Cryptosporidiosis

Current status and challenges in drug discovery against the globally important zoonotic cryptosporidiosis

The zoonotic cryptosporidiosis is globally distributed, one of the major diarrheal diseases in humans and animals. Cryptosporidium oocysts are also one of the major environmental concerns, making it a pathogen that fits well into the One Health concept. Despite its importance, fully effective drugs are not yet available. Anti-cryptosporidial drug discovery has historically faced many unusual challenges attributed to unique parasite biology and technical burdens. While significant progresses have been made recently, anti-cryptosporidial drug discovery still faces a major obstacle: identification of systemic drugs that can be absorbed by patients experiencing watery diarrhea and effectively pass through electron-dense (ED) band at the parasite-host cell interface to act on the epicellular parasite. There may be a need to develop an in vitro assay to effectively screen hits/leads for their capability to cross ED band. In the meantime, non-systemic drugs with strong mucoadhesive properties for extended gastrointestinal exposure may represent another direction in developing anti-cryptosporidial therapeutics. For developing both systemic and non-systemic drugs, a non-ruminant animal model exhibiting diarrheal symptoms suitable for routine evaluation of drug absorption and anti-cryptosporidial efficacy may be very helpful.

Genetic Diversity of Cryptosporidium hominis in a Bangladeshi Community as Revealed by Whole-Genome Sequencing

We studied the genetic diversity of Cryptosporidium hominis infections in slum-dwelling infants from Dhaka over a 2-year period. Cryptosporidium hominis infections were common during the monsoon, and were genetically diverse as measured by gp60 genotyping and whole-genome resequencing. Recombination in the parasite was evidenced by the decay of linkage disequilibrium in the genome over <300 bp. Regions of the genome with high levels of polymorphism were also identified. Yet to be determined is if genomic diversity is responsible in part for the high rate of reinfection, seasonality, and varied clinical presentations of cryptosporidiosis in this population.

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.

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.

The Burden of Cryptosporidium Diarrheal Disease among Children < 24 Months of Age in Moderate/High Mortality Regions of Sub-Saharan Africa and South Asia, Utilizing Data from the Global Enteric Multicenter Study (GEMS)

Background

The importance of Cryptosporidium as a pediatric enteropathogen in developing countries is recognized.

Methods

Data from the Global Enteric Multicenter Study (GEMS), a 3-year, 7-site, case-control study of moderate-to-severe diarrhea (MSD) and GEMS-1A (1-year study of MSD and less-severe diarrhea [LSD]) were analyzed. Stools from 12,110 MSD and 3,174 LSD cases among children aged <60 months and from 21,527 randomly-selected controls matched by age, sex and community were immunoassay-tested for Cryptosporidium. Species of a subset of Cryptosporidium-positive specimens were identified by PCR; GP60 sequencing identified anthroponotic C. parvum. Combined annual Cryptosporidium-attributable diarrhea incidences among children aged <24 months for African and Asian GEMS sites were extrapolated to sub-Saharan Africa and South Asian regions to estimate region-wide MSD and LSD burdens. Attributable and excess mortality due to Cryptosporidium diarrhea were estimated.

Findings

Cryptosporidium was significantly associated with MSD and LSD below age 24 months. Among Cryptosporidium-positive MSD cases, C. hominis was detected in 77.8% (95% CI, 73.0%-81.9%) and C. parvum in 9.9% (95% CI, 7.1%-13.6%); 92% of C. parvum tested were anthroponotic genotypes. Annual Cryptosporidium-attributable MSD incidence was 3.48 (95% CI, 2.27–4.67) and 3.18 (95% CI, 1.85–4.52) per 100 child-years in African and Asian infants, respectively, and 1.41 (95% CI, 0.73–2.08) and 1.36 (95% CI, 0.66–2.05) per 100 child-years in toddlers. Corresponding Cryptosporidium-attributable LSD incidences per 100 child-years were 2.52 (95% CI, 0.33–5.01) and 4.88 (95% CI, 0.82–8.92) in infants and 4.04 (95% CI, 0.56–7.51) and 4.71 (95% CI, 0.24–9.18) in toddlers. We estimate 2.9 and 4.7 million Cryptosporidium-attributable cases annually in children aged <24 months in the sub-Saharan Africa and India/Pakistan/Bangladesh/Nepal/Afghanistan regions, respectively, and ~202,000 Cryptosporidium-attributable deaths (regions combined). ~59,000 excess deaths occurred among Cryptosporidium-attributable diarrhea cases over expected if cases had been Cryptosporidium-negative.

