Cryptosporidium virulence determinants--are we there yet?

Cryptosporidiosis in a Zoonotic Gastrointestinal Disorder Perspective: Present Status, Risk Factors, Pathophysiology, and Treatment, Particularly in Immunocompromised Patients

Cryptosporidium infection is highly prevalent among immunocompromised patients with Acquired Immunodeficiency Syndrome, cancer, primary immunodeficiency, and organ transplant recipients. Comprehensive knowledge about Cryptosporidium infection provides the means for efficient diagnosis, treatment, and prevention. Therefore, with the objective of providing an in-depth analysis of Cryptosporidiosis in immunocompromised patients, this review presents a comprehensive understating of the prevalence, risk factors, pathophysiology of Cryptosporidium infection, clinical presentation in the immunocompromised, the immune response of the host, diagnostic methods performed in laboratory settings, possible treatments, and prevention methods, which can be used for further studies. Peer-reviewed, published, original articles on cryptosporidiosis in immunocompromised patients were searched using specific key-words on PubMed, ResearchGate, Google Scholar, and ScienceDirect databases. Articles which were accessible to the date of 18th of August 2023, were included in this comprehensive review. We analyzed reports on Cryptosporidium in immunocompromised patients with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), cancer, primary immunodeficiency, and organ transplant recipients. 134 Articles describing epidemiology, related risk factors, clinical presentation, diagnosis, and possible treatments in the light of pathogenesis, pathophysiology, and virulence factors of Cryptosporidium and immunology of the host are summarized in this study. Effective treatments to be administered, importance, and ways of prevention were identified. Cryptosporidium infection was found to be highly prevalent among immunocompromised in Asia, Africa, Europe, and North America. The immunity of the host and the decrease in CD4+ T-cell count were found to the main factors which decide the susceptibility and the severity of infection. Drugs that activate host immunity and suppress Cryptosporidium growth, along with supportive therapy, is an effective treatment. But prevention is the most effective strategy for immunocompromised patients; thus, a better understanding about the disease would lead to effective prevention.

Intestinal cDC1s provide cues required for CD4+ T cell-mediated resistance to Cryptosporidium

Cryptosporidium is an enteric pathogen and a prominent cause of diarrheal disease worldwide. Control of Cryptosporidium requires CD4+ T cells, but how protective CD4+ T cell responses are generated is poorly understood. Here, Cryptosporidium parasites that express MHCII-restricted model antigens were generated to understand the basis for CD4+ T cell priming and effector function. These studies revealed that parasite-specific CD4+ T cells are primed in the draining mesenteric lymph node but differentiate into Th1 cells in the gut to provide local parasite control. Although type 1 conventional dendritic cells (cDC1s) were dispensable for CD4+ T cell priming, they were required for CD4+ T cell gut homing and were a source of IL-12 at the site of infection that promoted local production of IFN-γ. Thus, cDC1s have distinct roles in shaping CD4+ T cell responses to an enteric infection: first, to promote gut homing from the mesLN, and second, to drive effector responses in the intestine.

Zoonotic Cryptosporidium meleagridis in urban invasive monk parakeets

Zoonotic Cryptosporidium meleagridis was identified in invasive monk parakeets (Myiopsitta monachus) from Santiago metropolis in Chile. Oocysts were isolated from nestlings' faeces, and a fragment of 18S ribosomal RNA gene was amplified and sequenced. This finding emphasizes the importance of permanent pathogen monitoring in synanthropic species with wide global distribution.

Intestinal cDC1s provide IL-12 dependent and independent functions required for CD4+ T cell-mediated resistance to Cryptosporidium

Cryptosporidium is an enteric pathogen that is a prominent cause of diarrheal disease. Control of this infection requires CD4+ T cells, though the processes that lead to T cell-mediated resistance have been difficult to assess. Here, Cryptosporidium parasites that express MHCII-restricted model antigens were generated to dissect the early events that influence CD4+ T cell priming and effector function. These studies highlight that parasite-specific CD4+ T cells are primed in the draining mesenteric lymph node (mesLN) and differentiate into Th1 cells in the gut, where they mediate IFN-γ-dependent control of the infection. Although type 1 conventional dendritic cells (cDC1s) were not required for initial priming of CD4+ T cells, cDC1s were required for CD4+ T cell expansion and gut homing. cDC1s were also a major source of IL-12 that was not required for priming but promoted full differentiation of CD4+ T cells and local production of IFN-γ. Together, these studies reveal distinct roles for cDC1s in shaping CD4+ T cell responses to enteric infection: first to drive early expansion in the mesLN and second to drive effector responses in the gut.

Differences in virulence and oocyst shedding profiles in lambs experimentally infected with different isolates of Cryptosporidium parvum

A wide spectrum of disease severity associated with cryptosporidiosis has been described, ranging from asymptomatic to fatal in both human and animal hosts. The reasons for the variations in severity are likely to be multifactorial, involving environmental, host and parasite factors. This paper describes two experimental infection trials in lambs, a symptomatic host for the parasite, to investigate variation in the clinical manifestations following infection with two distinct isolates of Cryptosporidium parvum. In the first experiment, groups of naïve lambs were challenged with one of two isolates (CP1 or CP2) at ​< ​1 week of age, to test the effect of the isolates on disease outcome. In a second experiment one group of lambs challenged at < 1 week of age (CP1) was then re-challenged with the same isolate at 6 weeks of age (CP1), while a second group was challenged for the first time at 6 weeks of age (CP1). This experiment examined age-related disease symptoms, oocyst shedding and the effect of prior exposure to the parasite on a subsequent homologous challenge. The two isolates were associated with significant differences in the demeanour of the animals and in the numbers of oocysts shed in the faeces. There were also differences in the duration and severity of diarrhoea, though these were not significant. The age of the lamb, at the time of a primary challenge (<1 week or 6 weeks), also resulted in differences in clinical outcomes, with younger lambs showing more severe clinical disease than the older lambs (feeding profiles and presentation of diarrhoea), while older lambs showed virtually no signs of infection but still produced large numbers of oocysts.

An update on Cryptosporidium biology and therapeutic avenues

Cryptosporidium species has been identified as an important pediatric diarrheal pathogen in resource-limited countries, particularly in very young children (0–24 months). However, the only available drug (nitazoxanide) has limited efficacy and can only be prescribed in a medical setting to children older than one year. Many drug development projects have started to investigate new therapeutic avenues. Cryptosporidium’s unique biology is challenging for the traditional drug discovery pipeline and requires novel drug screening approaches. Notably, in recent years, new methods of oocyst generation, in vitro processing, and continuous three-dimensional cultivation capacities have been developed. This has enabled more physiologically pertinent research assays for inhibitor discovery. In a short time, many great strides have been made in the development of anti-Cryptosporidium drugs. These are expected to eventually turn into clinical candidates for cryptosporidiosis treatment in the future. This review describes the latest development in Cryptosporidium biology, genomics, transcriptomics of the parasite, assay development, and new drug discovery.

