Cryptosporidiosis and the challenges of chemotherapy

Investigating Cryptosporidium spp. Using Genomic, Proteomic and Transcriptomic Techniques: Current Progress and Future Directions

Cryptosporidiosis is a widespread disease caused by the parasitic protozoan Cryptosporidium spp., which infects various vertebrate species, including humans. Once unknown as a gastroenteritis-causing agent, Cryptosporidium spp. is now recognized as a pathogen causing life-threatening disease, especially in immunocompromised individuals such as AIDS patients. Advances in diagnostic methods and increased awareness have led to a significant shift in the perception of Cryptosporidium spp. as a pathogen. Currently, genomic and proteomic studies play a main role in understanding the molecular biology of this complex-life-cycle parasite. Genomics has enabled the identification of numerous genes involved in the parasite's development and interaction with hosts. Proteomics has allowed for the identification of protein interactions, their function, structure, and cellular activity. The combination of these two approaches has significantly contributed to the development of new diagnostic tools, vaccines, and drugs for cryptosporidiosis. This review presents an overview of the significant achievements in Cryptosporidium research by utilizing genomics, proteomics, and transcriptomics approaches.

Cryptosporidiosis: From Prevention to Treatment, a Narrative Review

Cryptosporidiosis is a water- and food-borne zoonotic disease caused by the protozoon parasite of the genus Cryptosporidium. C. hominis and C. parvum are the main two species causing infections in humans and animals. The disease can be transmitted by the fecal-oral route as well as the respiratory route. The infective stage (sporulated oocysts) is resistant to different disinfectants including chlorine. Currently, no effective therapeutic drugs or vaccines are available to treat and control Cryptosporidium infection. To prevent cryptosporidiosis in humans and animals, we need to understand better how the disease is spread and transmitted, and how to interrupt its transmission cycle. This review focuses on understanding cryptosporidiosis, including its infective stage, pathogenesis, life cycle, genomics, epidemiology, previous outbreaks, source of the infection, transmission dynamics, host spectrum, risk factors and high-risk groups, the disease in animals and humans, diagnosis, treatment and control, and the prospect of an effective anti-Cryptosporidium vaccine. It also focuses on the role of the One Health approach in managing cryptosporidiosis at the animal-human-environmental interface. The summarized data in this review will help to tackle future Cryptosporidium infections in humans and animals and reduce the disease occurrence.

Deep glance on the antiparasitic anticancer activities of wheat germ oil in chronically infected immunosuppressed mice with cryptosporidiosis

Cryptosporidium species are the major cause of water-borne epidemics of diarrhea in both developing and developed countries that vary from self-limited in immunocompetent patients to severe life-threatening in the immunocompromised hosts. There was a proven correlation between cryptosporidiosis and colorectal cancers, although, studies in this field are still limited. Wheat germ oil (WGO) is a natural product with a known antiparasitic effect and potential antiproliferative activities. This study aimed to evaluate the antiparasitic and anticancer activities of WGO in chronically infected immunosuppressed mice compared to Nitazoxanide (NTZ). This experimental case-control study was performed in the period from January till September 2021. Eighty immunosuppressed bred laboratory mice were divided into 4 groups, 20 mice each; GI non-infected; negative control (NC), GII infected non treated; positive control (PC), GII infected, and treated with NTZ, GIV infected, and treated with WGO. Parasitological, histopathological, and immunohistochemical examinations were performed with estimating the rate of maximal survival for the study groups. Parasitological examination revealed a marked reduction in the mean Cryptosporidium spp. oocyst counts in the stool of GIV compared to PC, and GIII (P-value < 0.001). Histopathological and immunohistochemical examinations showed the best results with GIV which revealed restoration of normal villous pattern, with no dysplasia or malignancy could be detected. GIV showed the best survival rate compared to PC and GIII. WGO is an extremely promising agent that has an excellent therapeutic effect against cryptosporidiosis with the ability to control the tumorigenesis process in the chronically infected immunosuppressed hosts.

Molecular Basis of P131 Cryptosporidial-IMPDH Selectivity-A Structural, Dynamical and Mechanistic Stance

Cryptosporidiosis accounts for a surge in infant (<5 years) mortality and morbidity. To date, several drug discovery efforts have been put in place to develop effective therapeutic options against the causative parasite. Based on a recent report, P131 spares inosine monophosphate dehydrogenase (IMPDH) in a eukaryotic model (mouse IMPDH (mIMPDH)) while binding selectively to the NAD⁺ site in Cryptosporidium parvum (CpIMPDH). However, no structural detail exists on the underlining mechanisms of P131-CpIMPDH selective targeting till date. To this effect, we investigate the selective inhibitory dynamics of P131 in CpIMPDH relative to mIMPDH via molecular biocomputation methods. Pairwise sequence alignment revealed prominent variations at the NAD⁺ binding regions of both proteins that accounted for disparate P131 binding activities. The influence of these variations was further revealed by the MM/PBSA energy estimations coupled with per-residue energy decomposition which monitored the systematic binding of the compound. Furthermore, relative high-affinity interactions occurred at the CpIMPDH NAD⁺ site which were majorly mediated by SER22, VAL24, PRO26, SER354, GLY357, and TYR358 located on chain D. These residues are unique to the parasite IMPDH form and not in the eukaryotic protein, highlighting variations that account for preferential P131 binding. Molecular insights provided herein corroborate previous experimental reports and further underpin the basis of CpIMPDH inhibitor selectivity. Findings from this study could present attractive prospects toward the design of novel anticryptosporidials with improved selectivity and binding affinity against parasitic targets.

Necessity of Bumped Kinase Inhibitor Gastrointestinal Exposure in Treating Cryptosporidium Infection

There is a substantial need for novel therapeutics to combat the widespread impact caused by Crytosporidium infection. However, there is a lack of knowledge as to which drug pharmacokinetic (PK) characteristics are key to generate an in vivo response, specifically whether systemic drug exposure is crucial for in vivo efficacy. To identify which PK properties are correlated with in vivo efficacy, we generated physiologically based PK models to simulate systemic and gastrointestinal drug concentrations for a series of bumped kinase inhibitors (BKIs) that have nearly identical in vitro potency against Cryptosporidium but display divergent PK properties. When BKI concentrations were used to predict in vivo efficacy with a neonatal model of Cryptosporidium infection, these concentrations in the large intestine were the sole predictors of the observed in vivo efficacy. The significance of large intestinal BKI exposure for predicting in vivo efficacy was further supported with an adult mouse model of Cryptosporidium infection. This study suggests that drug exposure in the large intestine is essential for generating a superior in vivo response, and that physiologically based PK models can assist in the prioritization of leading preclinical drug candidates for in vivo testing.