Conclusions

The enormous African/Asian Cryptosporidium disease burden warrants investments to develop vaccines, diagnostics and therapies.

Cryptosporidium is a protozoan that causes diarrhea and malnutrition in young children in developing countries, and is associated with diarrhea cases and outbreaks in developed countries. To date, limited information exists on the burden of Cryptosporidium diarrheal disease in sub-Saharan Africa and South Asia, where most diarrheal disease deaths occur. We estimated the burden of Cryptosporidium-diarrhea and associated deaths in these regions using data from the Global Enteric Multicenter Study (GEMS). Cryptosporidium was associated with diarrhea mainly in children aged <24 months. Infections began in the first few months of life but clinical episodes of Cryptosporidium-associated diarrhea illness peaked at age 6–11 months. The annual number of Cryptosporidium-attributable diarrhea episodes was estimated at 2.9 and 4.7 million in children aged <24 months in sub-Saharan Africa and in the India/Pakistan/Bangladesh/Afghanistan/Nepal region of South Asia, respectively. In both regions combined, Cryptosporidium is estimated to contribute to approximately 202,000 deaths per year, and to ~59,000 more deaths in Cryptosporidium-attributable cases than if those cases had been negative for Cryptosporidium. Our study highlights the enormous burden attributable to Cryptosporidium in Africa and Asia, which underscores the need for developing vaccines and treatments to reduce this burden.

Prevalence of cryptosporidiosis in renal transplant recipients presenting with acute diarrhea at a single center in Pakistan

Background: Cryptosporidium is an intracellular protozoan organism which causes diarrhea, both in immunocompetent and immunocompromised hosts. Renal transplant recipients are prone to develop a variety of infections including protozoal infections.

Objectives: The aim of this study was to determine the prevalence of cryptosporidiosis in our renal transplant recipients presenting with acute diarrhea.

Patients and Methods: During six months of the study, 644 renal transplant recipients presented with acute diarrhea. Single stool sample was obtained for detailed analysis including gross and microscopic examination for red blood cells, pus cells, ova, cysts, and protozoa. The modified Ziehl-Neelsen (ZN) staining was done to identify the oocysts of cryptosporidia.

Results: Out of 644 renal transplant patients, oocysts of cryptosporidia were identified in 343 patients (53%). Detailed stool analysis of these patients showed the presence of numerous pus cells in 27 (7.9%) patients, co-infection with giardia intestinalis cysts in 15 (4.3%), and entamoeba histolytica cysts in 10 (2.9%). In all, out of 343 patients, 43 (12.5%) had dual infection with bacteria and protozoa in addition to cryptosporidiosis.

Conclusions: Cryptosporidium is an important pathogen causing acute diarrhea in renal transplant recipients in our set up. Stool examination is usually negative for pus cells. It is recommended that in all transplant recipients presenting with acute diarrhea modified ZN staining should be done to rule out cryptosporidiosis in highly endemic areas like Pakistan.

Comparative diagnostic techniques for cryptosporidium infection

Diarrhoea caused by Cryptosporidium is usually mild in immune competent individuals but severe in the young and those with underlying disease leading to compromised immunity. The conventional diagnosis of Cryptosporidium requires observation of the infective oocysts however, their tiny size yields indistinct results, thus limiting the effectiveness of the conventional diagnostic technique, modified Ziehl-Neelsen (ZN) differential staining. Consequent to the abovementioned limitation, ZN staining, sandwich antigen detection enzyme linked immunosorbent assay (sad-ELISA) and a direct polymerase chain reaction (PCR) assay techniques were evaluated for diagnostic efficacy. Stool samples were collected from 180 consenting adult patients attending outpatient and inpatient clinics at Victoria Hospital, Alice, Eastern Cape Province of South Africa. Subjects were stratified as; 35 HIV-positive and diarrhoeagenic, 125 HIV-negative diarrhoeagenic and 20 apparently healthy controls. Cryptosporidium incidence following diagnostic techniques were 13 (37.1%; ZN staining), 26 (74.3%; sad-ELISA) and 23 (65.7%; PCR), respectively, among HIV-positive diarrhoeagenic patients and 34 (27.2%; ZN staining), 96 (76.8%; sad-ELISA) and 89 (71.2%; PCR) among HIV-negative diarrhoeagenic patients. Sensitivity, specificity and predictive values of the diagnostic techniques’ efficiency were: sensitivity: 46.2% (HIV-positive) and 32.3% (HIV-negative) against the ZN technique and 96.9% against sad-ELISA and PCR, respectively, for both HIV-positive and -negative patients; specificity was 88.9% (HIV-positive) and 96.6% (HIV-negative) against the ZN technique. Lastly, the predictive values were 92.3% (HIV-positive) and 96.9% (HIV-negative), respectively, following ZN staining. The sad-ELISA technique proved more suitable for the determination of the presence of Cryptosporidium oocysts. The high incidence of Cryptosporidium in HIV-positive subjects as compared to the HIV-negative population accentuates the significance of cryptosporidiosis diagnosis in the treatment and management of HIV cases.