Removal of Giardia spp. cysts and Cryptosporididum spp. oocysts from anaerobic effluent by dissolved air flotation

Lab-scale studies were carried out to investigate the efficiency of dissolved air flotation (DAF) for the removal of Giardia spp. cysts and Cryptosporidium spp. oocysts from anaerobic effluent from the pilot UASB reactor. Raw wastewater, UASB and DAF effluent samples were collected weekly and protozoan (oo)cysts were concentrated using IMS followed by protozoa detection using immunofluorescense assay (IFA). The number of Cryptosporidium spp. oocysts in the raw wastewater was always lower than that of Giardia spp. cysts with 28-33 oocysts L^-1 and 3177-4267 cysts L^-1, respectively. Log₁₀ removal of Giardia cysts utilising polyaluminium chloride (PACl) was higher than that with FeCl₃, but no statistically significant difference between the two coagulants was observed. Cryptosporidium was absent in most of the treated effluent samples. The results indicate that DAF reached more than 2 log of cyst removal. In addition, the results demonstrated that these parasites are prevalent in the study area and E. coli and total coliforms were not good indicator microorganisms in terms of cyst and oocysts numbers.

Comparative genomic analysis of the principal Cryptosporidium species that infect humans

Cryptosporidium parasites are ubiquitous and can infect a broad range of vertebrates and are considered the most frequent protozoa associated with waterborne parasitic outbreaks. The intestine is the target of three of the species most frequently found in humans: C. hominis, C. parvum, and. C. meleagridis. Despite the recent advance in genome sequencing projects for this apicomplexan, a broad genomic comparison including the three species most prevalent in humans have not been published so far. In this work, we downloaded raw NGS data, assembled it under normalized conditions, and compared 23 publicly available genomes of C. hominis, C. parvum, and C. meleagridis. Although few genomes showed highly fragmented assemblies, most of them had less than 500 scaffolds and mean coverage that ranged between 35X and 511X. Synonymous single nucleotide variants were the most common in C. hominis and C. meleagridis, while in C. parvum, they accounted for around 50% of the SNV observed. Furthermore, deleterious nucleotide substitutions common to all three species were more common in genes associated with DNA repair, recombination, and chromosome-associated proteins. Indel events were observed in the 23 studied isolates that spanned up to 500 bases. The highest number of deletions was observed in C. meleagridis, followed by C. hominis, with more than 60 species-specific deletions found in some isolates of these two species. Although several genes with indel events have been partially annotated, most of them remain to encode uncharacterized proteins.

Cryptosporidium parvum gp40/15 Is Associated with the Parasitophorous Vacuole Membrane and Is a Potential Vaccine Target

Cryptosporidium parvum is a zoonotic intracellular protozoan responsible for the diarrheal illness cryptosporidiosis in humans and animals. Although a number of zoite surface proteins are known to be expressed during, and believed to be involved in, attachment and invasion of host cells, the molecular mechanisms by which C. parvum invades the host epithelial cells are not well understood. In the present study, we investigated the gene expression patterns, protein localization in developmental stages in culture, and in vitro neutralization characteristics of Cpgp40/15 and Cpgp40. Indirect immunofluorescence assay showed that Cpgp40/15 is associated with the parasitophorous vacuole membrane (PVM) during intracellular development. Both anti-gp40/15 and anti-gp40 antibodies demonstrated the ability to neutralize C. parvum infection in vitro. Further studies are needed to fully understand the specific role and functional mechanism of Cpgp40/15 (or gp40/15 complex) in the invasion of the host or in the PVM and to determine the feasibility of gp40/15 as a vaccine candidate for cryptosporidiosis in vivo.

Characterization of a Species-Specific Insulinase-Like Protease in Cryptosporidium parvum

Cryptosporidium parvum is an intracellular protozoan that can cause severe diarrhea in humans and various mammals. Results of a comparative genomic analysis indicated that genes encoding two C. parvum-specific insulinase-like proteases (INS19 and INS20), cgd6_5510 and cgd6_5520, are lost in many Cryptosporidium species. In this study, we provided evidence indicating that cgd6_5510 and cgd6_5520 are fragments of a full gene (cgd6_5520-5510) encoding one insulinase-like protease (INS20-19) that is similar in structure to classic insulinases. We expressed cgd6_5510 in Escherichia coli for antiserum preparation and found the protein (INS19) that was partially degraded. A ~180 kDa protein of INS20-19 was specifically recognized by the polyclonal anti-INS19 antiserum in sporozoite lysate. We observed that INS20-19 is likely a protein with high expression in the apical region of sporozoites, and neutralization of the protein led to a partial reduction of parasite load in HCT-8 and MDBK cell cultures at 24 h. Taken together, our findings support the involvement of INS20-19 in the invasion or early developmental process of C. parvum.

Revisiting the infectivity and pathogenicity of Cryptosporidium avium provides new information on parasitic sites within the host

Background

Cryptosporidium spp. are protozoans that cause diarrheal illness in humans and animals, including birds, worldwide. The present study was aimed to revisit the infectivity and pathogenicity of C. avium, recently considered to be a valid avian-infecting species of Cryptosporidium, and foster further understanding of its biological characteristics.

Results

Results showed that no Cryptosporidium oocysts were detected in the feces of experimentally inoculated BALB/c mice, Mongolian gerbils, quail or budgerigars within 30 days post-infection (dpi). Oocysts were first detected in feces of 3-day-old and 40-day-old hens at 8 and 9 dpi, respectively. In ducks infected with C. avium, oocysts were first detected at 9 dpi. Oocysts of infected animals were studied using a nested-polymerase chain reaction (PCR) technique for the SSU rRNA gene, actin gene, HSP70 gene and Cryptosporidium oocyst wall protein gene (COWP) detection. Restriction fragment length polymorphism (RFLP), using SspI and VspI restriction enzymes, was carried out to genotype the species and obtained amplification products were sequenced. Cryptosporidium developmental stages were found in the longitudinal plica of the bursa fabricii (BF) of hens, with high levels observed in histological sections and scanning electron microscopy. No pathological changes were observed.

