Cryptosporidium parvum at different developmental stages modulates host cell apoptosis in vitro

MiR-4521 affects the propagation of Cryptosporidium parvum in HCT-8 cells through targeting foxm1 by regulating cell apoptosis

Cryptosporidium parvum could regulate the expression of microRNAs of epithelial cells to facilitate its intracellular propagation. MiR-4521 has been reported to play an important role during the development and progression of tumors and infectious diseases by regulating cell proliferation, apoptosis, and autophagy. However, the implication of miR-4521 during C. parvum infection was still unknown. In this study, the expression of miR-4521 was found to be upregulated in HCT-8 cells infected with C. parvum from 8 h post-infection (pi) to 48 hpi, and its upregulation would be related with the TLR/NF-κB signal pathway during C. parvum infection. One potential target of miR-4521, foxm1, was down-regulated in HCT-8 cells from 24 hpi to 48 hpi, and the expression of foxm1 was negatively regulated by miR-4521. The target relationship between miR-4521 and foxm1 was further validated by using dual luciferase reporter assay. Further studies showed that miR-4521 promoted the propagation of C. parvum in HCT-8 cells through targeting foxm1 by regulating BCL2-mediating cell apoptosis. These results contribute to further understanding of the regulatory mechanisms of host miRNAs during Cryptosporidium infection.

Inhibition of Cell Apoptosis by Apicomplexan Protozoa-Host Interaction in the Early Stage of Infection

Apicomplexan protozoa, which are a group of specialized intracellular parasitic protozoa, infect humans and other animals and cause a variety of diseases. The lack of research on the interaction mechanism between Apicomplexan protozoa and their hosts is a key factor restricting the development of new drugs and vaccines. In the early stages of infection, cell apoptosis is inhibited by Apicomplexan protozoa through their interaction with the host cells; thereby, the survival and reproduction of Apicomplexan protozoa in host cells is promoted. In this review, the key virulence proteins and pathways are introduced regarding the inhibition of cell apoptosis by the interaction between the protozoa and their host during the early stage of Apicomplexan protozoa infection. It provides a theoretical basis for the development of drugs or vaccines for protozoal diseases.

A Cryptosporidium parvum vaccine candidate effect on immunohistochemical profiling of CD4+, CD8+, Caspase-3 and NF-κB in mice

BACKGROUND

Cryptosporidium parvum is a protozoan parasite of medical and veterinary importance that causes neonatal diarrhea in many vertebrate hosts. In this study, we evaluated the efficacy of an affinity-purified antigen as a C. parvum vaccine candidate using ileal and liver tissues of experimentally infected neonatal mice by immunohistochemical profiling and immune scoring of CD4+, CD8+, Caspase-3, and nuclear factor kappa B (NF-κB). This vaccine was prepared from the C. parvum oocysts antigen using immune affinity chromatography with cyanogen bromide-activated Sepharose-4B beads.

METHODS

Thirty neonatal mice were divided into three groups (10 mice/group): (1) non-immunized non-infected, (2) non-immunized infected (using gastric tubes with a single dose of 1 × 105 of C. parvum oocysts in 250 µl PBS solution 1 h before a meal) and (3) immunized (twice with 40 µg/kg of purified C. parvum antigen at 2-week intervals and then infected with 1 × 105 C. parvum oocysts simultaneously with the second group). After euthanizing the animals on the 10th day, post-infection, their ileal and liver tissues were collected and prepared for immunohistochemistry (IHC) staining to detect CD4+, CD8+, Caspase-3, and NF-κB levels, which are indicators for T helper cells, cytotoxic T cells, apoptosis, and inflammation, respectively.

RESULTS

The IHC results showed that CD4+, CD8+, Caspase-3, and NF-κB expression varied significantly (P < 0.001) in both organs in all the groups. We also recorded high CD4+ levels and low CD8+ expression in the non-immunized non-infected mice tissues, while the opposite was observed in the non-immunized infected mice tissues. In the immunized infected mice, the CD4+ level was higher than CD8 + in both organs. While the Caspase-3 levels were higher in the ileal tissue of non-immunized infected than immunized infected mice ileal tissues, the reverse was seen in the liver tissues of both groups. Furthermore, NF-κB expression was higher in the liver tissues of non-immunized infected mice than in immunized infected mice tissues. Therefore, the IHC results and immune-scoring program revealed a significant difference (P < 0.001) in the CD4+, CD8+, Caspase-3, and NF-κB expression levels in both ileal and liver tissues of all mice groups, which might be necessary for immunomodulation in these tissues.

CONCLUSIONS

The improvement observed in the immunized infected mice suggests that this vaccine candidate might protect against cryptosporidiosis.

Organoid-based in vitro systems to model Cryptosporidium parvum infection in 2D and 3D

Typical cancer cell-based culture systems cannot support the full life cycle of Cryptosporidium parvum, despite its monoxenous life cycle which is completed in the small intestine of a single host. There is a block to fertilization and zygote formation in vitro. In this paper, we adapted a 2D organoid derived monolayer system and a 3D inverted enteroid system for use in C. parvum culture. 3D inverted enteroids were successfully infected by C. parvum without the need for microinjection and supported subculture of C. parvum. Using the 2D organoid derived monolayer (ODM) system, the infection can be maintained for at least 3 weeks with new oocyst production throughout. Fertilization was confirmed based on successful mating of two strains of C. parvum. We demonstrated that the apparent block to fertilization in typical cell culture is overcome using ODMs.

Early immune and host cell responses to Cryptosporidium infection

Cryptosporidium spp. are opportunistic protozoan parasites that infect epithelial cells of the small intestine and cause diarrheal illness in both immunocompetent and immunodeficient individuals. These infections may be more severe in immunocompromised individuals and young children, especially in children under 2 in developing countries. The parasite has a global distribution and is an important cause of childhood diarrhea where it may result in cognitive impairment and growth deficits. Current therapies are limited with nitazoxanide being the only FDA-approved drug. However, it is not efficacious in immunocompromised patients. Additionally, there are no vaccines for cryptosporidiosis available. While acquired immunity is needed to clear Cryptosporidium parasites completely, innate immunity and early responses to infection are important in keeping the infection in check so that adaptive responses have time to develop. Infection is localized to the epithelial cells of the gut. Therefore, host cell defenses are important in the early response to infection and may be triggered through toll receptors or inflammasomes which induce a number of signal pathways, interferons, cytokines, and other immune mediators. Chemokines and chemokine receptors are upregulated which recruit immune cells such neutrophils, NK cells, and macrophages to the infection site to help in host cell defense as well as dendritic cells that are an important bridge between innate and adaptive responses. This review will focus on the host cell responses and the immune responses that are important in the early stages of infection.