Cryptosporidiosis in Haiti: surprisingly low level of species diversity revealed by molecular characterization of Cryptosporidium oocysts from surface water and groundwater

The protozoan parasite Cryptosporidium sp. has emerged as one of the most important water contaminants, causing waterborne outbreaks of diarrhoeal diseases worldwide. In Haiti, cryptosporidiosis is a frequent cause of diarrhoea in children under the age of five years, HIV-infected individuals, and people living in low socioeconomic conditions, mainly due to the consumption of water or food polluted by Cryptosporidium oocysts. The aim of this study was to detect and identify Cryptosporidium oocysts present in 12 water samples collected in Port-au-Prince and 4 water samples collected in Cap Haïtien. Initial detection consisted of immunomagnetic separation - immunofluorescence assay (IMS-IFA), which was confirmed by nested PCR, targeting the most polymorphic region of the 18S rRNA gene in 15/16 samples. Genotyping was performed by PCR-restriction fragment length polymorphism (RFLP) analysis and DNA sequencing. Under our working conditions, neither nested PCR-RFLP nor direct DNA sequencing revealed the expected species diversity, as only Cryptosporidium parvum was identified in the water samples studied. This study highlights the difficulty of detecting mixed populations of Cryptosporidium species in environmental samples.

[Molecular characterization of Cryptosporidium spp. isolated in humans in two different locations in Spain]

Molecular PCR based diagnostic techniques have enabled us to distinguish between the different, morphologically identical, Cryptosporidium species that can infect humans. Of the 23 recognized species in the genus, at least 9 are able to infect humans. As the intensity of the clinical manifestations, pathogenicity, excretion of oocysts, and incidence, are different between this species, molecular studies are crucial for a better understanding of the epidemiology of human cryptosporidiosis. Samples form two independent studies are analyzed in this publication. One included 23 samples from Madrid, and the other, 72 samples from La Coruña. All of them positive for Cryptosporidium spp. by microscopic methods and belonging to isolated cases of human cryptosporidiosis. For the identification of the species responsible for the infection, the 18S rDNA diagnostic region and the COWP gene diagnostic regions were used. Out of the 95 samples tested, in 77 cases we were able to extract and amplify DNA. In those cases the species responsible for the infection were: C. parvum (40 cases, 2 Madrid and 38 La Coruña), C. hominis (30 cases, 10 Madrid and 20 La Coruña) and C. meleagridis (2 cases, 1 Madrid and 1 La Coruña). In 5 samples it was impossible to detect the species responsible for the infection, but their positivity was confirmed by PCR (4 Madrid and 1 La Coruña). The genotypes of the isolates from patients correlated well with animals from the same regions.

Prevalences of Giardia lamblia and Cryptosporidium parvum infection in adults presenting with chronic diarrhoea

Giardia lamblia and Cryptosporidium parvum are both waterborne pathogens associated with diarrhoea in developing countries. In a recent study based at the Aga Khan University in Karachi, 334 adults aged 16-83 years (178 patients with chronic diarrhoea and 156 diarrhoea-free volunteers who acted as controls) were checked for infection with these parasites, using stool microscopy and/or PCR. Overall, 21 (6.3%) and 29 (8.7%) of the subjects were found positive for G. lamblia by microscopy and PCR, respectively, while the corresponding values for C. parvum were 13 (3.9%) and 14 (4.2%). Although, compared with the diarrhoea-free controls, the patients with diarrhoea were not significantly more likely to be found infected with Giardia, either by microscopy [15 (8.4%) v. six (3.8%); P=0.085] or PCR [19 (10.7%) v. 10 (6.4%); P=0.167], they were significantly more likely to be found infected with C. parvum, both by microscopy [11 (6.2%) v. two (1.3%); P=0.024] and by PCR [12 (6.7%) v. two (1.3%); P=0.014]. The 19 patients found PCR-positive for Giardia comprised 10 (67%) of the 15 found smear-positive for the same parasite but only nine (5%) of the 163 found smear-negative (k=0.545; P<0.001). Similarly, the 12 patients found PCR-positive for Cryptosporidium comprised all 11 (100%) patients found smear-positive for the same parasite but only one (0.6%) of the 167 found smear-negative (k=0.954; P<0.001). Although C. parvum was associated with chronic diarrhoea in the present study, the carriage of G. lamblia often appeared asymptomatic.