Bumped-Kinase Inhibitors for Cryptosporidiosis Therapy

Bumped kinase inhibitors (BKIs) of Cryptosporidium parvum calcium-dependent protein kinase 1 (CpCDPK1) are leading candidates for treatment of cryptosporidiosis-associated diarrhea. Potential cardiotoxicity related to anti-human ether-à-go-go potassium channel (hERG) activity of the first-generation anti-Cryptosporidium BKIs triggered further testing for efficacy. A luminescence assay adapted for high-throughput screening was used to measure inhibitory activities of BKIs against C. parvum in vitro. Furthermore, neonatal and interferon γ knockout mouse models of C. parvum infection identified BKIs with in vivo activity. Additional iterative experiments for optimum dosing and selecting BKIs with minimum levels of hERG activity and frequencies of other safety liabilities included those that investigated mammalian cell cytotoxicity, C. parvum proliferation inhibition in vitro, anti-human Src inhibition, hERG activity, in vivo pharmacokinetic data, and efficacy in other mouse models. Findings of this study suggest that fecal concentrations greater than parasite inhibitory concentrations correlate best with effective therapy in the mouse model of cryptosporidiosis, but a more refined model for efficacy is needed.

Effect of Egyptian propolis on cryptosporidiosis in immunosuppressed rats with special emphasis on oocysts shedding, leukogram, protein profile and ileum histopathology

OBJECTIVES

To investigate the activity of Egyptian propolis extracts (ethanol and water) on cryptosporidiosis in experimentally infected dexamethasone-immunosuppressed rats.

METHODS

A total of 180 male rats (190-220) g BWt were randomly divided into 9 equal groups (G1-G9). Groups of rats were kept as (G1): normal control, (G2-G9): immunosuppressed with dexamethasone and (G3-G9): infected with Cryptosporidium oocysts. Rats from (G4-G9) were given orally ethanol and water extract of propolis (at a dose of 50 mg/kg BWt) and nitazoxanide (standard anti-cryptosporidial drug at a dose of 100 mg/kg BWt) to infected rats with different regimes. Faecal pellets were collected from all groups to monitor oocysts shedding from the 2nd to the 15th day post infection. At the end of the experiment, blood was collected from all groups for determination of leukogram and serum proteins. Ileum specimens were also examined histopathologically.

RESULTS

The highest reduction of oocysts shedding in faecal samples was 88% in rats prophylactically treated with propolis ethanol extract at the 4th dpi, and in rats prophylactically treated with water extract of propolis, was 91% at the 6th dpi. There was a marked increase in neutrophils count and α₂- and β-globulins levels in infected rats treated with both extracts, while a significant decrease was detected in lymphocytes compared to the infected non treated group. β-Globulin level markedly increased in the rats administered nitazoxanide. Histopathological changes were observed in the ileum of rats infected with Cryptosporidium.

CONCLUSIONS

Egyptian propolis extracts have an activity on cryptosporidiosis in rats. Moreover, propolis modulated the immunity in dexamethasone-immunosuppressed rats.

Cryptosporidiosis in a buffalo calf at Meerut, Uttar Pradesh and its successful therapeutic management

Cryptosporidium spp. are recognized as one of the most important enteric pathogens causing enteritis and severe diarrhoea in calves up to 1 month of age. Although the infection may be responsible for some mortality, its impact is mainly associated with the impairment of gastrointestinal functions and lower performance of animals. A female buffalo calf of 25 days old was presented to OPD section, College of Veterinary and Animal Sciences, SVPUA&T, Meerut, with the symptoms of severe voluminous watery cholera like diarrhea with mucous and blood tinge since 4-5 days. On physical examination, calf was dehydrated, weak, and emaciated with normal temperature. Parasitological examination of the faeces by the direct smear and modified Ziehl-Neelsen staining technique revealed presence of high number of Cryptosporidium spp. oocysts. The affected female buffalo calf was treated with azithromycin and provided supportive care. Diarrohoeal symptoms were stopped from 3rd day and animal returned to normal condition by 7th day post treatment.

Serological detection and epidemiology of Neospora caninum and Cryptosporidium parvum antibodies in cattle in southern Egypt

Neospora caninum and Cryptosporidium parvum are intracellular protozoan parasites that are distributed worldwide and of major economical concern in cattle industry. N. caninum can cause abortion storms and high culling rates, whereas C. parvum has zoonotic implications and can cause diarrhea in calves. There are currently no data on the prevalence of neosporosis and cryptosporidiosis in humans or animals in southern Egypt. Prevalence of these two infections was determined in a sample of cattle from two different areas in southern Egypt, Sohag and Qena, using enzyme-linked immunosorbent assay. A total 301 cattle were sampled, of which 18.9% were positive for N. caninum, 35.9% were positive for C. parvum and 10.0% were positive for both. Geographical location and breeding system were considered as potential risk factors for C. parvum infection. A higher prevalence of infection was identified on small scale farms, compared with larger, intensive systems, with a prevalence of 50.2% compared with 37.8%, respectively. Animals in Sohag had a significantly higher prevalence compared with Qena, with a seroprevalence of 46.1% compared with 31.6%, respectively. In brief, marked seroprevalence recorded in this study indicates a high incidence of N. caninum and C. parvum infections in cattle, and this necessitates the application of more effective strategies for combating these types of infections on farms in Egypt.