The role of atypical MAP kinase 4 in the host interaction with Cryptosporidium parvum

Cryptosporidium parvum is an apicomplexan parasite that causes severe zoonotic diarrhea in humans and calves. Since there are no effective treatments or vaccines for infants or immunocompromised patients, it is important to understand the molecular mechanisms of the parasite-host interaction for novel drug discovery. Mitogen-activated protein kinase (MAP kinase) is a key host factor in interactions between host and various pathogens, including parasites. Although the function of conventional MAP kinases against parasite infection has been investigated, that of atypical MAP kinases remains largely unknown. Therefore, we focused on one of the atypical MAP kinases, MAPK4, and its effect on C. parvum infection in human intestinal cells. Here, we report that MAPK4-deficient intestinal cells showed a significant reduction in C. parvum infection. We also show that host MAPK4 has a role in host cell survival from C. parvum infection. In addition, we show that C. parvum requires host MAPK4 for its successful invasion and asexual reproduction. Taken together, our data suggest that MAPK4 is an important host factor contributing to C. parvum infection in human intestinal cells.

Hymenolepis diminuta Infection Affects Apoptosis in the Small and Large Intestine

The rat tapeworm Hymenolepis diminuta has been shown to cause alterations in gastrointestinal tissues. Since hymenolepiasis induces a number of reactions in the host, it is reasonable to assume that it may also be involved in the mechanisms of apoptosis in the intestines. Individual research tasks included an examination of the effect of H. diminuta infection on; (i) the cellular localization of the expression of pro-apoptotic protein Bax and anti-apoptotic protein Bcl-2, as well as caspase-3 and caspase-9, and (ii) the effects of the infection on the expression of Bcl-2, Bax, Cas-3 and Cas-9, at the mRNA and protein levels. Molecular tests (including mRNA (qRT PCR) and the protein (Western blot) expression of Bax, Bcl-2, and caspases-3, -9) and immunohistochemical tests were performed during the experiment. They showed that H. diminuta infection activates the intrinsic apoptosis pathway in the small and large intestine of the host. H. diminuta infection triggered the apoptosis via the activation of the caspase cascade, including Cas-3 and Cas-9. Hymenolepiasis enhanced apoptosis in the small and large intestine of the host by increasing the expression of the pro-apoptotic gene and protein Bax and by decreasing the expression of the anti-apoptotic gene and protein Bcl-2.

Is Cryptosporidium a hijacker able to drive cancer cell proliferation?

The pathophysiological mechanisms of Cryptosporidium infection are multifactorial and not completely understood. Some advances achieved recently revealed that the infection by Cryptosporidium parvum induces cytoskeleton remodeling and actin reorganization through the implication of several intracellular signals involving, for example, PI3K, Src, Cdc42 and GTPases. It has also been reported that the infection by C. parvum leads to the activation of NF-κβ, known to induce anti-apoptotic mechanisms and to transmit oncogenic signals to epithelial cells. Despite the growing evidence about the hijacking of cellular pathways, potentially being involved in cancer onset, this information has rarely been linked to the tumorigenic potential of the parasite. However, several evidences support an association between Cryptosporidium infection and the development of digestive neoplasia. To explore the dynamics of Cryptosporidium infection, an animal model of cryptosporidiosis using corticoid dexamethasone-treated adult SCID (severe combined immunodeficiency) mice, orally infected with C. parvum or Cryptosporidium muris oocysts was implemented. C. parvum-infected animals developed digestive adenocarcinoma. When mechanisms involved in this neoplastic process were explored, the pivotal role of the Wnt pathway together with the alteration of the cytoskeleton was confirmed. Recently, a microarray assay allowed the detection of cancer-promoting genes and pathways highly up regulated in the group of C. parvum infected animals when compared to non-infected controls. Moreover, different human cases/control studies reported significant higher prevalence of Cryptosporidium infection among patients with recently diagnosed colon cancer before any treatment when compared to the control group (patients without colon neoplasia but with persistent digestive symptoms). These results suggest that Cryptosporidium is a potential oncogenic agent involved in cancer development beyond the usual suspects. If Cryptosporidium is able to hijack signal transduction, then is very likely that this contributes to transformation of its host cell. More research in the field is required in order to identify mechanisms and molecular factors involved in this process and to develop effective treatment interventions.

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 Effects of Commercially Available Syzygium aromaticum, Anethum graveolens, Lactobacillus acidophilus LB, and Zinc as Alternatives Therapy in Experimental Mice Challenged with Cryptosporidium parvum

BACKGROUND

Waterborne cryptosporidiosis is the second cause of diarrhea in young children and immunocompromised hosts after rotavirus. Except for nitazoxanide (NTZ), there is no accredited cryptosporidiosis treatment to date. Therefore, there is an urgent need to find an effective and safe treatment for cryptosporidiosis. This study aimed to investigate the possible anti-protozoal effects of Syzygium aromaticum (clove) oil, Anethum graveolens (dill) seeds oil, Lactobacillus acidophilus LB, and zinc against Cryptosporidium parvum in comparison to NTZ.

METHODS

Besides the negative control, mice from six experimental groups (T1-T6) were infected with Cryptosporidium parvum oocysts. On the seventh day post-infection (PID), mice from five groups were treated for 8 consecutive days with NTZ, clove oil, dill seed oil, Lactobacillus acidophilus LB, and zinc commercial forms (T2-T5). Oocysts shedding rate, differences of mice body weight, serum IL10, and TNF-α, cryptosporidial antigen, and cd3 at the intestinal mucosa were evaluated at the end of the experiment.

RESULTS

The mean of the C. parvum oocysts' shedding rate was significantly lower in all treated groups than in the non-treated group. The oocysts reduction rate was the highest in zinc-treated mice (98.3%), Lactobacillus acidophilus LB and dill-treated groups (95.77%), and the NTZ-treated group (91.55%). Clove oil was the least effective, with a 74.65% reduction rate. Excluding the clove oil-treated group, immunohistochemical analysis revealed the clearance of the Cryptosporidium antigen in the intestinal tissue in all treated groups.