Conclusions

These findings indicate that the bursa fabricii may be the primary site of C. avium infection. More biological data are needed to support the establishment of new species and contribute to the taxonomy of Cryptosporidium.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3088-x) contains supplementary material, which is available to authorized users.

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.

Cryptosporidium infection in solid organ transplantation

Diarrhea is a common complication in solid organ transplant (SOT) recipients and may be attributed to immunosuppressive drugs or infectious organisms such as bacteria, viruses or parasites. Cryptosporidium usually causes self-limited diarrhea in immunocompetent hosts. Although it is estimated that cryptosporidium is involved in about 12% of cases of infectious diarrhea in developing countries and causes approximately 748000 cases each year in the United States, it is still an under recognized and important cause of infectious diarrhea in SOT recipients. It may run a protracted course with severe diarrhea, fluid and electrolyte depletion and potential for organ failure. Although diagnostic methodologies have improved significantly, allowing for fast and accurate identification of the parasite, treatment of the disease is difficult because antiparasitic drugs have modest activity at best. Current management includes fluid and electrolyte replacement, reduction of immunosuppression and single therapy with Nitazoxanide or combination therapy with Nitazoxanide and other drugs. Future drug and vaccine development may add to the currently poor armamentarium to manage the disease. The current review highlights key epidemiological, diagnostic and management issues in the SOT population.

Identification of invasion proteins of Cryptosporidium parvum

Host cell interactions and invasion by Cryptosporidium is a complex process mediated by zoites ligand-host cell receptors. Knowledge of proteins involved in this process will enable entry level inhibitors to be tried as therapeutic agents. In the present study, invasion proteins of Cryptosporidium parvum were studied in vitro. Cryptosporidium sporozoites membrane proteins were isolated and Cy5 dye labelled. They were then allowed to interact with the intact host cells. The interacting proteins were identified using 2-dimensional gel electrophoresis followed by mass spectrometry analysis. Sixty-one proteins were identified including twenty-seven previously reported invasion proteins. The newly identified proteins such as serine/threonine protein kinase, PI4 kinase, Hsp105 and coiled coil may have their roles in the parasitic invasion process. Thus, a new approach was used in the study to identify the probable proteins involved in invasion and/or host-parasite interactions. The advantage of this method is that it takes only a months' time instead of decades to identify these proteins involved in invasion process.

Detection and quantification of Cryptosporidium oocysts in environmental surfaces of an Equine Perinatology Unit

The presence of Cryptosporidium in institutions such as veterinary teaching hospitals, where students and staff are in frequent contact with animals, could represent a serious public health risk. In this study the detection and quantification of the Cryptosporidium oocysts present on the environmental surfaces of an Equine Perinatology Unit (EPU) were investigated. During 3 foaling seasons 175 samples obtained by swabbing an area of the floor and walls of boxes and utility rooms of EPU with sterile gauze, in 3 different moments. Samples were collected at the end of foaling season (July), after washing procedures (September) and after washing and disinfecting procedures, at the beginning of a new foaling season (December). All the samples were subjected to nested-PCR, followed by genotyping and sub-typing methods and to qPCR, allowing the oocyst quantification. Cryptosporidium spp. was detected in 14 samples, of which 11 were from walls and three were from floors. The highest number of oocysts was found in a sample collected from the floor of one utility room used for setting up therapies and treatments. In most cases, oocyst numbers, estimated by qPCR, were reduced or eliminated after washing and disinfecting procedures. The genotyping and sub-typing methods allowed identification of 2 subtypes of C. parvum (IIaA15G2R1 and IIdA23G1) and 1 of Cryptosporidium horse genotype (VIaA15G4) that were described in foals hospitalized at the EPU in the same years. The results of the present study show that qPCR can be used to evaluate Cryptosporidium contamination of environmental surfaces of a veterinary teaching hospital and the efficacy of the disinfection procedures.

Cryptosporidium pathogenicity and virulence

Cryptosporidium is a protozoan parasite of medical and veterinary importance that causes gastroenteritis in a variety of vertebrate hosts. Several studies have reported different degrees of pathogenicity and virulence among Cryptosporidium species and isolates of the same species as well as evidence of variation in host susceptibility to infection. The identification and validation of Cryptosporidium virulence factors have been hindered by the renowned difficulties pertaining to the in vitro culture and genetic manipulation of this parasite. Nevertheless, substantial progress has been made in identifying putative virulence factors for Cryptosporidium. This progress has been accelerated since the publication of the Cryptosporidium parvum and C. hominis genomes, with the characterization of over 25 putative virulence factors identified by using a variety of immunological and molecular techniques and which are proposed to be involved in aspects of host-pathogen interactions from adhesion and locomotion to invasion and proliferation. Progress has also been made in the contribution of host factors that are associated with variations in both the severity and risk of infection. Here we provide a review comprised of the current state of knowledge on Cryptosporidium infectivity, pathogenesis, and transmissibility in light of our contemporary understanding of microbial virulence.

Comparative genome analysis of two Cryptosporidium parvum isolates with different host range

Parasites of the genus Cryptosporidium infect the intestinal and gastric epithelium of different vertebrate species. Some of the many Cryptosporidium species described to date differ with respect to host range; whereas some species' host range appears to be narrow, others have been isolated from taxonomically unrelated vertebrates. To begin to investigate the genetic basis of Cryptosporidium host specificity, the genome of a Cryptosporidium parvum isolate belonging to a sub-specific group found exclusively in humans was sequenced and compared to the reference C. parvum genome representative of the zoonotic group. Over 12,000 single-nucleotide polymorphisms (SNPs), or 1.4 SNP per kilobase, were identified. The genome distribution of SNPs was highly heterogeneous, but non-synonymous and silent SNPs were similarly distributed. On many chromosomes, the most highly divergent regions were located near the ends. Genes in the most diverged regions were almost twice as large as the genome-wide average. Transporters, and ABC transporters in particular, were over-represented among these genes, as were proteins with predicted signal peptide. Possibly reflecting the presence of regulatory sequences, the distribution of intergenic SNPs differed according to the function of the downstream open reading frame. A 3-way comparison of the newly sequenced anthroponotic C. parvum, the reference zoonotic C. parvum and the human parasite Cryptosporidium hominis identified genetic loci where the anthroponotic C. parvum sequence is more similar to C. hominis than to the zoonotic C. parvum reference. Because C. hominis and anthroponotic C. parvum share a similar host range, this unexpected observation suggests that proteins encoded by these genes may influence the host range.