Parasitic diarrheal disease: drug development and targets

Diarrhea is the manifestation of gastrointestinal infection and is one of the major causes of mortality and morbidity specifically among the children of less than 5 years age worldwide. Moreover, in recent years there has been a rise in the number of reports of intestinal infections continuously in the industrialized world. These are largely related to waterborne and food borne outbreaks. These occur by the pathogenesis of both prokaryotic and eukaryotic organisms like bacteria and parasites. The parasitic intestinal infection has remained mostly unexplored and under assessed in terms of therapeutic development. The lack of new drugs and the risk of resistance have led us to carry out this review on drug development for parasitic diarrheal diseases. The major focus has been depicted on commercially available drugs, currently synthesized active heterocyclic compounds and unique drug targets, that are vital for the existence and growth of the parasites and can be further exploited for the search of therapeutically active anti-parasitic agents.

Binding mode of inhibitors and Cryptosporidium parvum IMP dehydrogenase: A combined ligand- and receptor-based study

A combined ligand- and target-based approach was used to analyse the interaction models of Cryptosporidium parvum inosine 5'-monophosphate dehydrogenase (CpIMPDH) with selective inhibitors. First, a ligand-based pharmacophore model was generated from 20 NAD(+) competitive CpIMPDH inhibitors with the HipHop module. The characteristic of the NAD(+) binding site of CpIMPDH was then described, and the binding modes of the representative inhibitors were studied by molecular docking. The combination of the pharmacophore model and the docking results allowed us to evaluate the pharmacophore features and structural information of the NAD(+) binding site of CpIMPDH. This research supports the proposal of an interaction model inside the NAD(+) binding site of CpIMPDH, consisting of four key interaction points: two hydrophobic-aromatic groups, a hydrophobic-aliphatic group and a hydrogen bond donor. This study also provides guidance for the design of more potent CpIMPDH inhibitors for the treatment of Cryptosporidium infections.

Three-dimensional structures in the design of therapeutics targeting parasitic protozoa: reflections on the past, present and future

Parasitic protozoa cause a range of diseases which threaten billions of human beings. They are responsible for tremendous mortality and morbidity in the least-developed areas of the world. Presented here is an overview of the evolution over the last three to four decades of structure-guided design of inhibitors, leads and drug candidates aiming at targets from parasitic protozoa. Target selection is a crucial and multi-faceted aspect of structure-guided drug design. The major impact of advances in molecular biology, genome sequencing and high-throughput screening is touched upon. The most advanced crystallographic techniques, including XFEL, have already been applied to structure determinations of drug targets from parasitic protozoa. Even cryo-electron microscopy is contributing to our understanding of the mode of binding of inhibitors to parasite ribosomes. A number of projects have been selected to illustrate how structural information has assisted in arriving at promising compounds that are currently being evaluated by pharmacological, pharmacodynamic and safety tests to assess their suitability as pharmaceutical agents. Structure-guided approaches are also applied to incorporate properties into compounds such that they are less likely to become the victim of resistance mechanisms. A great increase in the number of novel antiparasitic compounds will be needed in the future. These should then be combined into various multi-compound therapeutics to circumvent the diverse resistance mechanisms that render single-compound, or even multi-compound, drugs ineffective. The future should also see (i) an increase in the number of projects with a tight integration of structural biology, medicinal chemistry, parasitology and pharmaceutical sciences; (ii) the education of more `medicinal structural biologists' who are familiar with the properties that compounds need to have for a high probability of success in the later steps of the drug-development process; and (iii) the expansion of drug-development capabilities in middle- and low-income countries.

A nanotherapy strategy significantly enhances anticryptosporidial activity of an inhibitor of bifunctional thymidylate synthase-dihydrofolate reductase from Cryptosporidium

Cryptosporidiosis, a gastrointestinal disease caused by protozoans of the genus Cryptosporidium, is a common cause of diarrheal diseases and often fatal in immunocompromised individuals. Bifunctional thymidylate synthase-dihydrofolate reductase (TS-DHFR) from Cryptosporidium hominis (C. hominis) has been a molecular target for inhibitor design. C. hominis TS-DHFR inhibitors with nM potency at a biochemical level have been developed however drug delivery to achieve comparable antiparasitic activity in Cryptosporidium infected cell culture has been a major hurdle for designing effective therapies. Previous mechanistic and structural studies have identified compound 906 as a nM C. hominis TS-DHFR inhibitor in vitro, having μM antiparasitic activity in cell culture. In this work, proof of concept studies are presented using a nanotherapy approach to improve drug delivery and the antiparasitic activity of 906 in cell culture. We utilized PLGA nanoparticles that were loaded with 906 (NP-906) and conjugated with antibodies to the Cryptosporidium specific protein, CP2, on the nanoparticle surface in order to specifically target the parasite. Our results indicate that CP2 labeled NP-906 (CP2-NP-906) reduces the level of parasites by 200-fold in cell culture, while NP-906 resulted in 4.4-fold decrease. Moreover, the anticryptosporidial potency of 906 improved 15 to 78-fold confirming the utility of the antibody conjugated nanoparticles as an effective drug delivery strategy.

Synthesis, in vitro evaluation and cocrystal structure of 4-oxo-[1]benzopyrano[4,3-c]pyrazole Cryptosporidium parvum inosine 5'-monophosphate dehydrogenase (CpIMPDH) inhibitors

Cryptosporidium inosine 5′-monophosphate dehydrogenase (CpIMPDH) has emerged as a therapeutic target for treating Cryptosporidium parasites because it catalyzes a critical step in guanine nucleotide biosynthesis. A 4-oxo-[1]benzopyrano[4,3-c]pyrazole derivative was identified as a moderately potent (IC₅₀ = 1.5 μM) inhibitor of CpIMPDH. We report a SAR study for this compound series resulting in 8k (IC₅₀ = 20 ± 4 nM). In addition, an X-ray crystal structure of CpIMPDH·IMP·8k is also presented.

