Infectivity of Cryptosporidium parvum in healthy adults with pre-existing anti-C. parvum serum immunoglobulin G

Specific Cryptosporidium antigens associate with reinfection immunity and protection from cryptosporidiosis

There is no vaccine to protect from cryptosporidiosis, a leading cause of diarrhea in infants in low- and middle-income countries. Here, we comprehensively identified parasite antigens associated with protection from reinfection. A Cryptosporidium protein microarray was constructed by in vitro transcription and translation of 1,761 C. parvum, C. hominis, or C. meleagridis antigens, including proteins with a signal peptide and/or a transmembrane domain. Plasma IgG and/or IgA from Bangladeshi children longitudinally followed for cryptosporidiosis from birth to 3 years of age allowed for identification of 233 seroreactive proteins. Seven of these were associated with protection from reinfection. These included Cp23, Cp17, Gp900, and 4 additional antigens - CpSMP1, CpMuc8, CpCorA and CpCCDC1. Infection in the first year of life, however, often resulted in no detectable antigen-specific antibody response, and antibody responses, when detected, were specific to the infecting parasite genotype and decayed in the months after infection. In conclusion, humoral immune responses against specific parasite antigens were associated with acquired immunity. While antibody decay over time and parasite genotype-specificity may limit natural immunity, this work serves as a foundation for antigen selection for vaccine design.

Mining for crypto protection: a search for Cryptosporidium antibodies reveals antigens associated with immunity

Infectious diarrhea is a major cause of morbidity and mortality, particularly for children in low- and middle-income countries. Cryptosporidium is a diarrheal pathogen for which there is no vaccine and current therapies are only partially effective. In this issue of the JCI, Gilchrist, Campo, and colleagues surveyed a large cohort of Bangladeshi children to profile antibody responses against an array of Cryptosporidium proteins. They discovered 233 proteins to which children developed antibodies, identified seven as being associated with protection from reinfection, and provided insights regarding the longevity of Cryptosporidium antibodies and the development of antibody breadth. In this commentary, we discuss the burden of disease caused by Cryptosporidium and how these studies highlight the strategies to better manage this parasite.

Conservation, abundance, glycosylation profile, and localization of the TSP protein family in Cryptosporidium parvum

Cryptosporidium parvum is a zoonotic apicomplexan parasite and a common cause of diarrheal disease worldwide. The development of vaccines to prevent or limit infection remains an important goal for tackling cryptosporidiosis. At present, the only approved vaccine against any apicomplexan parasite targets a conserved adhesin possessing a thrombospondin repeat domain. C. parvum possesses 12 orthologous thrombospondin repeat domain-containing proteins known as CpTSP1-12, though little is known about these potentially important antigens. Here, we explore the architecture and conservation of the CpTSP protein family, as well as their abundance at the protein level within the sporozoite stage of the life cycle. We examine the glycosylation states of these proteins using a combination of glycopeptide enrichment techniques to demonstrate that these proteins are modified with C-, O-, and N-linked glycans. Using expansion microscopy, and an antibody against the C-linked mannose that is unique to the CpTSP protein family within C. parvum, we show that these proteins are found both on the cell surface and in structures that resemble the secretory pathway of C. parvum sporozoites. Finally, we generated a polyclonal antibody against CpTSP1 to show that it is found at the cell surface and within micronemes, in a pattern reminiscent of other apicomplexan motility-associated adhesins, and is present both in sporozoites and meronts. This work sheds new light on an understudied family of C. parvum proteins that are likely to be important to both parasite biology and the development of vaccines against cryptosporidiosis.

Controlled Human Infection Models To Accelerate Vaccine Development

The timelines for developing vaccines against infectious diseases are lengthy, and often vaccines that reach the stage of large phase 3 field trials fail to provide the desired level of protective efficacy. The application of controlled human challenge models of infection and disease at the appropriate stages of development could accelerate development of candidate vaccines and, in fact, has done so successfully in some limited cases. Human challenge models could potentially be used to gather critical information on pathogenesis, inform strain selection for vaccines, explore cross-protective immunity, identify immune correlates of protection and mechanisms of protection induced by infection or evoked by candidate vaccines, guide decisions on appropriate trial endpoints, and evaluate vaccine efficacy. We prepared this report to motivate fellow scientists to exploit the potential capacity of controlled human challenge experiments to advance vaccine development. In this review, we considered available challenge models for 17 infectious diseases in the context of the public health importance of each disease, the diversity and pathogenesis of the causative organisms, the vaccine candidates under development, and each model's capacity to evaluate them and identify correlates of protective immunity. Our broad assessment indicated that human challenge models have not yet reached their full potential to support the development of vaccines against infectious diseases. On the basis of our review, however, we believe that describing an ideal challenge model is possible, as is further developing existing and future challenge models.

Cryptosporidiosis outbreaks linked to the public water supply in a military camp, France

Introduction

Contaminated drinking and recreational waters account for most of the reported Cryptosporidium spp. exposures in high-income countries. In June 2017, two successive cryptosporidiosis outbreaks occurred among service members in a military training camp located in Southwest France. Several other gastroenteritis outbreaks were previously reported in this camp, all among trainees in the days following their arrival, without any causative pathogen identification. Epidemiological, microbiological and environmental investigations were carried out to explain theses outbreaks.

Material and methods

Syndromic diagnosis using multiplex PCR was used for stool testing. Water samples (100 L) were collected at 10 points of the drinking water installations and enumeration of Cryptosporidium oocysts performed. The identification of Cryptosporidium species was performed using real-time 18S SSU rRNA PCR and confirmed by GP60 sequencing.

Results

A total of 100 human cases were reported with a global attack rate of 27.8%. Cryptosporidium spp. was identified in 93% of stool samples with syndromic multiplex PCR. The entire drinking water network was contaminated with Cryptosporidium spp. The highest level of contamination was found in groundwater and in the water leaving the treatment plant, with >1,000 oocysts per 100 L. The same Cryptosporidium hominis isolate subtype IbA10G2 was identified in patients’ stool and water samples. Several polluting activities were identified within the protection perimeters of the water resource. An additional ultrafiltration module was installed at the outlet of the water treatment plant. After several weeks, no Cryptosporidium oocysts were found in the public water supply.

Conclusions

After successive and unexplained gastroenteritis outbreaks, this investigation confirmed a waterborne outbreak due to Cryptosporidium hominis subtype IbA10G2. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreak investigation. Our results also highlight the importance of better assessing the microbiological risk associated with raw water and the need for sensitive and easy-to-implement tools for parasite detection.

