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Techniques for sub-classifying morphologically identical Giardia duodenalis trophozoites have included comparisons of the electrophoretic mobility of enzymes and of chromosomes, and sequencing of genes encoding β-giardin, triose phosphate isomerase, the small subunit of ribosomal RNA and glutamate dehydrogenase. To date, G. duodenalis organisms have been sub-classified into eight genetic assemblages (designated A–H). Genotyping of G. duodenalis organisms isolated from various hosts has shown that assemblages A and B infect the largest range of host species, and appear to be the main (or possibly only) G. duodenalis assemblages that undeniably infect human subjects. In at least some cases of assemblage A or B infection in wild mammals, there is suggestive evidence that the infection had resulted from environmental contamination by G. duodenalis cysts of human origin. Les techniques pour sous-classer morphologiquement des trophozoïtes identiques de Giardia duodenalis ont inclus des comparaisons de la mobilité électrophorétique des enzymes et des chromosomes et le séquençage des gènes codant pour la β-giardine, la triose-phosphate isomérase, la petite sous-unité ribosomique de l’ARN et la glutamate déshydrogénase. À ce jour, G. duodenalis a été sous-classé en 8 assemblages génétiques (désignés par A-H). Le génotypage de G. duodenalis isolés à partir de divers hôtes a montré que les assemblages A et B infectent le grand plus grand nombre d’espèces d’hôtes, et semblent être les assemblages principaux (ou peut-être uniques) qui infectent les sujets humains de manière indéniable. Dans au moins certains cas d’infection chez les mammifères sauvages par les assemblages A ou B, des éléments indiquent que l’infection était due à la contamination de l’environnement par des kystes de G. duodenalis d’origine humaine.

The genome of the eukaryotic protist Giardia lamblia, an important human intestinal parasite, is compact in structure and content, contains few introns or mitochondrial relics, and has simplified machinery for DNA replication, transcription, RNA processing, and most metabolic pathways. Protein kinases comprise the single largest protein class and reflect Giardia's requirement for a complex signal transduction network for coordinating differentiation. Lateral gene transfer from bacterial and archaeal donors has shaped Giardia's genome, and previously unknown gene families, for example, cysteine-rich structural proteins, have been discovered. Unexpectedly, the genome shows little evidence of heterozygosity, supporting recent speculations that this organism is sexual. This genome sequence will not only be valuable for investigating the evolution of eukaryotes, but will also be applied to the search for new therapeutics for this parasite.

Sexual recombination is a hallmark of eukaryotic evolution. Without recombination, asexual eukaryotes should succumb to deleterious mutations and more rapidly evolving pathogens. Giardia duodenalis , a parasitic protist, sits within one of the earliest-branching eukaryotic lineages and has no known sexual stage. Whether Giardia are ‘ancient asexuals’ has been long explored but is unresolved. Here, we find clear evidence of sex in Giardia and also discover an asexual sublineage that has a broader host range than its sexual ancestor. This asexual lineage is not ancient, and is accumulating deleterious mutations. Unlike its sexual counterparts, its genetic variation lacks the signatures of selection and Red Queen coevolution. We propose a new hypothesis that explains how a mutational meltdown during Muller’s Ratchet might enable asexual pathogens to expand their host ranges transiently. Fittingly, our results suggest that Giardia is not the last exception to, but rather further evidence of, the essentiality of eukaryotic sex. Sexual reproduction is thought to be essential for long-term survival of eukaryotes. This study shows that Giardia, once suspected to be anciently asexual, retains evidence of sex while a newly derived asexual lineage is accumulating mutations and expanding its host range.

Giardia intestinalis is a parasitic protozoan that inhabits its vertebrate hosts' upper small intestine and is the most common cause of waterborne diarrhoea worldwide. Giardia trophozoites present few organelles, and among them, they possess peripheral vesicles (PVs), which are considered an endosomal–lysosomal system. All experimental procedures carried out until now indicate that Giardia ingests macromolecules by fluid-phase and receptor-mediated endocytic pathways. Still, there is no description concerning the interaction and ingestion of large materials. Here, we tested Giardia's capacity to interact with large particles; once, in vivo, it inhabits an environment with a microbiota. We tested protozoan interaction with yeasts, bacteria, latex beads, ferritin and albumin, in different times of interaction and used several microscopy techniques (light microscopy, scanning electron microscopy and transmission electron microscopy) to follow their fate. Giardia interacted with all of the materials we tested. Projections of the plasma membrane similar to pseudopods were seen. As albumin, small markers were found in the PVs while the larger materials were not seen there. Large vacuoles containing large latex beads were detected intracellularly. Thus, we observed that: (1) Giardia interacts with large materials; (2) Giardia can display an amoeboid shape and exhibit membrane projections when in contact with microorganisms and large inorganic materials; (3) the region of the exit of the ventral flagella is very active when in contact with large materials, although all cell surface also present activity in the interactions; (4) intracellular vacuoles, which are not the PVs, present ingested large beads.