Cryptosporidium parvum has an active hypusine biosynthesis pathway

The protozoan parasite Cryptosporidium parvum causes severe enteric infection and diarrheal disease with substantial morbidity and mortality in untreated AIDS patients and children in developing or resource-limited countries. No fully effective treatment is available. Hypusination of eIF5A is an important post-translational modification essential for cell proliferation. This modification occurs in a two step process catalyzed by deoxyhypusine synthase (DHS) followed by deoxyhypusine hydroxylase. An ORF of 1086bp was identified in the C. parvum (Cp) genome which encodes for a putative polypeptide of 362 amino acids. The recombinant CpDHS protein was purified to homogeneity and used to probe the enzyme's mechanism, structure, and inhibition profile in a series of kinetic experiments. Sequence analysis and structural modeling of CpDHS were performed to probe differences with respect to the DHS of other species. Unlike Leishmania, Trypanosomes and Entamoeba, Cryptosporidium contains only a single gene for DHS. Phylogenetic analysis shows that CpDHS is more closely related to apicomplexan DHS than kinetoplastid DHS. Important residues that are essential for the functioning of the enzyme including NAD(+) binding residues, spermidine binding residues and the active site lysine are conserved between CpDHS and human DHS. N(1)-guanyl-1,7-diaminoheptane (GC7), a potent inhibitor of DHS caused an effective inhibition of infection and growth of C. parvum in HCT-8 cells.

A review of chemotherapeutic approaches to the treatment of cryptosporidiosis

This review focuses on chemotherapies used against the parasite, Cryptosporidium parvum, the causative agent of cryptosporidiosis. Populations at risk from severe morbidity or mortality from cryptosporidiosis are discussed with particular reference to those infected with HIV. The review then examines chemotherapies used in the clinical setting, as well as a number of in vitro and in vivo experimental studies. It begins with a discussion of the targets within Cryptosporidium that have been the foci of past treatments and then examines novel target sites that may present an exploitable alternative. Some of the novel target sites discussed include the recently discovered apicomplexan plastid and its associated pathways. Lastly, the review examines tubulin as a potential anticryptosporidial target in view of the fact that it has been exploited successfully for almost 50 years for the treatment of helminthiasis. The review concludes with a five-year outlook on the future of anticryptosporidial drug design.

Present and future control of cryptosporidiosis in humans and animals

Although water treatment processes to remove Cryptosporidium are improving and detection methods for identifying the parasite in water are becoming more sensitive, outbreaks of cryptosporidiosis continue in the human population. Animals, especially dairy calves, often become infected as C. parvum oocysts are present in high numbers, remain viable for long periods of time after excretion and no disinfectants, prophylactic or therapeutic reagents exist. Vaccination against C. parvum is being attempted in ruminants for the purpose of generating hyperimmune colostrum containing antibodies that may be effective in passive immunotherapy against cryptosporidiosis in the young. A number of recombinant C. parvum surface or internal antigens have been expressed by DNA-cloning technology. Immune colostrum specific for several recombinant C. parvum proteins have demonstrated efficacy in murine and ruminant models against cryptosporidiosis. The P23 and CP15 antigens appear to be the most promising candidates for vaccine development. Recent studies have demonstrated efficacy of the drug nitazoxanide against C. parvum infection in humans. In the near future, control of this parasitic disease in humans and animals will rely on a combination of passive immunotherapy and selective drug treatment.

A cysteine protease inhibitor rescues mice from a lethal Cryptosporidium parvum infection

Cryptosporidiosis, caused by the protozoan parasite Cryptosporidium parvum, can stunt infant growth and can be lethal in immunocompromised individuals. The most widely used drugs for treating cryptosporidiosis are nitazoxanide and paromomycin, although both exhibit limited efficacy. To investigate an alternative approach to therapy, we demonstrate that the clan CA cysteine protease inhibitor N-methyl piperazine-Phe-homoPhe-vinylsulfone phenyl (K11777) inhibits C. parvum growth in mammalian cell lines in a concentration-dependent manner. Further, using the C57BL/6 gamma interferon receptor knockout (IFN-γR-KO) mouse model, which is highly susceptible to C. parvum, oral or intraperitoneal treatment with K11777 for 10 days rescued mice from otherwise lethal infections. Histologic examination of untreated mice showed intestinal inflammation, villous blunting, and abundant intracellular parasite stages. In contrast, K11777-treated mice (210 mg/kg of body weight/day) showed only minimal inflammation and no epithelial changes. Three putative protease targets (termed cryptopains 1 to 3, or CpaCATL-1, -2, and -3) were identified in the C. parvum genome, but only two are transcribed in infected mammals. A homology model predicted that K11777 would bind to cryptopain 1. Recombinant enzymatically active cryptopain 1 was successfully targeted by K11777 in a competition assay with a labeled active-site-directed probe. K11777 exhibited no toxicity in vitro and in vivo, and surviving animals remained free of parasites 3 weeks after treatment. The discovery that a cysteine protease inhibitor provides potent anticryptosporidial activity in an animal model of infection encourages the investigation and development of this biocide class as a new, and urgently needed, chemotherapy for cryptosporidiosis.

Optimization of benzoxazole-based inhibitors of Cryptosporidium parvum inosine 5'-monophosphate dehydrogenase

Cryptosporidium parvum is an enteric protozoan parasite that has emerged as a major cause of diarrhea, malnutrition, and gastroenteritis and poses a potential bioterrorism threat. C. parvum synthesizes guanine nucleotides from host adenosine in a streamlined pathway that relies on inosine 5'-monophosphate dehydrogenase (IMPDH). We have previously identified several parasite-selective C. parvum IMPDH (CpIMPDH) inhibitors by high-throughput screening. In this paper, we report the structure-activity relationship (SAR) for a series of benzoxazole derivatives with many compounds demonstrating CpIMPDH IC50 values in the nanomolar range and >500-fold selectivity over human IMPDH (hIMPDH). Unlike previously reported CpIMPDH inhibitors, these compounds are competitive inhibitors versus NAD(+). The SAR study reveals that pyridine and other small heteroaromatic substituents are required at the 2-position of the benzoxazole for potent inhibitory activity. In addition, several other SAR conclusions are highlighted with regard to the benzoxazole and the amide portion of the inhibitor, including preferred stereochemistry. An X-ray crystal structure of a representative E·IMP·inhibitor complex is also presented. Overall, the secondary amine derivative 15a demonstrated excellent CpIMPDH inhibitory activity (IC50 = 0.5 ± 0.1 nM) and moderate stability (t1/2 = 44 min) in mouse liver microsomes. Compound 73, the racemic version of 15a, also displayed superb antiparasitic activity in a Toxoplasma gondii strain that relies on CpIMPDH (EC50 = 20 ± 20 nM), and selectivity versus a wild-type T. gondii strain (200-fold). No toxicity was observed (LD50 > 50 μM) against a panel of four mammalian cells lines.

