Morphological characterization of Cryptosporidium parvum life-cycle stages in an in vitro model system

Mendelian segregation and high recombination rates facilitate genetic analyses in Cryptosporidium parvum

Very little is known about the process of meiosis in the apicomplexan parasite Cryptosporidium despite the essentiality of sex in its life cycle. Most cell lines only support asexual growth of Cryptosporidium parvum (C. parvum), but stem cell derived intestinal epithelial cells grown under air-liquid interface (ALI) conditions support the sexual cycle. To examine chromosomal dynamics during meiosis in C. parvum, we generated two transgenic lines of parasites that were fluorescently tagged with mCherry or GFP on chromosomes 1 or 5, respectively. Infection of ALI cultures or Ifngr1-/- mice with mCherry and GFP parasites resulted in cross-fertilization and the formation of "yellow" oocysts, which contain 4 haploid sporozoites that are the product of meiosis. Recombinant oocysts from the F1 generation were purified and used to infect HCT-8 cultures, and phenotypes of the progeny were observed by microscopy. All possible phenotypes predicted by independent segregation were represented equally (~25%) in the population, indicating that C. parvum chromosomes exhibit a Mendelian inheritance pattern. The most common pattern observed from the outgrowth of single oocysts included all possible parental and recombinant phenotypes derived from a single meiotic event, suggesting a high rate of crossover. To estimate the frequency of crossover, additional loci on chromosomes 1 and 5 were tagged and used to monitor intrachromosomal crosses in Ifngr1-/- mice. Both chromosomes showed a high frequency of crossover compared to other apicomplexans with map distances (i.e., 1% recombination) of 3-12 kb. Overall, a high recombination rate may explain many unique characteristics observed in Cryptosporidium spp. such as high rates of speciation, wide variation in host range, and rapid evolution of host-specific virulence factors.

Cultivation, cryopreservation, and transcriptomic studies of host-adapted Cryptosporidium parvum and Cryptosporidium hominis using enteroids

Cryptosporidium hominis and Cryptosporidium parvum are major causes of severe diarrhea. Comparative studies of them are hampered by the lack of effective cultivation and cryopreservation methods, especially for C. hominis. Here, we describe adapted murine enteroids for the cultivation and complete development of host-adapted C. parvum and C. hominis subtypes, producing oocysts infectious to mice. Using the system, we developed a cryopreservation method for Cryptosporidium isolates. In comparative RNA-seq analyses of C. hominis cultures, the enteroid system generated significantly more host and pathogen responses than the conventional HCT-8 cell system. In particular, the infection was shown to upregulate PI3K-Akt, Ras, TNF, NF-κB, IL-17, MAPK, and innate immunity signaling pathways and downregulate host cell metabolism, and had significantly higher expression of parasite genes involved in oocyst formation. Therefore, the enteroid system provides a valuable tool for comparative studies of the biology of divergent Cryptosporidium species and isolates.

Cryptosporidium life cycle small molecule probing implicates translational repression and an Apetala 2 transcription factor in macrogamont differentiation

The apicomplexan parasite Cryptosporidium is a leading cause of childhood diarrhea in developing countries. Current treatment options are inadequate and multiple preclinical compounds are being actively pursued as potential drugs for cryptosporidiosis. Unlike most apicomplexans, Cryptosporidium spp. sequentially replicate asexually and then sexually within a single host to complete their lifecycles. Anti-cryptosporidial compounds are generally identified or tested through in vitro phenotypic assays that only assess the asexual stages. Therefore, compounds that specifically target the sexual stages remain unexplored. In this study, we leveraged the ReFRAME drug repurposing library against a newly devised multi-readout imaging assay to identify small-molecule compounds that modulate macrogamont differentiation and maturation. RNA-seq studies confirmed selective modulation of macrogamont differentiation for 10 identified compounds (9 inhibitors and 1 accelerator). The collective transcriptomic profiles of these compounds indicates that translational repression accompanies Cryptosporidium sexual differentiation, which we validated experimentally. Additionally, cross comparison of the RNA-seq data with promoter sequence analysis for stage-specific genes converged on a key role for an Apetala 2 (AP2) transcription factor (cgd2_3490) in differentiation into macrogamonts. Finally, drug annotation for the ReFRAME hits indicates that an elevated supply of energy equivalence in the host cell is critical for macrogamont formation.

Mendelian segregation and high recombination rates facilitate genetic analyses in Cryptosporidium parvum

Very little is known about the process of meiosis in the apicomplexan parasite Cryptosporidium despite the essentiality of sex in its life cycle. Most cell lines only support asexual growth of Cryptosporidium parvum (C. parvum), but stem cell derived intestinal epithelial cells grown under air-liquid interface (ALI) conditions support the sexual cycle. To examine chromosomal dynamics during meiosis in C. parvum, we generated two transgenic lines of parasites that were fluorescently tagged with mCherry or GFP on chromosomes 1 or 5, respectively. Infection of ALI cultures or Ifngr1-/- mice with mCherry and GFP parasites produced "yellow" oocysts generated by cross-fertilization. Outcrossed oocysts from the F1 generation were purified and used to infect HCT-8 cultures, and phenotypes of the progeny were observed by microscopy. All possible phenotypes predicted by independent segregation were represented equally (~25%) in the population, indicating that C. parvum chromosomes exhibit a Mendelian inheritance pattern. Unexpectedly, the most common pattern observed from the outgrowth of single oocysts included all possible parental and recombinant phenotypes derived from a single meiotic event, suggesting a high rate of crossover. To estimate the frequency of crossover, additional loci on chromosomes 1 and 5 were tagged and used to monitor intrachromosomal crosses in Ifngr1-/- mice. Both chromosomes showed a high frequency of crossover compared to other apicomplexans with map distances (i.e., 1% recombination) of 3-12 kb. Overall, a high recombination rate may explain many unique characteristics observed in Cryptosporidium spp. such as high rates of speciation, wide variation in host range, and rapid evolution of host-specific virulence factors.