Experimental infection with Cryptosporidium parvum IIaA21G1R1 subtype in immunosuppressed mice

Cryptosporidium parvum subtype IIaA21G1R1 oocysts were used to infect dexamethasone immunosuppressed N: NIH Swiss mice. This is the first Cryptosporidium mouse model in which the relationship between infection and apoptosis has been histologically studied at each portion of the gut in order to observe this dynamic in chronic cryptosporidiosis. Histology showed developmental stages in the duodenum, proximal and distal jejunum, ileum, cecum and colon, with the small intestine remaining infected until day 35 post infection. At proximal jejunum an inverse correlation between infection and apoptosis was observed at days 28 and 35 p.i. Data suggests that jejunum could be an interesting place to carry out further studies on the dynamics of Cryptosporidium infection and apoptosis. Based on these findings, this mouse model was useful to evaluate clinical, parasitological and histological aspects of C. parvum subtype IIaA21G1R1 infection, and it will be an appropriate tool to investigate different aspects of Cryptosporidium infection.

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.

Fulminant cryptosporidiosis associated with digestive adenocarcinoma in SCID mice infected with Cryptosporidium parvum TUM1 strain

We recently demonstrated that Cryptosporidium parvum IOWA strain induces in situ ileo-caecal adenocarcinoma in an animal model. Herein, the ability of another C. parvum strain to induce digestive neoplasia in dexamethasone-treated SCID mice was explored. SCID mice infected with C. parvum TUM1 strain developed a fulminant cryptosporidiosis associated with intramucosal adenocarcinoma, which is considered an early histological sign of invasive cancer. Both evidence of a role of C. parvum in adenocarcinoma induction and the extended prevalence of cryptosporidiosis worldwide, suggest that the risk of C. parvum-induced gastro-intestinal cancer in humans should be assessed.

Multi-locus analysis of human infective Cryptosporidium species and subtypes using ten novel genetic loci

Background

Cryptosporidium is a protozoan parasite that causes diarrheal illness in a wide range of hosts including humans. Two species, C. parvum and C. hominis are of primary public health relevance. Genome sequences of these two species are available and show only 3-5% sequence divergence. We investigated this sequence variability, which could correspond either to sequence gaps in the published genome sequences or to the presence of species-specific genes. Comparative genomic tools were used to identify putative species-specific genes and a subset of these genes was tested by PCR in a collection of Cryptosporidium clinical isolates and reference strains.

Results

The majority of the putative species-specific genes examined were in fact common to C. parvum and C. hominis. PCR product sequence analysis revealed interesting SNPs, the majority of which were species-specific. These genetic loci allowed us to construct a robust and multi-locus analysis. The Neighbour-Joining phylogenetic tree constructed clearly discriminated the previously described lineages of Cryptosporidium species and subtypes.

Conclusions

Most of the genes identified as being species specific during bioinformatics in Cryptosporidium sp. are in fact present in multiple species and only appear species specific because of gaps in published genome sequences. Nevertheless SNPs may offer a promising approach to studying the taxonomy of closely related species of Cryptosporidia.

Molecular detection of Cryptosporidium cuniculus in rabbits in Australia

In the United Kingdom, rabbits have been reported to harbour genotypes of Cryptosporidium (now recognized as C. cuniculus) identical to those from human patients exhibiting symptoms of cryptosporidiosis. The high density of rabbits in many regions of Australia, including both rural and urban as well as natural water catchments areas, and the absence of any information on Cryptosporidium from lagomorphs in this country stimulated the present study. We undertook an epidemiological study that genetically characterized Cryptosporidium from rabbits from four locations in Victoria by PCR-coupled sequencing and phylogenetic analysis of sequence data for loci within the small subunit of nuclear ribosomal RNA (SSU; for specific identification) and the 60kDa glycoprotein gene (gp60; for genotypic/subgenotypic identification). Cryptosporidium was detected in 12 (6.8%) of 176 individual faecal samples. For SSU, all 12 sequences were identical to each other and to that of C. cuniculus. For pgp60, all corresponding sequences matched the known genotype Vb, and were classified as subgenotype VbA23R3 (n=11) and VbA26R4 (n=1), which are both new records. Present evidence indicates that genotype Vb is limited to rabbits; however, it would be premature to conclude that this genotype is not zoonotic. Future studies should focus on the zoonotic potential of C. cuniculus from rabbits and a wide range of yet unstudied animals. (Nucleotide sequences reported in this paper are available in the GenBank database under accession nos. HM852431-HM852433).

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.

Human immune responses in cryptosporidiosis

Immune responses play a critical role in protection from, and resolution of, cryptosporidiosis. However, the nature of these responses, particularly in humans, is not completely understood. Both innate and adaptive immune responses are important. Innate immune responses may be mediated by Toll-like receptor pathways, antimicrobial peptides, prostaglandins, mannose-binding lectin, cytokines and chemokines. Cell-mediated responses, particularly those involving CD4(+) T cells and IFN-gamma play a dominant role. Mucosal antibody responses may also be involved. Proteins mediating attachment and invasion may serve as putative protective antigens. Further knowledge of human immune responses in cryptosporidiosis is essential in order to develop targeted prophylactic and therapeutic interventions. This review focuses on recent advances and future prospects in the understanding of human immune responses to Cryptosporidium infection.

Genetic characterization of Cryptosporidium parvum from calves by mutation scanning and targeted sequencing--zoonotic implications

This study explored the genetic make-up of Cryptosporidium in fecal samples from 268 individual calves on pasture-based dairy farms in three regions of Victoria, Australia. An integrated approach, using PCR-coupled single-strand conformation polymorphism, targeted sequencing and phylogenetic analysis, was employed to classify the genetic variants (i.e. genotypes and subgenotypes) of Cryptosporidium parvum present in 124 (46.3%) samples and to infer their zoonotic potential. Genotypic and subgenotypic classification was achieved using a portion of the 60 kDa glycoprotein gene (designated pgp60); specific identity was verified using a region within the small subunit of the nuclear ribosomal RNA (pSSU). Twelve sequence types representing ten distinct subgenotypes were defined within genotype IIa, namely IIaA16G3R1 (n=7), IIaA17G2R1 (1), IIaA18G2R1a (2), IIaA18G2R1b (1), IIaA18G4R1 (1), IIaA19G3R1a (80), IIaA19G3R1b (1), IIaA20G2R1 (9), IIaA20G3R1 (1), IIaA20G4R1 (9), IIaA21G3R1 (1) and IIaA23G3R1 (9), of which IIaA18G2R1b, IIaA18G4R1 and IIaA19G3R1b are new records. All of the subgenotypes, except IIaA16G3R1, IIaA18G4R1 and IIaA20G4R1, have been detected previously in humans and are thus considered to be of zoonotic relevance. (Nucleotide sequences reported in this paper are available in the GenBank database under accession numbers FJ825018-FJ825029).