The reductase domain in a Type I fatty acid synthase from the apicomplexan Cryptosporidium parvum: restricted substrate preference towards very long chain fatty acyl thioesters

Background

The apicomplexan Cryptosporidium parvum genome possesses a 25-kb intronless open reading frame (ORF) that predicts a multifunctional Type I fatty acid synthase (CpFAS1) with at least 21 enzymatic domains. Although the architecture of CpFAS1 resembles those of bacterial polyketide synthases (PKSs), this megasynthase is predicted to function as a fatty acyl elongase as our earlier studies have indicated that the N-terminal loading unit (acyl-[ACP] ligase) prefers using intermediate to long chain fatty acids as substrates, and each of the three internal elongation modules contains a complete set of enzymes to produce a saturated fatty acyl chain. Although the activities of almost all domains were confirmed using recombinant proteins, that of the C-terminal reductase domain (CpFAS1-R) was yet undetermined. In fact, there were no published studies to report the kinetic features of any reductase domains in bacterial PKSs using purified recombinant or native proteins.

Results

In the present study, the identity of CpFAS1-R as a reductase is confirmed by in silico analysis on sequence similarity and characteristic motifs. Phylogenetic analysis based on the R-domains supports a previous notion on the bacterial origin of apicomplexan Type I FAS/PKS genes. We also developed a novel assay using fatty acyl-CoAs as substrates, and determined that CpFAS1-R could only utilize very long chain fatty acyl-CoAs as substrates (i.e., with activity on C26 > C24 > C22 > C20, but no activity on C18 and C16). It was capable of using both NADPH and NADH as electron donors, but prefers NADPH to NADH. The activity of CpFAS1-R displayed allosteric kinetics towards C26 hexacosanoyl CoA as a substrate (h = 2.0; V_max = 32.8 nmol min^-1 mg^-1 protein; and K₅₀ = 0.91 mM).

Conclusions

We have confirmed the activity of CpFAS1-R by directly assaying its substrate preference and kinetic parameters, which is for the first time for a Type I FAS, PKS or non-ribosomal peptide synthase (NRPS) reductase domain. The restricted substrate preference towards very long chain fatty acyl thioesters may be an important feature for this megasynthase to avoid the release of product(s) with undesired lengths.

Childhood cryptosporidiosis: a case report

Cryptosporidium has emerged as an important cause of diarrheal illness worldwide, especially amongst young children and patients with infectious or iatrogenic immune deficiencies. The authors describe a case of mild cryptosporidiosis in a well-nourished, immunocompetent, one-year-old child. Rapid clinical and parasitological improvement was observed after a 3-day course of nitazoxanide.

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.

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.

Cryptosporidiosis in paediatric renal transplantation

Diarrhoea in transplantation may be secondary to infectious agents and immunosuppressive drugs. The use of combined immunosuppressive drugs increases the incidence of infectious diarrhoea. We retrospectively collected all diarrhoea episodes during a 3-year period in 199 pediatric renal transplant recipients, including 47 patients receiving a kidney transplant during this period. We diagnosed 64 diarrhoea episodes (32% of the patients, 10.7% per year). Fourteen diarrhoea episodes could be attributed to the immunosuppressive treatment, and 12 remained without diagnosis. Nineteen patients (<10%) receiving mycophenolic acid (MPA) developed diarrhoea, 14 of whom had episodes attributable to the immunosuppressive treatment. Reducing the MPA dose or switching to another immunosuppressant did not induce graft rejection, if at all, for at least 6 months. Thirty-eight diarrhoea episodes were caused by infectious agents: viruses in 16 patients, bacterial agents in ten patients, Candida albicans in four cases and parasitic agents in eight cases (Giardia lambdia in one patient and Cryptosporidium in seven patients). In our cohort, Cryptosporidium was responsible for 18% of the infectious diarrhoea and 11% of all causes of diarrhoea, and it affected 3.5% of the newly transplanted patients during the 3-year study period. The clinical presentation of the disease was profuse and persistent diarrhoea with acute renal failure in all patients. We propose that oocysts be screened for in the stool during the early stages of tests for determining the origin of infectious diarrhoea. Disease treatment requires early specific treatment (nitazoxanide) for extended periods of time in conjunction with supportive rehydration.