CONCLUSION

The study has provided a rational basis for using these safe, cheap, and commercially available alternatives in treating cryptosporidiosis combined with NTZ.

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.

Management of cell death in parasitic infections

For a long time, host cell death during parasitic infection has been considered a reflection of tissue damage, and often associated with disease pathogenesis. However, during their evolution, protozoan and helminth parasites have developed strategies to interfere with cell death so as to spread and survive in the infected host, thereby ascribing a more intriguing role to infection-associated cell death. In this review, we examine the mechanisms used by intracellular and extracellular parasites to respectively inhibit or trigger programmed cell death. We further dissect the role of the prototypical “eat-me signal” phosphatidylserine (PtdSer) which, by being exposed on the cell surface of damaged host cells as well as on some viable parasites via a process of apoptotic mimicry, leads to their recognition and up-take by the neighboring phagocytes. Although barely dissected so far, the engagement of different PtdSer receptors on macrophages, by shaping the host immune response, affects the overall infection outcome in models of both protozoan and helminth infections. In this scenario, further understanding of the molecular and cellular regulation of the PtdSer exposing cell-macrophage interaction might allow the identification of new therapeutic targets for the management of parasitic infection.

The Mucosal Innate Immune Response to Cryptosporidium parvum, a Global One Health Issue

Cryptosporidium parvum is an apicomplexan parasite that infects the intestinal epithelium of humans and livestock animals worldwide. Cryptosporidiosis is a leading cause of diarrheal-related deaths in young children and a major cause of economic loss in cattle operations. The disease is especially dangerous to infants and immunocompromised individuals, for which there is no effective treatment or vaccination. As human-to-human, animal-to-animal and animal-to-human transmission play a role in cryptosporidiosis disease ecology, a holistic 'One Health' approach is required for disease control. Upon infection, the host's innate immune response restricts parasite growth and initiates the adaptive immune response, which is necessary for parasite clearance and recovery. The innate immune response involves a complex communicative interplay between epithelial and specialized innate immune cells. Traditional models have been used to study innate immune responses to C. parvum but cannot fully recapitulate natural host-pathogen interactions. Recent shifts to human and bovine organoid cultures are enabling deeper understanding of host-specific innate immunity response to infection. This review examines recent advances and highlights research gaps in our understanding of the host-specific innate immune response to C. parvum. Furthermore, we discuss evolving research models used in the field and potential developments on the horizon.

The influence of selected gastrointestinal parasites on apoptosis in intestinal epithelial cells

Studies on the parasite–host interaction may provide valuable information concerning the modulation of molecular mechanisms as well as of the host immune system during infection. To date, it has been demonstrated that intestinal parasites may affect, among others, the processes of digestion in the gastrointestinal system of the host, thus limiting the elimination of the parasite, the immune response as well as inflammation. However, the most recent studies suggest that intestinal parasites may also affect modulation of the apoptosis pathway of the host. The present paper presents the latest scientific information on the influence of intestinal parasite species (Blastocystis sp., Giardia sp., Cryptosporidium sp., Trichuris sp., Entamoeba histolytica, Nippostrongylus brasiliensis, Heligmosomoides polygyrus) on the molecular mechanisms of apoptosis in intestinal epithelial cells. This paper stresses that the interdependency between the intestinal parasite and the host results from the direct effect of the parasite and the host’s defense reactions, which lead to modulation of the apoptosis pathways (intrinsic and extrinsic). Moreover, the present paper presents the role of proteins involved in the mechanisms of apoptosis as well as the physiological role of apoptosis in the host’s intestinal epithelial cells.

Bovine Cryptosporidium parvum field isolates differ in cytopathogenicity in HCT-8 monolayers

Suckling calves are prone to Cryptosporidium infection. The variable degree of clinical disease is influenced by keeping conditions and immune status of the host, but diversity of isolate virulence may also contribute. The aim of the current study was to evaluate the cytopathogenic effects of 26 C. parvum field isolates by using a MTT assay in HCT-8 cell monolayers. Cell viability of monolayers inoculated with oocysts of the field isolates varied considerably with values of 17.7% (± 5.1%) to 99.5% (± 7.1%). A standard deviation of 18.6% was detected for cell viability of the in house reference strain, which were tested alongside in every assay. Field isolates were grouped in three categories of cytopathogenicity. Probably the length of storage has an effect on the level of the cell destruction category detected post infection in vitro. The applied tool may help to better understand the variable course of cryptosporidiosis in the field.

Comparative Pathobiology of the Intestinal Protozoan Parasites Giardia lamblia, Entamoeba histolytica, and Cryptosporidium parvum

Protozoan parasites can infect the human intestinal tract causing serious diseases. In the following article, we focused on the three most prominent intestinal protozoan pathogens, namely, Giardia lamblia, Entamoeba histolytica, and Cryptosporidium parvum. Both C. parvum and G. lamblia colonize the duodenum, jejunum, and ileum and are the most common causative agents of persistent diarrhea (i.e., cryptosporidiosis and giardiasis). Entamoeba histolytica colonizes the colon and, unlike the two former pathogens, may invade the colon wall and disseminate to other organs, mainly the liver, thereby causing life-threatening amebiasis. Here, we present condensed information concerning the pathobiology of these three diseases.

Cryptosporidium parvum Subtilisin-Like Serine Protease (SUB1) Is Crucial for Parasite Egress from Host Cells

Despite the severity and global burden of Cryptosporidium infection, treatments are less than optimal, and there is no effective vaccine. Egress from host cells is a key process for the completion of the life cycle of apicomplexan parasites. For Plasmodium species, subtilisin-like serine protease (SUB1) is a key mediator of egress. For Toxoplasma species, calcium-dependent protein kinases (CDPKs) are critical. In this study, we characterized Cryptosporidium SUB1 expression and evaluated its effect using an infection model. We found increased expression between 12 and 20 h after in vitro infection, prior to egress. We induced silencing of SUB1 (ΔSUB1) mRNA using SUB1 single-stranded antisense RNA coupled with human Argonaute 2. Silencing of SUB1 mRNA expression did not affect parasite viability, excystation, or invasion of target cells. However, knockdown led to a 95% decrease in the proportion of released merozoites in vitro (P < 0.0001). In contrast, silencing of CDPK5 had no effect on egress. Overall, our results indicate that SUB1 is a key mediator of Cryptosporidium egress and suggest that interruption of the life cycle at this stage may effectively inhibit the propagation of infection.