Genetic mapping and coccidial parasites: past achievements and future prospects

Coccidial parasites including Cryptosporidium parvum, Cyclospora cayetanensis, Neospora caninum, Toxoplasma gondii and the Eimeria species can cause severe disease of medical and veterinary importance. As many as one-third of the human population may carry T. gondii infection, and Eimeria are thought to cost the global poultry production industry in excess of US$2 billion per annum. Despite their significance, effective vaccines are scarce and have been confined to the veterinary field. As sequencing and genotyping technologies continue to develop, genetic mapping remains a valuable tool for the identification of genes that underlie phenotypic traits of interest and the assembly of contiguous genome sequences. For the coccidian, cross-fertilization still requires in vivo infection, a feature of their life cycle which limits the use of genetic mapping strategies. Importantly, the development of population-based approaches has now removed the need to isolate clonal lines for genetic mapping of selectable traits, complementing the classical clone-based techniques. To date, four coccidial species, representing three genera, have been investigated using genetic mapping. In this review we will discuss recent progress with these species and examine the prospects for future initiatives.

Description of fecal shedding of Cryptosporidium parvum oocysts in experimentally challenged dairy calves

The objective was to describe the probability of Cryptosporidium parvum fecal oocyst shedding at different magnitudes of exposure, the pattern of fecal shedding over time, and factors affecting fecal shedding in dairy calves. Within the first 24 h of life, 36 calves were experimentally challenged with C. parvum oocysts at one of four possible magnitudes of oral exposure (1 × 10³, 1 × 10⁴, 1 × 10⁵, and 1 × 10⁶ oocysts), and 7 control calves were sham dosed. Fecal shedding occurred in 33 (91.7 %) experimentally challenged calves and in none of the control calves. There was a difference in the log-total number of oocysts counted per gram of feces dry weight among the four exposure groups; calves with the lowest magnitude of exposure (1 × 10³ oocysts) shed less than the other three groups. At higher magnitudes of exposure, there was more variability in the range of fecal oocyst shedding. There was an inverse relationship between the log-total amount of oocysts counted per gram of feces dry weight and the number of days to the onset of fecal shedding per calf, i.e., the more time that elapsed to the onset of fecal shedding, the fewer oocysts that were shed. The pattern of fecal shedding over time for all calves shedding oocysts was curvilinear; the number of oocysts increased with time, reached a peak, and declined. Therefore, the dynamics of oocyst shedding can be influenced in part by limiting exposure among calves and delaying the onset of fecal oocyst shedding.

Exploring novel strategies for AIDS protozoal pathogens: α-helix mimetics targeting a key allosteric protein-protein interaction in C. hominis TS-DHFR

The bifunctional enzyme thymidylate synthase-dihydrofolate reductase (TS-DHFR) from the protozoal parasite Cryptosporidium hominis is a potential molecular target for the design of antiparasitic therapies for AIDS-related opportunistic infections. The enzyme exists as a homodimer with each monomer containing a unique swap domain known as a "crossover helix" that binds in a cleft on the adjacent DHFR active site. This crossover helix is absent in species containing monofunctional forms of DHFR such as human. An in-depth understanding of protein-protein interactions between the crossover helix and adjacent DHFR active site that might modulate enzyme integrity or function would allow for insights into rational design of species-specific allosteric inhibitors. Mutational analysis coupled with structural studies and biophysical and kinetic characterization of crossover helix mutants identifies this domain as essential for full enzyme stability and catalytic activity, and pinpoints these effects to distinct faces of the crossover helix important in protein-protein interactions. Moreover, targeting this helical protein interaction with α-helix mimetics of the crossover helix leads to selective inhibition and destabilization of the C. hominis TS-DHFR enzyme, thus validating this region as a new avenue to explore for species-specific inhibitor design.

Contamination of irrigation systems of dental units with Cryptosporidium species in Alexandria, Egypt: a neglected disinfection pitfall

PURPOSE

To investigate the contamination of the dental irrigation systems with Cryptosporidium species in Alexandria, Egypt.

METHODS

Forty water samples from all 20 working dental irrigation machines in a dental center in Alexandria were included in the study. Water samples were taken from the handpieces of dental irrigation machines in all studied units. After filtration through a membrane filter, water sample residues were stained using modified Ziehl-Neelsen staining and examined microscopically for Cryptosporidium spp.

RESULTS

Cryptosporidium spp. was found as a contaminant in 27.5% of water samples taken from dental irrigation machines.

CONCLUSION

This indicates a contamination by the public water supplies to which these dental irrigation machines are connected. This disinfection pitfall may pose an infection risk to those seeking dental care.

Analysis of monensin sensitivity in Toxoplasma gondii reveals autophagy as a mechanism for drug induced death

Understanding the mechanisms by which anti-parasitic drugs alter the physiology and ultimately kill is an important area of investigation. Development of novel parasitic drugs, as well as the continued utilization of existing drugs in the face of resistant parasite populations, requires such knowledge. Here we show that the anti-coccidial drug monensin kills Toxoplasma gondii by inducing autophagy in the parasites, a novel mechanism of cell death in response to an antimicrobial drug. Monensin treatment results autophagy, as shown by translocation of ATG8 to autophagosomes, as well as causing marked morphological changes in the parasites' mitochondria. Use of the autophagy inhibitor 3-methyladenine blocks autophagy and mitochondrial alterations, and enhances parasite survival, in monensin-exposed parasites, although it does not block other monensin-induced effects on the parasites, such as late S-phase cell cycle arrest. Monensin does not induce autophagy in a parasite strain deficient in the mitochondrial DNA repair enzyme TgMSH-1 an enzyme that mediates monensin-induced late S-phase arrest. TgMSH-1 therefore either mediates cell cycle arrest and autophagy independently, or autophagy occurs downstream of cell cycle arrest in a manner analogous to apoptosis of cells arrested in G₂ of the cell cycle. Overall, our results point to autophagy as a potentially important mode of cell death of protozoan parasites in response to antimicrobial drugs and indicate that disruption of the autophagy pathway could result in drug resistance.