Comparison of in vitro growth characteristics of Cryptosporidium hominis (IdA15G1) and Cryptosporidium parvum (Iowa-IIaA17G2R1 and IIaA18G3R1)

Cryptosporidium is a major cause of diarrhoeal disease and mortality in young children in resource-poor countries, for which no vaccines or adequate therapeutic options are available. Infection in humans is primarily caused by two species: C. hominis and C. parvum. Despite C. hominis being the dominant species infecting humans in most countries, very little is known about its growth characteristics and life cycle in vitro, given that the majority of our knowledge of the in vitro development of Cryptosporidium has been based on C. parvum. In the present study, the growth and development of two C. parvum isolates (subtypes Iowa-IIaA17G2R1 and IIaA18G3R1) and one C. hominis isolate (subtype IdA15G1) in HCT-8 cells were examined and compared at 24 h and 48 h using morphological data acquired with scanning electron microscopy. Our data indicated no significant differences in the proportion of meronts or merozoites between species or subtypes at either time-point. Sexual development was observed at the 48-h time-point across both species through observations of both microgamonts and macrogamonts, with a higher frequency of macrogamont observations in C. hominis (IdA15G1) cultures at 48-h post-infection compared to both C. parvum subtypes. This corresponded to differences in the proportion of trophozoites observed at the same time point. No differences in proportion of microgamonts were observed between the three subtypes, which were rarely observed across all cultures. In summary, our data indicate that asexual development of C. hominis is similar to that of C. parvum, while sexual development is accelerated in C. hominis. This study provides new insights into differences in the in vitro growth characteristics of C. hominis when compared to C. parvum, which will facilitate our understanding of the sexual development of both species.

Cryptosporidium mortiferum n. sp. (Apicomplexa: Cryptosporidiidae), the species causing lethal cryptosporidiosis in Eurasian red squirrels (Sciurus vulgaris)

BACKGROUND

Cryptosporidium spp. are globally distributed parasites that infect epithelial cells in the microvillus border of the gastrointestinal tract of all classes of vertebrates. Cryptosporidium chipmunk genotype I is a common parasite in North American tree squirrels. It was introduced into Europe with eastern gray squirrels and poses an infection risk to native European squirrel species, for which infection is fatal. In this study, the biology and genetic variability of different isolates of chipmunk genotype I were investigated.

METHODS

The genetic diversity of Cryptosporidium chipmunk genotype I was analyzed by PCR/sequencing of the SSU rRNA, actin, HSP70, COWP, TRAP-C1 and gp60 genes. The biology of chipmunk genotype I, including oocyst size, localization of the life cycle stages and pathology, was examined by light and electron microscopy and histology. Infectivity to Eurasian red squirrels and eastern gray squirrels was verified experimentally.

RESULTS

Phylogenic analyses at studied genes revealed that chipmunk genotype I is genetically distinct from other Cryptosporidium spp. No detectable infection occurred in chickens and guinea pigs experimentally inoculated with chipmunk genotype I, while in laboratory mice, ferrets, gerbils, Eurasian red squirrels and eastern gray squirrels, oocyst shedding began between 4 and 11 days post infection. While infection in mice, gerbils, ferrets and eastern gray squirrels was asymptomatic or had mild clinical signs, Eurasian red squirrels developed severe cryptosporidiosis that resulted in host death. The rapid onset of clinical signs characterized by severe diarrhea, apathy, loss of appetite and subsequent death of the individual may explain the sporadic occurrence of this Cryptosporidium in field studies and its concurrent spread in the population of native European squirrels. Oocysts obtained from a naturally infected human, the original inoculum, were 5.64 × 5.37 μm and did not differ in size from oocysts obtained from experimentally infected hosts. Cryptosporidium chipmunk genotype I infection was localized exclusively in the cecum and anterior part of the colon.

CONCLUSIONS

Based on these differences in genetics, host specificity and pathogenicity, we propose the name Cryptosporidium mortiferum n. sp. for this parasite previously known as Cryptosporidium chipmunk genotype I.

In Vitro Susceptibility of Cryptosporidium parvum to Plant Antiparasitic Compounds

Cryptosporidium parvum is a significant cause of watery diarrhoea in humans and other animals worldwide. Although hundreds of novel drugs have been evaluated, no effective specific chemotherapeutic intervention for C. parvum has been reported. There has been much recent interest in evaluating plant-derived products in the fight against gastrointestinal parasites, including C. parvum. This study aimed to identify extracts from 13 different plant species that provide evidence for inhibiting the growth of C. parvum in vitro. Efficacy against C. parvum was detected and quantified using quantitative PCR and immunofluorescence assays. All plant extracts tested against C. parvum showed varying inhibition activities in vitro, and none of them produced a cytotoxic effect on HCT-8 cells at concentrations up to 500 µg/mL. Four plant species with the strongest evidence of activity against C. parvum were Curcuma longa, Piper nigrum, Embelia ribes, and Nigella sativa, all with dose-dependent efficacy. To the authors' knowledge, this is the first time that these plant extracts have proven to be experimentally efficacious against C. parvum. These results support further exploration of these plants and their compounds as possible treatments for Cryptosporidium infections.

Effects of selected condensed tannins on Cryptosporidium parvum growth and proliferation in HCT-8 cell cultures

Infections with Cryptosporidium spp. constitute a substantial public health burden and are responsible for widespread production losses in cattle herds. Reducing disease and shedding of Cryptosporidium spp. oocysts is an important One Health goal. There are very few therapeutic options available to treat cryptosporidiosis. Interest in plant bioactive compounds to mitigate the spread of anthelmintic resistance in ruminants has led to investigation of these phytocompounds against other parasitic taxa. Condensed tannins (CTs) are plant secondary metabolites that have shown potential against nematodes in vitro and in vivo but their applicability to Cryptosporidium spp. is comparatively under-explored. Cryptosporidium parvum infected human ileocecal colorectal adenocarcinoma (HCT)-8 cell cultures were treated with escalating doses of highly purified and well-characterized CTs from five plant species, big trefoil (Lotus pedunculatus), black currant (Ribes nigrum), sainfoin (Onobrychis viciifolia), white clover (Trifolium repens) and grapeseed (Vitis vinifera) for 44 h. Quantitative-PCR (qPCR) analysis revealed that none of the CTs examined demonstrated inhibitory potential against the parasite. Substantial inhibition of C. parvum by paromomycin was observed in positive controls in all assays (76.94-90.72% inhibition), proving the validity of the assay. Despite the lack of inhibition, these results represent an important step towards identifying alternative treatment options against this parasite.

Protein Kinase C-α Is a Gatekeeper of Cryptosporidium Sporozoite Adherence and Invasion

Cryptosporidium infection is a leading cause of diarrhea-associated morbidity and mortality in young children globally. Single nucleotide polymorphisms (SNPs) in the human protein kinase C-α (PRKCA) gene region have been associated with susceptibility to cryptosporidiosis. Here, we examined the role of protein kinase C-α (PKCα) activity in human HCT-8 intestinal epithelial cells during infection with Cryptosporidium parvum sporozoites. To delineate the role of PKCα in infection, we developed a fluorescence-based imaging assay to differentiate adherent from intracellular parasites. We tested pharmacological agonists and antagonists of PKCα and measured the effect on C. parvum sporozoite adherence to and invasion of HCT-8 cells. We demonstrate that both PKCα agonists and antagonists significantly alter parasite adherence and invasion in vitro. We found that HCT-8 cell PKCα is activated by C. parvum infection. Our findings suggest intestinal epithelial cell PKCα as a potential host-directed therapeutic target for cryptosporidiosis and implicate PKCα activity as a mediator of parasite adherence and invasion.