Regulation of apoptosis-related genes during interactions between oyster hemocytes and the alveolate parasite Perkinsus marinus

The alveolate Perkinsus marinus is the most devastating parasite of the eastern oyster Crassostrea virginica. The parasite is readily phagocytosed by oyster hemocytes, but instead of intracellular killing and digestion, P. marinus can survive phagocytosis and divide in host cells. This intracellular parasitism is accompanied by a regulation of host cell apoptosis. This study was designed to gain a better understanding of the molecular mechanisms of apoptosis regulation in oyster hemocytes following exposure to P. marinus. Regulation of apoptosis-related genes in C. virginica, and apoptosis-regulatory genes in P. marinus, were investigated via qPCR to assess the possible pathways involved during these interactions. In vitro experiments were also carried out to evaluate the effect of chemical inhibitors of P. marinus antioxidant processes on hemocyte apoptosis. Results indicate the involvement of the mitochondrial pathway (Bcl-2, anamorsin) of apoptosis in C. virginica exposed to P. marinus. In parallel, the antioxidants peroxiredoxin and superoxide dismutase were regulated in P. marinus exposed to C. virginica hemocytes suggesting that apoptosis regulation in infected oysters may be mediated by anti-oxidative processes. Chemical inhibition of P. marinus superoxide dismutase resulted in a marked increase of reactive oxygen species production and apoptosis in infected hemocytes. The implication of oxygen-dependent apoptosis during P. marinus infection and disease development in C. virginica is discussed.

Expression Profiles of mRNA and lncRNA in HCT-8 Cells Infected With Cryptosporidium parvum IId Subtype

Cryptosporidium parvum is one of the most important enteric protozoan pathogens, responsible for severe diarrhea in immunocompromised human and livestock. However, few effective agents were available for controlling this parasite. Accumulating evidences suggest that long non-coding RNA (lncRNA) played key roles in many diseases through regulating the gene expression. Here, the expression profiles of lncRNAs and mRNAs were analyzed in HCT-8 cells infected with C. parvum IId subtype using microarray assay. A total of 821 lncRNAs and 1,349 mRNAs were differentially expressed in infected cells at 24 h post infection (pi). Of them, all five types of lncRNAs were identified, including 22 sense, 280 antisense, 312 intergenic, 44 divergent, 33 intronic lncRNAs, and 130 lncRNAs that were not found the relationship with mRNAs’ location. Additionally, real-time polymerase chain reactions of 10 lncRNAs and 10 mRNAs randomly selected were successfully confirmed the microarray results. The co-expression and target prediction analysis indicated that 27 mRNAs were cis-regulated by 29 lncRNAs and 109 were trans-regulated by 114 lncRNAs. These predicted targets were enriched in several pathways involved in the interaction between host and C. parvum, e.g., hedgehog signaling pathway, Wnt signaling pathway, and tight junction, suggesting that these differentially expressed lncRNAs would play important regulating roles during the infection of C. parvum IId subtype.

Development of a Cytopathic Effect-Based Phenotypic Screening Assay against Cryptosporidium

Cryptosporidiosis is a diarrheal disease predominantly caused by Cryptosporidium parvum ( Cp) and Cryptosporidium hominis ( Ch), apicomplexan parasites which infect the intestinal epithelial cells of their human hosts. The only approved drug for cryptosporidiosis is nitazoxanide, which shows limited efficacy in immunocompromised children, the most vulnerable patient population. Thus, new therapeutics and in vitro infection models are urgently needed to address the current unmet medical need. Toward this aim, we have developed novel cytopathic effect (CPE)-based Cp and Ch assays in human colonic tumor (HCT-8) cells and compared them to traditional imaging formats. Further model validation was achieved through screening a collection of FDA-approved drugs and confirming many previously known anti- Cryptosporidium hits as well as identifying a few novel candidates. Collectively, our data reveals this model to be a simple, functional, and homogeneous gain of signal format amenable to high throughput screening, opening new avenues for the discovery of novel anticryptosporidials.

High association of Cryptosporidium spp. infection with colon adenocarcinoma in Lebanese patients

Background

The association between Cryptosporidium and human colon cancer has been reported in different populations. However, this association has not been well studied. In order to add new strong arguments for a probable link between cryptosporidiosis and colon human cancer, the aim of this study was to determine prevalence and to identify species of Cryptosporidium among Lebanese patients.

Methodology and principal findings

Overall, 218 digestive biopsies were collected in Tripoli, Lebanon, from three groups of patients: (i) patients with recently diagnosed colon intraepithelial neoplasia/adenocarcinoma before any treatment (n = 72); (ii) patients with recently diagnosed stomach intraepithelial neoplasia/adenocarcinoma before any treatment (n = 21); and (iii) patients without digestive intraepithelial neoplasia/adenocarcinoma but with persistent digestive symptoms (n = 125). DNA extraction was performed from paraffin-embedded tissue. The presence of the parasite in tissues was confirmed by PCR, microscopic observation and immunofluorescence analysis. We identified a high rate (21%) of Cryptosporidium presence in biopsies from Lebanese patients with recently diagnosed colonic neoplasia/adenocarcinoma before any treatment. This prevalence was significantly higher compared to 7% of Cryptosporidium prevalence among patients without colon neoplasia but with persistent gastrointestinal symptoms (OR: 4, CI: 1.65–9.6, P = 0.001). When the comparison was done against normal biopsies, the risk of infection increased 11-fold in the group of patients with colon adenocarcinoma (OR: 11.315, CI: 1.44–89.02, P = 0.003).

Conclusions

This is the first study performed in Lebanon reporting the prevalence of Cryptosporidium among patients with digestive cancer. These results show that Cryptosporidium is strongly associated with human colon cancer being maybe a potential etiological agent of this disease.

