the association between the presence of such (oo)cysts in waters with other biotic or abiotic factors, with inconclusive findings. In this regard, the aim of this study was the development of an holistic approach leveraging Machine Learning (ML) and eXplainable Artificial Intelligence (XAI) techniques, in order to provide empirical evidence related to the presence and prediction of Cryptosporidium oocysts and Giardia cysts in water samples. To meet this objective, we initially modelled the complex relationship between Cryptosporidium and Giardia (oo)cysts and a set of parasitological, microbiological, physicochemical and meteorological parameters via a model-agnostic meta-learner algorithm that provides flexibility regarding the selection of the ML model executing the fitting task. Based on this generic approach, a set of four well-known ML candidates were, empirically, evaluated in terms of their predictive capabilities. Then, the best-performed algorithms, were further examined through XAI techniques for gaining meaningful insights related to the explainability and interpretability of the derived solutions. The findings reveal that the Random Forest achieves the highest prediction performance when the objective is the prediction of both contamination and contamination intensity with Cryptosporidium oocysts in a given water sample, with meteorological/physicochemical and microbiological markers being informative, respectively. For the prediction of contamination with Giardia, the eXtreme Gradient Boosting with physicochemical parameters was the most efficient algorithm, while, the Support Vector Regression that takes into consideration both microbiological and meteorological markers was more efficient for evaluating the contamination intensity with cysts. The results of the study designate that the adoption of ML and XAI approaches can be considered as a valuable tool for unveiling the complicated correlation of the presence and contamination intensity with these zoonotic parasites that could constitute, in turn, a basis for the development of monitoring platforms and early warning systems for the prevention of waterborne disease outbreaks.

Probiotics: an alternative anti-parasite therapy

This paper review about probiotic effects and mechanism of action against the gut and non-gut helminths and protozoan parasites. Gastrointestinal parasitic infections are considered a serious health problem and are widely distributed globally. The disease process which emanates from this parasite infection provides some of the many public and veterinary health problems in the tropical and sub-tropical countries. Prevention and control of the parasite disease is through antihelmintic and anti-protozoan drugs, but, due to the increasing emergence of such drug resistance, eradication of parasite infestation in human and livestock still lingers a challenge, which requires the development of new alternative strategies. The use of beneficial microorganisms i.e. probiotics is becoming interesting due to their prophylactic application against several diseases including parasite infections. Recent studies on the interactions between probiotics, parasites and host immune cells using animal models and in vitro culture systems has increased considerably and draw much attention, yet the mechanisms of actions mediating the positive effects of these beneficial microorganisms on the hosts remain unexplored. Therefore, the aim of the present review is to summarize the latest findings on the probiotic research against the gut and non-gut parasites of significance.

Inhibition of Giardia duodenalis by isocryptolepine -triazole adducts and derivatives

Giardia duodenalis, a widespread parasitic flagellate protozoan causing giardiasis, affects millions annually, particularly impacting children and travellers. With no effective vaccine available, treatment primarily relies on the oral administration of drugs targeting trophozoites in the small intestine. However, existing medications pose challenges due to side effects and drug resistance, necessitating the exploration of novel therapeutic options. Isocryptolepine, derived from Cryptolepis sanguinolenta, has demonstrated promising antimicrobial and anticancer properties. This study evaluated eighteen isocryptolepine-triazole adducts for their antigiardial activities and cytotoxicity, with ISO2 demonstrating potent antigiardial activity and minimal cytotoxicity on human intestinal cells. Metabolomics analysis revealed significant alterations in G. duodenalis metabolism upon ISO2 treatment, particularly affecting phospholipid metabolism. Notably, the upregulation of phytosphingosine and triglycerides, and downregulation of certain fatty acids, suggest a profound impact on membrane composition and integrity, potentially contributing to the parasite's demise. Pathway analysis highlighted glycerophospholipid metabolism, cytochrome b5 family heme/steroid binding domain, and P-type ATPase mechanisms as critical pathways affected by ISO2 treatment, underscoring its importance as a potential target for antigiardial therapy. These findings shed light on the mode of action of ISO2 against G. duodenalis and provide valuable insights for further drug development. Moreover, the study also offers a promising avenue for the exploration of isocryptolepine derivatives as novel therapeutic agents for giardiasis, addressing the urgent need for more effective and safer treatment options.

Nourseothricin as a novel drug for selection of transgenic Giardia lamblia

Functional gene and protein characterizations in parasitic protists are often limited by their genetic tractability. Despite the development of CRISPR-Cas9-derived or inspired approaches for a handful of protist parasites, the overall genetic tractability of these organisms remains limited. The intestinal parasite Giardia lamblia is one such species, with the added challenge of a paucity of reliable selection markers. To address this limitation, we tested the feasibility of using Nourseothricin as an effective selection agent in Giardia. Here, we report that axenically-grown WB Giardia cells are sensitive to Nourseothricin and that engineering expression of the streptothricin acetyltransferase (SAT-1) gene from Streptomyces rochei in transgenic parasites confers resistance to this antibiotic. Furthermore, we determine that SAT-1-expressing parasites are cross-resistant neither to Neomycin nor Puromycin, which are widely used to select for transgenic parasites. Consequently, we show that Nourseothricin can be used in sequential combination with both Neomycin and Puromycin to select for dual transfection events. This work increases the number of reliable selection agents and markers for Giardia genetic manipulation, expanding the limited molecular toolbox for this species of global medical importance.

Postnatal zinc deficiency due to giardiasis disrupts hippocampal and cerebellar development

BACKGROUND

Giardiasis and zinc deficiency have been identified as serious health problems worldwide. Although Zn depletion is known to occur in giardiasis, no work has investigated whether changes occur in brain structures.

METHODS

Three groups of gerbils were used: control (1), orogastrically inoculated on day 3 after birth with trophozoites of two isolates of Giardia intestinalis (HGINV/WB) group (2 and 3). Estimates were made at five ages covering: establishment of infection, Giardia population growth, natural parasite clearance and a post-infection age. QuantiChrome zinc assay kit, cresyl violet staining and TUNEL technique were used.

RESULTS

A significant decrease (p<0.01) in tissue zinc was observed and persisted after infection. Cytoarchitectural changes were observed in 75% of gerbils in the HGINV or WB groups. Ectopic pyramidal neurons were found in the cornus ammonis (CA1-CA3). At 60 and 90 days of age loss of lamination was clearly visible in CA1. In the dentate gyrus (DG), thinning of the dorsal lamina and abnormal thickening of the ventral lamina were observed from 30 days of age. In the cerebellum, we found an increase (p<0.01) in the thickness of the external granular layer (EGL) at 14 days of age that persisted until day 21 (C 3 ± 0.3 μm; HGINV 37 ± 5 μm; WB 28 ± 3 μm); Purkinje cell population estimation showed a significant decrease; a large number of apoptotic somas were observed scattered in the molecular layer; in 60 and 90 days old gerbils we found granular cell heterotopia and Purkinje cell ectopia. The pattern of apoptosis was different in the cerebellum and hippocampus of parasitized gerbils.

CONCLUSION

The morphological changes found suggest that neuronal migration is affected by zinc depletion caused by giardiasis in early postnatal life; for the first time, the link between giardiasis-zinc depletion and damaged brain structures is shown. This damage may explain the psychomotor/cognitive delay associated with giardiasis. These findings are alarming. Alterations in zinc metabolism and signalling are known to be involved in many brain disorders, including autism.

Giardia intestinalis extracellular vesicles induce changes in gene expression in human intestinal epithelial cells in vitro

Giardiasis is a common waterborne zoonotic disease caused by Giardia intestinalis. Upon infection, Giardia releases excretory and secretory products (ESPs) including secreted proteins (SPs) and extracellular vesicles (EVs). Although the interplay between ESPs and intestinal epithelial cells (IECs) has been previously described, the functions of EVs in these interactions and their differences from those of SPs require further exploration. In the present study, EVs and EV-depleted SPs were isolated from Giardia ESPs. Proteomic analyses of isolated SPs and EVs showed 146 and 91 proteins, respectively. Certain unique and enriched proteins have been identified in SPs and EVs. Transcriptome analysis of Caco-2 cells exposed to EVs showed 96 differentially expressed genes (DEGs), with 56 upregulated and 40 downregulated genes. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA) indicated that Caco-2 genes related to metabolic processes, the HIF-1 signaling pathway, and the cAMP signaling pathway were affected. This study provides new insights into host-parasite interactions, highlighting the potential significance of EVs on IECs during infections.