Drug combination therapy in control of cryptosporidiosis in Ludhiana district of Punjab

The present report describes outbreak of cryptosporidiosis in neonatal cross bred cattle calves ageing 1–2 months in an organized dairy farm. The protozoan infection was confirmed by identifying bright red oocysts of Cryptosporidium spp. in the faecal samples after staining with modified acid Fast Zeihl–Neelsen stain. Metronidazole and furazolidone combination was able to induce clinically and parasitological recovery. This is believed to be the first report on the successful use of this drug combination against cryptosporidiosis.

Novel anti-Cryptosporidium activity of known drugs identified by high-throughput screening against parasite fatty acyl-CoA binding protein (ACBP)

BACKGROUND

Cryptosporidium parvum causes an opportunistic infection in AIDS patients, and no effective treatments are yet available. This parasite possesses a single fatty acyl-CoA binding protein (CpACBP1) that is localized to the unique parasitophorous vacuole membrane (PVM). The major goal of this study was to identify inhibitors from known drugs against CpACBP1 as potential new anti-Cryptosporidium agents.

METHODS

A fluorescence assay was developed to detect CpACBP1 activity and to identify inhibitors by screening known drugs. Efficacies of top CpACBP1 inhibitors against Cryptosporidium growth in vitro were evaluated using a quantitative RT-PCR assay.

RESULTS

Nitrobenzoxadiazole-labelled palmitoyl-CoA significantly increased the fluorescent emission upon binding to CpACBP1 (excitation/emission 460/538 nm), which was quantified to determine the CpACBP1 activity and binding kinetics. The fluorescence assay was used to screen a collection of 1040 compounds containing mostly known drugs, and identified the 28 most active compounds that could inhibit CpACBP1 activity with sub-micromolar IC(50) values. Among them, four compounds displayed efficacies against parasite growth in vitro with low micromolar IC(50) values. The effective compounds were broxyquinoline (IC(50) 64.9 μM), cloxyquin (IC(50) 25.1 μM), cloxacillin sodium (IC(50) 36.2 μM) and sodium dehydrocholate (IC(50) 53.2 μM).

CONCLUSIONS

The fluorescence ACBP assay can be effectively used to screen known drugs or other compound libraries. Novel anti-Cryptosporidium activity was observed in four top CpACBP1 inhibitors, which may be further investigated for their potential to be repurposed to treat cryptosporidiosis and to serve as leads for drug development.

ABC transporters involved in drug resistance in human parasites

The ABC (ATP-binding cassette) protein superfamily is a ubiquitous and functionally versatile family of proteins that is conserved from archaea to humans. In eukaryotes, most of these proteins are implicated in the transport of a variety of molecules across cellular membranes, whereas the remaining ones are involved in biological processes unrelated to transport. The biological functions of several ABC proteins have been described in clinically important parasites and nematode worms and include vesicular trafficking, phospholipid movement, translation and drug resistance. This chapter reviews our current understanding of the role of ABC proteins in drug resistance and treatment failure in apicomplexan, trypanosomatid and amitochondriate parasites of medical relevance as well as in helminths.

Structure of triosephosphate isomerase from Cryptosporidium parvum

Cryptosporidium parvum is one of several Cryptosporidium spp. that cause the parasitic infection cryptosporidiosis. Cryptosporidiosis is a diarrheal infection that is spread via the fecal-oral route and is commonly caused by contaminated drinking water. Triosephosphate isomerase is an enzyme that is ubiquitous to all organisms that perform glycolysis. Triosephosphate isomerase catalyzes the formation of glyceraldehyde 3-phosphate from dihydroxyacetone phosphate, which is a critical step to ensure the maximum ATP production per glucose molecule. In this paper, the 1.55 Å resolution crystal structure of the open-loop form of triosephosphate isomerase from C. parvum Iowa II is presented. An unidentified electron density was found in the active site.

Molecular analysis of Cryptosporidium parvum HNJ-1 isolated in Japan

Cryptosporidium parvum HNJ-1 is widely used as a reference strain in Japan. In the present study, the parasite was subjected for further molecular analysis including transcribed ribosomal region (ITS rRNA), dihydrofolate reductase (DHFR) and surface glycoprotein (GP60) genes. Partial sequence analysis of these genes indicated extensive polymorphism in ITS region compared with relevant sequences of other Cryptosporidium parvum isolates. In addition, this strain was identified as C. parvum IIaA15G2R1 subtype, based on the sequence results of GP60 gene locus.

Cryptosporidiosis in people: it's not just about the cows

Cryptosporidiosis is one of the most common causes of infectious diarrhea in people. Although dairy calves are high-risk hosts, the role of other livestock, pets, and humans in the disease should not be underestimated. Some Cryptosporidium species and strains are specific to people, others are specific to animals while some are zoonotic pathogens. Cryptosporidium hominis is the species responsible for the majority of human cases in the United States, Sub-Saharan Africa, and Asia, while Cryptosporidium parvum accounts for more human cases in Europe and particularly in the United Kingdom. A deeper understanding of Cryptosporidium host range, reservoirs, and transmission is needed to develop preventive strategies to protect the general public.

Prodrug activation by Cryptosporidium thymidine kinase

Cryptosporidium spp. cause acute gastrointestinal disease that can be fatal for immunocompromised individuals. These protozoan parasites are resistant to conventional antiparasitic chemotherapies and the currently available drugs to treat these infections are largely ineffective. Genomic studies suggest that, unlike other protozoan parasites, Cryptosporidium is incapable of de novo pyrimidine biosynthesis. Curiously, these parasites possess redundant pathways to produce dTMP, one involving thymidine kinase (TK) and the second via thymidylate synthase-dihydrofolate reductase. Here we report the expression and characterization of TK from C. parvum. Unlike other TKs, CpTK is a stable trimer in the presence and absence of substrates and the activator dCTP. Whereas the values of k(cat) = 0.28 s(-1) and K(m)(,ATP) = 140 microm are similar to those of human TK1, the value of K(m)(thymidine) = 48 microm is 100-fold greater, reflecting the abundance of thymidine in the gastrointestinal tract. Surprisingly, the antiparasitic nucleosides AraT, AraC, and IDC are not substrates for CpTK, indicating that Cryptosporidium possesses another deoxynucleoside kinase. Trifluoromethyl thymidine and 5-fluorodeoxyuridine are good substrates for CpTK, and both compounds inhibit parasite growth in an in vitro model of C. parvum infection. Trifluorothymidine is also effective in a mouse model of acute disease. These observations suggest that CpTK-activated pro-drugs may be an effective strategy for treating cryptosporidiosis.