Innate immune responses play a key role in controlling infection of the intestinal epithelium by Cryptosporidium

Cryptosporidium infection leads to acute diarrhea worldwide. The development of cryptosporidiosis is closely related to the immune status of its host, affecting primarily young ruminants, infants, and immunocompromised individuals. In recent years, several studies have improved our knowledge on the immune mechanisms responsible for the control of the acute phase of the infection and have highlighted the importance of innate immunity. The parasite develops in the apical side of intestinal epithelial cells, giving these cells a central role, as they are both the exclusive host cell for replication of the parasite and participate in the protective immune response. Epithelial cells signal the infection by producing chemokines, attracting immune cells to the infected area. They also actively participate in host defense by inducing apoptosis and releasing antimicrobial peptides, free or incorporated into luminal exosomes, with parasiticidal activity. The parasite has developed several escape mechanisms to slow down these protective mechanisms. Recent development of several three-dimensional culture models and the ability to genetically manipulate Cryptosporidium will greatly help to further investigate host-pathogen interactions and identify virulence factors. Intestinal epithelial cells require the help of immune cells to clear the infection. Intestinal dendritic cells, well known for their ability to induce and orchestrate adaptive immunity, play a key role in controlling the very early steps of Cryptosporidium parvum infection by acting as immunological sentinels and active effectors. However, inflammatory monocytes, which are quickly and massively recruited to the infected mucosa, seem to participate in the loss of epithelial integrity. In addition to new promising chemotherapies, we must consider stimulating the innate immunity of neonates to strengthen their ability to control Cryptosporidium development. The microbiota plays a fundamental role in the development of intestinal immunity and may be considered to be a third actor in host-pathogen interactions. There is an urgent need to reduce the incidence of this yet poorly controlled disease in the populations of developing countries, and decrease economic losses due to infected livestock.

Improvement of in vitro evaluation of chemical disinfectants for efficacy on Cryptosporidium parvum oocysts

Cryptosporidium parvum has been suggested as a suitable target for in vitro efficacy testing of disinfectants. To improve validity of a method based on exposure of HCT-8 monolayers to C. parvum oocysts we here critically evaluate and we propose certain procedural steps needed for the validation of disinfectants. Within a range of 0.02% to 0.4%, sodium taurocholate at 0.2% stimulated infection most efficiently while preserving host cell integrity. The course of invasion was monitored for periods of 30-240min post infection (p.i.). FACS analysis revealed that the proportion of sporozoites liberated from oocysts in the presence of 0.2% sodium taurocholate increased within 120min of incubation but remained constant thereafter. Maximum invasion of cells measured by qPCR was reached 180min p.i. and therefore set as invasion endpoint. As monolayers harvested 24h or 48h p.i. did not differ in the quantity of parasite hsp70 gene copies, DNA extraction can be performed as early as 24h p.i. Incubation of oocysts with 20% H₂O₂ for 2h resulted in inactivation of more than 99.5% both at room temperature and 10°C and appeared thus suitable as positive chemical treatment control. Four washing procedures considered to remove potentially toxic residual disinfectant from oocyst suspensions were tested. An application of a combination of DMSO (Dimethylsulfoxid), Tween20 and WSH (water of standardized hardness) appeared most efficient without deleterious effect of disinfectant residuals on the cell monolayer viability when oocysts accordingly washed were applied. In conclusion, for standardized in vitro evaluation of chemical disinfectants in C. parvum infected HTC-8 monolayers. (i) excystation medium should contain 0.2 % sodium taurocholate. (ii) excystation medium should be replaced by growth medium after 180 min. (iii) monolayers should be harvested 24 h p.i. for DNA preparation. (iv) ocysts exposed to 20 % H₂O₂ should be included as positive controls. (v) disinfected oocysts should be washed with DMSO/Tween20/WSH before they are transferred to monolayers.

Pathogenic Mechanisms of Cryptosporidium and Giardia

Intestinal protozoa are important etiological agents of diarrhea, particularly in children, yet the public health risk they pose is often neglected. Results from the Global Enteric Multicenter Study (GEMS) showed that Cryptosporidium is among the leading causes of moderate to severe diarrhea in children under 2 years. Likewise, Giardia infects approximately 200 million individuals worldwide, and causes acute diarrhea in children under 5 years. Despite this recognized role as pathogens, the question is why and how these parasites cause disease in some individuals but not in others. This review focuses on known pathogenic mechanisms of Cryptosporidium and Giardia, and infection progress towards disease.

Infection Strategies of Intestinal Parasite Pathogens and Host Cell Responses

Giardia lamblia, Cryptosporidium sp., and Entamoeba histolytica are important pathogenic intestinal parasites and are amongst the leading causes worldwide of diarrheal illness in humans. Diseases caused by these organisms, giardiasis, cryptosporidiosis, and amoebiasis, respectively, are characterized by self-limited diarrhea but can evolve to long-term complications. The cellular and molecular mechanisms underlying the pathogenesis of diarrhea associated with these three pathogens are being unraveled, with knowledge of both the strategies explored by the parasites to establish infection and the methods evolved by hosts to avoid it. Special attention is being given to molecules participating in parasite–host interaction and in the mechanisms implicated in the diseases’ pathophysiologic processes. This review focuses on cell mechanisms that are modulated during infection, including gene transcription, cytoskeleton rearrangements, signal transduction pathways, and cell death.

CDPKs of Cryptosporidium parvum--stage-specific expression in vitro

Cryptosporidium parvum is a zoonotic agent that bears a high risk for the health of particularly immunocompromised humans and animals. As currently available drugs and therapies against cryptosporidiosis do not turn out satisfactory, more intensive research on the control of this parasite is necessary. The genus Cryptosporidium is unique within the phylum Apicomplexa as its localisation is intracellular but extracytoplasmatic. Infection of host cells is initially a parasite-driven process, but the signalling events and their downstream actions within Cryptosporidium are poorly understood. Calcium-dependent protein kinases (CDPKs) are probably involved in the regulation of invasion and egress. Previously described in plants, algae and other Apicomplexa, CDPKs are not found in vertebrates. They are thus promising targets for pharmaceutical intervention. While CDPK1 is well characterised in Toxoplasma gondii (TgCDPK1) and Plasmodium falciparum (PfCDPK1), only little information exists about the expression and function of CDPK in C. parvum. Here, we describe results of the in silico analysis of seven CpCDPKs. Five CpCDPKs contain potential sites for N-myristoylation and N-palmitoylation. In a nested 3' rapid amplification of cDNA ends (RACE)-PCR, expression of six CpCDPKs resulted in distinct bands in infected cell cultures and extracts of freshly excysted sporozoites. The length of the 3' untranslated region (3' UTR) is described as well. Our results indicate CDPK expression to be stage specific on the mRNA level.