Cryptosporidiosis remains a neglected infectious disease, even in high-income countries. Most of the reported cases and outbreaks are related to drinking water and recreational water contaminated with Cryptosporidium spp. In Europe, the search for Cryptosporidium spp. and other parasites in stool or water samples is not routinely performed by laboratories, especially in the absence of dedicated national guidance on testing. In France, cryptosporidiosis is not a notifiable disease. In order to better assess the pathogens involved in foodborne and waterborne disease outbreaks a new outbreak investigation strategy was implemented in the French Armed Forces including: systematic stool sampling, routine syndromic multiplex PCR diagnoses, and pathogens genotyping. After several unexplained gastroenteritis outbreaks in a military camp in France, we identified the same C. hominis IbA10G2 isolate in the stools of patients and in the entire water distribution network. The highest levels of contamination were found in groundwater and in the water leaving the treatment plant. Our study demonstrates the value of syndromic diagnosis for gastroenteritis outbreaks investigation and highlights the importance of better assessing the microbiological risks associated with raw water.

Review of generic screening level assumptions for quantitative microbial risk assessment (QMRA) for estimating public health risks from Australian drinking water sources contaminated with Cryptosporidium by recreational activities

As urban communities continue to grow, demand for recreational access (including swimming) in drinking water sources have increased, yet relatively little is understood about the public health implications this poses for drinking water consumers. Preventative risk-based approaches to catchment management, informed by quantitative microbial risk assessment (QMRA), requires accurate input data to effectively model risks. A sound understanding of the knowledge gaps is also important to comprehend levels of uncertainty and help prioritise research needs. Cryptosporidium is one of the most important causes of waterborne outbreaks of gastroenteritis globally due to its resistance to chlorine. This review was undertaken by Water Research Australia to provide the most up-to-date information on current Cryptosporidium epidemiological data and underlying assumptions for exposure assessment, dose response and risk assessment for generic components of QMRA for Cryptosporidium and highlights priorities for common research. Key interim recommendations and guidelines for numerical values for relatively simple screening level QMRA modelling are provided to help support prospective studies of risks to drinking water consumers from Cryptosporidium due to body-contact recreation in source water. The review does not cover site-specific considerations, such as the levels of activity in the source water, the influence of dilution and inactivation in reservoirs, or water treatment. Although the focus is Australia, the recommendations and numerical values developed in this review, and the highlighted research priorities, are broadly applicable across all drinking source water sources that allow recreational activities.

Cryptosporidiosis outbreak in Amazonia, French Guiana, 2018

BACKGROUND

Cryptosporidiosis outbreaks in South America are poorly documented. In March 2018, 51 cases of cryptosporidiosis were reported in Maripasoula, a village located in a remote forest area along the border between Surinam and French Guiana.

METHOD

To identify the origin of the epidemic, we performed epidemiological, microbiological, and environmental investigations. Only the cases involving diarrhoea and Cryptosporidium-positive stool were considered as bona fide, while cases involving diarrhoea and close contact with a confirmed case were classified as "possible".

RESULTS

We identified 16 confirmed cases and 35 possible ones. Confirmed cases comprised nine children (median age of 18 months, range: 6-21), one immunocompromised adult and six soldiers. One child required a hospitalisation for rehydration. All 16 Cryptosporidium stools were PCR positive, and sequencing of the gp60 gene confirmed only one Cryptosporidium hominis subtype IbA10G2. Tap water consumption was the only common risk factor identified. Contamination of the water network with Cryptosporidium parvum subtype IIdA19G2 was found.

CONCLUSION

Water quality is a major public health issue in Amazonian French Guiana, especially for population at risk (children, people with comorbidity, travelers). For them, alternative water supply or treatment should be implemented.

The enteric pathogen Cryptosporidium parvum exports proteins into the cytosol of the infected host cell

The parasite Cryptosporidium is responsible for diarrheal disease in young children causing death, malnutrition, and growth delay. Cryptosporidium invades enterocytes where it develops in a unique intracellular niche. Infected cells exhibit profound changes in morphology, physiology, and transcriptional activity. How the parasite effects these changes is poorly understood. We explored the localization of highly polymorphic proteins and found members of the Cryptosporidium parvum MEDLE protein family to be translocated into the cytosol of infected cells. All intracellular life stages engage in this export, which occurs after completion of invasion. Mutational studies defined an N-terminal host-targeting motif and demonstrated proteolytic processing at a specific leucine residue. Direct expression of MEDLE2 in mammalian cells triggered an ER stress response, which was also observed during infection. Taken together, our studies reveal the presence of a Cryptosporidium secretion system capable of delivering parasite proteins into the infected enterocyte.

Environmental risk assessment by using disability adjusted life year via constructing of a generalized linear model for morbidity estimation of waterborne pathogens

The Environmental burden of disease (EBD) quantitatively evaluates the health impacts of pathogens by using the disability-adjusted life year (DALY) method. The life loss due to morbidity is a general expression for the EBD outcome and, thus, morbidity analysis is indispensable. Considering the deficiency of previous morbidity analysis methods, the objective of this study was to construct a linear morbidity model by using a generalized linear model (GLM) as a template and introducing exposure dose, pathogen toxicity and human immunity as impact variables. Human experimental data were collected for model fitting, and the results indicated a good fit of the majority of the pathogen data. Consequently, two practical cases of water reuse in Xi'an Siyuan University (Case 1) and Lake Cui, Kunming (Case 2) were selected for model validation. Results for case 1 indicated the major EBD to be attributed to rotaviruses (5.57 × 10^-7 DALYs, 95% confidence interval (CI): 4.46 × 10^-7-1.72 × 10^-4 DALYs) and sprinkling irrigation (5.12 × 10^-7 DALYs, 95% CI: 1.95 × 10^-7-1.47 × 10¹ DALYs). Conversely, that for case 2 is mainly attributed to noroviruses (1.42 × 10^-7 DALYs, 95% CI: 7.51 × 10^-11-2.67 × 10^-4 DALYs) and road flushing (1.62 × 10^-7 DALYs, 95% CI: 1.16 × 10^-7-2.67 × 10^-4 DALYs). However, comparison with the suggested threshold of 10^-6 DALYs indicated the EBDs for both cases are acceptable and, thus, water reuse is confirmed to be safe. The methodology for morbidity modelling proposed in this research can effectively compensate for missing data in DALY calculation and, thereby, help to optimize the process for EBD evaluation.