The Oesophageal Squamous Cell Carcinoma Cell Line COLO-680N Fails to Support Sustained Cryptosporidium parvum Proliferation

Cryptosporidium parvum is an important diarrhoea-associated protozoan, which is difficult to propagate in vitro. In 2017, a report described a continuous culture of C. parvum Moredun strain, in the oesophageal squamous cell carcinoma cell line COLO-680N, as an easy-to-use system for C. parvum propagation and continuous production of oocysts. Here, we report that—using the Köllitsch strain of C. parvum—even though COLO-680N cells, indeed, allowed parasite invasion and early asexual parasite replication, C. parvum proliferation decreased after the second day post infection. Considering recurring studies, reporting on successful production of newly generated Cryptosporidium oocysts in the past, and the subsequent replication failure by other research groups, the current data stand as a reminder of the importance of reproducibility of in vitro systems in cryptosporidiosis research. This is of special importance since it will only be possible to develop promising strategies to fight cryptosporidiosis and its ominous consequences for both human and animal health by a continuous and reliable methodological progress.

QSAR and deep learning model for virtual screening of potential inhibitors against Inosine 5' Monophosphate dehydrogenase (IMPDH) of Cryptosporidium parvum

Cryptosporidium parvum (Cp) causes a gastro-intestinal disease called Cryptosporidiosis. C. parvum Inosine 5' monophosphate dehydrogenase (CpIMPDH) is responsible for the production of guanine nucleotides. In the present study, 37 known urea-based congeneric compounds were used to build a 2D and 3D QSAR model against CpIMPDH. The built models were validated based on OECD principles. A deep learning model was adopted from a framework called Deep Purpose. The model was trained with 288 known active compounds and validated using a test set. From the training set of the 3D QSAR, a pharmacophore model was built and the best pharmacophore hypotheses were scored and sorted using a phase-hypo score. A phytochemical database was screened using both the pharmacophore model and a deep learning model. The screened compounds were considered for glide XP docking, followed by quantum polarized ligand docking. Finally, the best compound among them was considered for molecular dynamics simulation study.

Hide-and-Seek: A Game Played between Parasitic Protists and Their Hosts

After invading the host organism, a battle occurs between the parasitic protists and the host's immune system, the result of which determines not only whether and how well the host survives and recovers, but also the fate of the parasite itself. The exact weaponry of this battle depends, among others, on the parasite localisation. While some parasitic protists do not invade the host cell at all (extracellular parasites), others have developed successful intracellular lifestyles (intracellular parasites) or attack only the surface of the host cell (epicellular parasites). Epicellular and intracellular protist parasites have developed various mechanisms to hijack host cell functions to escape cellular defences and immune responses, and, finally, to gain access to host nutrients. They use various evasion tactics to secure the tight contact with the host cell and the direct nutrient supply. This review focuses on the adaptations and evasion strategies of parasitic protists on the example of two very successful parasites of medical significance, Cryptosporidium and Leishmania, while discussing different localisation (epicellular vs. intracellular) with respect to the host cell.

Nutrient Acquisition and Attachment Strategies in Basal Lineages: A Tough Nut to Crack in the Evolutionary Puzzle of Apicomplexa

Apicomplexa are unicellular eukaryotes that parasitise a wide spectrum of invertebrates and vertebrates, including humans. In their hosts, they occupy a variety of niches, from extracellular cavities (intestine, coelom) to epicellular and intracellular locations, depending on the species and/or developmental stages. During their evolution, Apicomplexa thus developed an exceptionally wide range of unique features to reach these diversified parasitic niches and to survive there, at least long enough to ensure their own transmission or that of their progeny. This review summarises the current state of knowledge on the attachment/invasive and nutrient uptake strategies displayed by apicomplexan parasites, focusing on trophozoite stages of their so far poorly studied basal representatives, which mostly parasitise invertebrate hosts. We describe their most important morphofunctional features, and where applicable, discuss existing major similarities and/or differences in the corresponding mechanisms, incomparably better described at the molecular level in the more advanced Apicomplexa species, of medical and veterinary significance, which mainly occupy intracellular niches in vertebrate hosts.

Preliminary Characterization of Two Small Insulinase-Like Proteases in Cryptosporidium parvum

Cryptosporidium parvum is a major cause of moderate-to-severe diarrhea in humans and animals. Its compact genome contains 22 genes encoding divergent insulinase-like proteases (INS), which are poorly characterized. In this study, two small members of this family, INS-21 encoded by cgd7_2080 and INS-23 encoded by cgd5_3400, were cloned, expressed, and characterized to understand their functions. Recombinant INS-21 and INS-23 were expressed in Escherichia coli and polyclonal antibodies against these two proteins were prepared. The cgd7_2080 gene had a high transcription level during 0–2 h of in vitro C. parvum culture, while cgd5_3400 was highly transcribed at 0–6 h. INS-21 was mostly located in the apical region of sporozoites and merozoites whereas INS-23 was found as spots in sporozoites and merozoites. The immunoelectron microscopy confirmed the expression of INS-21 in the apical region of sporozoites while INS-23 appeared to be expressed in the dense granules of sporozoites. The neutralization efficiency was approximately 35%, when the cultures were treated with anti-INS23 antibodies. These results suggest that INS-21 and INS-23 are expressed in different organelles and might have different functions in the development of C. parvum.

Cryptosporidium myocastoris n. sp. (Apicomplexa: Cryptosporidiidae), the Species Adapted to the Nutria (Myocastor coypus)

Cryptosporidium spp., common parasites of vertebrates, remain poorly studied in wildlife. This study describes the novel Cryptosporidium species adapted to nutrias (Myocastor coypus). A total of 150 faecal samples of feral nutria were collected from locations in the Czech Republic and Slovakia and examined for Cryptosporidium spp. oocysts and specific DNA at the SSU, actin, HSP70, and gp60 loci. Molecular analyses revealed the presence of C. parvum (n = 1), C. ubiquitum subtype family XIId (n = 5) and Cryptosporidium myocastoris n. sp. XXIIa (n = 2), and XXIIb (n = 3). Only nutrias positive for C. myocastoris shed microscopically detectable oocysts, which measured 4.8–5.2 × 4.7–5.0 µm, and oocysts were infectious for experimentally infected nutrias with a prepatent period of 5–6 days, although not for mice, gerbils, or chickens. The infection was localised in jejunum and ileum without observable macroscopic changes. The microvilli adjacent to attached stages responded by elongating. Clinical signs were not observed in naturally or experimentally infected nutrias. Phylogenetic analyses at SSU, actin, and HSP70 loci demonstrated that C. myocastoris n. sp. is distinct from other valid Cryptosporidium species.