Study of the distribution of active caspase-3-positive cells in turbot, Scophthalmus maximus (L.), enteromyxosis

Enteromyxosis caused by Enteromyxum scophthalmi is one of the parasitizations with a higher economic impact on turbot, Scophthalmus maximus (L.), aquaculture. This myxosporean produces severe catarrhal enteritis with abundant inflammatory infiltrates in the lamina propria-submucosa (LP), epithelial detachment and leucocyte depletion of the lymphohaematopoietic organs. Some advances made on the pathogenesis pointed to a role of apoptosis in the enteromyxosis. Therefore, the main aim of this work was to employ the TUNEL assay and the anti-(active caspase-3) immunohistochemical assay to detect apoptotic cells in both healthy and E. scophthalmi-infected turbot in order to establish the presence and distribution of apoptotic cells during development of the disease. More apoptotic cells located within the gastrointestinal epithelium were observed in the initial stages of the infection in E. scophthalmi-infected turbot compared with non-infected turbot. As the infection progressed, a higher degree of apoptosis occurred in the epithelium of folds heavily parasitized. In the severely infected turbot, apoptosis was also found among the leucocytes of the intestinal inflammatory infiltrates. Moreover, the number of active caspase-3-positive cells in the lymphohaematopoietic organs tended to increase with disease severity. In view of the results, increased apoptosis in the epithelium may favour the scaling that occurs during enteromyxosis and cell death of leucocytes in the intestinal LP, contributing to leucocyte depletion in severe cases.

Malaria parasite liver stages render host hepatocytes susceptible to mitochondria-initiated apoptosis

Intracellular eukaryotic parasites and their host cells constitute complex, coevolved cellular interaction systems that frequently cause disease. Among them, Plasmodium parasites cause a significant health burden in humans, killing up to one million people annually. To succeed in the mammalian host after transmission by mosquitoes, Plasmodium parasites must complete intracellular replication within hepatocytes and then release new infectious forms into the blood. Using Plasmodium yoelii rodent malaria parasites, we show that some liver stage (LS)-infected hepatocytes undergo apoptosis without external triggers, but the majority of infected cells do not, and can also resist Fas-mediated apoptosis. In contrast, apoptosis is dramatically increased in hepatocytes infected with attenuated parasites. Furthermore, we find that blocking total or mitochondria-initiated host cell apoptosis increases LS parasite burden in mice, suggesting that an anti-apoptotic host environment fosters parasite survival. Strikingly, although LS infection confers strong resistance to extrinsic host hepatocyte apoptosis, infected hepatocytes lose their ability to resist apoptosis when anti-apoptotic mitochondrial proteins are inhibited. This is demonstrated by our finding that B-cell lymphoma 2 family inhibitors preferentially induce apoptosis in LS-infected hepatocytes and significantly reduce LS parasite burden in mice. Thus, targeting critical points of susceptibility in the LS-infected host cell might provide new avenues for malaria prophylaxis.

Proteasome inhibition of pathologic shedding of enterocytes to defend barrier function requires X-linked inhibitor of apoptosis protein and nuclear factor κB

BACKGROUND & AIMS

Although we are beginning to understand where, when, and how intestinal epithelial cells are shed, physiologically, less is understood about alterations in cell fate during minimally invasive epithelial infections. We used a piglet model of Cryptosporidium parvum infection to determine how elimination of infected enterocytes is balanced with the need to maintain barrier function.

METHODS

We studied the effects of enterocyte shedding by C parvum-infected ileum on barrier function ex vivo with Ussing chambers. The locations and activities of caspase-3, nuclear factor κB (NF-κB), and inhibitor of apoptosis proteins (IAP) were assayed by enzyme-linked immunosorbent assay, immunoblot, and tissue immunoreactivity analyses and using specific pharmacologic inhibitors. The location, specificity, and magnitude of enterocyte shedding were quantified using special stains and light microscopy.

RESULTS

Infection with C parvum activated apoptotic signaling pathways in enterocytes that resulted in cleavage of caspase-3. Despite caspase-3 cleavage, enterocyte shedding was confined to villus tips, coincident with apoptosis, and observed more frequently in infected cells. Epithelial expression of X-linked inhibitor of apoptosis protein (XIAP), activation of NF-κB, and proteasome activity were required for control of cell shedding and barrier function. The proteasome blocked activity of caspase-3; this process was mediated by expression of XIAP, which bound to cleaved caspase-3.

CONCLUSIONS

We have identified a pathway by which villus epithelial cells are maintained during C parvum infection. Loss of barrier function is reduced by active retention of infected enterocytes until they reach the villus tip. These findings might be used to promote clearance of minimally invasive enteropathogens, such as by increasing the rate of migration of epithelial cells from the crypt to the villus tip.

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.

Parasites and malignancies, a review, with emphasis on digestive cancer induced by Cryptosporidium parvum (Alveolata: Apicomplexa)

The International Agency for Research on Cancer (IARC) identifies ten infectious agents (viruses, bacteria, parasites) able to induce cancer disease in humans. Among parasites, a carcinogenic role is currently recognized to the digenetic trematodes Schistosoma haematobium, leading to bladder cancer, and to Clonorchis sinensis or Opisthorchis viverrini, which cause cholangiocarcinoma. Furthermore, several reports suspected the potential association of other parasitic infections (due to Protozoan or Metazoan parasites) with the development of neoplastic changes in the host tissues. The present work shortly reviewed available data on the involvement of parasites in neoplastic processes in humans or animals, and especially focused on the carcinogenic power of Cryptosporidium parvum infection. On the whole, infection seems to play a crucial role in the etiology of cancer.

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.

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.