Analysis of the genetic diversity within Cryptosporidium hominis and Cryptosporidium parvum from imported and autochtonous cases of human cryptosporidiosis by mutation scanning

The present study investigated sequence variation in part of the 60 kilodalton glycoprotein (pgp60) gene among Cryptosporidium hominis and Cryptosporidium parvum isolates (n=115) from citizens of the UK inferred to have been infected whilst travelling abroad (to 25 countries) or in the UK. The genomic DNA samples from these isolates were subjected to PCR-coupled single-strand conformation polymorphism analysis, followed by targeted sequencing of pgp60. Individual samples were classified to the genotypic and subgenotypic levels based on phylogenetic analysis (Bayesian inference) of pgp60 data, including published sequences for comparison. Based on this analysis, five C. hominis (Ia-If) and four C. parvum (IIa, IIc-IIe) genotypes were identified, equating to 16 and 10 subgenotypes, respectively. Of these genotypes, C. hominis Ib was predominant (n=82). Interestingly, one subgenotype (C. hominis Ib A10G2R2) accounted for the majority of the samples examined and was identified in travellers to 14 countries; the examination of published records suggested that C. hominis Ib A10G2R2 has a global distribution. Numerous new and seemingly rare subgenotypes (eight for C. hominis and six for C. parvum) were also discovered. In conclusion, the present study revealed substantial genetic variation in pgp60 within both C. hominis and C. parvum and emphasizes the need to undertake investigations of human and animal populations in countries for which there is no information on the genetic make-up of Cryptosporidium infecting humans.

Classification of Cryptosporidium species from patients with sporadic cryptosporidiosis by use of sequence-based multilocus analysis following mutation scanning

In the present study, we analyzed genetic variation in Cryptosporidium species from humans (n = 62) with clinical cryptosporidiosis in South Australia. Sequence variation was assessed in regions within the small subunit of nuclear rRNA (p-SSU), the 70-kDa heat shock protein (p-hsp70), and the 60-kDa glycoprotein (p-gp60) genes by employing single-strand conformation polymorphism analysis and sequencing. Based on the analyses of p-SSU and p-hsp70, Cryptosporidium hominis (n = 38) and Cryptosporidium parvum (n = 24) were identified. The analysis of p-gp60 revealed eight distinct subgenotypes, classified as C. hominis IaA17R1 (n = 3), IbA9G3R2 (n = 14), IbA10G2R2 (n = 20), and IfA12G1R1 (n = 1), as well as C. parvum IIaA18G3R1 (n = 15), IIaA20G3R1 (n = 6), IIaA22G4R1 (n = 2), and IIcA5G3R2 (n = 1). Subgenotypes IaA17R1 and IIaA22G4R1 are new. Of the six other subgenotypes, IbA10G2R2, IIaA18G3R1, IIaA20G3R1, and IIcA5G3R2 were reported previously from the state of Victoria. This is the fourth record in Australia of C. parvum subgenotype IIaA18G3R1 from humans, which, to date, has been isolated only from cattle in other countries. This subgenotype might be a significant contributor to sporadic human cryptosporidiosis and may indicate a greater zoonotic contribution to the infection of humans in the area of study. Comparative analyses revealed, for the first time, the differences in the genetic makeup of Cryptosporidium populations between two relatively close, major metropolitan cities.

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.

Molecular basis of Cryptosporidium-host cell interactions: recent advances and future prospects

Host-parasite interactions mediating attachment of Cryptosporidium spp. to host cells and invasion of the cell membrane are complex processes that involve multiple parasite and host molecules. Knowledge of the molecular basis of these processes is crucial for understanding the pathogenic mechanisms underlying infection and for designing strategies to combat cryptosporidiosis. Recent progress in this field has been greatly facilitated by the completion of the genome sequences of Cryptosporidium parvum and Cryptosporidium hominis and by success in heterologous expression of Cryptosporidium genes in the related apicomplexan Toxoplasma gondii. However, although a number of Cryptosporidium proteins implicated in mediating host-parasite interactions have been identified, progress in establishing their functional role has been hindered by the inability to genetically manipulate the parasite and to continuously propagate it in vitro. This article reviews the recent advances in knowledge regarding the Cryptosporidium proteins mediating attachment to and invasion of host epithelial cells, and outlines prospects for future research in this field.

New drugs and treatment for cryptosporidiosis

PURPOSE OF REVIEW

There is a history of inadequate treatments for cryptosporidiosis and a lack of understanding of the species that cause human disease. Against this background, we review the efficacy of antiparasitic agents, particularly nitazoxanide, which has led to increased treatment options, the potential for immunotherapy, and consider the role of highly active antiretroviral therapy in reducing the incidence of this opportunistic infection.

RECENT FINDINGS

Nitazoxanide is effective for cryptosporidiosis in immunocompetent and probably immunocompromised patients (with an alteration in the duration of treatment or the dosing regimen). HIV-infected patients on highly active antiretroviral therapy have a dramatically lower incidence of cryptosporidiosis, attributable to the effects of intestinal immune reconstitution as well as the effect on the CD4 cell count. Protease inhibitors have a direct inhibitory effect on Cryptosporidium infection, suggesting a further reason for the reduction in the incidence of cryptosporidiosis and implying a further possible therapeutic modality.

SUMMARY

Cryptosporidiosis remains a significant public health threat. Risk avoidance guidance could be viewed in the more relative terms of risk management depending on the degree of immunosuppression. Of established efficacy in immunocompetent patients, nitazoxanide is also useful for immunocompromised patients. Better prevention and treatment options mean that, in the immunocompromised, this disease is now less common. Immune reconstitution is the key to prevention. Further database mining of the Cryptosporidium genome will assist in the discovery of new genes, biochemical pathways and protective antigens that can be targeted to develop novel therapies for cryptosporidiosis.

Crystallization of three key glycolytic enzymes of the opportunistic pathogen Cryptosporidium parvum

Cryptosporidium parvum is one of the major causes of waterborne diseases worldwide. This protozoan parasite depends mainly on the anaerobic oxidation of glucose for energy production. In order to identify the differences in the three-dimensional structure of key glycolytic enzymes of C. parvum and its human host, we have expressed, purified and crystallized recombinant versions of three important glycolytic enzymes of the parasite, namely, glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase and lactate dehydrogenase. Lactate dehydrogenase has been crystallized in the absence and in the presence of its substrates and cofactors, while pyruvate kinase and glyceraldehyde 3-phosphate dehydrogenase were crystallized only in the apo-form. X-ray diffraction data have been collected for all crystals.