Metabolic Signatures of Cryptosporidium parvum-Infected HCT-8 Cells and Impact of Selected Metabolic Inhibitors on C. parvum Infection under Physioxia and Hyperoxia

Cryptosporidium parvum is an apicomplexan zoonotic parasite recognized as the second leading-cause of diarrhoea-induced mortality in children. In contrast to other apicomplexans, C. parvum has minimalistic metabolic capacities which are almost exclusively based on glycolysis. Consequently, C. parvum is highly dependent on its host cell metabolism. In vivo (within the intestine) infected epithelial host cells are typically exposed to low oxygen pressure (1-11% O₂, termed physioxia). Here, we comparatively analyzed the metabolic signatures of C. parvum-infected HCT-8 cells cultured under both, hyperoxia (21% O₂), representing the standard oxygen condition used in most experimental settings, and physioxia (5% O₂), to be closer to the in vivo situation. The most pronounced effect of C. parvum infection on host cell metabolism was, on one side, an increase in glucose and glutamine uptake, and on the other side, an increase in lactate release. When cultured in a glutamine-deficient medium, C. parvum infection led to a massive increase in glucose consumption and lactate production. Together, these results point to the important role of both glycolysis and glutaminolysis during C. parvum intracellular replication. Referring to obtained metabolic signatures, we targeted glycolysis as well as glutaminolysis in C. parvum-infected host cells by using the inhibitors lonidamine [inhibitor of hexokinase, mitochondrial carrier protein (MCP) and monocarboxylate transporters (MCT) 1, 2, 4], galloflavin (lactate dehydrogenase inhibitor), syrosingopine (MCT1- and MCT4 inhibitor) and compound 968 (glutaminase inhibitor) under hyperoxic and physioxic conditions. In line with metabolic signatures, all inhibitors significantly reduced parasite replication under both oxygen conditions, thereby proving both energy-related metabolic pathways, glycolysis and glutaminolysis, but also lactate export mechanisms via MCTs as pivotal for C. parvum under in vivo physioxic conditions of mammals.

First report of Cryptosporidium spp. infection and risk factors in black-boned goats and black-boned sheep in China

Cryptosporidium is an opportunistic protozoan parasite that can inhabit in the gastrointestinal tract of various hosts. Cryptosporidium infection in black-boned goats and black-boned sheep may pose a threat to the survival and productivity, causing considerable economic losses to the livestock industry. However, it is yet to know whether black-boned goats and black-boned sheep in China are infected with Cryptosporidium. Thus, the objective of the present study was to investigate the prevalence and associated risk factors of Cryptosporidium infection in black-boned goats and black-boned sheep in Yunnan province, China. A total of 590 fecal samples were obtained from black-boned goats and black-boned sheep from five counties in Yunnan province, and the prevalence and species distribution of Cryptosporidium were determined by amplification of the 18S rDNA fragment using the nested PCR. The overall Cryptosporidium prevalence was 13.2% (78/590), with 18.0% (55/305) in black-boned goats and 8.1% (23/285) in black-boned sheep. The age and sampling site were identified as main factors that result in significant differences in Cryptosporidium prevalence. Three species, namely C. muris, C. xiaoi, and C. ubiquitum, were identified in black-boned goats and black-boned sheep in the present study, with C. muris (46/78) as the predominant species. This is the first report of Cryptosporidium infection in black-boned goats and black-boned sheep in China, and the findings will facilitate better understanding, prevention, and control of Cryptosporidium infection in black-boned goats and black-boned sheep in China.

Assessment of differences between DNA content of cell-cultured and freely suspended oocysts of Cryptosporidium parvum and their suitability as DNA standards in qPCR

BACKGROUND

Although more modern methods are available, quantitative PCR (qPCR) is reproducible, sensitive and specific with instruments and expertise readily available in many laboratories. As such, the use of qPCR in Cryptosporidium research is well established and still widely used by researchers globally. This method depends upon the generation of standards at different concentrations to generate standard curves subsequently used for the quantification of DNA.

METHODS

We assessed four types of DNA template used to generate standard curves in drug screening studies involving Cryptosporidium spp.: (i) serially diluted Cryptosporidium parvum oocysts (106-1); (ii) diluted template DNA from pure oocysts (×10-×106 dilution of 106 oocyst DNA template); (iii) oocysts incubated in human ileocecal adenocarcinoma (HCT-8) cells (105-1 and 5 × 104-50); and (iv) diluted DNA template (5 × 104) from cell culture incubated parasites (×10-×1000).

RESULTS

Serial dilutions of both cell culture and pure oocyst suspension DNA template yielded better linearity than cell culture derived standards, with dilutions of 106 oocysts exhibiting similar quantification cycle (Cq) values to those obtained from DNA template dilutions of 106 oocysts. In contrast, cell culture incubated oocysts demonstrated significantly higher DNA content than equivalent freely suspended oocysts and diluted DNA template from both cell culture derived and freely suspended oocysts across numerous concentrations.

CONCLUSIONS

For many studies involving Cryptosporidium, only relative DNA content is required and as such, the superior linearity afforded by freely suspended oocysts and diluted DNA template (from either cell culture derived standards or freely suspended oocysts) will allow for more accurate relative quantification in each assay. Parasite division in the cell culture standards likely explains the higher DNA content found. These standards, therefore, have the potential to more accurately reflect DNA content in cell culture assays, and despite more modern methods available for absolute quantification, i.e. droplet digital PCR (ddPCR), the ubiquity of qPCR for the foreseeable future encourages further investigation into the reduced linearity observed in these standards such as varying oocyst seeding density, non-linear growth rates and assay efficiency.

Characterization of INS-15, A Metalloprotease Potentially Involved in the Invasion of Cryptosporidium parvum

Cryptosporidium parvum is a protozoan parasite that can cause moderate-to-severe diarrhea. Insulinase-like proteases (INS) are one of the largest protein families within the small proteome of the pathogen. However, their roles in C. parvum biology remain un-elucidated. In this study, a member of the protein family, INS-15 of C. parvum encoded by cgd3_4260, was cloned, expressed and characterized to understand its function. INS-15 and its domain I were expressed in Escherichia coli and polyclonal antibodies against the domain I and one specific polypeptide were prepared in rabbits. The role of INS-15 protein in the C. parvum invasion was preliminarily studied. Recombinant INS-15 protein and its domain I were successfully expressed in E. coli, together with various degraded products. The cgd3_4260 gene had a peak expression at 2 h of in vitroC. parvum culture, while the INS-15 protein was expressed in the mid-anterior region of sporozoites and the area of merozoites opposite to the nucleus. Anti-INS-15 domain I antibodies reduced the invasion of C. parvum sporozoites by over 40%. The anterior location of INS-15 in invasion stages and partial reduction of in vitro growth indicate that INS-15 plays some roles in the invasion or early development of C. parvum.