Challenges in understanding the immunopathogenesis of Cryptosporidium infections in humans. Eur J Clin Microbiol Infect Dis. 2011;30:1461-1472. [PMID: 21484252 DOI: 10.1007/s10096-011-1246-6]

Water and foodborne enteric cryptosporidiosis is a globally emerging public health issue. Although the clinical manifestations of enteric cryptosporidiosis are generally limited to intestinal infection and subsequent diarrhoea, extra-intestinal invasion has also been diagnosed in immunocompromised individuals, particularly in those infected with human immunodeficiency virus (HIV) or AIDS. Due to an inadequate understanding of Cryptosporidium immunopathogenesis in humans, the development of vaccines or therapeutic agents and their application in diseases management is difficult. Current therapeutic measures are not fully effective in the treatment of the disease. Therefore, the implementation of strategies designed to control the chain of cryptosporidiosis transmission (environment ↔ human ↔ food/water ↔ animal) is a critical but challenging issue to public health authorities across the world. Several excellent studies have been done on innate, acquired and mucosal immunity against Cryptosporidium infections using animal models, in vitro human cell lines and human volunteers. However, there are still multiple challenges in understanding the intestinal immune response (immunopathogenesis) to Cryptosporidium infection in humans. This paper reviews recent updates on immunopathogenesis and immune responses to Cryptosporidium infection in humans, while also discussing the current limitations that exist regarding a precise understanding of the immunopathological mechanisms.

Development of Cryptosporidium parvum-induced gastrointestinal neoplasia in severe combined immunodeficiency (SCID) mice: severity of lesions is correlated with infection intensity

We reported previously that Cryptosporidium parvum was able to induce intestinal tumors in severe combined immunodeficiency (SCID) mice treated with corticoids. To further characterize this Cryptosporidium-induced cell transformation, SCID mice treated with dexamethasone were challenged with C. parvum oocysts, and euthanatized sequentially after infection for histologic examination. Ki-67 was used as a marker of cellular proliferation. Our previous results were confirmed, and it was also found that mice receiving higher inocula (10(6)-10(7)) experienced more severe neoplastic development. Additionally, neoplastic changes were observed not only in the caecum but also in the stomach and duodenum of some animals. Interestingly, SCID mice (6/6) inoculated with 10(5)-10(7) oocysts showed high grade intraepithelial neoplasia or adenomas with high grade dysplasia in the caecum after Day 46 post-infection (PI). Immunohistochemistry for Ki-67 staining indicated the neoplastic process associated to cryptosporidiosis, and evidenced the first immunohistochemical alterations at early stages of the process, even at 3 weeks PI.

Comparative efficacy of conventional primer sets in detection of Cryptosporidium parvum for diagnostic use

In this study, the sensitivity and specificity of different previously described primer sets for Cryptosporidium parvum detection by polymerase chain reaction (PCR) was evaluated. For this purpose, the primer sets defined by Cacciò et al. (FEMS Microbiol Lett 170(1):173-179, 1999) (tub), Widmer et al. (Appl Environ Microbiol 64(11):4477-4481, 1998) (btub) and Rochelle et al. (Appl Environ Microbiol 63:2029-2037, 1997) (cphsp), respectively, were used. Deoxyribonucleic acid (DNA) was isolated from three different sample materials: (1) from the faeces of an experimentally C. parvum-infected calf, (2) from purified C. parvum oocysts, and (3) from C. parvum-infected HCT-8 cell cultures. The DNA samples were subjected to PCR reactions with each of the three given primer sets to investigate sensitivity and suitability for routine use. The primers described by Cacciò et al. (FEMS Microbiol Lett 170(1):173-179, 1999) (TUB) were superior regarding sensitivity and specificity in terms of detection of C. parvum in faeces, in purified oocysts and also in cell culture, and may thus be applied for routine diagnostic use in common sample materials.

Cell sorting-assisted microarray profiling of host cell response to Cryptosporidium parvum infection

To study the transcriptional response of mammalian cells to infection with the intracellular apicomplexan parasite Cryptosporidium parvum, infected and uninfected cells were recovered from C. parvum-infected cell monolayers. This approach, which contrasts with a more conventional experimental design that compares infected to uninfected cell monolayers, enabled the identification of functional categories of genes that are differentially transcribed as a direct consequence of the presence of intracellular parasites. Among several categories of upregulated genes, glycoprotein metabolism was significantly overrepresented. To investigate whether these transcriptional changes affected the composition of the surface of infected cells, cells were probed with fluorescently labeled lectins. Among a panel of seven lectins, soybean agglutinin, which recognizes N-acetyl-d-galactosamine, generated the largest difference in fluorescence between infected and uninfected cells. The origin of the fluorescent signal emitted by infected cells was further investigated and attributed to the overexpression of glycoprotein on the surface of infected cells, as well as the presence of glycoprotein located in the proximity of intracellular parasites.

Pathophysiology of diarrhea in calves

Infectious diarrhea in calves is most commonly associated with enterotoxigenic Escherichia coli, Cryptosporidium parvum, rotavirus, coronavirus, or some combination of these pathogens. Each of these agents leads to diarrhea through either secretion or malabsorption/maldigestion, though the specific mechanisms and pathways may differ. Specific pharmacologic control and treatment are dependent on gaining a greater understanding of the pathophysiology of these organisms.

Biphasic modulation of apoptotic pathways in Cryptosporidium parvum-infected human intestinal epithelial cells

The impact of Cryptosporidium parvum infection on host cell gene expression was investigated by microarray analysis with an in vitro model using human ileocecal HCT-8 adenocarcinoma cells. We found changes in 333 (2.6%) transcripts at at least two of the five (6, 12, 24, 48, and 72 h) postinfection time points. Fifty-one of the regulated genes were associated with apoptosis and were grouped into five clusters based on their expression patterns. Early in infection (6 and 12 h), genes with antiapoptotic roles were upregulated and genes with apoptotic roles were downregulated. Later in infection (24, 48, and 72 h), proapoptotic genes were induced and antiapoptotic genes were downregulated, suggesting a biphasic regulation of apoptosis: antiapoptotic state early and moderately proapoptotic state late in infection. This transcriptional profile matched the actual occurrence of apoptosis in the infected cultures. Apoptosis was first detected at 12 h postinfection and increased to a plateau at 24 h, when 20% of infected cells showed nuclear condensation. In contrast, experimental silencing of Bcl-2 induced apoptosis in 50% of infected cells at 12 h postinfection. This resulted in a decrease in the infection rate and a reduction in the accumulation of meront-containing cells. To test the significance of the moderately proapoptotic state late in the infection, we inhibited apoptosis using pancaspase inhibitor Z-VAD-FMK. This treatment also affected the progression of C. parvum infection, as reinfection, normally seen late (24 h to 48 h), did not occur and accumulation of mature meronts was impaired. Control of host apoptosis is complex and crucial to the life of C. parvum. Apoptosis control has at least two components, early inhibition and late moderate promotion. For a successful infection, both aspects appear to be required.