Expression of P23 of Cryptosporidium parvum in Toxoplasma gondii and Evaluation of its Protective Effects

In this study, P23 of Cryptosporidium parvum sporozoites, an immunodominant surface protein, was stably expressed in Toxoplasma gondii (Tg/P23) and its protective effects were evaluated in a mouse model. The molecular weight and antigenic property of P23 expressed by Tg/P23 were similar to those of the native P23. Mice immunized with lysed Tg/P23 tachyzoites produced specific neutralizing antibodies against C. parvum. These findings indicate that the T. gondii vector may provide a new tool for the production of a recombinant vaccine against cryptosporidiosis in animals.

Cryptosporidium: a water-borne zoonotic parasite

Of 155 species of mammals reported to be infected with Cryptosporidium parvum or C. parvum-like organisms most animals are found in the Orders Artiodactyla, Primates, and Rodentia. Because Cryptosporidium from most of these animals have been identified by oocyst morphology alone with little or no host specificity and/or molecular data to support identification it is not known how many of the reported isolates are actually C. parvum or other species. Cryptosporidiosis is a cause of morbidity and mortality in animals and humans, resulting primarily in diarrhea, and resulting in the most severe infections in immune-compromised individuals. Of 15 named species of Cryptosporidium infectious for nonhuman vertebrate hosts C. baileyi, C. canis, C. felis, C. hominis, C. meleagridis, C. muris, and C. parvum have been reported to also infect humans. Humans are the primary hosts for C. hominis, and except for C. parvum, which is widespread amongst nonhuman hosts and is the most frequently reported zoonotic species, the remaining species have been reported primarily in immunocompromised humans. The oocyst stage can remain infective under cool, moist conditions for many months, especially where water temperatures in rivers, lakes, and ponds remain low but above freezing. Surveys of surface water, groundwater, estuaries, and seawater have dispelled the assumption that Cryptosporidium oocysts are present infrequently and in geographically isolated locations. Numerous reports of outbreaks of cryptosporidiosis related to drinking water in North America, the UK, and Japan, where detection methods are in place, indicate that water is a major vehicle for transmission of cryptosporidiosis.

[Cryptosporidium oocyst viability and infectivity evaluation by flow cytometry]

Evaluating waterborne Cryptosporidium sp. oocyst infectivity is presently a major Issue for the estimation of environmental risks. The aim of this presentation, was to describe a new model suitable for determining in vivo oocyst infectivity. In this model, infection was assessed in suckling mice seven days after oocyst ingestion by measuring the number of gut oocysts using flow cytometry. Four days old mice were orally infected by serially diluted C. parvum oocyst suspensions. This model was found highly sensitive since ingestion of 1-10 oocysts resulted in infection in 70% of animals. Assays with Cryptosporidium oocysts from the environment suggest that this model may contribute to the evaluation of environmental risks due to the parasite.

Current progress in the fatty acid metabolism in Cryptosporidium parvum

Cryptosporidium parvum is one of the apicomplexans that can cause severe diarrhea in humans and animals. The slow development of anti-cryptosporidiosis chemotherapy is primarily due to the poor understanding on the basic metabolic pathways in this parasite. Many well-defined or promising drug targets found in other apicomplexans are either absent or highly divergent in C. parvum. The recently discovered apicoplast and its associated Type II fatty acid synthetic enzymes in Plasmodium, Toxoplasma, and Eimeria apicomplexans are absent in C. parvum, suggesting this parasite is unable to synthesize fatty acids de novo. However, C. parvum possesses a giant Type I fatty acid synthase (CpFAS1) that makes very long chain fatty acids using mediate or long chain fatty acids as precursors. Cryptosporidium also contains a Type I polyketide synthase (CpPKS1) that is probably involved in the production of unknown polyketide(s) from a fatty acid precursor. In addition to CpFAS1 and CpPKS1, a number of other enzymes involved in fatty acid metabolism have also been identified. These include a long chain fatty acyl elongase (LCE), a cytosolic acetyl-CoA carboxylase (ACCase), three acyl-CoA synthases (ACS), and an unusual "long-type" acyl-CoA binding protein (ACBP), which allows us to hypothetically reconstruct the highly streamlined fatty acid metabolism in this parasite. However, C. parvum lacks enzymes for the oxidation of fatty acids, indicating that fatty acids are not an energy source for this parasite. Since fatty acids are essential components of all biomembranes, molecular and functional studies on these critical enzymes would not only deepen our understanding on the basic metabolism in the parasites, but also point new directions for the drug discovery against C. parvum and other apicomplexan-based diseases.

Functional characterization of replication protein A2 (RPA2) from Cryptosporidium parvum

Replication protein A (RPA) is a heterotrimeric complex of single-stranded DNA-binding proteins that play multiple roles in eukaryotic DNA metabolism. The RPA complex is typically composed of heterologous proteins (termed RPA1, RPA2 and RPA3) in animals, plants and fungi, which possess different functions. Previously, two distinct, short-type RPA large subunits (CpRPA1 and CpRPA1B) from the apicomplexan parasite Cryptosporidium parvum were characterized. Here are reported the identification and characterization of a putative middle RPA subunit (CpRPA2) from this unicellular organism. Although the CpRPA2 gene encodes a predicted 40.1 kDa peptide, which is larger than other RPA2 subunits characterized to date, Western blot analysis of oocyst preparations detected a native CpRPA2 protein with a molecular mass of approximately 32 kDa, suggesting that CpRPA2 might undergo post-translational cleavage or the gene was translated at an alternative start codon. Immunofluorescence microscopy using a rabbit anti-CpRPA2 antibody revealed that CpRPA2 protein was mainly distributed in the cytosol (rather than the nuclei) of C. parvum sporozoites. Semi-quantitative RT-PCR data indicated that CpRPA2 was differentially expressed in a tissue culture model with highest expression in intracellular parasites infecting HCT-8 cells for 36 and 60 h. Sequence comparison suggests that RPA2 is a group of poorly conserved proteins. Nonetheless, functional analyses of recombinant proteins confirmed that CpRPA2 is a single-stranded DNA-binding protein and that it could serve as an in vitro phosphorylation target by a DNA-dependent protein kinase. The minimal length of poly(dT) required for CpRPA2 binding is 17 nucleotides, and the DNA-binding capability was inhibited by phosphorylation in vitro. These observations provide additional evidence on the divergence of RPA proteins between C. parvum and host, implying that the parasite DNA replication machinery could be explored as a chemotherapeutic target.