Assessment of Drug Activities against Giardia Using Hyperspectral Raman Microscopy

This study demonstrates the capability of Raman microscopy for detecting structural differences in Giardia cells exposed to different drugs and incubation times. While metronidazole (MTZ) visibly affects the cells by inducing extracellular vesicle releases of toxic iron intermediates and modified triple-bond moieties, oseltamivir (OSM) alters the phenylalanine and lipid structures. Modifications in the heme protein environment and the transformation of iron from ferric to ferrous observed for both drug treatments are more notable for MTZ. Different contents and amounts of vesicle excretion are detected for 24 h or 48 h with MTZ incubation. At a shorter drug exposure, releases of altered proteins, glycogen, and phospholipids dominate. Agglomerates of transformed iron complexes from heme proteins and multiple-bond moieties prevail at 48 h of treatment. No such vesicle releases are present in the case of OSM usage. Drug incorporations into the cells and their impact on the plasma membrane and the dynamics of lipid raft confirmed by confocal fluorescence microscopy reveal a more destructive extent by OSM, corroborating the Raman results. Raman microscopy provides a broader understanding of the multifaceted factors and mechanisms responsible for giardiasis treatment or drug resistance by enabling a label-free, simultaneous monitoring of structural changes at the cellular and molecular levels.

In vivo Validation of Hsp90 Trans-splicing in Giardia lamblia: Highlighting the Role of Cis-elements

Giardia lambliacauses giardiasis, one of the most common human infectious diseases globally. Previous studies from our lab have shown that hsp90 gene ofGiardia is split into two halves, namely hspN and hspC. The independent pre-mRNAs of these split genes join by trans-splicing, producing a full-length Hsp90 (FlHsp90) mRNA. Genetic manipulation of the participating genes is necessary to understand the mechanism and significance of such trans-splicing based expression of Hsp90. In this study, we have performed transfection based exogenous expression of hspN and/or hspC in G. lamblia. We electroporated a plasmid containing the Avi-tagged hspN component of Hsp90 and examined its fate in G. lamblia. We show that the exogenously expressed hspN RNA gets trans-spliced to endogenously expressed hspC RNA, giving rise to a hybrid-FlHsp90. We highlight the importance of cis-elements in this trans-splicing reaction through mutational analysis. The episomal plasmid carrying deletions in the intronic region of hspN, showed inhibition of the trans-splicing reaction.Additionally, exogenous hspC RNA also followed the same fate as of exogenous hspN, while upon co-transfection with episomal hspN, they underwent trans-splicing with each other. Using eGFP as a test protein, we have shown that intronic sequences of hsp90 gene can guide trans-splicing mediated repair of any associated exonic sequences. Our study provides in vivo validation of Hsp90 trans-splicing, showing crucial role of cis-elements and importantly highlights the potential of hsp90 intronic sequences to function as a minimal splicing tool.

Systematic Review of Diagnostic Approaches for Human Giardiasis: Unveiling Optimal Strategies

Giardiasis, caused by the protozoan Giardia intestinalis, affects around 400 million people worldwide, emphasizing the critical need for accurate diagnosis to enhance human health, especially in children. Prolonged giardiasis in childhood can lead to intellectual deficits and other complications. A variety of diagnostic tools, including microscopic, immunological, and molecular methods, are available for detecting G. intestinalis infection. Choosing the most suitable method can be challenging due to the abundance of options. This systematic review assesses the reliability and applicability of these diagnostic modalities. Utilizing the Dimensions and Wordart platforms for data analysis, we focus on relevant literature addressing diagnostic methods for human giardiasis. Microscopic techniques, particularly Ritchie's method, emerge as the primary choice, followed by enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). PCR's limited use is attributed to its high cost and infrastructure challenges in developing nations. In conclusion, our analysis supports microscopic methods as the gold standard for giardiasis diagnosis. However, in cases where symptoms persist despite a negative diagnosis, employing more sensitive diagnostic approaches is advisable.

Giardiasis and diarrhea in dogs: Does the microbiome matter?

BACKGROUND

Giardia duodenalis (Gd) causes intestinal parasitosis. The involvement of the intestinal microbiome in determining the infection's clinical phenotype is unknown.

OBJECTIVE

Investigate the fecal microbiome features in dogs with giardiasis.

ANIMALS AND METHODS

Cross-sectional study, including fecal samples of kenneled dogs with Gd diagnosed by fecal Giardia antigen dot ELISA. The fecal microbial compositional characteristics and dysbiosis index (DI) were compared between diarrheic and nondiarrheic dogs.

RESULTS

Fecal samples of 38 Gd-infected dogs (diarrheic, 21; nondiarrheic, 17) were included. No differences were found in Faith's phylogenic diversity and beta diversity (weighted UniFrac distances) and in specific taxa abundances at the phylum, genus, and species levels, as well as in alpha and beta diversities between diarrheic and nondiarrheic dogs, and also when divided by sex or age. Among diarrheic dogs, alpha diversity was higher in males than in females (pairwise Kruskal-Wallis, q = 0.01). Among males, fecal abundances of the genus Clostridium (W = 19) and Clostridium spiroforme species (W = 33) were higher in diarrheic compared to nondiarrheic dogs. In diarrheic dog fecal samples, Proteobacteria were more prevalent (W = 1), whereas Verrucomicrobia were less prevalent in dogs <1 year of age than in older dogs. The fecal sample DI of 19 diarrheic and 19 nondiarrheic dogs was similar (median, -0.2; range, -4.3 to 4.5 and median, -1.0; range, -4.3 to 5.8, respectively).

CONCLUSIONS

The fecal microbial composition of symptomatic and asymptomatic dogs with giardiasis is similar. Based on fecal DI, giardiasis is not characterized by prominent dysbiosis. Other host and parasite characteristics might determine the severity of giardiasis in dogs.

Evaluation of the Antiparasitic, Antihepatotoxicity, and Antioxidant Efficacy of Quercetin and Chitosan, Either Alone or in Combination, against Infection Induced by Giardia lamblia in Male Rats

Giardia lamblia (G. lamblia) is one of the most common protozoal infections and a key cause of malabsorption, some cases of mental developmental issues in children, and reduced body weight. The known antiparasitic medications, which are the standard drugs used for parasitic treatment, have several side effects and sometimes exhibit low efficacy. Therefore, the current study aimed to evaluate the treatment with quercetin (QC) or chitosan (CH), either alone or in combination, as possible alternative therapeutic agents that may alleviate the side effects of G. lamblia infections and restore the normal architecture of the intestinal muscles. They are investigated as alternatives to other routinely administered drugs that may gradually lose their efficacy due to human resistance to therapeutic agents. This study was carried out on 50 male albino rats that were divided into five groups with 10 rats in each group: the control group (Group I), the infected non-treated group (Group II), the infected group treated with QC (Group III), the infected treated group with CH (Group IV), and the infected group treated with a combination of QC and CH (Group V). The effect was first evaluated by counting the G. lamblia fecal cysts in the stool, examining histopathological sections of the intestine with the appearance of trophozoites in the infected group, and conducting a transmission electron microscopic examination of the tissues of the small intestine. Alterations in the biochemical parameters of liver and kidney function and the antioxidant enzymes in the liver tissues of SOD, CAT, and GSH, and non-enzymatic markers of lipid peroxidation (MDA) were evaluated. The results showed a significant decline in the number of parasites in the stool samples, with a marked elevation in the number of trophozoites in the intestinal sections of the infected non-treated group as compared to the infected treated groups. The last group, which was treated with a combination of QC and CH, showed the best results in terms of a decline in the infection rate of G. lamblia in stool samples, with a marked and clear improvement in the intestinal mucosa, regular muscles with normal enteric ganglions, and reduced rates of intestinal injuries caused by G. lamblia trophozoites. Both QC and CH had non-toxic effects on the biochemical parameters of the liver and kidneys, as well as pronounced antioxidant activities due to the elevation of SOD, CAT, and GSH in conjunction with a decline in the levels of MDA. A combination of QC and CH can be considered a potent antiparasitic, anti-hepatotoxic, and antioxidant therapeutic agent; it could constitute a promising alternative treatment agent against G. lamblia infection.

[Feline and canine giardiosis: An Update]

Giardia duodenalis is a facultative pathogenic intestinal parasite. Giardiosis in dogs and cats may appear with or without clinical signs. Typical signs include diarrhea with or without vomiting. The prevalence in young animals is high and may amount to up to 50%. There are 8 different genotypes (A - H), which are called assemblages. Assemblages C and D are most common in dogs and assemblage F most frequent in cats. However, animals may also be infected with the zoonotically effective assemblages A and B or exhibit mixed infections. The immunofluorescence test (IFA), the enzyme-linked immunosorbent assay (ELISA) and fecal centrifugation using zinc sulphate solution are currently recommended as diagnostic methods. Polymerase chain reaction (PCR) may be used to determine the corresponding assemblage. Approved treatments for giardiosis include fenbendazole and metronidazole. In addition, undertaking specific hygiene measures is warranted. Only animals showing clinical signs or those living in the same household with high-risk patients (e. g. immunosuppressed humans) are recommended to receive medication. The aim of treatment is clinical improvement of the diseased dogs and cats. Frequently, complete elimination of Giardia is not attained.