Giardia duodenalis , Cryptosporidium spp. and Toxoplasma gondii are protozoan parasites that have been highlighted as emerging foodborne pathogens by the Food and Agriculture Organization of the United Nations and the World Health Organization. According to the European Food Safety Authority, 4786 foodborne and waterborne outbreaks were reported in Europe in 2016, of which 0.4% were attributed to parasites including Cryptosporidium , Giardia and Trichinella . Until 2016, no standardized methods were available to detect Giardia, Cryptosporidium and Toxoplasma (oo)cysts in food. Therefore, no regulation exists regarding these biohazards. Nevertheless, considering their low infective dose, ingestion of foodstuffs contaminated by low quantities of these three parasites can lead to human infection. To evaluate the risk of protozoan parasites in food, efforts must be made towards exposure assessment to estimate the contamination along the food chain, from raw products to consumers. This requires determining: (i) the occurrence of infective protozoan (oo)cysts in foods, and (ii) the efficacy of control measures to eliminate this contamination. In order to conduct such assessments, methods for identification of viable (i.e. live) and infective parasites are required. This review describes the methods currently available to evaluate infectivity and viability of G. duodenalis cysts , Cryptosporidium spp. and T. gondii oocysts, and their potential for application in exposure assessment to determine the presence of the infective protozoa and/or to characterize the efficacy of control measures. Advantages and limits of each method are highlighted and an analytical strategy is proposed to assess exposure to these protozoa. Giardia duodenali s, Cryptosporidium spp. et Toxoplasma gondii sont des parasites protozoaires qui ont été soulignés comme agents pathogènes émergents dans les aliments par l’Organisation des Nations Unies pour l’alimentation et l’agriculture et l’Organisation Mondiale de la Santé. Selon l’Autorité Européenne de Sécurité des Aliments, 4786 épidémies d’origine alimentaire et hydrique ont été enregistrées en Europe en 2016, dont 0.4% ont été attribuées à des parasites, incluant Cryptosporidium , Giardia et Trichinella . Jusqu’en 2016, aucune méthode standardisée n’était disponible pour détecter les kystes de Giardia et les oocystes de Cryptosporidium et Toxoplasma dans les aliments. Aucune réglementation n’est donc proposée concernant ces dangers. Cependant, compte tenu de leur faible dose infectieuse, l’ingestion d’une quantité d’aliments faiblement contaminés peut entraîner une infection de l’homme. Pour évaluer le risque lié aux protozoaires dans les aliments, des efforts doivent être faits dans l’évaluation de l’exposition pour estimer la contamination le long de la chaîne alimentaire, depuis la matière première jusqu’aux consommateurs. Cette évaluation nécessite de déterminer   : (i) la prévalence de parasites infectieux dans les aliments, (ii) l’efficacité des mesures de maîtrise pour éliminer cette contamination. Pour mener une telle évaluation, des méthodes capables d’identifier des parasites viables (vivants) et infectieux sont requises. Cette revue décrit les méthodes actuellement disponibles permettant d’évaluer l’infectiosité et la viabilité des kystes de G. duodenalis et des oocystes de Cryptosporidium spp. et T. gondii, et leur potentiel pour être appliquées dans l’évaluation de l’exposition pour déterminer la présence de parasites infectieux et/ou caractériser l’efficacité des mesures de maîtrise. Les avantages et limites de chaque méthode sont présentés et une stratégie d’analyses est proposée pour évaluer l’exposition à ces protozoaires.

Background The two intestinal protozoan parasites Giardia duodenalis and Cryptosporidium parvum cause infections in a wide spectrum of vertebrates and have also been shown to infect suitable hosts simultaneously. To investigate potential effects between these parasites and on host cells, a co-infection model with IPEC-J2 cells was established. Methods Optimal infection conditions and several infection doses of both parasites were tested. The effect of Giardia growth medium on IPEC-J2 cells was analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay, while the effect of different infection doses of each parasite on host cell viability was investigated by CellTiter Blue cell viability assay. For co-infection, IPEC-J2 cells were first infected with C. parvum sporozoites, and 3.5 h later, G. duodenalis trophozoites were added. Parasite propagation during single infection and co-infection were analyzed by quantitative real-time polymerase chain reaction (qPCR) as well as immunofluorescent staining. Results The infection with C. parvum sporozoites had no significant impact on cell viability, while G. duodenalis trophozoites affected cell culture in a dose dependent manner. The amount of gene copies of C. parvum in single and co-infected cells did not differ significantly, while statistically higher amounts of G. duodenalis gene copies in co-infected cell cultures were identified. Conclusions In this study, single infections and co-infections of IPEC-J2 cells with C. parvum and G. duodenalis were established and optimized over a period of 72 h. Graphical Abstract

Giardia duodenalis is a ubiquitous flagellated protozoan parasite known to cause giardiasis throughout the world. Potential transmission vehicles for this zoonotic parasite are both water and food sources. As such consumption of water contaminated by feces, or food sources washed in contaminated water containing parasite cysts, may result in outbreaks. This creates local public health risks which can potentially cause widespread infection and long-term post-infection sequelae. This paper provides an up-to-date overview of G. duodenalis assemblages, sub-assemblages, hosts and locations identified. It also summarizes knowledge of potential infection/transmission routes covering water, food, person-to-person infection and zoonotic transmission from livestock and companion animals. Public health implications focused within the UK, based on epidemiological data, are discussed and recommendations for essential Giardia developments are highlighted.