Opportunities and Challenges in Developing a Cryptosporidium Controlled Human Infection Model for Testing Antiparasitic Agents

Cryptosporidiosis is a leading cause of moderate-to-severe diarrhea in low- and middle-income countries, responsible for high mortality in children younger than two years of age, and it is also strongly associated with childhood malnutrition and growth stunting. There is no vaccine for cryptosporidiosis and existing therapeutic options are suboptimal to prevent morbidity and mortality in young children. Recently, novel therapeutic agents have been discovered through high-throughput phenotypic and target-based screening strategies, repurposing malaria hits, etc., and these agents have a promising preclinical in vitro and in vivo anti-Cryptosporidium efficacy. One key step in bringing safe and effective new therapies to young vulnerable children is the establishment of some prospect of direct benefit before initiating pediatric clinical studies. A Cryptosporidium controlled human infection model (CHIM) in healthy adult volunteers can be a robust clinical proof of concept model for evaluating novel therapeutics. CHIM could potentially accelerate the development path to pediatric studies by establishing the safety of a proposed pediatric dosing regimen and documenting preliminary efficacy in adults. We present, here, perspectives regarding the opportunities and perceived challenges with the Cryptosporidium human challenge model.

Identification and characterization of a new 34 kDa MORN motif-containing sporozoite surface-exposed protein, Cp-P34, unique to Cryptosporidium

Despite the public health impact of childhood diarrhea caused by Cryptosporidium, effective drugs and vaccines against this parasite are unavailable. Efforts to identify vaccine targets have focused on critical externally exposed virulence factors expressed in the parasite s invasive stages. However, no single surface antigen has yet been found that can elicit a significant protective immune response and it is likely that pooling multiple immune targets will be necessary. Discovery of surface proteins on Cryptosporidium sporozoites is therefore vital to this effort to develop a multi-antigenic vaccine. In this study we applied a novel single-domain camelid antibody (VHH) selection method to identify immunogenic proteins expressed on the surface of Cryptosporidium parvum sporozoites. By this approach, VHHs were identified that recognize two sporozoite surface-exposed antigens, the previously identified gp900 and an unrecognized immunogenic protein, Cp-P34. This Cp-P34 antigen, which contains multiple Membrane Occupation and Recognition Nexus (MORN) repeats, is found in excysted sporozoites as well as in the parasite s intracellular stages. Cp-P34 appears to accumulate inside the parasite and transiently appears on the surface of sporozoites to be shed in trails. Identical or nearly identical orthologs of Cp-P34 are found in the Cryptosporidium hominis and Cryptosporidium tyzzeri genomes. Except for the conserved MORN motifs, the Cp-P34 gene shares no significant homology with genes of other protozoans and thus appears to be unique to Cryptosporidium spp. Cp-P34 elicits immune responses in naturally exposed alpacas and warrants further investigation as a potential vaccine candidate.

Protection From Natural Immunity Against Enteric Infections and Etiology-Specific Diarrhea in a Longitudinal Birth Cohort

BACKGROUND

The degree of protection conferred by natural immunity is unknown for many enteropathogens, but it is important to support the development of enteric vaccines.

METHODS

We used the Andersen-Gill extension of the Cox model to estimate the effects of previous infections on the incidence of subsequent subclinical infections and diarrhea in children under 2 using quantitative molecular diagnostics in the MAL-ED cohort. We used cross-pathogen negative control associations to correct bias due to confounding by unmeasured heterogeneity of exposure and susceptibility.

RESULTS

Prior rotavirus infection was associated with a 50% lower hazard (calibrated hazard ratio [cHR], 0.50; 95% confidence interval [CI], 0.41-0.62) of subsequent rotavirus diarrhea. Strong protection was evident against Cryptosporidium diarrhea (cHR, 0.32; 95% CI, 0.20-0.51). There was also protection due to prior infections for norovirus GII (cHR against diarrhea, 0.67; 95% CI, 0.49-0.91), astrovirus (cHR, 0.62; 95% CI, 0.48-0.81), and Shigella (cHR, 0.79; 95% CI, 0.65-0.95). Minimal protection was observed for other bacteria, adenovirus 40/41, and sapovirus.

CONCLUSIONS

Natural immunity was generally stronger for the enteric viruses than bacteria, potentially due to less antigenic diversity. Vaccines against major causes of diarrhea may be feasible but likely need to be more immunogenic than natural infection.

PREVALENCE OF ZOONOTIC CRYPTOSPORIDIUM SPP. ISOLATES IN NJORO SUB-COUNTY, NAKURU COUNTY, KENYA

BACKGROUND

There is no information on human and animal Cryptosporidium spp. in Njoro sub- county. The risk posed to humans and animals within the sub-county is therefore unknown.

MATERIALS AND METHODS

A total of 1476 animal and 378 human fecal samples were evaluated. Multivariate logistic regression was used to evaluate association between infection status and the predisposing factors. Results were expressed as odds ratio (OR) with a 95% confidence interval. Chi-square and Maentel-Haenszel tests were used to quantify relationships among variables.

RESULTS

Prevalence of Cryptosporidium spp. was 9.8% in humans, 10.8% in cows, 19.6% in sheep and 4.5% in goats. Prevalence in humans was significantly higher in females 12/37. Infection was highest in the elderly (27.27%), and significantly lower in adolescents and adults at 8.66% and 9.59%, respectively. Goats had lowest overall parasitization at all levels, while sheep had the highest parasitization at levels (+1 and +2). Relatively, humans had the highest parasite counts +3 cases (1.5%).

CONCLUSION

Cryptosporidium spp. is prevalent in Njoro sub-county and domestic animals are important reservoirs and a potential source of zoonosis in humans. Children, elderly and females are at increased risk of infection, especially during rainy season. The study recommends maintenance of proper sanitation when handling domestic animals, treatment of drinking water and use of alternative safer sources of water in order to reduce infection.