Genomic survey maps differences in the molecular complement of vesicle formation machinery between Giardia intestinalis assemblages

Giardia intestinalis is a globally important microbial pathogen with considerable public health, agricultural, and economic burden. Genome sequencing and comparative analyses have elucidated G. intestinalis to be a taxonomically diverse species consisting of at least eight different sub-types (assemblages A-H) that can infect a great variety of animal hosts, including humans. The best studied of these are assemblages A and B which have a broad host range and have zoonotic transmissibility towards humans where clinical Giardiasis can range from asymptomatic to diarrheal disease. Epidemiological surveys as well as previous molecular investigations have pointed towards critical genomic level differences within numerous molecular pathways and families of parasite virulence factors within assemblage A and B isolates. In this study, we explored the necessary machinery for the formation of vesicles and cargo transport in 89 Canadian isolates of assemblage A and B G. intestinalis. Considerable variability within the molecular complement of the endolysosomal ESCRT protein machinery, adaptor coat protein complexes, and ARF regulatory system have previously been reported. Here, we confirm inter-assemblage, but find no intra-assemblage variation within the trafficking systems examined. This variation includes losses of subunits belonging to the ESCRTIII as well as novel lineage specific duplications in components of the COPII machinery, ARF1, and ARFGEF families (BIG and CYTH). Since differences in disease manifestation between assemblages A and B have been controversially reported, our findings may well have clinical implications and even taxonomic, as the membrane trafficking system underpin parasite survival, pathogenesis, and propagation.

Guidelines for the purification and characterization of extracellular vesicles of parasites

Parasites are responsible for the most neglected tropical diseases, affecting over a billion people worldwide (WHO, 2015) and accounting for billions of cases a year and responsible for several millions of deaths. Research on extracellular vesicles (EVs) has increased in recent years and demonstrated that EVs shed by pathogenic parasites interact with host cells playing an important role in the parasite's survival, such as facilitation of infection, immunomodulation, parasite adaptation to the host environment and the transfer of drug resistance factors. Thus, EVs released by parasites mediate parasite-parasite and parasite-host intercellular communication. In addition, they are being explored as biomarkers of asymptomatic infections and disease prognosis after drug treatment. However, most current protocols used for the isolation, size determination, quantification and characterization of molecular cargo of EVs lack greater rigor, standardization, and adequate quality controls to certify the enrichment or purity of the ensuing bioproducts. We are now initiating major guidelines based on the evolution of collective knowledge in recent years. The main points covered in this position paper are methods for the isolation and molecular characterization of EVs obtained from parasite-infected cell cultures, experimental animals, and patients. The guideline also includes a discussion of suggested protocols and functional assays in host cells.

Lipidome of extracellular vesicles from Giardia lamblia

Extracellular vesicles (EVs) (exossomes, microvesicles and apoptotic bodies) have been well acknowledged as mediators of intercellular communications in prokaryotes and eukaryotes. Lipids are essential molecular components of EVs but at the moment the knowledge about the lipid composition and the function of lipids in EVs is limited and as for now none lipidomic studies in Giardia EVs was described. Therefore, the focus of the current study was to conduct, for the first time, the characterization of the polar lipidome, namely phospholipid and sphingolipid profiles of G. lamblia trophozoites, microvesicles (MVs) and exosomes, using C18-Liquid Chromatography-Mass Spectrometry (C18-LC-MS) and Tandem Mass Spectrometry (MS/MS). A total of 162 lipid species were identified and semi-quantified, in the trophozoites, or in the MVs and exosomes belonging to 8 lipid classes, including the phospholipid classes phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylinositol (PI), cardiolipins (CL), the sphingolipid classes sphingomyelin (SM) and ceramides (Cer), and cholesterol (ST), and 3 lipid subclasses that include lyso PC (LPC), lyso PE (LPE) and lyso PG (LPG), but showing different abundances. This work also identified, for the first time, in G. lamblia trophozoites, the lipid classes CL, Cer and ST and subclasses of LPC, LPE and LPG. Univariate and multivariate analysis showed clear discrimination of lipid profiles between trophozoite, exosomes and MVs. The principal component analysis (PCA) plot of the lipidomics dataset showed clear discrimination between the three groups. Future studies focused on the composition and functional properties of Giardia EVs may prove crucial to understand the role of lipids in host-parasite communication, and to identify new targets that could be exploited to develop novel classes of drugs to treat giardiasis.

Transcriptomic analysis of albendazole resistance in human diarrheal parasite Giardia duodenalis

Benzimidazole-2-carbamates (BZ, e.g., albendazole; ALB), which bind β-tubulin to disrupt microtubule polymerization, are one of two primary compound classes used to treat giardiasis. In most parasitic nematodes and fungi, BZ-resistance is caused by β-tubulin mutations and its molecular mode of action (MOA) is well studied. In contrast, in Giardia duodenalis BZ MOA or resistance is less well understood, may involve target-specific and broader impacts including cellular damage and oxidative stress, and its underlying cause is not clearly determined. Previously, we identified acquisition of a single nucleotide polymorphism, E198K, in β-tubulin in ALB-resistant (ALB-R) G. duodenalis WB-1B relative to ALB-sensitive (ALB-S) parental controls. E198K is linked to BZ-resistance in fungi and its allelic frequency correlated with the magnitude of BZ-resistance in G. duodenalis WB-1B. Here, we undertook detailed transcriptomic comparisons of these ALB-S and ALB-R G. duodenalis WB-1B cultures. The primary transcriptional changes with ALB-R in G. duodenalis WB-1B indicated increased protein degradation and turnover, and up-regulation of tubulin, and related genes, associated with the adhesive disc and basal bodies. These findings are consistent with previous observations noting focused disintegration of the disc and associated structures in Giardia duodenalis upon ALB exposure. We also saw transcriptional changes with ALB-R in G. duodenalis WB-1B consistent with prior observations of a shift from glycolysis to arginine metabolism for ATP production and possible changes to aspects of the vesicular trafficking system that require further investigation. Finally, we saw mixed transcriptional changes associated with DNA repair and oxidative stress responses in the G. duodenalis WB-1B line. These changes may be indicative of a role for H₂O₂ degradation in ALB-R, as has been observed in other G. duodenalis cell cultures. However, they were below the transcriptional fold-change threshold (log₂FC > 1) typically employed in transcriptomic analyses and appear to be contradicted in ALB-R G. duodenalis WB-1B by down-regulation of the NAD scavenging and conversion pathways required to support these stress pathways and up-regulation of many highly oxidation sensitive iron-sulphur (FeS) cluster based metabolic enzymes.

Regulatory Functions of Hypoxia in Host-Parasite Interactions: A Focus on Enteric, Tissue, and Blood Protozoa

Body tissues are subjected to various oxygenic gradients and fluctuations and hence can become transiently hypoxic. Hypoxia-inducible factor (HIF) is the master transcriptional regulator of the cellular hypoxic response and is capable of modulating cellular metabolism, immune responses, epithelial barrier integrity, and local microbiota. Recent reports have characterized the hypoxic response to various infections. However, little is known about the role of HIF activation in the context of protozoan parasitic infections. Growing evidence suggests that tissue and blood protozoa can activate HIF and subsequent HIF target genes in the host, helping or hindering their pathogenicity. In the gut, enteric protozoa are adapted to steep longitudinal and radial oxygen gradients to complete their life cycle, yet the role of HIF during these protozoan infections remains unclear. This review focuses on the hypoxic response to protozoa and its role in the pathophysiology of parasitic infections. We also discuss how hypoxia modulates host immune responses in the context of protozoan infections.

A potential role for Giardia chaperone protein GdDnaJ in regulating Giardia proliferation and Giardiavirus replication

BACKGROUND

Giardia duodenalis (referred to as Giardia) is a flagellated binucleate protozoan parasite, which causes one of the most common diarrheal diseases, giardiasis, worldwide. Giardia can be infected by Giardiavirus (GLV), a small endosymbiotic dsRNA virus belongs to the Totiviridae family. However, the regulation of GLV and a positive correlation between GLV and Giardia virulence is yet to be elucidated.