Identification of adaptive inhibitors of Cryptosporidium parvum fatty acyl-coenzyme A synthetase isoforms by virtual screening

Cryptosporidiosis is a significant cause of gastroenteritis in both humans and livestock in developing countries. The only FDA-approved drug available against the same is nitazoxanide, with questionable efficacy in malnourished children and immunocompromised patients. Recent in vitro studies have indicated the viability of Triacsin C as a potential drug candidate, which targets the parasite's long-chain fatty acyl coenzyme A synthetase enzyme (LC-FACS), a critical component of the fatty acid metabolism pathway. We have used this molecule as a baseline to propose more potent versions thereof. We have applied a combined approach of substructure replacement, literature search, and database screening to come up with 514 analogs of Triacsin C. A virtual screening protocol was carried out which lead us to identify a potential hit compound. This was further subjected to a 100-ns molecular dynamics simulation in complex to determine its stability and binding characteristics. After which, the ADME/tox properties were predicted to assess its viability as a drug. The molecule R134 was identified as the best hit due to its highest average binding affinity, stability in complex when subjected to MD simulations, and reasonable predicted ADMET (Absorption, Distribution, Metabolism, Excretion and Toxicity) properties comparable to those of the Triacsin C parent molecule. We have proposed R134 as a putative drug candidate against the Cryptosporidium parvum LC-FACS enzyme isoforms, following an in silico protocol. We hope the results will be helpful when planning future in vitro experiments for identifying drugs against Cryptosporidium.

Past and future trends of Cryptosporidium in vitro research

Cryptosporidium is a genus of single celled parasites capable of infecting a wide range of animals including humans. Cryptosporidium species are members of the phylum apicomplexa, which includes well-known genera such as Plasmodium and Toxoplasma. Cryptosporidium parasites cause a severe gastro-intestinal disease known as cryptosporidiosis. They are one of the most common causes of childhood diarrhoea worldwide, and infection can have prolonged detrimental effects on the development of children, but also can be life threatening to HIV/AIDS patients and transplant recipients. A variety of hosts can act as reservoirs, and Cryptosporidium can persist in the environment for prolonged times as oocysts. While there has been substantial interest in these parasites, there is very little progress in terms of treatment development and understanding the majority of the life cycle of this unusual organism. In this review, we will provide an overview on the existing knowledge of the biology of the parasite and the current progress in developing in vitro cultivation systems. We will then describe a synopsis of current and next generation approaches that could spearhead further research in combating the parasite.

Characterization of MEDLE-1, a protein in early development of Cryptosporidium parvum

Background

Cryptosporidium spp. are important diarrhea-causing pathogens in humans and animals. Comparative genomic analysis indicated that Cryptosporidium-specific MEDLE family proteins may contribute to host adaptation of Cryptosporidium spp., and a recent study of one member of this family, CpMEDLE-2 encoded by cgd5_4590, has provided evidence supporting this hypothesis. In this study, another member of the protein family, CpMEDLE-1 of Cryptosporidium parvum encoded by cgd5_4580, which is distinct from CpMEDLE-2 and has no signature motif MEDLE, was cloned, expressed and characterized to understand its function.

Methods

CpMEDLE-1 was expressed in Escherichia coli and polyclonal antibodies against the recombinant CpMEDLE-1 protein were prepared in rabbits. Quantitative PCR was used to analyze the expression profile of cgd5_4580 in C. parvum culture. Immunofluorescence staining was used to locate CpMEDLE-1 expression in life-cycle stages, and in vitro neutralization assay with antibodies was adopted to assess the role of the protein in C. parvum invasion.

Results

The results indicated that cgd5_4580 had a peak expression at 2 h of C. parvum culture. CpMEDLE-1 was located in the mid-anterior region of sporozoites, probably within the dense granules. The neutralization efficiency of anti-CpMEDLE-1 antibodies was approximately 40%.

Conclusions

The differences in protein and gene expression profiles between CpMEDLE-1 and CpMEDLE-2 suggest that MEDLE proteins have different subcellular locations, are developmentally regulated, could be potentially involved in the transcriptional regulation of the expression of parasite or host proteins and may exert their functions in different stages of the invasion and development process.

Response of cell lines to actual and simulated inoculation with Cryptosporidium proliferans

The need for an effective treatment against cryptosporidiosis has triggered studies in the search for a working in vitro model. The peculiar niche of cryptosporidia at the brush border of host epithelial cells has been the subject of extensive debates. Despite extensive research on the invasion process, it remains enigmatic whether cryptosporidian host-parasite interactions result from an active invasion process or through encapsulation. We used HCT-8 and HT-29 cell lines for in vitro cultivation of the gastric parasite Cryptosporidium proliferans strain TS03. Using electron and confocal laser scanning microscopy, observations were carried out 24, 48 and 72 h after inoculation with a mixture of C. proliferans oocysts and sporozoites. Free sporozoites and putative merozoites were observed apparently searching for an appropriate infection site. Advanced stages, corresponding to trophozoites and meronts/gamonts enveloped by parasitophorous sac, and emptied sacs were detected. As our observations showed that even unexcysted oocysts became enveloped by cultured cell projections, using polystyrene microspheres, we evaluated the response of cell lines to simulated inoculation with cryptosporidian oocysts to verify innate and parasite-induced behaviour. We found that cultured cell encapsulation of oocysts is induced by parasite antigens, independent of any active invasion/motility.

The truth about in vitro culture of Cryptosporidium species

Cryptosporidium research has focused on the development of infection control, and effective therapy that has thus far been hampered by the inability to culture Cryptosporidium in vitro. Other limitations include inadequate animal models, cumbersome screening procedures for chemotherapeutic approaches and a lack of tools for genetic manipulation. These limitations can, however, be eased by the improvement and focused development of in vitro cultivation. The ability to culture relevant Cryptosporidium isolates in vitro and to propagate the life cycle stages that are responsible for causing disease in an infected host is still a critical link. This ability will facilitate other relevant approaches, e.g., the ability to knockout genes and the application of broader screening for drug discoveries and vaccine developments, in combination with new discoveries on the parasite's basic biology, genetic manipulation and new life cycle stages. Success in this effort represents an essential step towards significant progress in the control of cryptosporidiosis.