A probable means to an end: exploring P131 pharmacophoric scaffold to identify potential inhibitors of Cryptosporidium parvum inosine monophosphate dehydrogenase

Compound P131 has been established to inhibit Cryptosporidium parvum's inosine monophosphate dehydrogenase (CpIMPDH). Its inhibitory activity supersedes that of paromomycin, which is extensively used in treating cryptosporidiosis. Through the per-residue energy decomposition approach, crucial moieties of P131 were identified and subsequently adopted to create a pharmacophore model for virtual screening in the ZINC database. This search generated eight ADMET-compliant hits that were examined thoroughly to fit into the active site of CpIMPDH via molecular docking. Three compounds ZINC46542062, ZINC58646829, and ZINC89780094, with favorable docking scores of - 8.3 kcal/mol, - 8.2 kcal/mol, and - 7.5 kcal/mol, were selected. The potential inhibitory mechanism of these compounds was probed using molecular dynamics simulation and Molecular Mechanics Generalized Poisson Boltzmann Surface Area (MM/PBSA) analyses. Results revealed that one of the hits (ZINC46542062) exhibited a lower binding free energy of - 39.52 kcal/mol than P131, which had - 34.6 kcal/mol. Conformational perturbation induced by the binding of the identified hits to CpIMPDH was similar to P131, suggesting a similarity in inhibitory mechanisms. Also, in silico investigation of the properties of the hit compounds implied superior physicochemical properties with regards to their synthetic accessibility, lipophilicity, and number of hydrogen bond donors and acceptors in comparison with P131. ZINC46542062 was identified as a promising hit compound with the highest binding affinity to the target protein and favorable physicochemical and pharmacokinetic properties relative to P131. The identified compounds can serve as a basis for conducting further experimental investigations toward the development of anticryptosporidials, which can overcome the challenges of existing therapeutic options. Graphical abstract P131 and the identified compounds docked in the NAD⁺ binding site of Cryptosporidium parvum IMPDH.

Demonstrating the Benefits of Predictive Bayesian Dose-Response Relationships Using Six Exposure Studies of Cryptosporidium parvum

A conventional dose-response function can be refitted as additional data become available. A predictive dose-response function in contrast does not require a curve-fitting step, only additional data and presents the unconditional probabilities of illness, reflecting the level of information it contains. In contrast, the predictive Bayesian dose-response function becomes progressively less conservative as more information is included. This investigation evaluated the potential for using predictive Bayesian methods to develop a dose-response for human infection that improves on existing models, to show how predictive Bayesian statistical methods can utilize additional data, and expand the Bayesian methods for a broad audience including those concerned about an oversimplification of dose-response curve use in quantitative microbial risk assessment (QMRA). This study used a dose-response relationship incorporating six separate data sets for Cryptosporidium parvum. A Pareto II distribution with known priors was applied to one of the six data sets to calibrate the model, while the others were used for subsequent updating. While epidemiological principles indicate that local variations, host susceptibility, and organism strain virulence may vary, the six data sets all appear to be well characterized using the Bayesian approach. The adaptable model was applied to an existing data set for Campylobacter jejuni for model validation purposes, which yielded results that demonstrate the ability to analyze a dose-response function with limited data using and update those relationships with new data. An analysis of the goodness of fit compared to the beta-Poisson methods also demonstrated correlation between the predictive Bayesian model and the data.

Cryptosporidium Infections in Africa-How Important Is Zoonotic Transmission? A Review of the Evidence

Cryptosporidium, a protozoan parasite in the phylum Apicomplexa, is the etiological agent of cryptosporidiosis, an intestinal infection characterized by profuse watery diarrhea. Over 30 species of Cryptosporidium are recognized, some host specific whereas others infect a broader host range. Cryptosporidium hominis and Cryptosporidium parvum are the species most commonly associated with human infection; C. hominis is largely associated only with human infections, but C. parvum is also associated with infection in animals, especially young ruminants. In some regions, cryptosporidiosis is a serious veterinary problem, particularly for calves, and lambs. Many outbreaks of human cryptosporidiosis have been associated with zoonotic transmission following contact with infected animals. In Africa, where cryptosporidiosis is a major contributor to pediatric morbidity and mortality, evidence suggests transmission is principally anthroponotic. Given the frequent close contact between humans and animals in Africa, the apparent predominance of human-to-human transmission is both interesting and puzzling. In this article, after a brief “text book” introduction to the parasite, we consider in separate sections the different aspects of relevance to Cryptosporidium transmission in African countries, describing different aspects of the various species and subtypes in human and animal infections, considering livestock management practices in different African countries, and looking for any characteristic “hot spots” where zoonotic transmission has apparently occurred. Studies where transmission networks have been investigated are particularly relevant. Finally, in a separate section, we try to gather these different strands of evidence together in order to assess the reasons behind the apparent predominance of anthroponotic transmission in Africa. Reviewing the available evidence provides an opportunity to re-think transmission pathways, not only in Africa but also elsewhere, and also to pose questions. Does the predominance of human-to-human transmission in Africa reflect a relative absence of zoonotic C. parvum in African livestock? Are Africans less susceptible to zoonotic Cryptosporidium infection, perhaps resulting from early immunostimulation by C. hominis or due to inherent genetic traits? Is the African environment—in all its variety—simply more detrimental to oocyst survival? Will the so-called hypertransmissible subtypes, currently relatively rare in Africa, be introduced from Europe or elsewhere, and, if so, will they fade out or establish and spread? Our intention with this manuscript is not only to summarize and consolidate diverse data, thereby providing an overview of data gaps, but also to provide food for thought regarding transmission of a parasite that continues to have a considerable impact on both human and animal health.

Co-infection risk assessment of Giardia and Cryptosporidium with HIV considering synergistic effects and age sensitivity using disability-adjusted life years

Co-infection with multiple pathogens, especially the spread of Giardia and Cryptosporidium in source water among those with immunodeficiency, is common worldwide, which will result in an increase in overall risk. In this study, the quantitative microbial risk assessment model was used to estimate the cumulative risk of co-infection with Giardia and Cryptosporidium promoted by HIV, considering age sensitivity. The sensitivity of population segments with different ages was estimated by the optimization method, based on clinical data of cryptosporidiosis and giardiasis with age structure. The factors of co-infection enhancement were used to quantify HIV synergism with the action of other pathogens. The removal rates of Giardia and Cryptosporidium through water treatment were estimated by a model involving turbidity and particles. The results showed that children (0-4 years) were 17.911-fold more sensitive to infection with Giardia than adults (15-64 years), and that with Cryptosporidium was 10.592-fold. Removal rates of these parasites in water treatment plants in major cities in China were estimated to be 2.03 log₁₀. Considering the HIV-synergistic and age-susceptibility effects, the cumulative risk of exposure to Giardia or Cryptosporidium was about 38.781 × 10^-6DALYs (Disability-adjusted life years) per person per year, which was much higher than the reference risk level recommended by the World Health Organization (10^-6DALYs). The methodology and results of this study will be useful in better evaluating and reducing the burden due to infection of Giardia and/or Cryptosporidium in China and other countries.