METHODS

To identify potential regulators of GLV, we performed a yeast two-hybrid (Y2H) screen to search for interacting proteins of RdRp. GST pull-down, co-immunoprecipitation and bimolecular fluorescence complementation (BiFC) assay were used to verify the direct physical interaction between GLV RdRp and its new binding partner. In addition, their in vivo interaction and colocalization in Giardia trophozoites were examined by using Duolink proximal ligation assay (Duolink PLA).

RESULTS

From Y2H screen, the Giardia chaperone protein, Giardia DnaJ (GdDnaJ), was identified as a new binding partner for GLV RdRp. The direct interaction between GdDnaJ and GLV RdRp was verified via GST pull-down, co-immunoprecipitation and BiFC. In addition, colocalization and in vivo interaction between GdDnaJ and RdRp in Giardia trophozoites were confirmed by Duolink PLA. Further analysis revealed that KNK437, the inhibitor of GdDnaJ, can significantly reduce the replication of GLVs and the proliferation of Giardia.

CONCLUSION

Taken together, our results suggested a potential role of GdDnaJ in regulating Giardia proliferation and GLV replication through interaction with GLV RdRp.

Giardia hinders growth by disrupting nutrient metabolism independent of inflammatory enteropathy

Giardia lamblia (Giardia) is among the most common intestinal pathogens in children in low- and middle-income countries (LMICs). Although Giardia associates with early-life linear growth restriction, mechanistic explanations for Giardia-associated growth impairments remain elusive. Unlike other intestinal pathogens associated with constrained linear growth that cause intestinal or systemic inflammation or both, Giardia seldom associates with chronic inflammation in these children. Here we leverage the MAL-ED longitudinal birth cohort and a model of Giardia mono-association in gnotobiotic and immunodeficient mice to propose an alternative pathogenesis of this parasite. In children, Giardia results in linear growth deficits and gut permeability that are dose-dependent and independent of intestinal markers of inflammation. The estimates of these findings vary between children in different MAL-ED sites. In a representative site, where Giardia associates with growth restriction, infected children demonstrate broad amino acid deficiencies, and overproduction of specific phenolic acids, byproducts of intestinal bacterial amino acid metabolism. Gnotobiotic mice require specific nutritional and environmental conditions to recapitulate these findings, and immunodeficient mice confirm a pathway independent of chronic T/B cell inflammation. Taken together, we propose a new paradigm that Giardia-mediated growth faltering is contingent upon a convergence of this intestinal protozoa with nutritional and intestinal bacterial factors.

Trophozoite fitness dictates the intestinal epithelial cell response to Giardia intestinalis infection

Giardia intestinalis is a non-invasive, protozoan parasite infecting the upper small intestine of most mammals. Symptomatic infections cause the diarrhoeal disease giardiasis in humans and animals, but at least half of the infections are asymptomatic. However, the molecular underpinnings of these different outcomes of the infection are still poorly defined. Here, we studied the early transcriptional response to G. intestinalis trophozoites, the disease-causing life-cycle stage, in human enteroid-derived, 2-dimensional intestinal epithelial cell (IEC) monolayers. Trophozoites preconditioned in media that maximise parasite fitness triggered only neglectable inflammatory transcription in the IECs during the first hours of co-incubation. By sharp contrast, "non-fit" or lysed trophozoites induced a vigorous IEC transcriptional response, including high up-regulation of many inflammatory cytokines and chemokines. Furthermore, "fit" trophozoites could even suppress the stimulatory effect of lysed trophozoites in mixed infections, suggesting active G. intestinalis suppression of the IEC response. By dual-species RNA-sequencing, we defined the IEC and G. intestinalis gene expression programs associated with these differential outcomes of the infection. Taken together, our results inform on how G. intestinalis infection can lead to such highly variable effects on the host, and pinpoints trophozoite fitness as a key determinant of the IEC response to this common parasite.

ROS-AMPK/mTOR-dependent enterocyte autophagy is involved in the regulation of Giardia infection-related tight junction protein and nitric oxide levels

Giardia duodenalis, a cosmopolitan noninvasive protozoan parasite of zoonotic concern and public health importance, infects the upper portions of the small intestine and causes one of the most common gastrointestinal diseases globally termed giardiasis, especially in situations lacking safe drinking water and adequate sanitation services. The pathogenesis of giardiasis is complex and involves multiple factors from the interaction of Giardia and intestinal epithelial cells (IECs). Autophagy is an evolutionarily conserved catabolic pathway that involves multiple pathological conditions including infection. Thus far, it remains uncertain if autophagy occurs in Giardia-infected IECs and if autophagic process is associated with the pathogenic factors of giardiasis, such as tight junction (TJ) barrier defects and nitric oxide (NO) release of IECs. Here Giardia-in vitro exposed IECs showed upregulation of a series of autophagy-related molecules, such as LC3, Beclin1, Atg7, Atg16L1, and ULK1, and downregulation of p62 protein. IEC autophagy induced by Giardia was further assessed by using autophagy flux inhibitor, chloroquine (CQ), with the ratio of LC3-II/LC3-I significantly increased and downregulated p62 significantly reversed. Inhibition of autophagy by 3-methyladenine (3-MA) rather than CQ could markedly reverse Giardia-induced downregulation of TJ proteins (claudin-1, claudin-4, occludin, and ZO-1; also known as epithelial cell markers) and NO release, implying the involvement of early-stage autophagy in TJ/NO regulation. We subsequently confirmed the role of ROS-mediated AMPK/mTOR signaling in modulating Giardia-induced autophagy, TJ protein expression, and NO release. In turn, impairment of early-stage autophagy by 3-MA and late-stage autophagy by CQ both exhibited an exacerbated effect on ROS accumulation in IECs. Collectively, we present the first attempt to link the occurrence of IEC autophagy with Giardia infection in vitro, and provides novel insights into the contribution of ROS-AMPK/mTOR-dependent autophagy to Giardia infection-related downregulation of TJ protein and NO levels.

Mass Spectrometry-Based Metabolomics Revealed Effects of Metronidazole on Giardia duodenalis

Giardia duodenalis is a significant protozoan that affects humans and animals. An estimated 280 million G. duodenalis diarrheal cases are recorded annually. Pharmacological therapy is crucial for controlling giardiasis. Metronidazole is the first-line therapy for treating giardiasis. Several metronidazole targets have been proposed. However, the downstream signaling pathways of these targets with respect to their antigiardial action are unclear. In addition, several giardiasis cases have demonstrated treatment failures and drug resistance. Therefore, the development of novel drugs is an urgent need. In this study, we performed a mass spectrometry-based metabolomics study to understand the systemic effects of metronidazole in G. duodenalis. A thorough analysis of metronidazole processes helps identify potential molecular pathways essential for parasite survival. The results demonstrated 350 altered metabolites after exposure to metronidazole. Squamosinin A and N-(2-hydroxyethyl)hexacosanamide were the most up-regulated and down-regulated metabolites, respectively. Proteasome and glycerophospholipid metabolisms demonstrated significant differential pathways. Comparing glycerophospholipid metabolisms of G. duodenalis and humans, the parasite glycerophosphodiester phosphodiesterase was distinct from humans. This protein is considered a potential drug target for treating giardiasis. This study improved our understanding of the effects of metronidazole and identified new potential therapeutic targets for future drug development.

Specific TLR-mediated HSP70 activation plays a potential role in host defense against the intestinal parasite Giardia duodenalis

Giardia duodenalis, an important flagellated noninvasive protozoan parasite, infects the upper small intestine and causes a disease termed giardiasis globally. Few members of the heat shock protein (HSP) family have been shown to function as potential defenders against microbial pathogens, while such information is lacking for Giardia. Here we initially screened and indicated that in vitro Giardia challenge induced a marked early upregulation of HSP70 in intestinal epithelial cells (IECs). As noted previously, apoptotic resistance, nitric oxide (NO)-dependent cytostatic effect and parasite clearance, and epithelial barrier integrity represent effective anti-Giardia host defense mechanisms. We then explored the function of HSP70 in modulating apoptosis, NO release, and tight junction (TJ) protein levels in Giardia-IEC interactions. HSP70 inhibition by quercetin promoted Giardia-induced IEC apoptosis, viability decrease, NO release reduction, and ZO-1 and occludin downregulation, while the agonist celastrol could reverse these Giardia-evoked effects. The results demonstrated that HSP70 played a previously unrecognized and important role in regulating anti-Giardia host defense via attenuating apoptosis, promoting cell survival, and maintaining NO and TJ levels. Owing to the significance of apoptotic resistance among those defense-related factors mentioned earlier, we then elucidated the anti-apoptotic mechanism of HSP70. It was evident that HSP70 could negatively regulate apoptosis in an intrinsic way via direct inhibition of Apaf-1 or ROS-Bax/Bcl-2-Apaf-1 axis, and in an extrinsic way via cIAP2-mediated inhibition of RIP1 activity. Most importantly, it was confirmed that HSP70 exerted its host defense function by downregulating apoptosis via Toll-like receptor 4 (TLR4) activation, upregulating NO release via TLR4/TLR2 activation, and upregulating TJ protein expression via TLR2 activation. HSP70 represented a checkpoint regulator providing the crucial link between specific TLR activation and anti-Giardia host defense responses. Strikingly, independent of the checkpoint role of HSP70, TLR4 activation was proven to downregulate TJ protein expression, and TLR2 activation to accelerate apoptosis. Altogether, this study identified HSP70 as a potentially vital defender against Giardia, and revealed its correlation with specific TLR activation. The clinical importance of HSP70 has been extensively demonstrated, while its role as an effective therapeutic target in human giardiasis remains elusive and thus needs to be further clarified.