Novel Bioengineered Three-Dimensional Human Intestinal Model for Long-Term Infection of Cryptosporidium parvum

Cryptosporidium spp. are apicomplexan parasites of global importance that cause human diarrheal disease. In vitro culture models that may be used to study this parasite and that have physiological relevance to in vivo infection remain suboptimal. Thus, the pathogenesis of cryptosporidiosis remains poorly characterized, and interventions for the disease are limited. In this study, we evaluated the potential of a novel bioengineered three-dimensional (3D) human intestinal tissue model (which we developed previously) to support long-term infection by Cryptosporidium parvum Infection was assessed by immunofluorescence assays and confocal and scanning electron microscopy and quantified by quantitative reverse transcription-PCR. We found that C. parvum infected and developed in this tissue model for at least 17 days, the extent of the study time used in the present study. Contents from infected scaffolds could be transferred to fresh scaffolds to establish new infections for at least three rounds. Asexual and sexual stages and the formation of new oocysts were observed during the course of infection. Additionally, we observed ablation, blunting, or distortion of microvilli in infected epithelial cells. Ultimately, a 3D model system capable of supporting continuous Cryptosporidium infection will be a useful tool for the study of host-parasite interactions, identification of putative drug targets, screening of potential interventions, and propagation of genetically modified parasites.

It's official - Cryptosporidium is a gregarine: What are the implications for the water industry?

Parasites of the genus Cryptosporidium are a major cause of diarrhoea and ill-health in humans and animals and are frequent causes of waterborne outbreaks. Until recently, it was thought that Cryptosporidium was an obligate intracellular parasite that only replicated within a suitable host, and that faecally shed oocysts could survive in the environment but could not multiply. In light of extensive biological and molecular data, including the ability of Cryptosporidium to complete its life cycle in the absence of a host and the production of novel extracellular stages, Cryptosporidium has been formally transferred from the Coccidia, to a new subclass, Cryptogregaria, with gregarine parasites. In this review, we discuss the close relationship between Cryptosporidium and gregarines and discuss the implications for the water industry.

Electron microscopic observation of the early stages of Cryptosporidium parvum asexual multiplication and development in in vitro axenic culture

The stages of Cryptosporidium parvum asexual exogenous development were investigated at high ultra-structural resolution in cell-free culture using transmission electron microscopy (TEM). Early C. parvum trophozoites were ovoid in shape, 1.07 × 1.47 μm(2) in size, and contained a large nucleus and adjacent Golgi complex. Dividing and mature meronts containing four to eight developing merozoites, 2.34 × 2.7 μm(2) in size, were observed within the first 24h of cultivation. An obvious peculiarity was found within the merozoite pellicle, as it was composed of the outer plasma membrane with underlying middle and inner membrane complexes. Further novel findings were vacuolization of the meront's residuum and extension of its outer pellicle, as parasitophorous vacuole-like membranes were also evident. The asexual reproduction of C. parvum was consistent with the developmental pattern of both eimerian coccidia and Arthrogregarinida (formerly Neogregarinida). The unique cell-free development of C. parvum described here, along with the establishment of meronts and merozoite formation, is the first such evidence obtained from in vitro cell-free culture at the ultrastructural level.

The Ultra-Structural Similarities between Cryptosporidium parvum and the Gregarines

Using a transmission electron microscopy-based approach, this study details the striking similarities between Cryptosporidium parvum and the gregarines during in vitro axenic development at high ultra-structural resolution. C. parvum zoites displayed three unusual regions within uninucleated parasites: epimerite-like, protomerite-like, and the cell body; these regions exhibited a high degree of morphological similarity to gregarine-like trophozoites. The presence of a mucron-like bulging structure at the side of the free ovoid gregarine-like zoites was observed after 2 h of cultivation. An irregular pattern of epicytic-like folds were found to cover the surface of the parasites 24 h postcultivation. Some extracellular stages were paired in laterocaudal or side-side syzygy, with the presence of a fusion zone between some of these zoites. The present findings are in agreement with phylogenetic studies that have proposed a sister relationship with gregarines. Cryptosporidium appears to exhibit tremendous variety in cell structure depending on the surrounding environment, thereby mimicking the "primitive" gregarines in terms of the co-evolution strategy between the parasites and their environments. Given this degree of similarity, different aspects of the evolutionary biology of Cryptosporidium need to be examined, considering the knowledge gained from the study of gregarines.

Extracellular excystation and development of Cryptosporidium: tracing the fate of oocysts within Pseudomonas aquatic biofilm systems

Background

Aquatic biofilms often serve as environmental reservoirs for microorganisms and provide them with a nutrient-rich growth environment under harsh conditions. With regard to Cryptosporidium, biofilms can serve as environmental reservoirs for oocysts, but may also support the growth of additional Cryptosporidium stages.

Results

Here we used confocal laser scanning microscopy, scanning electron microscopy (SEM), and flow cytometry to identify and describe various Cryptosporidium developmental stages present within aquatic biofilm systems, and to directly compare these to stages produced in cell culture. We also show that Cryptosporidium has the ability to form a parasitophorous vacuole independently, in a host-free biofilm environment, potentially allowing them to complete an extracellular life cycle. Correlative data from confocal and SEM imaging of the same cells confirmed that the observed developmental stages (including trophozoites, meronts, and merozoites) were Cryptosporidium. These microscopy observations were further supported by flow cytometric analyses, where excysted oocyst populations were detected in 1, 3 and 6 day-old Cryptosporidium-exposed biofilms, but not in biofilm-free controls.

Conclusions

These observations not only highlight the risk that aquatic biofilms pose in regards to Cryptosporidium outbreaks from water distribution systems, but further indicate that even simple biofilms are able to stimulate oocyst excystation and support the extracellular multiplication and development of Cryptosporidium within aquatic environments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-014-0281-8) contains supplementary material, which is available to authorized users.

Characterization of a novel otubain-like cysteine protease of Cryptosporidium parvum

Otubains are a recently discovered family of cysteine proteases that participate in the ubiquitin pathway. Here, we partially characterized the biochemical properties of a cysteine protease of Cryptosporidium parvum, which is closely related to otubains. The gene encoding otubain-like cysteine protease of C. parvum (CpOTU) contained the aspartate, cysteine and histidine residues that form the catalytic triad of otubains. The modified ubiquitin-associated domain and LxxL motif were identified in CpOTU. The recombinant CpOTU showed the isopeptidase activity at neutral pH values and its activity was effectively inhibited by ubiquitin aldehyde, N-ethylmaleimide and iodoacetic acid. Interestingly, CpOTU had an unusual C-terminal extension of 217 amino acids compared to mammalian otubains, and the C-terminal extension is essential for the activity of the enzyme. Expression of CpOTU peaked in the oocyst stage of the parasite, which suggested its potential physiological role for the oocyst stage.