Cryptosporidium infection in rural Gambian children: Epidemiology and risk factors

Background

Cryptosporidium is a major pathogen associated with diarrheal disease in young children. We studied Cryptosporidium diarrhea in children enrolled in the Global Enteric Multicenter Study (GEMS) in rural Gambia.

Methods

We recruited children <5 years of age with moderate-to-severe diarrhea (MSD) for 3 years (2008–2010), and children with either MSD or less severe diarrhea (LSD) for one year (November 2011-November 2012) at sentinel health centers. One or more randomly selected controls were matched to each case. Stool samples were tested to identify Cryptosporidium by immunoassay. A subset of randomly selected case-controls pairs were tested for Cryptosporidium species. We investigated the epidemiology of, and evaluated possible risk factors for, Cryptosporidium-positive diarrhea.

Results

We enrolled 1938 cases (1381 MSD, 557 LSD) and 2969 matched controls; 231/1929 (12.0%) of diarrhea cases and 141/2962 (4.8%) of controls were positive for Cryptosporidium. Most Cryptosporidium diarrhea cases (85.7%, 198/231) were aged 6–23 months, and most (81.4%, 188/231) occurred during the rainy season. Cryptosporidium hominis (C. hominis) was the predominant (82.6%) species. We found associations between increased risk of Cryptosporidium-positive MSD or LSD, or both, with consumption of stored drinking water and certain animals living in the compound—cow, cat (MSD only) and rodents (LSD only). Larger households, fowl living in the compound, and the presence of Giardia infection were associated with decreased risk of Cryptosporidium MSD and LSD.

Conclusion

Cryptosporidium-positive diarrhea is prevalent in this setting, especially at 6–23 months of age. The preponderance of Cryptosporidium infection in the rainy season and increased risk of Cryptosporidium-positive diarrhea with consumption of stored drinking water suggest water-borne transmission. Further investigation is needed to clarify the role of animals and contamination of stored drinking water in Cryptosporidium transmission.

Cryptosporidium, a protozoan parasite, is one of the most common diarrheal pathogens in young children living in developing countries. We describe the prevalence and risk factors for Cryptosporidium diarrhea in under-five children in The Gambia using data from the Global Enteric Study (GEMS), conducted in seven developing countries in Asia and Africa (2008–2012). We enrolled 1938 diarrhea cases and 2969 matched controls. We found that 12.0% of diarrhea cases and 4.8% controls were positive for Cryptosporidium. Most (85.7%) Cryptosporidium diarrhea cases were aged 6–23 months, and most (81.4%) occurred during the rainy season. Cryptosporidium hominis was the predominant species (82.6%). We found that consumption of stored drinking water and animals (cow, cat, rodents) living in the compound are potential risk factors for Cryptosporidium diarrhea. Improved drinking water storage may reduce the burden of Cryptosporidium diarrhea in a resource poor hygienic and sanitation setting.

A Genetically Tractable, Natural Mouse Model of Cryptosporidiosis Offers Insights into Host Protective Immunity

Cryptosporidium is a leading cause of diarrheal disease and an important contributor to early childhood mortality, malnutrition, and growth faltering. Older children in high endemicity regions appear resistant to infection, while previously unexposed adults remain susceptible. Experimental studies in humans and animals support the development of disease resistance, but we do not understand the mechanisms that underlie protective immunity to Cryptosporidium. Here, we derive an in vivo model of Cryptosporidium infection in immunocompetent C57BL/6 mice by isolating parasites from naturally infected wild mice. Similar to human cryptosporidiosis, this infection causes intestinal pathology, and interferon-γ controls early infection while T cells are critical for clearance. Importantly, mice that controlled a live infection were resistant to secondary challenge and vaccination with attenuated parasites provided protection equal to live infection. Both parasite and host are genetically tractable and this in vivo model will facilitate mechanistic investigation and rational vaccine design.

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We isolated and sequenced Cryptosporidium tyzzeri, a natural mouse pathogen

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C. tyzzeri can be genetically manipulated using CRISPR-driven homologous repair

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C. tyzzeri models human cryptosporidiosis with T cell- and IFN-γ-dependent resolution

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Mice develop protective immunity following both live infection and vaccination

An exploration of the disease burden due to Cryptosporidium in consumed surface water for sub-Saharan Africa

The protozoan pathogen Cryptosporidium is an important cause of diarrhoeal disease, but in many contexts its burden remains uncertain. The Global Waterborne Pathogen model for Cryptosporidium (GloWPa-Crypto) predicts oocyst concentrations in surface water at 0.5 by 0.5° (longitude by latitude) resolution, allowing us to assess the burden specifically associated with the consumption of contaminated surface water at a large scale. In this study, data produced by the GloWPa-Crypto model were used in a quantitative microbial risk assessment (QMRA) for sub-Saharan Africa, one of the regions most severely affected by diarrhoeal disease. We first estimated the number of people consuming surface water in this region and assessed both direct consumption and consumption from a piped (treated) supply. The disease burden was expressed in disability adjusted life years (DALYs). We estimate an annual number of 4.3 × 10⁷ (95% uncertainty interval [UI] 7.4 × 10⁶-5.4 × 10⁷) cases which represent 1.6 × 10⁶ (95% UI 3.2 × 10⁵-2.3 × 10⁶) DALYs. Relative disease burden (DALYs per 100,000 persons) varies widely, ranging between 1.3 (95% UI 0.1-5.7) for Senegal and 1.0 × 10³ (95% UI 4.2 × 10²-1.4 × 10³) for Eswatini. Countries that carry the highest relative disease burden are primarily located in south and south-east sub-Saharan Africa and are characterised by a relatively high HIV/AIDS prevalence. Direct surface water consumption accounts for the vast majority of cases, but the results also point towards the importance of stable drinking water treatment performance. This is, to our knowledge, the first study to utilise modelled data on pathogen concentrations in a large scale QMRA. It demonstrates the potential value of such data in epidemiological research, particularly regarding disease aetiology.