Giardia duodenalis Styles, 1902 Prevalence in Cattle (Bos taurus Linnaeus, 1758) in Europe: A Systematic Review

Giardia duodenalis Styles, 1902 is an infectious agent which can cause enteritic disease in cattle (Bos taurus Linnaeus, 1758) worldwide. As a zoonotic protozoan, it is important to acknowledge Giardia prevalence and assemblages found in cattle and risk factors associated with the Giardia infection in herds. This systematic review aims to estimate the prevalence of G. duodenalis and its assemblages in cattle and to identify the risk factors associated with Giardia infection in cattle in Europe. A systematic review was performed according to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines to collect information from published studies in Europe. A total of 1414 studies were identified and 17 relevant studies were included in this review. Mean Giardia prevalence in cattle in Europe was 35.1%, with the highest prevalence found in neonatal animals (39.6%), but mean heard prevalence was 67.0%. Mixed infections of Giardia assemblages A and E were found most frequently (55.6%), while assemblages A and B were found more frequently in animals under 24 months old. Risk factors, such as deep litter with run-out, prolonged calf contact with the dam, and seasonality, such as winter and spring, were found to be potential risk factors for Giardia presence in the herds.

Genetic diversity in the metronidazole metabolism genes nitroreductases and pyruvate ferredoxin oxidoreductases in susceptible and refractory clinical samples of Giardia lamblia

The effectiveness of metronidazole against the tetraploid intestinal parasite Giardia lamblia is dependent on its activation/inactivation within the cytoplasm. There are several activating enzymes, including pyruvate ferredoxin reductase (PFOR) and nitroreductase (NR) 1 which metabolize metronidazole into toxic forms, while NR2 on the other hand inactivates it. Metronidazole treatment failures have been increasing rapidly over the last decade, indicating genetic resistance mechanisms. Analyzing genetic variation in the PFOR and NR genes in susceptible and refractory Giardia isolates may help identify potential markers of resistance. Full length PFOR1, PFOR2, NR1 and NR2 genes from clinical culturable isolates and non-cultured clinical Giardia assemblage B samples were cloned, sequenced and single nucleotide variants (SNVs) were analyzed to assess genetic diversity and alleles. A similar ratio of amino acid changing SNVs per gene length was found for the NRs; 4.2% for NR1 and 6.4% for NR2, while the PFOR1 and PFOR2 genes had less variability with a ratio of 1.1% and 1.6%, respectively. One of the samples from a refractory case had a nonsense mutation which caused a truncated NR1 gene in one out of six alleles. Further, we found three NR2 alleles with frameshift mutations, possibly causing a truncated protein in two susceptible isolates. One of these isolates was homozygous for the affected NR2 allele. Three nsSNVs with potential for affecting protein function were found in the ferredoxin domain of the PFOR2 gene. The considerable variation and discovery of mutations possibly causing dysfunctional NR proteins in clinical Giardia assemblage B isolates, reveal a potential for genetic link to metronidazole susceptibility and resistance.

Genomic comparisons confirm Giardia duodenalis sub-assemblage AII as a unique species

Giardia duodenalis is a parasitic flagellated protozoan which infects a wide range of mammalian hosts, including humans, and is subdivided into at least eight genetic assemblages commonly thought to represent cryptic species. Molecular studies have shown that G. duodenalis assemblage A, which parasitizes humans and animals, contains several phylogenetically distinct groupings known as sub-assemblages. Molecular studies employing poor phylogenetic-resolution markers routinely recover these sub-assemblages, implying that they represent evolutionarily distinct clades and possibly cryptic species, a hypothesis which is supported by epidemiologic trends. Here, we further tested this hypothesis by using available data from 41 whole genomes to characterize sub-assemblages and coalescent techniques for statistical estimation of species boundaries coupled to functional gene content analysis, thereby assessing the stability and distinctiveness of clades. Our analysis revealed two new sub-assemblage clades as well as novel signatures of gene content geared toward differential host adaptation and population structuring via vertical inheritance rather than recombination or panmixia. We formally propose sub-assemblage AII as a new species, Giardia hominis, while preserving the name Giardia duodenalis for sub-assemblage AI. Additionally, our bioinformatic methods broadly address the challenges of identifying cryptic microbial species to advance our understanding of emerging disease epidemiology, which should be broadly applicable to other lower eukaryotic taxa of interest. Giardia hominis n. sp. Zoobank LSID: urn:lsid: zoobank.org:pub:4298F3E1-E3EF-4977-B9DD-5CC59378C80E.

Giardia duodenalis: Flavohemoglobin is involved in drug biotransformation and resistance to albendazole

Giardia duodenalis causes giardiasis, a major diarrheal disease in humans worldwide whose treatment relies mainly on metronidazole (MTZ) and albendazole (ABZ). The emergence of ABZ resistance in this parasite has prompted studies to elucidate the molecular mechanisms underlying this phenomenon. G. duodenalis trophozoites convert ABZ into its sulfoxide (ABZSO) and sulfone (ABZSOO) forms, despite lacking canonical enzymes involved in these processes, such as cytochrome P450s (CYP450s) and flavin-containing monooxygenases (FMOs). This study aims to identify the enzyme responsible for ABZ metabolism and its role in ABZ resistance in G. duodenalis. We first determined that the iron-containing cofactor heme induces higher mRNA expression levels of flavohemoglobin (gFlHb) in Giardia trophozoites. Molecular docking analyses predict favorable interactions of gFlHb with ABZ, ABZSO and ABZSOO. Spectral analyses of recombinant gFlHb in the presence of ABZ, ABZSO and ABZSOO showed high affinities for each of these compounds with Kd values of 22.7, 19.1 and 23.8 nM respectively. ABZ and ABZSO enhanced gFlHb NADH oxidase activity (turnover number 14.5 min-1), whereas LC-MS/MS analyses of the reaction products showed that gFlHb slowly oxygenates ABZ into ABZSO at a much lower rate (turnover number 0.01 min-1). Further spectroscopic analyses showed that ABZ is indirectly oxidized to ABZSO by superoxide generated from the NADH oxidase activity of gFlHb. In a similar manner, the superoxide-generating enzyme xanthine oxidase was able to produce ABZSO in the presence of xanthine and ABZ. Interestingly, we find that gFlHb mRNA expression is lower in albendazole-resistant clones compared to those that are sensitive to this drug. Furthermore, all albendazole-resistant clones transfected to overexpress gFlHb displayed higher susceptibility to the drug than the parent clones. Collectively these findings indicate a role for gFlHb in ABZ conversion to its sulfoxide and that gFlHb down-regulation acts as a passive pharmacokinetic mechanism of resistance in this parasite.

Giardia duodenalis enolase is secreted as monomer during trophozoite-epithelial cell interactions, activates plasminogen and induces necroptotic damage

Enolase, a multifunctional protein expressed by multiple pathogens activates plasminogen to promote proteolysis on components of the extracellular matrix, an important event in early host-pathogen interactions. A secreted form of enolase that is released upon the interaction of trophozoites with epithelial cells has been detected in the secretome of G. duodenalis. However, the role of enolase in the host-pathogen interactions remains largely unknown. In this work, the effects of G. duodenalis enolase (Gd-eno) on the epithelial cell model (IEC-6) were analyzed. Firstly, the coding sequence of Giardia enolase was cloned and the recombinant protein used to raise antibodies that were then used to define the localization and role of enolase in epithelial cell-trophozoite interactions. Gd-eno was detected in small cytoplasmic vesicles as well as at the surface and is enriched in the region of the ventral disk of Giardia trophozoites. Moreover, the blocking of the soluble monomeric form of the enzyme, which is secreted upon interaction with IEC-6 cells by the anti-rGd-eno antibodies, significantly inhibited trophozoite attachment to intestinal IEC-6 cell monolayers. Further, rGd-eno was able to bind human plasminogen (HsPlg) and enhanced plasmin activity in vitro when the trophozoites were incubated with the intrinsic plasminogen activators of epithelial cells. In IEC-6 cells, rGd-eno treatment induced a profuse cell damage characterized by copious vacuolization, intercellular separation and detachment from the substrate; this effect was inhibited by either anti-Gd-eno Abs or the plasmin inhibitor ϵ- aminocaproic acid. Lastly, we established that in epithelial cells rGd-eno treatment induced a necroptotic-like process mediated by tumor necrosis factor α (TNF-α) and the apoptosis inducing factor (AIF), but independent of caspase-3. All together, these results suggest that Giardia enolase is a secreted moonlighting protein that stimulates a necroptotic-like process in IEC-6 epithelial cells via plasminogen activation along to TNFα and AIF activities and must be considered as a virulence factor.