Intron-containing beta-tubulin transcripts in Cryptosporidium parvum cultured in vitro

The genome of Cryptosporidium parvum contains a relatively small number of introns, which includes the beta-tubulin gene with only a single intron. Recently, it was observed that the intron was not removed from some of the beta-tubulin transcripts in the late life cycle stages cultured in vitro. Although normally spliced beta-tubulin mRNA was detected in all parasite intracellular stages by RT-PCR (e.g. HCT-8 or Caco-2 cells infected with C. parvum for 12-72 h), at 48-72 h post-infection unprocessed beta-tubulin transcripts containing intact introns started to appear in parasite mRNA within infected host cells. The intron-containing transcripts could be detected by fluorescence in situ hybridization (FISH) using an intron-specific probe. The intron-containing beta-tubulin transcripts appeared unique to the in vitro-cultured C. parvum, since they were not detected in parasite-infected calves at 72 h. As yet, it is unclear whether the late life cycle stages of C. parvum are partially deficient in intron-splicing or the intron-splicing processes have merely slowed, both of which would allow the detection of intron-containing transcripts. Another possible explanation is that the decay in transcript processing might simply be due to the onset of parasite death. Nonetheless, the appearance of intron-containing transcripts coincides with the arrest of C. parvum development in vitro. This unusual observation prompts speculation that the abnormal intron-splicing of beta-tubulin transcripts may be one of the factors preventing complete development of this parasite in vitro. Furthermore, the presence of both processed and unprocessed introns in beta-tubulin transcripts in vitro may provide a venue for studying overall mechanisms for intron-splicing in this parasite.

Differential expression and interaction of transcription co-activator MBF1 with TATA-binding protein (TBP) in the apicomplexan Cryptosporidium parvum

All gene-specific transcriptional activators initiate gene transcriptions by binding to promoter sequences and recruiting general transcription factors including TATA-binding protein (TBP) to upstream of targeted genes. Some of them require multiprotein bridging factors (MBFs); for example, the type 1 MBF (MBF1) which interconnects the gene activator with TBP. In this study, the properties of a previously cloned type 1 multiprotein bridging factor (CpMBF1) and a newly identified TBP (CpTBP1) from the apicomplexan Cryptosporidium parvum were investigated. Genes encoding both proteins were differentially expressed as determined by semi-quantitative RT-PCRs during the parasite life cycle, but in different patterns. The highest level of expression of CpMBF1 was in the well-developed intracellular parasites, whereas that of CpTBP1 was found in intact oocysts and late intracellular stages, possibly correlated with the formation of oocysts. Both CpMBF1 and CpTBP1 were expressed as maltose-binding protein fusion proteins. The function of CpTBP1 was confirmed by its ability to bind a biotinylated DNA oligonucleotide containing TATA consensus sequence. The interaction between CpMBF1 and CpTBP1 was also observed by an electrophoretic mobility shift assay. Since little is known about the regulation and control of gene activity in C. parvum, this study may point to a new direction for the study of gene activation associated with the development of the complex life cycle of this parasite.

Biology, persistence and detection of Cryptosporidium parvum and Cryptosporidium hominis oocyst

Cryptosporidium parvum and Cryptosporidium hominis are obligate enteric protozoan parasites which infect the gastrointestinal tract of animals and humans. The mechanism(s) by which these parasites cause gastrointestinal distress in their hosts is not well understood. The risk of waterborne transmission of Cryptosporidium is a serious global issue in drinking water safety. Oocysts from these organisms are extremely robust, prevalent in source water supplies and capable of surviving in the environment for extended periods of time. Resistance to conventional water treatment by chlorination, lack of correlation with biological indicator microorganisms and the absence of adequate methods to detect the presence of infectious oocysts necessitates the development of consistent and effective means of parasite removal from the water supply. Additional research into improving water treatment and sewage treatment practices is needed, particularly in testing the efficiency of ozone in oocyst inactivation. Timely and efficient detection of infectious C. parvum and C. hominis oocysts in environmental samples requires the development of rapid and sensitive techniques for the concentration, purification and detection of these parasites. A major factor confounding proper detection remains the inability to adequately and efficiently concentrate oocysts from environmental samples, while limiting the presence of extraneous materials. Molecular-based techniques are the most promising methods for the sensitive and accurate detection of C. parvum and C. hominis. With the availability of numerous target sequences, RT-PCR will likely emerge as an important method to assess oocyst viability. In addition, a multiplex PCR for the simultaneous detection of C. parvum, C. hominis and other waterborne pathogens such as Giardia lamblia would greatly benefit the water industry and protect human health.

Rapid displacement of Cryptosporidium parvum type 1 by type 2 in mixed infections in piglets

Genotypes 1 and 2 of Cryptosporidium parvum are the primary types associated with infections in humans, with type 1 being by far the predominant genotype. The frequency of mixed infection with both genotypes in humans is relatively rare, while type 1, which experimentally infects other mammals, has been found to naturally infect almost exclusively humans. One possible explanation for the absence of type 1 in other mammals and the low frequency of mixed infections in humans is the inability of type 1 to compete with type 2 in nature when both occur simultaneously. To investigate this, we challenged gnotobiotic piglets with equal number of oocysts of type 1 and type 2, given either simultaneously or with type 2 given 24 or 48 h after type 1. The genotype of the oocysts excreted in feces and the relative distribution of each of the genotypes throughout the gut at necropsy were determined. Regardless of the time interval between challenges with the two genotypes, type 2 invariably displaced type 1. The rate of displacement was rapid when both genotypes were given simultaneously, after which no traces of type 1 were detected in the feces or in gut sections by PCR. Infection with type 1 24 or 48 h before challenge with type 2, while permitting type 1 to become established, was still rapidly eliminated within 3 days after challenge with type 2. These observations have major implications regarding the relative perpetuation and survival of these two genotypes in mammals.

Cryptosporidium and host resistance: historical perspective and some novel approaches

Cryptosporidium parvum is recognized as a major cause of diarrheal disease in neonatal bovine calves. In addition, this protozoan parasite has emerged as an important cause of disease in both immunocompromised and immunocompetent humans. Despite years of research, no consistently effective means of prevention or treatment are readily available for cryptosporidiosis in any species. Infection through ingestion of contaminated water has been widely documented; C. parvum was reported to be responsible for the largest waterborne outbreak of infectious disease in US history. In addition to its role as a primary disease agent, C. parvum has potential to initiate or exacerbate other gastrointestinal disorders, such as inflammatory bowel disease. Thus, control of C. parvum infection in both animals and humans remains an important objective. Research in our laboratory has focused on understanding mechanisms of resistance to C. parvum. We have demonstrated that acquisition of intestinal flora increases resistance to C. parvum. Substances present in the intestinal mucosa of adult animals can transfer resistance when fed to susceptible infants. Both expression of intestinal enzymes and rate of proliferation of epithelial cells may be altered following C. parvum infection. These and other changes may have profound effects on host resistance to C. parvum.