Oligonucleotide-gold nanoparticle networks for detection of Cryptosporidium parvum heat shock protein 70 mRNA

We report on a novel strategy for the detection of mRNA targets derived from Cryptosporidium parvum oocysts by the use of oligonucleotide-gold nanoparticles. Gold nanoparticles are functionalized with oligonucleotides which are complementary to unique sequences present on the heat shock protein 70 (HSP70) DNA/RNA target. The results indicate that the presence of HPS70 targets of increasing complexity causes the formation of oligonucleotide-gold nanoparticle networks which can be visually monitored via a simple colorimetric readout measured by a total internal reflection imaging setup. Furthermore, the induced expression of HSP70 mRNA in Cryptosporidium parvum oocysts via a simple heat shock process provides nonenzymatic amplification such that the HSP70 mRNA derived from as few as 5 x 10(3) purified C. parvum oocysts was successfully detected. Taken together, these results support the use of oligonucleotide-gold nanoparticles for the molecular diagnosis of cryptosporidiosis, offering new opportunities for the further development of point-of-care diagnostic assays with low-cost, robust reagents and simple colorimetric detection.

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.

The pathology of malabsorption: current concepts

Intestinal malabsorption results from a wide variety of causes, which can most easily be organized into three groups. Maldigestion arises from problems with mixing or with digestive mediators, and includes post-gastrectomy patients and those with deficiencies of pancreatic or intestinal enzymes, or of bile salts. Mucosal and mural causes of malabsorption are abundant, and include gluten-sensitive enteropathy, tropical sprue, autoimmune enteropathy, and HIV/AIDS-related enteropathy, as well as mural conditions such as systemic sclerosis. Finally, microbial causes of malabsorption include bacterial overgrowth, Whipple's disease, and numerous infections or infestations that are most frequently seen in immunocompromised patients. An overview of the most common and interesting entities in each of these categories follows, along with a discussion of current concepts. Mucosal conditions and microbial causes of malabsorption are given special attention.

Prevalence rate of Cryptosporidium infection in hemodialysis patients in Iran

Cryptosporidium is one of the most common causes of diarrhea in the world, which can be severe and prolonged in immunocompromised patients. We compared the prevalence rate of Cryptosporidium infection in hemodialysis patients and 2 control groups (i.e., their healthy family members and normal population). Stool specimens of 104 adult outpatient chronic hemodialysis patients, their 91 healthy family members, and 140 healthy individuals were examined for the presence of Cryptosporidium oocysts by using a modified acid-fast staining method. Twelve (11.5%) dialysis patients were infected with Cryptosporidium. This was significantly higher than 4 (4.4%), and 5 (3.6%) cases in the 2 control groups, respectively (p < 0.05). There was no significant difference between the 2 control groups. The prevalence rate of Cryptosporidium infection did not correlate with patients' sex, age, duration of dialysis, history of kidney transplantation, or history of taking immunosuppressive drugs. However, it was significantly higher in diabetics vs. nondiabetics (19.4% vs. 8.3%, respectively, p < 0.05). Our results indicate that the prevalence rate of Cryptosporidium infection is considerably higher in dialysis patients than in the general population. Moreover, dialyzed diabetic patients had the highest rate of infection. As hemodialysis patients are candidates for renal transplantation, general preventive measures against acquiring Cryptosporidium infection must be considered.