Giardial lipid rafts share virulence factors with secreted vesicles and participate in parasitic infection in mice

Giardia lamblia, a protozoan parasite, is a major cause of waterborne infection, worldwide. While the trophozoite form of this parasite induces pathological symptoms in the gut, the cyst form transmits the infection. Since Giardia is a noninvasive parasite, the actual mechanism by which it causes disease remains elusive. We have previously reported that Giardia assembles cholesterol and GM1 glycosphingolipid-enriched lipid rafts (LRs) that participate in encystation and cyst production. To further delineate the role of LRs in pathogenesis, we isolated LRs from Giardia and subjected them to proteomic analysis. Various cellular proteins including potential virulence factors—e.g., giardins, variant surface proteins, arginine deaminases, elongation factors, ornithine carbomyltransferases, and high cysteine-rich membrane proteins—were found to be present in LRs. Since Giardia secretes virulence factors encapsulated in extracellular vesicles (EVs) that induce proinflammatory responses in hosts, EVs released by the parasite were isolated and subjected to nanoparticle tracking and proteomic analysis. Two types of EV—i.e., small vesicles (SVs; <100 nm, exosome-like particles) and large vesicles (LVs; 100–400 nm, microvesicle-like particles)—were identified and found to contain a diverse group of proteins including above potential virulence factors. Although pretreatment of the parasite with two giardial lipid raft (gLR) disruptors, nystatin (27 μM) and oseltamivir (20 μM), altered the expression profiles of virulence factors in LVs and SVs, the effects were more robust in the case of SVs. To examine the potential role of rafts and vesicles in pathogenicity, Giardia-infected mice were treated with oseltamivir (1.5 and 3.0 mg/kg), and the shedding of cysts were monitored. We observed that this drug significantly reduced the parasite load in mice. Taken together, our results suggest that virulence factors partitioning in gLRs, released into the extracellular milieu via SVs and LVs, participate in spread of giardiasis and could be targeted for future drug development.

Nucleosome Structures Built from Highly Divergent Histones: Parasites and Giant DNA Viruses

In eukaryotes, genomic DNA is bound with histone proteins and packaged into chromatin. The nucleosome, a fundamental unit of chromatin, regulates the accessibility of DNA to enzymes involved in gene regulation. During the past few years, structural analyses of chromatin architectures have been limited to evolutionarily related organisms. The amino acid sequences of histone proteins are highly conserved from humans to yeasts, but are divergent in the deeply branching protozoan groups, including human parasites that are directly related to human health. Certain large DNA viruses, as well as archaeal organisms, contain distant homologs of eukaryotic histone proteins. The divergent sequences give rise to unique and distinct nucleosome architectures, although the fundamental principles of histone folding and DNA contact are highly conserved. In this article, we review the structures and biophysical properties of nucleosomes containing histones from the human parasites Giardia lamblia and Leishmania major, and histone-like proteins from the Marseilleviridae amoeba virus family. The presented data confirm the sharing of the overall DNA compaction system among evolutionally distant species and clarify the deviations from the species-specific nature of the nucleosome.

CFDA-AM staining to assess the metabolic activity of Giardia duodenalis cysts inactivated by chlorine, boiling and ultraviolet irradiation

Giardia duodenalis is responsible for several waterborne gastrointestinal outbreaks worldwide. In addition to limitations presented by the main disinfection methods, assessing the inactivation efficiency of cysts after the treatment also poses challenges. Thus, this study aimed to use the 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM) staining protocol to evaluate the viability of G. duodenalis cysts inactivated by different UV and chlorination doses and boiling times. Under epifluorescent microscopy, metabolically active cysts that presented green fluorescence were considered viable. In contrast, when no green fluorescence could be observed, organisms were considered non-viable. Although statistical analysis revealed that increasing the UV dose did not significantly decrease the percentage of viable cysts, the fluorescence signal intensity decreased considerably when the cysts were irradiated with a dose equal to or greater than 80 mJ cm^-2. Regarding chlorination and boiling treatments, this study demonstrated that no cyst showed fluorescence at the lowest NaClO concentration (0.5 mg/L) and in the shortest boiling time (2 min). Despite some limitations regarding the use of metabolic activity as a viability marker, this methodology is rapid, easy to run and cost-effective. Thus, we conclude that the CFDA-AM staining protocol has the potential to be used to assess Giardia cyst inactivation, although further research is required.

Implementation of a tunable t-CRISPRi system for gene regulation in Giardia duodenalis

Giardia duodenalis, is a binuclear and microaerophilic protozoan that causes giardiasis. Up to date, several molecular approaches have been taken to understand the molecular mechanisms of diverse cellular processes in this parasitic protozoan. However, the role of many genes involved in these processes needs further analysis. The CRISPR interference (CRISPRi) system has been widely used, as a constitutive expression system for gene silencing purposes in several parasites, including Giardia. The aim of this work was to implement a tunable t-CRISPRi system in Giardia to silence abundant, moderately and low expressed genes, by constructing an optimized and inducible plasmid for the expression of both gRNA and dCas9. A doxycycline inducible pRan promoter was used to express dCas9 and each gRNA, consistently dCas9 expression and nuclear localization were confirmed by Western-blot and immunofluorescence in transfected trophozoites. The transcriptional repression was performed on α-tubulin (high expression), giardipain-1 (moderate expression) and Sir2 and Sir4 (low expression) genes. The α-tubulin gene knock-down caused by dCas9 doxycycline-induction was confirmed by a decrease in its protein expression which was of 50% and 60% at 24 and 48 h, respectively. This induced morphological alterations in flagella. The giardipain-1 knock down, showed a decrease in protein expression of 40 and 50% at 12 and 24 h, respectively, without affecting trophozoites viability, consistent with this a zymogram analysis on giardipain-1 knock down revealed a decrease in giardipain-1 protease activity. When repressing sirtuins expression, a total repression was obtained but trophozoites viability was compromised. This approach provides a molecular tool for a tailored repression to produce specific gene knockdowns.

Label-free detection and enumeration of Giardia cysts in agitated suspensions using in situ microscopy

Laboratory procedures performed in water treatment studies frequently require the characterization of (oo)cyst suspensions. Standard methods commonly used are laborious, expensive and time-consuming, besides requiring well-trained personnel to prepare samples with fluorescent staining and perform analysis under fluorescence microscopy. In this study, an easy cost-effective in situ microscope was assessed to acquire images of Giardia cysts directly from agitated suspensions without using any chemical labels or sample preparation steps. An image analysis algorithm analyzes the acquired images, and automatically enumerates and provides morphological information of cysts within 10 min. The proposed system was evaluated at different cyst concentrations, achieving a limit of detection of ~30 cysts/mL. The proposed system overcomes cost, time and labor demands by standard methods and has the potential to be an alternative technique for the characterization of Giardia cyst suspensions in resource-limited facilities, since it is independent of experts and free of consumables.

Precise gene models using long-read sequencing reveal a unique poly(A) signal in Giardia lamblia

During pre-mRNA processing, the poly(A) signal is recognized by a protein complex that ensures precise cleavage and polyadenylation of the nascent transcript. The location of this cleavage event establishes the length and sequence of the 3' UTR of an mRNA, thus determining much of its post-transcriptional fate. Using long-read sequencing, we characterize the polyadenylation signal and related sequences surrounding Giardia lamblia cleavage sites for over 2600 genes. We find that G. lamblia uses an AGURAA poly(A) signal, which differs from the mammalian AAUAAA. We also describe how G. lamblia lacks common auxiliary elements found in other eukaryotes, along with the proteins that recognize them. Further, we identify 133 genes with evidence of alternative polyadenylation. These results suggest that despite pared-down cleavage and polyadenylation machinery, 3' end formation still appears to be an important regulatory step for gene expression in G. lamblia.