Centrins, Ca2+‐binding proteins conserved in eukaryotes, are the key components of the microtubule‐organizing center. Giardia lamblia possesses two centrins (GL50803_6744: centrin 1; GL50803_104685: centrin 2) localized in the basal bodies during cell division. G. lamblia centrin 2 (Glcent2) is also found in the nuclei of interphase Giardia, with its N‐terminal half being necessary for this localization. Morpholino‐mediated knockdown of Glcents resulted in abnormal nuclear positioning and cytokinesis, causing cell malformations, including ventral discs and flagella defects. Small ubiquitin‐like modifier (SUMO)ylation is a posttranslational modification, which modulates several cellular processes. Here, we demonstrated that Glcents are substrates of SUMO through in vitro SUMOylation and immunoprecipitation experiments. Additionally, treatment of Giardia with ginkgolic acid, which inhibits the E1 enzyme of the SUMO pathway, and CRISPRi‐mediated inhibition of G. lamblia Ubc9, the E2 conjugation enzyme involved in SUMOylation, resulted in defects in the localization of Glcents. Blocking SUMOylation resulted in the arrest of Giardia cells and conformational changes, including alterations in the ventral disc shape, posterolateral flanges, and peripheral vesicles. Taken together, we demonstrated that Glcents function in Giardia cell cycle progression and morphogenesis, with the activity of both Glcents being modulated by SUMOylation. Two Giardia lamblia centrins (Glcents) play a role in cell cycle progression and morphogenesis of Giardia. Both Glcents are substrates of GlSUMO, suggesting a role of SUMOylation in their proper localization. SUMOylation is also involved in regulating vacuole formation in Giardia.

A 24-year-old man with a kidney transplant presented with a 3-day history of diarrhea. An examination of a saline wet mount of a stool sample showed an organism moving in a “falling leaf” pattern (shown in a video).

Giardia duodenalis and Cryptosporidium spp. are significant zoonotic parasites that cause diarrhea and affect a diverse range of hosts. This study aimed to investigate the infection rates of these parasites in captive wildlife at Beijing Zoo. A total of 445 fecal samples were collected and analyzed using PCR. The infection rate of G. duodenalis was 3.82% (17/445), with assemblage A ( n  = 1), assemblage B ( n  = 13), and assemblage E ( n  = 3) identified. The infection rate of Cryptosporidium spp. was 0.22% (1/445), with only one instance of C. ryanae identified from cattle ( Bos taurus ). To the best of our knowledge, this study enhances the understanding of the host range of G. duodenalis in captive wildlife within China, highlighting infections in Corsac Fox ( Vulpes corsac ), Indian Rhinoceros ( Rhinoceros unicornis ), and Giraffe ( Giraffa camelopardalis ). These findings indicate that the infection rates of G. duodenalis and Cryptosporidium spp. in captive wildlife at Beijing Zoo are low, while showing that the known host range of G. duodenalis is expanding. Giardia duodenalis et Cryptosporidium spp. sont des parasites zoonotiques importants qui provoquent des diarrhées et affectent une gamme diversifiée d’hôtes. Cette étude visait à examiner les taux d’infection de ces parasites chez la faune captive au zoo de Pékin. Au total, 445 échantillons fécaux ont été collectés et analysés par PCR. Le taux d’infection de G. duodenalis était de 3,82 % (17/445), avec l’assemblage A ( n  = 1), l’assemblage B ( n  = 13) et l’assemblage E ( n  = 3) identifiés. Le taux d’infection de Cryptosporidium spp. était de 0,22 % (1/445), avec un seul cas de C. ryanae identifié chez des bovins ( Bos taurus ). À notre connaissance, cette étude améliore la compréhension de la gamme d’hôtes de G. duodenalis chez la faune captive en Chine, mettant en évidence des infections chez le renard corsac ( Vulpes corsac ), le rhinocéros indien ( Rhinoceros unicornis ) et la girafe ( Giraffa camelopardalis ). Ces résultats indiquent que les taux d’infection de G. duodenalis et de Cryptosporidium spp. dans la faune captive du zoo de Pékin sont faibles, tout en montrant que la gamme d’hôtes connue de G. duodenalis est en expansion.