Functional characterization of a fatty acyl-CoA-binding protein (ACBP) from the apicomplexan Cryptosporidium parvum

In this paper, the identification and functional analysis of a fatty acyl-CoA-binding protein (ACBP) gene from the opportunistic protist Cryptosporidium parvum are described. The CpACBP1 gene encodes a protein of 268 aa that is three times larger than typical ACBPs (i.e. approximately 90 aa) of humans and animals. Sequence analysis indicated that the CpACBP1 protein consists of an N-terminal ACBP domain (approximately 90 aa) and a C-terminal ankyrin repeat sequence (approximately 170 aa). The entire CpACBP1 ORF was engineered into a maltose-binding protein fusion system and expressed as a recombinant protein for functional analysis. Acyl-CoA-binding assays clearly revealed that the preferred binding substrate for CpACBP1 is palmitoyl-CoA. RT-PCR, Western blotting and immunolabelling analyses clearly showed that the CpACBP1 gene is mainly expressed during the intracellular developmental stages and that the level increases during parasite development. Immunofluorescence microscopy showed that CpACBP1 is associated with the parasitophorous vacuole membrane (PVM), which implies that this protein may be involved in lipid remodelling in the PVM, or in the transport of fatty acids across the membrane.

Two distinct oxysterol binding protein-related proteins in the parasitic protist Cryptosporidium parvum (Apicomplexa)

Two distinct oxysterol binding protein (OSBP)-related proteins (ORPs) have been identified from the parasitic protist Cryptosporidium parvum (CpORP1 and CpORP2). The short-type CpOPR1 contains only a ligand binding (LB) domain, while the long-type CpORP2 contains Pleckstrin homology (PH) and LB domains. Lipid-protein overlay assays using recombinant proteins revealed that CpORP1 and CpORP2 could specifically bind to phosphatidic acid (PA), various phosphatidylinositol phosphates (PIPs), and sulfatide, but not to other types of lipids with simple heads. Cholesterol was not a ligand for these two proteins. CpOPR1 was found mainly on the parasitophorous vacuole membrane (PVM), suggesting that CpORP1 is probably involved in the lipid transport across this unique membrane barrier between parasites and host intestinal lumen. Although Cryptosporidium has two ORPs, other apicomplexans including Plasmodium, Toxoplasma, and Eimeria possess only a single long-type ORP, suggesting that this family of proteins may play different roles among apicomplexans.

Acute diarrheal disease in children: epidemiology, prevention, and treatment

Diarrhea is one of the most common causes of morbidity and mortality in children worldwide. The causes of acute diarrhea in children vary with the location, time of year, and population studied. There is increasing recognition of a widening array of enteric pathogens associated with diarrheal diseases. Adequate fluid and electrolyte replacement and maintenance are key to managing diarrheal illnesses. Thorough clinical and epidemiologic evaluation is needed to define the severity and type of illness, exposures, and whether the patient in is immunocompromised to direct the performance of selective diagnosis cultures, toxin testing, parasite studies, and the administration of antimicrobial therapy.

Application of quantitative real-time reverse transcription-PCR in assessing drug efficacy against the intracellular pathogen Cryptosporidium parvum in vitro

We report here on a quantitative real-time reverse transcription-PCR (qRT-PCR) assay for assessing drug efficacy against the intracellular pathogen Cryptosporidium parvum. The qRT-PCR assay detects 18S rRNA transcripts from both parasites, that is, the cycle threshold for 18S rRNA from parasites (C(T)([P18S])) and host cells (C(T)([H18S])), and evaluates the relative expression between parasite and host rRNA levels (i.e., deltaC(T) = C(T)([P18S]) - C(T)([H18S])) to minimize experimental and operational errors. The choice of qRT-PCR over quantitative PCR (qPCR) in this study is based on the observations that (i) the relationship between the logarithm of infected parasites (log[P]) and the normalized relative level of rRNA (deltadeltaC(T)) is linear, with a fourfold dynamic range, by qRT-PCR but sigmoidal (nonlinear) by qPCR; and (ii) the level of RNA represents that of live parasites better than that of DNA, because the decay of RNA (99% in approximately 3 h) in dead parasites is faster than that of DNA (99% in approximately 24 to 48 h) under in vitro conditions. The reliability of the qRT-PCR method was validated by testing the efficacies of nitazoxanide and paromomycin on the development of two strains of C. parvum (IOWA and KSU-1) in HCT-8 cells in vitro. Both compounds displayed dose-dependent inhibitions. The observed MIC50 values for nitazoxanide and paromomycin were 0.30 to 0.45 micro/ml and 89.7 to 119.0 microg/ml, respectively, comparable to the values reported previously. Using the qRT-PCR assay, we have also observed that pyrazole could inhibit C. parvum development in vitro (MIC50 = 15.8 mM), suggesting that the recently discovered Cryptosporidium alcohol dehydrogenases may be explored as new drug targets.