The controversies surrounding Giardia intestinalis assemblages A and B

Giardia intestinalis continues to be one of the most encountered parasitic diseases around the world. Although more frequently detected in developing countries, Giardia infections nonetheless pose significant public health problems in developed countries as well. Molecular characterisation of Giardia isolates from humans and animals reveals that there are two genetically different assemblages (known as assemblage A and B) that cause human infections. However, the current molecular assays used to genotype G. intestinalis isolates are quite controversial. This is in part due to a complex phenomenon where assemblages are incorrectly typed and underreported depending on which targeted locus is sequenced. In this review, we outline current knowledge based on molecular epidemiological studies and raise questions as to the reliability of current genotyping assays and a lack of a globally accepted method. Additionally, we discuss the clinical symptoms caused by G. intestinalis infection and how these symptoms vary depending on the assemblage infecting an individual. We also introduce the host-parasite factors that play a role in the subsequent clinical presentation of an infected person, and explore which assemblages are most seen globally.

Giardia intestinalis and its Endomembrane System

Giardia intestinalis has unique characteristics, even in the absence of certain organelles. For instance, Golgi and mitochondria are not found. On the other hand, there is a network of peripheral vacuoles (PVs) and mitosomes. The endoplasmic reticulum (ER), nuclear membrane, peroxisomes, and lipid bodies are present. The peripheral vacuole system seems to play several simultaneous roles. It is involved in the endocytic activity of the trophozoite but also has characteristics of early and late endosomes and even lysosomes, establishing a connection with the ER. Some of the PVs contain small vesicles, acting as multivesicular bodies, including the release of exosomes. The mitosomes are surrounded by two membranes, divide during mitosis, and are distributed throughout the cell. They do not contain DNA, enzymes involved in the citric acid cycle, respiratory chain, or ATP synthesis. However, they contain the iron-sulfur complex and transporters as TOM and TIM. Some mitosomes are linked to flagellar axonemes through a fibrillar connection. During encystation, two types of larger cytoplasmic vesicles appear. One originating from the ER contains the cyst wall proteins. Another contains carbohydrates. Both migrate to the cell periphery and fuse with plasma membrane secreting their contents to give rise to the cell wall.

Transfer RNA-Derived Small RNAs in the Pathogenesis of Parasitic Protozoa

Transfer RNA (tRNA)-derived small RNAs (tsRNAs) are newly identified non-coding small RNAs that have recently attracted attention due to their functional significance in both prokaryotes and eukaryotes. tsRNAs originated from the cleavage of precursor or mature tRNAs by specific nucleases. According to the start and end sites, tsRNAs can be broadly divided into tRNA halves (31–40 nucleotides) and tRNA-derived fragments (tRFs, 14–30 nucleotides). tsRNAs have been reported in multiple organisms to be involved in gene expression regulation, protein synthesis, and signal transduction. As a novel regulator, tsRNAs have also been identified in various protozoan parasites. The conserved biogenesis of tsRNAs in early-branching eukaryotes strongly suggests the universality of this machinery, which requires future research on their shared and potentially disparate biological functions. Here, we reviewed the recent studies of tsRNAs in several representative protozoan parasites including their biogenesis and the roles in parasite biology and intercellular communication. Furthermore, we discussed the remaining questions and potential future works for tsRNAs in this group of organisms.

Helicobacter pylori Pathogenicity Islands and Giardia lamblia Cysteine Proteases in Role of Coinfection and Pathogenesis

Helicobacter pylori is a well-known human-specific stomach pathogen that infects more than half of the world’s population. The infection with this bacterium can cause a variety of gastrointestinal problems, including chronic gastritis, peptic ulcers, and even cancer. H. pylori is a highly infectious bacterium. H. pylori causes an increase in gastric mucosa pH or gastric mucosa intestinal metaplasia. These modifications in the stomach environment are necessary for G. lamblia colonization to occur. Giardia lamblia is a flagellate protozoan parasite that can cause giardiasis in humans and other mammals. It dwells in the duodenum and upper jejunum. Globally, over 280 million cases of human giardiasis are predicted to occur each year. Simultaneous human colonization by G. lamblia and H. pylori is a typical occurrence since the viruses’ predisposing factors are similar in both groups. Giardiasis is a parasitic infection that affects both children and adults worldwide. Infection with Giardia is more common in underdeveloped countries. Globally, more than 200 million cases of giardiasis are detected each year. In contrast, the presence of G. lamblia in the host body triggers an immunological response comparable to that of H. pylori, with lymphocytes strongly polarized towards Th1. As a result, their combined presence exacerbates host tissue damage. The major goal of this seminar is to describe the pathophysiology, immunology, and clinical aspects of G. lamblia and H. pylori coinfection using a comprehensive search of PubMed, Lancet, and Google Scholar sources. Upper gastrointestinal problems such as upper abdominal pain, abdominal bloating, nausea, vomiting, epigastric pain/burning, and belching are all caused by both organisms. Differentiation by physical examination is impossible in people infected with both bacteria. For this coinfection distinction, a laboratory diagnosis is required. G. lamblia and H. pylori, when present together, have a synergistic effect on the host and can cause serious damage. As a result, researchers should delve deeper into the mechanics underlying this potential microbial interaction.

Prevalence of Giardia duodenalis Among Dogs in China from 2001 to 2021: A Systematic Review and Meta-Analysis

Giardia duodenalis has a wide range of host species and is a common causative agent of diarrheal disease in humans and animals. This study conducted a systematic review and meta-analysis to evaluate the pooled prevalence of Giardia among dogs in China. We extracted 33 studies related to the prevalence of G. duodenalis in dogs, with samples taken from 2001 to 2021. The random-effect model was used to calculate pooled prevalence estimates with 95% confidence intervals, and the analyzed data were from 14 provinces in China. The estimated overall prevalence of G. duodenalis among dogs in China was 11.2%. The prevalence of Giardia was significantly higher in Northwestern China (35.7%) than in other regions. The prevalence in 2010 or later (11.8%) was significantly higher than in 2010 or before (6.9%). The estimated prevalence detected by microscopy (9.3%) was lower than molecular (12.3%) and serological (14.3%) ones. The prevalence was higher in dogs <1 year of age (12.2%) than that >1 year (5.4%). Among the genotype groups, the positive rate of assemblage A (5.2%) was significantly higher than that of other assemblages. Depending on the dog' type, the prevalence of G. duodenalis in stray dogs (3.5%) was lower than that in pet dogs (6.7%) and intensively breeding dogs (11.8%). In addition, no correlation was found between Giardia positive rate and the dogs' gender (p > 0.05). We also analyzed the effects of different geographic factor subgroups (longitude, latitude, precipitation, temperature, humidity, and altitude) on the prevalence of G. duodenalis in dogs in China. The results showed that giardiasis was widespread in dogs in China. It is suggested that corresponding control scheme and effective management measures should be formulated and applied to reduce the transmission of G. duodenalis according to the difference in geographical conditions in different areas.

A Detailed Gene Expression Map of Giardia Encystation

Giardia intestinalis is an intestinal protozoan parasite that causes diarrheal infections worldwide. A key process to sustain its chain of transmission is the formation of infectious cysts in the encystation process. We combined deep RNAseq of a broad range of encystation timepoints to produce a high-resolution gene expression map of Giardia encystation. This detailed transcriptomic map of encystation confirmed a gradual change of gene expression along the time course of encystation, showing the most significant gene expression changes during late encystation. Few genes are differentially expressed early in encystation, but the major cyst wall proteins CWP-1 and -2 are highly up-regulated already after 3.5 h encystation. Several transcription factors are sequentially up-regulated throughout the process, but many up-regulated genes at 7, 10, and 14 h post-induction of encystation have binding sites in the upstream regions for the Myb2 transcription factor, suggesting that Myb2 is a master regulator of encystation. We observed major changes in gene expression of several meiotic-related genes from 10.5 h of encystation to the cyst stage, and at 17.5 h encystation, there are changes in many different metabolic pathways and protein synthesis. Late encystation, 21 h to cysts, show extensive gene expression changes, most of all in VSP and HCMP genes, which are involved in antigenic variation, and genes involved in chromatin modifications. This high-resolution gene expression map of Giardia encystation will be an important tool in further studies of this important differentiation process.