Modelling the fate and transport of Cryptosporidium, a zoonotic and waterborne pathogen, in the Daning River watershed of the Three Gorges Reservoir Region, China

Oospores of Cryptosporidium, a waterborne pathogen of great concern, are widely distributed in surface waters in China and pose a threat to human health. This study seeks to explore the spatio-temporal patterns of Cryptosporidium concentrations. We focus on the Daning River watershed (4166 km²) of the Three Gorges Reservoir Region (TGR) during the period 2008 to 2013 and use the SWAT (Soil and Water Assessment Tool) model to test two mitigation scenarios. Based on data on animal husbandry, population, agriculture and WWTPs (wastewater treatment plants), Cryptosporidium transport in the Daning River watershed was simulated using a calibrated hydrological and sediment transport model. Our model results showed that the average annual concentration of oocysts in the whole watershed was 9.5 oocysts/10L, but high spatial variability occurred, ranging from 0.7 to 33.4 oocysts/10L. Highest monthly mean oocysts concentrations at the outlets of the sub-basins were found at high runoff and high fertilization or at the lowest flow, while minimum monthly mean oocysts concentrations were recorded at high runoff only. A model parameter sensitivity analysis showed that the Cryptosporidium soil partitioning coefficient (BACTKDQ) and the temperature adjustment factor for Cryptosporidium die-off (THBACT) were the only two sensitive parameters among the microbial parameters. The construction of multiple WWTPs throughout the watershed and composting of 50% of the feces from rural citizens and livestock up to 56 days before its application as fertilizer could significantly reduce the concentration of oocysts. Our Cryptosporidium transport model and simulation results may assist in the establishment of better pollution control countermeasures in the Daning River and other similar watersheds.

Risk factors for Cryptosporidium infection in low and middle income countries: A systematic review and meta-analysis

BACKGROUND

Cryptosporidium infection causes gastrointestinal disease and has a worldwide distribution. The highest burden is in developing countries.

OBJECTIVES

We sought to conduct a systematic review and meta-analysis to identify Cryptosporidium risk factors in Low and Middle Income countries (LMICs).

METHODS

Medline Ovid and Scopus databases were searched with no restriction on year or language of publication. All references were screened independently in duplicate and were included if they presented data on at least 3 risk factors. Meta-analyses using random effects models were used to calculate overall estimates for each exposure.

RESULTS

The most frequently reported risk factors in the 15 included studies were overcrowding, household diarrhoea, poor quality drinking water, animal contact, open defecation/ lack of toilet and breastfeeding. The combined odds ratio for animal contact was 1.98 (95%CI: 1.11-3.54) based on 11 studies and for diarrhoea in the household 1.98 (95%CI: 1.13-3.49) based on 4 studies. Open defecation was associated with a pooled odds ratio of 1.82 (95%CI: 1.19-2.8) based on 5 studies. Poor drinking water quality was not associated with a significant Cryptosporidium risk, odds ratio 1.06 (95%CI: 0.77-1.47). Breastfeeding was protective with pooled odds ratio 0.4 (95%CI: 0.13-1.22), which was not statistically significant.

CONCLUSIONS

Based on the included studies, crowded living conditions, animal contact and open defecation are responsible for the majority of Cryptosporidium cases in LMICs. Future studies investigating Cryptosporidium risk factors should have a good study design and duration, include appropriate number of cases, select suitable controls, investigate multiple relevant risk factors, fully report data and perform multivariate analysis.

Cryptosporidium parvum decay during air drying and stockpiling of mesophilic anaerobically digested sewage sludge in a simulation experiment and oocyst counts in sludge collected from operational treatment lagoons in Victoria, Australia

The inactivation of Cryptosporidium species oocysts during sewage sludge treatment is important to protect human health when the residual biosolids are applied to agricultural land. Quantifying the decay of Cryptosporidium species during sludge treatment for microbiological assurance purposes is difficult if low numbers are present in wastewater. The rate of decay of Cryptosporidium parvum oocysts during solar/air drying treatment and in sludge stockpiles in temperate environment conditions was simulated in laboratory inoculation experiments using sludge sampled from a mesophilic anaerobic digester. Oocyst numbers were also determined in settled lagoon sludge samples collected from three operational rural wastewater treatment plants (WWTPs). C. parvum oocysts were enumerated by immunomagnetic separation followed by staining with vital dyes and examination by confocal laser scanning microscopy. An air-drying/storage period equivalent to 11 weeks was required for a 1 log₁₀ reduction of viable oocysts inoculated into digested sludge. Oocyst viability in air-dried and stored digested sludge decreased with time, but was independent of sludge desiccation and dry solids (DS) content. No oocysts were detected in sludge samples collected from the anaerobic digester, and the average concentration of oocysts found in settled lagoon sludge from the rural WWTP was 4.6 × 10² oocysts/g DS.

Impact of confinement housing on study end-points in the calf model of cryptosporidiosis

BACKGROUND

Diarrhea is the second leading cause of death in children < 5 years globally and the parasite genus Cryptosporidium is a leading cause of that diarrhea. The global disease burden attributable to cryptosporidiosis is substantial and the only approved chemotherapeutic, nitazoxanide, has poor efficacy in HIV positive children. Chemotherapeutic development is dependent on the calf model of cryptosporidiosis, which is the best approximation of human disease. However, the model is not consistently applied across research studies. Data collection commonly occurs using two different methods: Complete Fecal Collection (CFC), which requires use of confinement housing, and Interval Collection (IC), which permits use of box stalls. CFC mimics human challenge model methodology but it is unknown if confinement housing impacts study end-points and if data gathered via this method is suitable for generalization to human populations.

METHODS

Using a modified crossover study design we compared CFC and IC and evaluated the impact of housing on study end-points. At birth, calves were randomly assigned to confinement (n = 14) or box stall housing (n = 9), or were challenged with 5 x 107 C. parvum oocysts, and followed for 10 days. Study end-points included fecal oocyst shedding, severity of diarrhea, degree of dehydration, and plasma cortisol.

FINDINGS

Calves in confinement had no significant differences in mean log oocysts enumerated per gram of fecal dry matter between CFC and IC samples (P = 0.6), nor were there diurnal variations in oocyst shedding (P = 0.1). Confinement housed calves shed significantly more oocysts (P = 0.05), had higher plasma cortisol (P = 0.001), and required more supportive care (P = 0.0009) than calves in box stalls.

CONCLUSION

Housing method confounds study end-points in the calf model of cryptosporidiosis. Due to increased stress data collected from calves in confinement housing may not accurately estimate the efficacy of chemotherapeutics targeting C. parvum.