A GFP-based motif-trap reveals a novel mechanism of targeting for the Toxoplasma ROP4 protein

The protozoan parasite Toxoplasma gondii is a highly specialized eukaryote that contains a remarkable number of intracellular compartments, some unique to Apicomplexans and others typical of eukaryotes in general. We have established a green fluorescent protein (GFP)-based motif-trap to identify proteins targeted to different intracellular locations and subsequently the signals responsible for this sorting. The motif-trap involves the transfection and integration of a linearized GFP construct which lacks a promoter and an initiator methionine codon. FACS is used to isolate parasites in which GFP fuses in-frame into a coding region followed by screening by fluorescence microscopy for those containing GFP targeted to specific intracellular compartments. GFP trapping was successful using vectors designed for integration into regions encoding exons and vectors that were engineered with a splice acceptor site for integration into regions encoding introns. This strategy differs from most protein traps in that the resulting fusions are expressed from the endogenous promoter and starting methionine. Thus, problems from inappropriate expression levels or the creation of fortuitous targeting signals seen in library-based traps are diminished. Using this approach, we have trapped GFP localized to a number of intracellular compartments including the nucleus, nucleolus, endoplasmic reticulum, cytosol, parasite surface and rhoptries of Toxoplasma. Further analysis of a parasite clone containing GFP targeted to the rhoptries shows GFP fused to the gene encoding the rhoptry protein ROP4 and has elucidated an additional mechanism for targeting of this protein.

Management of children with infection-associated persistent diarrhea

Diarrhea is the leading cause of death in children younger than 5 years of age; persistent diarrhea accounts for 30 to 50 percent of those deaths in developing countries. Malnutrition, immunosuppression, young age, and an increase in the preceding diarrhea burdens are risk factors for the development of persistent diarrhea. Although many viruses, bacteria, and parasites can produce persistent diarrhea, enteropathogenic Escherichia coli , enteroaggregative E. coli, Giardia, Cryptosporidium , and Cyclospora are the most important of these agents. With currently available tests, identifying a specific cause usually is difficult. Newer sensitive molecular tests must be used for studying the epidemiology of persistent diarrhea in children. Management includes rehydration, adequate diet, micronutrient supplementation, and antimicrobials. Persistent diarrhea seriously affects nutritional status, growth, and intellectual function. Meeting these challenges is profoundly important, particularly in developing countries.

Cryptosporidiosis in children

Cryptosporidiosis is an important enteric parasitic infection that is associated with significant morbidity and mortality, especially among individuals who are immunosuppressed and infants and children in the developing world. The seroprevalence of this pathogen is high worldwide, suggesting that exposure occurs commonly. The routes of Cryptosporidium spp. transmission are waterborne, food-borne, and occasionally person-to-person. Infected patients can be asymptomatic or develop watery diarrhea and associated enteric symptoms, which are self-limited in immunocompetent persons. In contrast, immunodeficient individuals develop severe, chronic diarrhea that rarely can lead to extra intestinal cryptosporidiosis. Although the diagnosis of Cryptosporidium infection can be established by examining a modified acid-fast stain of stool for the presence of oocysts, enzyme-linked immunoassays are now the diagnostic modalities of choice. Recent clinical trials in pediatric cryptosporidiosis have shown nitazoxanide to be effective therapy.

Emerging parasitic infections

Parasitic infections are felt by most individuals to have little impact on the health and well being of most inhabitants of Canada, Western Europe, and the United States. As the authors show in this article, parasites are always "emerging" somewhere and have a significant impact on those areas of the world. Moreover, as we are becoming an ever-smaller global village, catastrophes and instability in the Third World affect control of parasitic diseases endemic to those areas, ensuring greater chances of transmission to visitors there. The foundation of successful limitation of parasitic diseases in both developing and developed regions is still accurate and rapid diagnosis.

Infection with Cryptosporidium hominis and reinfection with Cryptosporidium parvum in a transplanted ileum

A transplanted ileum was found to be infected with Cryptosporidium hominis 6 days after transplantation. Although the infection resolved, the ileum was later found to be infected with Cryptosporidium parvum. The presence of the parasite was not always correlated with diarrhea. No other gastrointestinal symptom was ever detected. Treatment with azithromycin and paromomycin apparently failed.