Characterization of biochemical properties of a selenium-independent glutathione peroxidase ofCryptosporidium parvum

Glutathione peroxidase (GPx; EC 1.11.1.9) is an important antioxidant enzyme that catalyses the reduction of organic and inorganic hydroperoxides to water in oxygen-consuming organisms, using glutathione as an electron donor. Here, we report the characterization of a GPx ofCryptosporidium parvum(CpGPx). CpGPx contained a standard UGU codon for cysteine instead of a UGA opal codon for seleno-cysteine (SeCys) at the active site, and no SeCys insertion sequence (SECIS) motif was identified within the 3′-untranslated region (UTR) of CpGPx, which suggested its selenium-independent nature.In silicoand biochemical analyses indicated that CpGPx is a cytosolic protein with a monomeric structure. Recombinant CpGPx was active over a wide pH range and was stable under physiological conditions. It showed a substrate preference against organic hydroperoxides, such as cumene hydroperoxide andt-butyl hydroperoxide, but it also showed activity against inorganic hydroperoxide, hydrogen peroxide. Recombinant CpGPx was not inhibited by potassium cyanide or by sodium azide. The enzyme effectively protected DNA and protein from oxidative damage induced by hydrogen peroxide, and was functionally expressed in various developmental stages ofC. parvum. These results collectively suggest the essential role of CpGPx for the parasite's antioxidant defence system.

Life cycle ofCryptosporidium murisin two rodents with different responses to parasitization

This study focuses on mapping the life cycle ofCryptosporidium murisin two laboratory rodents; BALB/c mice and the southern multimammate ratMastomys coucha, differing in their prepatent and patent periods. Both rodents were simultaneously experimentally inoculated with viable oocysts ofC. muris(strain TS03). Animals were dissected and screened for the presence of the parasite using a combined morphological approach and nested PCR (SSU rRNA) at different times after inoculation. The occurrence of first developmental stages ofC. murisin stomach was detected at 2·5 days post-infection (dpi). The presence of Type II merogony, appearing 36 h later than Type I merogony, was confirmed in both rodents. Oocysts exhibiting different size and thickness of their wall were observed from 5 dpi onwards in stomachs of both host models. The early phase of parasitization in BALB/c mice progressed rapidly, with a prepatent period of 7·5–10 days; whereas inM. coucha, the developmental stages ofC. muriswere first observed 12 h later in comparison with BALB/c mice and prepatent period was longer (18–21 days). Similarly, the patent periods of BALB/c mice andM. couchadiffered considerably, i.e. 10–15 daysvschronic infection throughout the life of the host, respectively.

Multiplication of the waterborne pathogen Cryptosporidium parvum in an aquatic biofilm system

BACKGROUND

In natural aquatic environments biofilms are known to act as environmental reservoirs for Cryptosporidium parvum oocysts. However, the fate of these oocysts within biofilms has yet to be determined.

METHODS

This study aimed to identify if biofilms have the ability to support the multiplication of Cryptosporidium by measuring the change in parasite number over time using quantitative polymerase chain reaction (qPCR) and detecting the possible extracellular developmental stages using a combination of confocal microscopy and immunolabelling techniques. Pseudomonas aeruginosa biofilm flow cell systems were established and C. parvum oocysts were constantly supplied over a six day period.

RESULTS

A significant (P<0.001) increase in Cryptosporidium was detected as the biofilm matured, with the total number of C. parvum multiplying 2-3 fold during this period. With this, various Cryptosporidium developmental stages (sporozoites, trophozoites, type I and II meronts) were identified from the biofilm.

CONCLUSION

This is the first study demonstrating that biofilms not only serve as an environmental reservoir for oocysts, but are also capable of supporting the multiplication of Cryptosporidium over time in an aquatic environment.

Pomegranate (Punica granatum) peel is effective in a murine model of experimental Cryptosporidium parvum ultrastructural studies of the ileum

The current treatments for cryptosporidiosis are ineffective, and there is an urgent need to search for more effective and safer alternatives. One such alternative may be treatments derived from natural resources. The pomegranate peel has been used effectively in traditional medicine to cure diarrhea and dysentery. The purpose of this study was to examine the effectiveness of a Punica granatum (pomegranate) peel suspension as a treatment for Cryptosporidium parvum infection. In this study, the effects of this treatment on the ultrastructure of both the intestinal epithelial layer of infected nursling mice and the parasite were observed with a transmission electron microscope. The histological study focused on the examination of the microvilli, columnar epithelium, goblet cells, lamina propria, and crypts of Lieberkuhn. Examination of the ileums of infected mice that received the pomegranate peel suspension demonstrated that the general structure of the ileal tissue of these mice was similar to that of the control group. In the infected mice treated with the suspension, but not the infected/untreated mice, there was an improvement in all ultrastructure aspects at 28days post-inoculation. The study of the ultrastructure of the parasite (C. parvum) in mice treated with the suspension showed that there was decomposition in the parasite to the extent that in some cases we were unable to identify the stage of the parasite due to the severe degeneration. Significant decomposition of the nutrition organ was also observed. Additionally, microgamonte and macrogamonte were not observed in the suspension-treated group, explaining the disappearance of the sexual phases of the parasite in the lumens of this group. In all, this examination demonstrated the restoration of the normal structures of villi and the disappearance of acute symptoms in the suspension-treated mice and showed that the suspension directly affected the parasite at various stages of its development and led to its decomposition and death.

Dysfunctions at human intestinal barrier by water-borne protozoan parasites: lessons from cultured human fully differentiated colon cancer cell lines

Some water-borne protozoan parasites induce diseases through their membrane-associated functional structures and virulence factors that hijack the host cellular molecules and signalling pathways leading to structural and functional lesions in the intestinal barrier. In this Microreview we analyse the insights on the mechanisms of pathogenesis of Entamoeba intestinalis, Giardia and Cryptosporidium observed in the human colon carcinoma fully differentiated colon cancer cell lines, cell subpopulations and clones expressing the structural and functional characteristics of highly specialized fully differentiated epithelial cells lining the intestinal epithelium and mimicking structurally and functionally an intestinal barrier.

In vitro culture systems for the study of apicomplexan parasites in farm animals

In vitro culture systems represent powerful tools for the study of apicomplexan parasites such as Cryptosporidium, Eimeria, Sarcocystis, Neospora, Toxoplasma, Besnoitia, Babesia and Theileria, all with high relevance for farm animals. Proliferative stages of these parasites have been cultured in vitro employing a large variety of cell culture and explant approaches. For some, such as Cryptosporidium and Eimeria, the sexual development has been reproduced in cell cultures, while for others, animal experimentation is required to fulfill the life cycle. In vitro cultures have paved the way to exploit the basic biology of these organisms, and had a major impact on the development of tools for diagnostic purposes. With the aid of in vitro cultivation, studies on host-parasite interactions, on factors involved in innate resistance, stage conversion and differentiation, genetics and transfection technology, vaccine candidates and drug effectiveness could be carried out. The use of transgenic parasites has facilitated high-throughput screening of anti-microbial compounds that are active against the proliferative stages. Here, we review the basic features of cell culture-based in vitro systems for apicomplexan parasites that are relevant for farm animals, and discuss their applications with a focus on drug identification and studies of stage differentiation.