Molecular analysis of the 18S rRNA gene of Cryptosporidium parasites from patients with or without human immunodeficiency virus infections living in Kenya, Malawi, Brazil, the United Kingdom, and Vietnam

An 840-bp fragment of the 18S rRNA gene was used to identify Cryptosporidium spp. recovered from human immunodeficiency virus (HIV)-infected and -uninfected patients from Kenya, Malawi, Brazil, the United Kingdom, and Vietnam. Initial identification was by Ziehl-Neelsen acid-fast staining. Confirmation was by nested PCR, targeting the most polymorphic region of the 18S rRNA gene. Genotyping was by restriction endonuclease digestion of the PCR product followed by nucleotide sequencing. Among 63 isolates analyzed, four genotypes of Cryptosporidium were identified; 75% of the isolates were of the C. parvum human genotype, while the potentially zoonotic species were of the C. parvum bovine genotype (21.7%), the C. meleagridis genotype (1.6% [one isolate]), and the C. muris genotype (1.6% [one case]). HIV-infected individuals were more likely to have zoonotic genotypes than the HIV-uninfected individuals. Among the C. parvum group, strains clustered distinctly into either human or bovine genotypes regardless of the geographical origin, age, or HIV status of the patients. The intragenotypic variation observed in the C. parvum human genotype was extensive compared to that within the C. parvum bovine genotype group. The variation within genotypes was conserved in all geographical regions regardless of the patients' HIV status. The extensive diversity within genotypes at the 18S rRNA gene locus may limit its application to phylogenetic analyses.

Polyclonal Fab phage display libraries with a high percentage of diverse clones to Cryptosporidium parvum glycoproteins

The protozoan parasite Cryptosporidium parvum is regarded as a major public health problem world-wide, especially for immunocompromised individuals. Although no effective therapy is presently available, specific immune responses prevent or terminate cryptosporidiosis and passively administered antibodies have been found to reduce the severity of infection. Therefore, as an immunotherapeutic approach against cryptosporidiosis, we set out to develop C. parvum-specific polyclonal antibody libraries, standardised, perpetual mixtures of polyclonal antibodies, for which the genes are available. A combinatorial Fab phage display library was generated from the antibody variable region gene repertoire of mice immunised with C. parvum surface and apical complex glycoproteins which are believed to be involved in mediating C. parvum attachment and invasion. The variable region genes used to construct this starting library were shown to be diverse by nucleotide sequencing. The library was subjected to one round of antigen selection on C. parvum glycoproteins or a C. parvum oocyst/sporozoite preparation. The two selected libraries showed specific reactivity to the glycoproteins as well as to the oocyst/sporozoite preparation, with 50-73% antigen-reactive members. Fingerprint analysis of individual clones from the two antigen-selected libraries showed high diversity, confirming the polyclonality of the selected libraries. Furthermore, immunoblot analysis on the oocyst/sporozoite and glycoprotein preparations with selected library phage showed reactivity to multiple bands, indicating diversity at the antigen level. These C. parvum-specific polyclonal Fab phage display libraries will be converted to libraries of polyclonal full-length antibodies by mass transfer of the selected heavy and light chain variable region gene pairs to a mammalian expression vector. Such polyclonal antibody libraries would be expected to mediate effector functions and provide optimal passive immunity against cryptosporidiosis.

Parasitic infections of the gastrointestinal tract

Intestinal parasites continue to be a significant health problem in both developed and developing countries. In developed countries, protozoans are more commonly the cause of gastrointestinal infections than are helminths. Some protozoan parasites have stages in which, in addition to being resistant to chemicals used for water treatment, they are small enough to pass through commonly used filtration processes. The relatively large size of helminth eggs increases the likelihood of their removal during water filtration. The direct impact of protozoan parasites on both human and animal health is considerable, and there is some evidence that infection may contribute to the development of various forms of intestinal dysregulation as well as disseminated infection, especially in AIDS patients. Protozoans of special interest, due to either their frequency of isolation or their role as emerging pathogens, include Giardia duodenalis, Cryptosporidium parvum, Cyclospora cayetanensis, and the microsporidians, Enterocytozoon bieneusi and Encephalitozoon intestinalis.

Heterogeneous expression and functional analysis of two distinct replication protein A large subunits from Cryptosporidium parvum

Replication protein A is a single stranded DNA-binding protein that has multiple roles in eukaryotic DNA metabolism. Typically, eukaryotic replication protein A is a stable heterotrimeric complex with three subunits of 70 kDa (RPA1), 32 kDa (RPA2) and 14 kDa (RPA3). We have previously cloned and characterised an RPA1 subunit from Cryptosporidium parvum, which shares high homology with other eukaryotic replication protein A 1 proteins, but lacks an N-terminal domain. Here, we have identified a second replication protein A 1 (termed CpRPA1B) from the ongoing C. parvum genome-sequencing project. The deduced protein sequence to CpRPA1B shows only 16% sequence identity with CpRPA1, indicating that two different types of RPA1 subunits are present in C. parvum. The CpRPA1B gene predicts a 75.5 kDa peptide similar in size to those of higher eukaryotes, but in contrast to the 53.9 kDa N-terminal short-type CpRPA1 protein. However, western blot analysis suggested that, although the entire CpRPA1B open reading frame might be translated, the protein may be cleaved by posttranslational modification, similar to that observed with the replication protein A 1 gene product in Plasmodium falciparum. Indirect immunofluorescence studies indicated a diffused pattern for both proteins in sporozoites. However, differential localisation was observed with CpRPA1 to the anterior region that contains the apical-complex and CpRPA1B to the central region in/or around the nuclei of the sporozoites. Both CpRPA1 and CpRPA1B full-length open reading frames were expressed for functionality assays. The CpRPA1 and CpRPA1B recombinant proteins were expressed in bacterial Escherichia coli as maltose-binding protein fusion proteins and the entire fusion proteins were assayed for their DNA-binding properties. Studies indicate that CpRPA1B binds ssDNA of >or=5 nucleotides (dT), while CpRPA1 only binds ssDNA >or=20 nucleotides (dT). This study indicates that C. parvum possesses two different types of replication protein A large subunits (replication protein A 1), both differing significantly from their hosts.