Evidence for intestinal heterogenic expression of di-tripeptides transporter PepT1 during experimental cryptosporidiosis in neonatal rats

Cryptosporidium parvum is a protozoan parasite that causes intestinal malabsorptive syndrome and malnutrition. Considering the importance of di-tripeptide absorption for nutritional status, we previously investigated the regulation of PepT1 transporter in the suckling rat model of acute cryptosporidiosis and showed that PepT1 protein expression and activity were not modified in the parasitized intestine. Here we used confocal microscopy performed on intestinal villi to determine the subcellular localization of PepT1 together with f-actin and parasites. For this purpose, confocal microscopy using vibratome thick sections was developed on the distal small intestine, the preferential site of parasite implantation. Results showed major heterogeneity of apical PepT1 expression among enterocytes, which did not correlate with actin staining or parasite implantation. These results underscore the importance of considering the effect of C. parvum at the cellular scale and not only in the entire epithelium.

Cryptosporidium infection of human intestinal epithelial cells increases expression of osteoprotegerin: a novel mechanism for evasion of host defenses

Cryptosporidium parasites are pathogens of human intestinal epithelial cells. To determine which genes are regulated during early infection, human ileal mucosa cultured as explants was infected with C. parvum or C. hominis, and gene expression was analyzed by microarray. The gene for osteoprotegerin (OPG) was up-regulated by both parasites. OPG mRNA was also significantly increased in biopsy specimens obtained from a volunteer experimentally infected with C. meleagridis, compared with levels in a prechallenge biopsy specimen. After in vitro infection of HCT-8 cells, there was an early peak in production of OPG mRNA protein. Treatment of infected cells with the OPG ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induced epithelial cell apoptosis and reduced parasite numbers, and recombinant OPG blocked these effects. These results suggest a novel TRAIL-mediated pathway for elimination of Cryptosporidium infection and a role for OPG in modulating this host response.

Inhibition of apoptosis in Cryptosporidium parvum-infected intestinal epithelial cells is dependent on survivin

Cryptosporidium parvum is an obligate intracellular protozoan capable of causing severe diarrheal disease in a wide variety of mammals, including humans. C. parvum infection has been associated with induction of apoptosis in exposed epithelial cells, and we now demonstrate that apoptosis is restricted to a subset of cells actively infected with C. parvum. Approximately 20% of the infected cells underwent apoptosis within 48 h of infection, suggesting that the majority of the infected cells are rescued from apoptosis. C. parvum infection resulted in low-level activation of multiple members of the caspase family, including caspase-2, -3, -4, -6, -8, and -9. The kinetics of caspase activation correlated with apoptosis over a 48-h time course. Pan caspase inhibitors reduced apoptosis of epithelial cells infected by C. parvum. Furthermore, C. parvum infection inhibited staurosporine-induced apoptosis and caspase-3/7 activation at 24 h and 48 h. Infection with C. parvum led to upregulation of genes encoding inhibitors of apoptosis proteins (IAPs), including c-IAP1, c-IAP2, XIAP, and survivin. Knockdown of survivin gene expression, but not that of c-IAP1, c-IAP2, or XIAP expression, increased caspase-3/7 activity as well as apoptosis of infected cells and decreased C. parvum 18S rRNA levels. These data suggest that the apoptotic response of infected intestinal epithelial cells is actively suppressed by C. parvum via upregulation of survivin, favoring parasite infection.

The public health and clinical significance of Giardia and Cryptosporidium in domestic animals

Giardia and Cryptosporidium are common enteric parasites of domestic animals, particularly dogs, cats and livestock. Their occurrence is of potential significance from both clinical and public health perspectives yet, until recently, confusion over the taxonomy of these organisms prevented a clear understanding of the epidemiology of infections with both Giardia and Cryptosporidium. The recent application of molecular epidemiological tools has helped to resolve taxonomic issues, allowing cycles of transmission to be determined. In addition, advances have been made in elucidating mechanisms associated with pathogenesis, whereas only limited progress has been achieved in the areas of chemotherapy and prophylaxis.

Cryptosporidium parvum, a potential cause of colic adenocarcinoma

Background

Cryptosporidiosis represents a major public health problem. This infection has been reported worldwide as a frequent cause of diarrhoea. Particularly, it remains a clinically significant opportunistic infection among immunocompromised patients, causing potentially life-threatening diarrhoea in HIV-infected persons. However, the understanding about different aspects of this infection such as invasion, transmission and pathogenesis is problematic. Additionally, it has been difficult to find suitable animal models for propagation of this parasite. Efforts are needed to develop reproducible animal models allowing both the routine passage of different species and approaching unclear aspects of Cryptosporidium infection, especially in the pathophysiology field.

Results

We developed a model using adult severe combined immunodeficiency (SCID) mice inoculated with Cryptosporidium parvum or Cryptosporidium muris while treated or not with Dexamethasone (Dex) in order to investigate divergences in prepatent period, oocyst shedding or clinical and histopathological manifestations. C. muris-infected mice showed high levels of oocysts excretion, whatever the chemical immunosuppression status. Pre-patent periods were 11 days and 9.7 days in average in Dex treated and untreated mice, respectively. Parasite infection was restricted to the stomach, and had a clear preferential colonization for fundic area in both groups. Among C. parvum-infected mice, Dex-treated SCID mice became chronic shedders with a prepatent period of 6.2 days in average. C. parvum-inoculated mice treated with Dex developed glandular cystic polyps with areas of intraepithelial neoplasia, and also with the presence of intramucosal adenocarcinoma.

Conclusion

For the first time C. parvum is associated with the formation of polyps and adenocarcinoma lesions in the gut of Dex-treated SCID mice. Additionally, we have developed a model to compare chronic muris and parvum cryptosporidiosis using SCID mice treated with corticoids. This reproducible model has facilitated the evaluation of clinical signs, oocyst shedding, location of the infection, pathogenicity, and histopathological changes in the gastrointestinal tract, indicating divergent effects of Dex according to Cryptosporidium species causing infection.