In vitro evaluation of the suppressive effect of chitosan/poly(vinyl alcohol) microspheres on attachment of C. parvum to enterocytic cells

We present a new strategy to suppress the attachment of Cryptosporidium parvum to the enterocytes cell surface by bioadhesive microspheres. An optimized microsphere system based on chitosan/poly(vinyl alcohol) was prepared by experimental design for the delivery of Diloxanide Furoate-cyclodextrin complex. Formulations were characterized in terms of size, surface charge, drug release, IR spectroscopy and morphology. Bioadhesion properties of chitosan/poly(vinyl alcohol) microspheres, evaluated in the human enterocytic HCT-8 model, were concentration and time dependent. In vitro efficacy of chitosan/poly(vinyl alcohol) microspheres against Cryptosporidium was tested in infected cultures and stages of parasite were assessed by immunofluorescence. The degree of adherence to cells and the inhibition of infectivity were directly related with the lowest level of cross-linking. The C. parvum attachment to cells surface was efficiently suppressed by a concentration of 100 μg/ml of microspheres. TEM observations showed no epithelial-cell damage when microspheres were co-incubated in infected cultures. These results were coincident with the lack of toxicity in cytocompatibility studies. Microspheres remained adhered after 72 h to the apical area of enterocytes. The results suggest that chitosan/poly(vinyl alcohol) with adequate size and appropriate surface characteristics suppress by impairment the attachment of sporozoites to enterocytes and may have a great potential in the oral chemotherapy of Cryptosporidium infections.

The Cryptosporidium parvum transcriptome during in vitro development

Cryptosporidiosis is caused by an obligate intracellular parasite that has eluded global transcriptional or proteomic analysis of the intracellular developmental stages. The transcript abundance for 3,302 genes (87%) of the Cryptosporidium parvum protein coding genome was elucidated over a 72 hr infection within HCT8 cells using Real Time-PCR. The parasite had detectable transcription of all genes in vitro within at least one time point tested, and adjacent genes were not co-regulated. Five genes were not detected within the first 24 hr of infection, one containing two AP2 domains. The fewest genes detected were at 2 hr post infection, while 30% (985) of the genes have their highest expression at 48 and/or 72 hr. Nine expression clusters were formed over the entire 72 hr time course and indicate patterns of transcriptional increases at each of the 7 time points collected except 36 hr, including genes paralleling parasite 18S rRNA transcript levels. Clustering within only the first 24 hr of infection indicates spikes in expression at each of the 4 time points, a group paralleling 18S rRNA transcript levels, and a cluster with peaks at both 6 and 24 hr. All genes were classified into 18 functional categories, which were unequally distributed across clusters. Expression of metabolic, ribosomal and proteasome proteins did not parallel 18S rRNA levels indicating distinct biochemical profiles during developmental stage progression. Proteins involved in translation are over-represented at 6 hr, while structural proteins are over-represented at 12 hr. Standardization methods identified 107 genes with <80% at a single of its total expression at a single time point over 72 hr. This comprehensive transcriptome of the intracellular stages of C. parvum provides insight for understanding its complex development following parasitization of intestinal epithelial cells.

Cryptosporidiosis-an overview

Apicomplexan protozoan parasites of the genus Cryptosporidium infect the gastrointestinal tract and lungs of a wide variety of animals, including humans. The majority of human infections are due to either Cryptosporidium hominis (C. hominis) and/or Cryptosporidium parvum (C. parvum). The parasite has a complex life cycle that includes both asexual and sexual stages. While there are invasive free living stages, proliferation and differentiation take place within a unique parasitrophorous vacuole under the host cell brush border but outside the host cell cytoplasm. Infection is spread by environmentally resistant spores that primarily contaminate drinking water and occasionally food sources, which may cause significant outbreaks of diarrhea that generally lasts less than 2 w in immunocompetent individuals. In immunodeficient or immunosuppressed individuals, diarrhea may be copious and can result in significant morbidity and mortality, particularly in AIDS patients. Although diagnosis is relatively simple, effective drug treatment, particulary for infections in immunodeficient patients, has not been uniformly successful. This overview summarizes the species known to infect humans, aspects of the parasite life cycle, sources of infection, the pathophysiology of cryptosporidiosis, the immune response to infection, diagnosis, treatment and some aspects of cryptosporidiosis in China.

Labeling surface epitopes to identify Cryptosporidium life stages using a scanning electron microscopy-based immunogold approach

The Apicomplexan parasite Cryptosporidium parvum is responsible for the widespread disease cryptosporidiosis, in both humans and livestock. The nature of C. parvum infection is far from understood and many questions remain in regard to host-parasite interactions, limiting successful treatment of the disease. To definitively identify a range of C. parvum stages in cell culture and to begin to investigate host cell interactions in some of the lesser known life stages, we have utilized a combined scanning electron microscopy and immunolabeling approach, correlating high resolution microstructural information with definitive immunogold labeling of Cryptosporidium stages. Several life cycle stages, including oocysts, merozoites I, trophozoites, gamonts and microgametocytes, were successfully immunolabeled in an in vitro model system. Developing oocysts were clearly immunolabeled, but this did not persist once excystation had occurred. Immunolabeling visualized on the host cell surface adjacent to invasive merozoites is likely to be indicative of receptor shedding, with merozoites also initiating host responses that manifested as abnormal microvilli on the host cell surface. Small sub-micron stages such as microgametocytes, which were impossible to identify as single entities without immunolabeling, were readily visualized and observed to attach to host cells via novel membranous projections. Epicellular parasites also expressed Cryptosporidium-derived epitopes within their encapsulating membrane. These data have allowed us to confidently identify a variety of C. parvum stages in cell culture at high resolution. With this, we provide new insight into C. parvum - host cell interactions and highlight future opportunities for investigating and targeting receptor-mediated interactions between Cryptosporidium life cycle stages and host cells.

Zoonotic enteric protozoa

A growing number of enteric protozoan species are considered to have zoonotic potential. Their clinical impact varies and in many cases is poorly defined. Similarly, the epidemiology of infections, particularly the role of non-human hosts, requires further study. In this review, new information on the life cycles and transmission of Giardia, Cryptosporidium, Entamoeba, Blastocystis and Balantidium are examined in the context of zoonotic potential, as well as polyparasitism and clinical significance.