Cryptosporidium in humans and animals-a one health approach to prophylaxis

Cryptosporidium is a major cause of moderate-to-severe diarrhoea in humans worldwide, second only to rotavirus. Due to the wide host range and environmental persistence of this parasite, cryptosporidiosis can be zoonotic and associated with foodborne and waterborne outbreaks. Currently, 31 species are recognized as valid, and of these, Cryptosporidium hominis and Cryptosporidium parvum are responsible for the majority of infections in humans. The immune status of the host, both innate and adaptive immunity, has a major impact on the severity of the disease and its prognosis. Immunocompetent individuals typically experience self-limiting diarrhoea and transient gastroenteritis lasting up to 2 weeks and recover without treatment, suggesting an efficient host antiparasite immune response. Immunocompromised individuals can suffer from intractable diarrhoea, which can be fatal. Effective drug treatments and vaccines are not yet available. As a result of this, the close cooperation and interaction between veterinarians, health physicians, environmental managers and public health operators is essential to properly control this disease. This review focuses on a One Health approach to prophylaxis, including the importance of understanding transmission routes for zoonotic Cryptosporidium species, improved sanitation and better risk management, improved detection, diagnosis and treatment and the prospect of an effective anticryptosporidial vaccine.

Natural History of Cryptosporidiosis in a Birth Cohort in Southern India

In an Indian birth cohort, we demonstrate a high and early burden of cryptosporidiosis by polymerase chain reaction and serology. Reinfection was common and infections clustered in a subset of children. Prior infection provided some protection against subsequent infection, but not disease.

Background.

Cryptosporidium is a leading cause of moderate to severe childhood diarrhea in resource-poor settings. Understanding the natural history of cryptosporidiosis and the correlates of protection are essential to develop effective and sustainable approaches to disease control and prevention.

Methods.

Children (N = 497) were recruited at birth in semiurban slums in Vellore, India, and followed for 3 years with twice-weekly home visits. Stool samples were collected every 2 weeks and during diarrheal episodes were tested for Cryptosporidium species by polymerase chain reaction (PCR). Serum samples obtained every 6 months were evaluated for seroconversion, defined as a 4-fold increase in immunoglobulin G directed against Cryptosporidium gp15 and/or Cp23 antigens between consecutive sera.

Results.

Of 410 children completing follow-up, 397 (97%) acquired cryptosporidiosis by 3 years of age. PCR identified 1053 episodes of cryptosporidiosis, with an overall incidence of 0.86 infections per child-year by stool and serology. The median age for the first infection was 9 (interquartile range, 4–17) months, indicating early exposure. Although infections were mainly asymptomatic (693 [66%]), Cryptosporidium was identified in 9.4% of diarrheal episodes. The proportion of reinfected children was high (81%) and there was clustering of asymptomatic and symptomatic infections (P < .0001 for both). Protection against infection increased with the order of infection but was only 69% after 4 infections. Cryptosporidium hominis (73.3%) was the predominant Cryptosporidium species, and there was no species-specific protection.

Conclusions.

There is a high burden of endemic cryptosporidiosis in southern India. Clustering of infection is suggestive of host susceptibility. Multiple reinfections conferred some protection against subsequent infection.

Environmental transmission of diarrheal pathogens in low and middle income countries

Every year, more than half a million children die due to diarrheal diseases. Recent studies have identified the most important etiologies of diarrheal disease are enterotoxigenic and enteropathogenic E. coli, Shigella spp., rotavirus, norovirus and Cryptosporidium spp. These etiologies are unsurprisingly characterized by a combination of high shedding, high infectivity, and transmissibility through multiple environmental reservoirs. The relative importance of the transmission routes is likely site-specific. So the impact of interventions, which typically target only one or two environmental reservoirs, is likely also site-specific. The factors influencing the transmission routes most important for diarrheal disease are complex, including - at a minimum - etiology of endemic disease; and water, sanitation, and hygiene infrastructure and practices. The site-specific nature - and complexity of transmission - helps explain the observed variation in impacts of water, sanitation, and hygiene interventions. It may also render efforts to estimate or quantify global means for interventions' impacts irrelevant. The theme of this Perspective is that greater reductions in diarrheal disease transmission in LMICs can be achieved by designing interventions to interrupt the most important environmental transmission pathways. Intervention choice should be informed by site-specific conditions, most notably: diarrheal etiology and existing water, sanitation, and hygiene infrastructure and practices. The theme is discussed through the lens of the characteristics of the most important diarrheal diseases (shedding, infectivity, growth, and persistence) and the general characteristics of environmental reservoirs (exposure pathways and fecal contamination). The discussion highlights when interventions - and combinations of interventions - will be most effective at reducing diarrheal disease burden.

Removal of Cryptosporidium by wastewater treatment processes: a review

Cryptosporidium is a protozoan parasite that infects humans and various animal species. The environmental stability and the low infectious dose of Cryptosporidium facilitate its transmission by water and food. Discharge of untreated wastewater may result in waterborne or foodborne Cryptosporidium outbreaks, therefore a suitable treatment may prevent its dissemination. Most studies on the prevalence of Cryptosporidium oocysts in wastewater have reported a concentration range between 10 and 200 oocysts/L and a prevalence of 6 to 100%. Activated sludge has been found to be ineffective for the removal of Cryptosporidium oocysts. Stabilization ponds and constructed wetlands are efficient for the reduction of Cryptosporidium from wastewater, especially when the retention time is longer than 20 days at suitable sunlight and temperature. High rate filtration and chlorine disinfection are inefficient for the reduction of Cryptosporidium from effluents, whereas ultrafiltration and UV irradiation were found to be very efficient for the reduction of Cryptosporidium oocysts. Adequate tertiary treatment may result in high quality effluent with low risk of Cryptosporidium for unrestricted irrigation and other non-potable applications.

Cryptosporidiosis outbreak in visitors of a UK industry-compliant petting farm caused by a rare Cryptosporidium parvum subtype: a case-control study

A case-control study was conducted to investigate an outbreak of 46 cases of cryptosporidiosis in visitors to a petting farm in England. Details of exposures on the farm were collected for 38 cases and 39 controls, recruited through snowball sampling. Multivariable logistic regression identified that cases were 5·5 times more likely than controls to have eaten without washing their hands [95% confidence interval (CI) 1·51–19·9, P = 0·01] and 10 times less likely to report being informed of risk of infection on arrival (odds ratio 0·10, 95% CI 0·01–0·71, P = 0·02). An uncommon Cryptosporidium parvum gp60 subtype (IIaA19G1R1) was identified in a lamb faecal sample and all subtyped cases (n = 22). We conclude that lack of verbal advice and non-compliance with hand washing are significantly associated with a risk of cryptosporidiosis on open farms. These findings highlight the public health importance of effectively communicating risk to petting farm visitors in order to prevent future outbreaks of zoonotic infections.