DNA topoisomerases in apicomplexan parasites: promising targets for drug discovery

The phylum Apicomplexa includes a large group of protozoan parasites responsible for a wide range of animal and human diseases. Destructive pathogens, such as Plasmodium falciparum and Plasmodium vivax, causative agents of human malaria, Cryptosporidium parvum, responsible of childhood diarrhoea, and Toxoplasma gondii, responsible for miscarriages and abortions in humans, are frequently associated with HIV immunosuppression in AIDS patients. The lack of effective vaccines, along with years of increasing pressure to eradicate outbreaks with the use of drugs, has favoured the formation of multi-drug resistant strains in endemic areas. Almost all apicomplexan of medical interest contain two endosymbiotic organelles that contain their own mitochondrial and apicoplast DNA. Apicoplast is an attractive target for drug testing because in addition to harbouring singular metabolic pathways absent in the host, it also has its own transcription and translation machinery of bacterial origin. Accordingly, apicomplexan protozoa contain an interesting mixture of enzymes to unwind DNA from eukaryotic and prokaryotic origins. On the one hand, the main mechanism of DNA unwinding includes the scission of one-type I-or both DNA strands-type II eukaryotic topoisomerases, establishing transient covalent bonds with the scissile end. These enzymes are targeted by camptothecin and etoposide, respectively, two natural drugs whose semisynthetic derivatives are currently used in cancer chemotherapy. On the other hand, DNA gyrase is a bacterial-borne type II DNA topoisomerase that operates within the apicoplast and is effectively targeted by bacterial antibiotics like fluoroquinolones and aminocoumarins. The present review is an update on the new findings concerning topoisomerases in apicomplexan parasites and the role of these enzymes as targets for therapeutic agents.

Genetic richness and diversity in Cryptosporidium hominis and C. parvum reveals major knowledge gaps and a need for the application of "next generation" technologies--research review

Cryptosporidium species (apicomplexan protists) are a major cause of diarrhoeal disease (= cryptosporidiosis) in humans worldwide. The impact of cryptosporidiosis is also compounded by the spread of HIV/AIDS and a lack of cost-effective anti-cryptosporidial chemotherapeutics or vaccines. Mitigation of the impact of cryptosporidiosis in humans needs to focus on prevention and control strategies, built on a sound understanding of the epidemiology of Cryptosporidium species. Refined epidemiological studies rely on the use of molecular tools employing informative genetic markers. Currently, the 60-kDa glycoprotein gene (gp60) is the most suitable and widely used genetic marker for Cryptosporidium species infecting humans. Here, we undertake an analysis of all publicly-available gp60 sequence data and associated literature for C. hominis and C. parvum, and yield useful insights into the richness, diversity and distribution of genetic variants, and link these variants to human cryptosporidiosis. This global analysis reveals that, despite high genetic richness in Cryptosporidium isolates from humans, there is a surprisingly low diversity. It also highlights limited knowledge about the genetics of cryptosporidiosis in developing nations and in many animals that might act as infection sources. Clearly, there is a major need for more comprehensive studies of Cryptosporidium infecting humans and other animals in Africa and Asia. As molecular technologies improve and become affordable, future studies should utilize "next generation" sequencing and bioinformatic platforms to conduct comparative 'genome sequence surveys' to test the validity of current genetic classifications based on gp60 data. Complemented by in vitro and in vivo investigations, these biotechnological advances will also assist significantly in the search for new intervention strategies against human cryptosporidiosis.

Functional expression of a DNA-topoisomerase IB from Cryptosporidium parvum

Cryptosporidium parvum, one of the most important causative organisms of human diarrheas during childhood, contains a monomeric DNA-topoisomerase IB (CpTopIB) in chromosome 7. Heterologous expression of CpTopIB gene in a budding yeast strain lacking this activity proves that the cryptosporidial enzyme is functional in vivo. The enzymatic activity is comprised in a single polypeptide, which contains all the structural features defining a fully active TopIB. Relaxation activity of the yeast extracts was detected only when CpTopIB ORF was expressed in a yeast expression system showing time and protein dependence under steady state kinetic conditions. The susceptibility of CpTopIB-transformed yeast to the irreversible inhibitor camptothecin and its water-soluble derivatives (topotecan and SN-38) was assessed.

Functional characterization of the nucleotide binding domain of the Cryptosporidium parvum CpABC4 transporter: an iron-sulfur cluster transporter homolog

In a previous study, we showed that the Cryptosporidium parvum ATP half-transporter CpABC4 (cgd1_1350) transcript was up-regulated in response to drug treatment with paromomycin and cyclosporine A in an in vitro infection model. CpABC4 may be directly or indirectly involved in the metabolic interactions between host and parasite in response to drug treatment and/or be involved in the intrinsic resistance to chemotherapy. In order to characterize the catalytic site of this transporter, an extended region of the nucleotide-binding domain of CpABC4 (H6-1350NBD) was expressed and purified as an N-terminal hexahistidine-tagged protein in E. coli. The presence of a single tryptophan residue enabled the intrinsic fluorescence to be monitored in response to binding of different compounds. A dose-dependent quenching of the domain's intrinsic fluorescence was observed with its natural substrate, ATP and the fluorescent analogue TNP-ATP. A similar effect was observed with progesterone as well as the flavonoids quercetin and silibinin, previously shown to inhibit parasite development in a cell-based assay. The purified domain also exhibited ATPase activity in the nanomolar range, which further confirmed correct folding and activity of the recombinant domain. The H6-1350NBD serves as a tool to test and design stereospecific inhibitors of the catalytic site, as well as other compounds that bind elsewhere in the domain that may indirectly interact with the catalytic site of the NBD of the CpABC4 transporter.

