Effect of select medium supplements on in vitro development of Cryptosporidium andersoni in HCT-8 cells

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.

A new in vitro model using small intestinal epithelial cells to enhance infection of Cryptosporidium parvum

To better understand and study the infection of the protozoan parasite Cryptosporidium parvum, a more sensitive in vitro assay is required. In vivo, this parasite infects the epithelial cells of the microvilli layer in the small intestine. While cell infection models using colon, kidney, and stomach cells have been studied to understand the infectivity potential of the oocysts, an ideal in vitro model would be readily-available, human-derived, and originating from the small intestine. In this study, we developed a reproducible, quantitative infection model using a non-carcinoma, human small intestinal epithelial cell type, named FHs 74 Int. Our results show that FHs 74 Int cells are productively infected by viable oocysts, and exhibit higher levels of infection susceptibility compared to other cell types. Moreover, infection rate of the sporozoites on the monolayer was found to be comparable or better than other cell types. We furthermore demonstrate that infection can be improved by 65% when pre-treated oocysts are directly inoculated on cells, compared to inoculation of excysted sporozoites on cells. Identification of a better infection model, which captures the preferred site of infection in humans, will facilitate studies on the host pathogenesis mechanisms of this important parasitic human pathogen.

An evaluation of the potential use of Cryptosporidium species as agents for deliberate release

INTRODUCTION

We evaluated the potential of Cryptosporidium spp. for intentional transmission as a terrorist tactic in asymmetric conflicts in terms of the recognised optimum conditions for biological warfare.

METHODS

Published and widely accepted criteria regarding the optimum conditions for the success of biological warfare based on experience from passive biological warfare research were applied to hypothetical intentional Cryptosporidium spp. transmission.

RESULT

The feasibility of the use of Cryptosporidium spp. transmission for terrorist purposes was established. Particularly on tropical deployments with poor hygiene conditions, such attacks might have a good chance of remaining undetected as a deliberate terrorist attack.

CONCLUSIONS

Intentional transmission should be suspected in cases of sudden outbreaks of cryptosporidiosis, particularly where adequate food and drinking water hygiene precautions are being enforced. Appropriate diagnostic procedures should be available so that the diagnosis is not missed.

Cryptic parasite revealed improved prospects for treatment and control of human cryptosporidiosis through advanced technologies

Cryptosporidium is an important genus of parasitic protozoa of humans and other vertebrates and is a major cause of intestinal disease globally. Unlike many common causes of infectious enteritis, there are no widely available, effective vaccine or drug-based intervention strategies for Cryptosporidium, and control is focused mainly on prevention. This approach is particularly deficient for infections of severely immunocompromised and/or suppressed, the elderly or malnourished people. However, cryptosporidiosis also presents a significant burden on immunocompetent individuals, and can, for example have lasting effects on the physical and mental development of children infected at an early age. In the last few decades, our understanding of Cryptosporidium has expanded significantly in numerous areas, including the parasite life-cycle, the processes of excystation, cellular invasion and reproduction, and the interplay between parasite and host. Nonetheless, despite extensive research, many aspects of the biology of Cryptosporidium remain unknown, and treatment and control are challenging. Here, we review the current state of knowledge of Cryptosporidium, with a focus on major advances arising from the recently completed genome sequences of the two species of greatest relevance in humans, namely Cryptosporidium hominis and Cryptosporidium parvum. In addition, we discuss the potential of next-generation sequencing technologies, new advances in in silico analyses and progress in in vitro culturing systems to bridge these gaps and to lead toward effective treatment and control of cryptosporidiosis.

In vitro determination of anticryptosporidial activity of phytogenic extracts and compounds

Cryptosporidiosis caused by Cryptosporidium spp. is an important diarrhoeal disease observed in farm animals and humans, especially in young or immunocompromised individuals. A novel cell culture assay for testing extracts and pure compounds against Cryptosporidium parvum in 96-well microplate format was established and evaluated. It is based on previously described indirect fluorescent antibody techniques and was optimised for higher sample throughput. Rapid assessment of minimal inhibitory concentrations (MICs) was done by checking each well microscopically for the presence or absence of parasite stages. As a novelty, parasite development was quantified by enumeration of clusters of secondary infection (CSI), which typically appeared upon infection with a distinct parasite inoculum after a defined incubation time. Host cell (HCT-8) viability was measured by an integrated non-destructive water-soluble tetrazolium salt assay (WST-1), which facilitated discrimination of antiparasitic activity from possible cytotoxic effects of a test compound against the host cells. Host cell viability was regarded unimpaired when cultures had 75% or more viability when compared to control cultures without test substance. In this study, a maximum density of distinguishable CSI was obtained when cultures were infected with 2.5 × 10(3) oocysts and incubated for 48 h. The applicable inoculum has to be optimised for each batch of oocysts and before each experimental series. Parasite development was inhibited completely by monensin at 134 nM and silymarin at 50 mg/mL. These concentrations were non-toxic to the host cells and comparable to literature data. The percentages of parasite inhibition were determined for monensin and a 50% inhibitory concentration (IC(50)) of 36.6 nM (27.4-45.5) and a 90% inhibitory concentration of 65.9 nM (54.8-90.2) were calculated. The introduced assay is economic because relatively low parasite numbers may be used. If MICs are determined, evaluation is fast, as each well is viewed only briefly under the fluorescence microscope for presence or absence of CSI. Furthermore it is highly critical because only full parasite inhibition is assessed. Counting of CSI is more laborious and time-consuming, but it allows calculation of parasite inhibition rates and parameters like the half maximal inhibitory concentration (IC(50)). This assay shall be used to assess anticryptosporidial activities of various plant waste materials and by-products from the food and the pharmaceutical industries in the course of the EU project SAFEWASTES. Comparison with in vivo models should be performed to further corroborate the results. Automated evaluation by flow cytometry might facilitate higher sample throughput and reduce operator bias.

Evolution of Cryptosporidium in vitro culture

This overview discusses findings from culturing Cryptosporidium spp. in cell and axenic cultures as well as factors limiting the development of this parasite in cultivation systems during recent years. A systematic review is undertaken of findings regarding the life cycle of the parasite, taking into account physiological, biochemical and genetic aspects, in the hope that this attempt will facilitate future approaches to research and developments in the understanding of Cryptosporidium biology.