"Immunoinformatic Identification of T-Cell and B-Cell Epitopes From Giardia lamblia Immunogenic Proteins as Candidates to Develop Peptide-Based Vaccines Against Giardiasis"

Giardiasis is one of the most common gastrointestinal infections worldwide, mainly in developing countries. The etiological agent is the Giardia lamblia parasite. Giardiasis mainly affects children and immunocompromised people, causing symptoms such as diarrhea, dehydration, abdominal cramps, nausea, and malnutrition. In order to develop an effective vaccine against giardiasis, it is necessary to understand the host-Giardia interactions, the immunological mechanisms involved in protection against infection, and to characterize the parasite antigens that activate the host immune system. In this study, we identify and characterize potential T-cell and B-cell epitopes of Giardia immunogenic proteins by immunoinformatic approaches, and we discuss the potential role of those epitopes to stimulate the host´s immune system. We selected the main immunogenic and protective proteins of Giardia experimentally investigated. We predicted T-cell and B-cell epitopes using immunoinformatic tools (NetMHCII and BCPREDS). Variable surface proteins (VSPs), structural (giardins), metabolic, and cyst wall proteins were identified as the more relevant immunogens of G. lamblia. We described the protein sequences with the highest affinity to bind MHC class II molecules from mouse (I-A^k and I-A^d) and human (DRB1*03:01 and DRB1*13:01) alleles, as well as we selected promiscuous epitopes, which bind to the most common range of MHC class II molecules in human population. In addition, we identified the presence of conserved epitopes within the main protein families (giardins, VSP, CWP) of Giardia. To our knowledge, this is the first in silico study that analyze immunogenic proteins of G. lamblia by combining bioinformatics strategies to identify potential T-cell and B-cell epitopes, which can be potential candidates in the development of peptide-based vaccines. The bioinformatics analysis demonstrated in this study provides a deeper understanding of the Giardia immunogens that bind to critical molecules of the host immune system, such as MHC class II and antibodies, as well as strategies to rational design of peptide-based vaccine against giardiasis.

High-fat diet increases the severity of Giardia infection in association with low-grade inflammation and gut microbiota dysbiosis

Exogenous factors that may influence the pathophysiology of Giardia infection remain incompletely understood. We have investigated the role of dietary fat in the pathogenesis of Giardia infection. Male 3 to 4-week-old C57BL/6 mice were fed either a low fat (LF) or a high fat (HF) diet for 12 days and challenged with G. duodenalis. In infected animals, the trophozoite burden was higher in HF + Giardia mice compared to the LF + Giardia group at day 7 post infection. Fatty acids exerted direct pro-growth effects on Giardia trophozoites. Analysis of disease parameters showed that HF + Giardia mice exhibited more mucosal infiltration by inflammatory cells, decreased villus/crypt ratios, goblet cell hyperplasia, mucus disruption, increased gut motility, and elevated fecal water content compared with LF + Giardia. HF diet-dependent exacerbation of Giardia-induced goblet cell hyperplasia was associated with elevated Atoh1 and Muc2 gene expression. Gut microbiota analysis revealed that the HF diet alone induces a taxonomic shift. HF + Giardia mice exhibited microbiota dysbiosis characterized by an increase of Firmicutes and a decrease of Bacteroidetes and significant changes in α- and β-diversity metrics. Taken together, the findings suggest that a HF diet exacerbates the outcome of Giardia infection. The data demonstrate that elevated dietary fat represents an important exogenous factor promoting the pathophysiology of giardiasis.

Effect of dexamethasone on experimental enteritis produced by Giardia lamblia in a Meriones unguiculatus model

Our aim was to evaluate the impact of immunosuppression on the development of giardiasis. Thirty-six gerbils (4-6 weeks old) were distributed in four groups containing nine animals each: Control (CT); Control-Infected by Giardia lamblia (CTIn), Immunosuppressed (IS), and Immunosuppressed-Infected by G. lamblia (ISIn). Animals in the IS and ISIn groups received intramuscular dexamethasone solution for 25 days. On the 11th day, the animals in the CTIn and ISIn groups were inoculated with G. lamblia. After 14 days of infection, the 25th day of the experiment, all groups were euthanized. Four hours after euthanasia, the intestinal permeability was evaluated and sections of the duodenum and spleen were harvested for morphometric and histopathological analyses. Immunosuppressed groups showed a significant increase in intestinal permeability compared to control and infected groups. Considering that the infection can become chronic in immunosuppressed groups, we should be alert to the possibilities of chronic inflammatory changes, both locally and systemically, due to the loss of the intestinal barrier. Lesions were observed in the duodenal mucosa of the gerbils of the CTIn group, with reduced villi size, crypt hyperplasia, edema, and the presence of inflammatory infiltrate in the lamina propria. In the ISIn group, we observed no inflammation, long and intact villi, and a significant increase in the area of intestinal mucins, despite the large number of trophozoites identified. Our results suggest that exacerbation of the immune response has a direct relationship with the appearance of lesions during enteritis produced by G. lamblia in the assessed model.

Giardia duodenalis: Biology and Pathogenesis

Giardia duodenalis captured the attention of Leeuwenhoek in 1681 while he was examining his own diarrheal stool, but, ironically, it did not really gain attention as a human pathogen until the 1960s, when outbreaks were reported. Key technological advances, including in vitro cultivation, genomic and proteomic databases, and advances in microscopic and molecular approaches, have led to an understanding that this is a eukaryotic organism with a reduced genome rather than a truly premitochondriate eukaryote. This has included the discovery of mitosomes (vestiges of mitochondria), a transport system with many of the features of the Golgi apparatus, and even evidence for a sexual or parasexual cycle. Cell biology approaches have led to a better understanding of how Giardia survives with two nuclei and how it goes through its life cycle as a noninvasive organism in the hostile environment of the lumen of the host intestine. Studies of its immunology and pathogenesis have moved past the general understanding of the importance of the antibody response in controlling infection to determining the key role of the Th17 response. This work has led to understanding of the requirement for a balanced host immune response that avoids the extremes of an excessive response with collateral damage or one that is unable to clear the organism. This understanding is especially important in view of the remarkable ranges of early manifestations, which range from asymptomatic to persistent diarrhea and weight loss, and longer-term sequelae that include growth stunting in children who had no obvious symptoms and a high frequency of postinfectious irritable bowel syndrome (IBS).

Cryo-EM structure of the nucleosome core particle containing Giardia lamblia histones

Giardia lamblia is a pathogenic unicellular eukaryotic parasite that causes giardiasis. Its genome encodes the canonical histones H2A, H2B, H3, and H4, which share low amino acid sequence identity with their human orthologues. We determined the structure of the G. lamblia nucleosome core particle (NCP) at 3.6 Å resolution by cryo-electron microscopy. G. lamblia histones form a characteristic NCP, in which the visible 125 base-pair region of the DNA is wrapped in a left-handed supercoil. The acidic patch on the G. lamblia octamer is deeper, due to an insertion extending the H2B α1 helix and L1 loop, and thus cannot bind the LANA acidic patch binding peptide. The DNA and histone regions near the DNA entry-exit sites could not be assigned, suggesting that these regions are asymmetrically flexible in the G. lamblia NCP. Characterization by thermal unfolding in solution revealed that both the H2A–H2B and DNA association with the G. lamblia H3–H4 were weaker than those for human H3–H4. These results demonstrate the uniformity of the histone octamer as the organizing platform for eukaryotic chromatin, but also illustrate the unrecognized capability for large scale sequence variations that enable the adaptability of histone octamer surfaces and confer internal stability.

Probiotics in the management of Giardia duodenalis: an update on potential mechanisms and outcomes

Giardia duodenalis is a common cause of infection in children and travelers. The most frequent symptom is diarrhea in these patients. G. duodenalis trophozoites use a highly specialized adhesive disc to attach the host intestinal epithelium to induce intestinal damages. Pathological features of the small intestine following giardiasis include villous atrophy; infiltration of granulocytes, lymphocytes, and plasma cells into the lamina propria; and nodular lymphoid hyperplasia. The disturbed intestinal microbiota has been observed in patients with giardiasis. Therefore, a growing body of evidence has emphasized restoring the gut microbiome by probiotics in giardiasis. This study aimed to review the literature to find the pathologic features of giardiasis and its relationship with imbalanced microbiota. Then, benefits of probiotics in giardiasis and their potential molecular mechanisms were discussed. It has been illustrated that using probiotics (e.g., Lactobacillus and Saccharomyces) can reduce the time of gastrointestinal symptoms and repair the damages, particularly in giardiasis. Probiotics' capability in restoring the composition of commensal microbiota may lead to therapeutic outcomes. According to preclinical and clinical studies, probiotics can protect against parasite-induced mucosal damages via increasing the antioxidant capacity, suppressing oxidative products, and regulating the systemic and mucosal immune responses. In addition, they can reduce the proportion of G. duodenalis load by directly targeting the parasite. They can destroy the cellular architecture of parasites and suppress the proliferation and growth of trophozoites via the production of some factors with anti-giardial features. Further researches are required to find suitable probiotics for the prevention and treatment of giardiasis.