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.

An apicomplexan ankyrin-repeat histone deacetylase with relatives in photosynthetic eukaryotes

Cryptosporidium parvum is a member of the Apicomplexa that lacks a plastid and associated nuclear-encoded genes, which has hampered its use in evolutionary comparisons with algae and eliminated a pool of potentially useful drug targets. Here we show that apicomplexan parasites possess an unusual family of class II histone deacetylase (HDAC) proteins with orthologues that are present in other chromalveolates and primitive algae. A striking feature of these HDAC proteins is the presence of ankyrin repeats in the amino-terminus that appear to be required for enzyme activity. In vitro and in vivo analyses of the C. parvum orthologue indicate that this subclass of chromatin-remodelling proteins is targeted by the anti-cancer drug suberoylanilide hydroxamic acid and that these proteins are most likely involved in the essential process of H4 histone deacetylation that coincides with DNA replication. We propose that members of this novel class of histone deacetylase can serve as promising new targets for treatments against debilitating diseases such as cryptosporidosis, toxoplasmosis and malaria.

Novel non-active site inhibitor of Cryptosporidium hominis TS-DHFR identified by a virtual screen

The essential enzyme thymidylate synthase-dihydrofolate reductase (TS-DHFR) is a validated drug target for many pathogens, but has been elusive in Cryptosporidium hominis, as active site inhibitors of the enzymes from related parasitic protozoa show decreased potency and lack of species specificity over the human enzymes. As a rational approach to discover novel inhibitors, we conducted a virtual screen of a non-active site pocket in the DHFR linker region. From this screen, we have identified and characterized a noncompetitive inhibitor, flavin mononucleotide (FMN), with micromolar potency that is selective for ChTS-DHFR versus the human enzymes. These results describe a novel allosteric pocket amenable to inhibitor targeting, and a lead compound with which to move towards potent, selective inhibitors of ChTS-DHFR.

High resolution melting-curve (HRM) analysis for the diagnosis of cryptosporidiosis in humans

Cryptosporidiosis of humans is an intestinal disease caused predominantly by infection with Cryptosporidium hominis or C. parvum. This disease is transmitted mainly via the faecal-oral route (water or food) and has major socioeconomic impact globally. The diagnosis and genetic characterization of the main species and population variants (also called "genotypes" and "subgenotypes") of Cryptosporidium infecting humans is central to the prevention, surveillance and control of cryptosporidiosis, particularly as there is presently no cost effective anti-cryptosporidial chemotherapeutic regimen or vaccine available. In the present study, we established a polymerase chain reaction (PCR)-coupled high resolution melting-curve (HRM) analysis method, utilizing the second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA as the genetic marker, for the diagnosis of Cryptosporidium hominis, C. parvum or C. meleagridis infection. An evaluation of the method revealed intra- and inter-assay variabilities of <1.5 and 3.5%, respectively. Cryptosporidium hominis, C. parvum and C. meleagridis were detected in 97, 44 and 2, respectively, of the 143 Cryptosporidium oocyst DNA samples originating from Australians with clinical cryptosporidiosis. The melting profiles characterized by peaks of 72.47+/-0.33 degrees C and 74.19+/-0.45 degrees C (profile 1), 72.17+/-0.32 degrees C (profile 2) and 73.33+/-0.03 degrees C (profile 3) genetically identified as C. hominis, C. parvum and C. meleagridis, respectively. In conclusion, PCR-coupled melting analysis of ITS-2 achieved the diagnosis of Cryptosporidium hominis, C. parvum or C. meleagridis infection. This approach is well suited for the rapid screening of large numbers of Cryptosporidium oocyst DNA samples and, although qualitative, is significantly less time-consuming to carry out than electrophoretic analysis and has the added advantage of data storage and analysis capabilities in silico. This method provides a useful tool for investigating the epidemiology and outbreaks of cryptosporidiosis, and could be applicable to species of Cryptosporidium other than those investigated herein.

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.

Targeting a prokaryotic protein in a eukaryotic pathogen: identification of lead compounds against cryptosporidiosis

Cryptosporidium parvum is an important human pathogen and potential bioterrorism agent. No vaccines exist against C. parvum, the drugs currently approved to treat cryptosporidiosis are ineffective, and drug discovery is challenging because the parasite cannot be maintained continuously in cell culture. Mining the sequence of the C. parvum genome has revealed that the only route to guanine nucleotides is via inosine-5'-monophosphate dehydrogenase (IMPDH). Moreover, phylogenetic analysis suggests that the IMPDH gene was obtained from bacteria by lateral gene transfer. Here we exploit the unexpected evolutionary divergence of parasite and host enzymes by designing a high-throughput screen to target the most diverged portion of the IMPDH active site. We have identified four parasite-selective IMPDH inhibitors that display antiparasitic activity with greater potency than paromomycin, the current gold standard for anticryptosporidial activity.

Cryptosporidium--biotechnological advances in the detection, diagnosis and analysis of genetic variation

Cryptosporidiosis is predominantly a gastrointestinal disease of humans and other animals, caused by various species of protozoan parasites representing the genus Cryptosporidium. This disease, transmitted mainly via the faecal-oral route (in water or food), is of major socioeconomic importance worldwide. The diagnosis and genetic characterization of the different species and population variants (usually recognised as "genotypes" or "subgenotypes") of Cryptosporidium is central to the prevention, surveillance and control of cryptosporidiosis, particularly given that there is presently no broadly applicable treatment regimen for this disease. Although traditional phenotypic techniques have had major limitations in the specific diagnosis of cryptosporidiosis, there have been major advances in the development of molecular analytical and diagnostic tools. This article provides a concise account of Cryptosporidium and cryptosporidiosis, and focuses mainly on recent advances in nucleic acid-based approaches for the diagnosis of cryptosporidiosis and analysis of genetic variation within and among species of Cryptosporidium. These advances represent a significant step toward an improved understanding of the epidemiology as well as the prevention and control of cryptosporidiosis.