Simultaneous detection of Entamoeba histolytica, Giardia lamblia, and Cryptosporidium parvum in fecal samples by using multiplex real-time PCR

Entamoeba histolytica, Giardia lamblia, and Cryptosporidium are three of the most important diarrhea-causing parasitic protozoa. For many years, microscopic examination of stool samples has been considered to be the "gold standard" for diagnosis of E. histolytica, G. lamblia, and C. parvum infections. Recently, more specific and sensitive alternative methods (PCR, enzyme-linked immunosorbent assay, and direct fluorescent-antibody assay) have been introduced for all three of these parasitic infections. However, the incorporation in a routine diagnostic laboratory of these parasite-specific methods for diagnosis of each of the respective infections is time-consuming and increases the costs of a stool examination. Therefore, a multiplex real-time PCR assay was developed for the simultaneous detection of E. histolytica, G. lamblia, and C. parvum in stool samples. The multiplex PCR also included an internal control to determine efficiency of the PCR and detect inhibition in the sample. The assay was performed on species-specific DNA controls and a range of well-defined stool samples, and it achieved 100 percent specificity and sensitivity. The use of this assay in a diagnostic laboratory would provide sensitive and specific diagnosis of the main parasitic diarrheal infections and could improve patient management and infection control.

A role for coccidian cGMP-dependent protein kinase in motility and invasion

The coccidian parasite cGMP-dependent protein kinase is the primary target of a novel coccidiostat, the trisubstituted pyrrole 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H-pyrrol-3-yl] pyridine (compound 1), which effectively controls the proliferation of Eimeria tenella and Toxoplasma gondii parasites in animal models. The efficacy of compound 1 in parasite-specific metabolic assays of infected host cell monolayers is critically dependent on the timing of compound addition. Simultaneous addition of compound with extracellular E. tenella sporozoites or T. gondii tachyzoites inhibited [3H]-uracil uptake in a dose-dependent manner, while minimal efficacy was observed if compound addition was delayed, suggesting a block in host cell invasion. Immunofluorescence assays confirmed that compound 1 blocks the attachment of Eimeria sporozoites or Toxoplasma tachyzoites to host cells and inhibits parasite invasion and gliding motility. Compound 1 also inhibits the secretion of micronemal adhesins (E. tenella MIC1, MIC2 and T. gondii MIC2), an activity closely linked to invasion and motility in apicomplexan parasites. The inhibition of T. gondii MIC2 adhesin secretion by compound 1 was not reversed by treatment with calcium ionophores or by ethanol (a microneme secretagogue), suggesting a block downstream of calcium-dependent events commonly associated with the discharge of the microneme organelle in tachyzoites. Transgenic Toxoplasma strains expressing cGMP-dependent protein kinase mutant alleles that are refractory to compound 1 (including cGMP-dependent protein kinase knock-out lines complemented by such mutants) were used as tools to validate the potential role of cGMP-dependent protein kinase in invasion and motility. In these strains, parasite adhesin secretion, gliding motility, host cell attachment and invasion displayed a reduced sensitivity to compound 1. These data clearly demonstrate that cGMP-dependent protein kinase performs an important role in the host-parasite interaction.

Integrated mapping, chromosomal sequencing and sequence analysis of Cryptosporidium parvum

The apicomplexan Cryptosporidium parvum is one of the most prevalent protozoan parasites of humans. We report the physical mapping of the genome of the Iowa isolate, sequencing and analysis of chromosome 6, and approximately 0.9 Mbp of sequence sampled from the remainder of the genome. To construct a robust physical map, we devised a novel and general strategy, enabling accurate placement of clones regardless of clone artefacts. Analysis reveals a compact genome, unusually rich in membrane proteins. As in Plasmodium falciparum, the mean size of the predicted proteins is larger than that in other sequenced eukaryotes. We find several predicted proteins of interest as potential therapeutic targets, including one exhibiting similarity to the chloroquine resistance protein of Plasmodium. Coding sequence analysis argues against the conventional phylogenetic position of Cryptosporidium and supports an earlier suggestion that this genus arose from an early branching within the Apicomplexa. In agreement with this, we find no significant synteny and surprisingly little protein similarity with Plasmodium. Finally, we find two unusual and abundant repeats throughout the genome. Among sequenced genomes, one motif is abundant only in C. parvum, whereas the other is shared with (but has previously gone unnoticed in) all known genomes of the Coccidia and Haemosporida. These motifs appear to be unique in their structure, distribution and sequences.