Serum Anti-Cryptosporidial gp15 Antibodies in Mothers and Children Less than 2 Years of Age in India

Little is known about the type and longevity of the humoral response to cryptosporidial infections in developing countries. We evaluated serum antibody response to Cryptosporidium gp15 in 150 sets of maternal, preweaning and postinfection/end-of-follow-up sera from children followed up to 2 years of age to determine the influence of maternal and preweaning serological status on childhood cryptosporidiosis. Fifty two percent (N = 78) of mothers and 20% (N = 30) of children were seropositive preweaning. However, most positive preweaning samples from children were collected early in life indicating transplacental transfer and subsequent rapid waning of antibodies. Although 62% (N = 94) of children had a parasitologically confirmed cryptosporidial infection (detected by stool polymerase chain reaction) during the follow-up, only 54% (N = 51) of children were seropositive postinfection. Given there were striking differences in seropositivity depending on when the sample was collected, even though Cryptosporidium was detected in the stool of the majority of the children, this study indicates that antibodies wane rapidly. During follow-up, the acquisition or severity of cryptosporidial infections was not influenced by maternal (P = 0.331 and 0.720, respectively) as well as the preweaning serological status of the child (P = 0.076 and 0.196, respectively).

Design, recruitment, and microbiological considerations in human challenge studies

Since the 18th century a wealth of knowledge regarding infectious disease pathogenesis, prevention, and treatment has been accumulated from findings of infection challenges in human beings. Partly because of improvements to ethical and regulatory guidance, human challenge studies-involving the deliberate exposure of participants to infectious substances-have had a resurgence in popularity in the past few years, in particular for the assessment of vaccines. To provide an overview of the potential use of challenge models, we present historical reports and contemporary views from experts in this type of research. A range of challenge models and practical approaches to generate important data exist and are used to expedite vaccine and therapeutic development and to support public health modelling and interventions. Although human challenge studies provide a unique opportunity to address complex research questions, participant and investigator safety is paramount. To increase the collaborative effort and future success of this area of research, we recommend the development of consensus frameworks and sharing of best practices between investigators. Furthermore, standardisation of challenge procedures and regulatory guidance will help with the feasibility for using challenge models in clinical testing of new disease intervention strategies.

Cryptosporidium muris: infectivity and illness in healthy adult volunteers

Although Cryptosporidium parvum and C. hominis cause the majority of human cryptosporidiosis cases, other Cryptosporidium species are also capable of infecting humans, particularly when individuals are immunocompromised. Ten C. muris cases have been reported, primarily in human immunodeficiency virus (HIV) -positive patients with diarrhea. However, asymptomatic cases were reported in two HIV-negative children, and in another case, age and immune status were not described. This study examines the infectivity of C. muris in six healthy adults. Volunteers were challenged with 10(5) C. muris oocysts and monitored for 6 weeks for infection and/or illness. All six patients became infected. Two patients experienced a self-limited diarrheal illness. Total oocysts shed during the study ranged from 6.7 × 10(6) to 4.1 × 10(8), and the number was slightly higher in volunteers with diarrhea (2.8 × 10(8)) than asymptomatic shedders (4.4 × 10(7)). C. muris-infected subjects shed oocysts longer than occurred with other species studied in healthy volunteers. Three volunteers shed oocysts for 7 months. Physical examinations were normal, with no reported recurrence of diarrhea or other gastrointestinal complaints. Two persistent shedders were treated with nitazoxanide, and the infection was resolved. Thus, healthy adults are susceptible to C. muris, which can cause mild diarrhea and result in persistent, asymptomatic infection.

A review of the global burden, novel diagnostics, therapeutics, and vaccine targets for cryptosporidium

Cryptosporidium spp are well recognised as causes of diarrhoeal disease during waterborne epidemics and in immunocompromised hosts. Studies have also drawn attention to an underestimated global burden and suggest major gaps in optimum diagnosis, treatment, and immunisation. Cryptosporidiosis is increasingly identified as an important cause of morbidity and mortality worldwide. Studies in low-resource settings and high-income countries have confirmed the importance of cryptosporidium as a cause of diarrhoea and childhood malnutrition. Diagnostic tests for cryptosporidium infection are suboptimum, necessitating specialised tests that are often insensitive. Antigen-detection and PCR improve sensitivity, and multiplexed antigen detection and molecular assays are underused. Therapy has some effect in healthy hosts and no proven efficacy in patients with AIDS. Use of cryptosporidium genomes has helped to identify promising therapeutic targets, and drugs are in development, but methods to assess the efficacy in vitro and in animals are not well standardised. Partial immunity after exposure suggests the potential for successful vaccines, and several are in development; however, surrogates of protection are not well defined. Improved methods for propagation and genetic manipulation of the organism would be significant advances.

Effects of drinking-water filtration on Cryptosporidium seroepidemiology, Scotland

Improved filtration is associated with reduced prevalence of antibodies against Cryptosporidium spp.

Continuous exposure to low levels of Cryptosporidium oocysts is associated with production of protective antibodies. We investigated prevalence of antibodies against the 27-kDa Cryptosporidium oocyst antigen among blood donors in 2 areas of Scotland supplied by drinking water from different sources with different filtration standards: Glasgow (not filtered) and Dundee (filtered). During 2006–2009, seroprevalence and risk factor data were collected; this period includes 2007, when enhanced filtration was introduced to the Glasgow supply. A serologic response to the 27-kDa antigen was found for ≈75% of donors in the 2 cohorts combined. Mixed regression modeling indicated a 32% step-change reduction in seroprevalence of antibodies against Cryptosporidium among persons in the Glasgow area, which was associated with introduction of enhanced filtration treatment. Removal of Cryptosporidium oocysts from water reduces the risk for waterborne exposure, sporadic infections, and outbreaks. Paradoxically, however, oocyst removal might lower immunity and increase the risk for infection from other sources.

Survival of Microorganisms on Inanimate Surfaces

In healthcare settings microbial contaminated surfaces play an important role in indirect transmission of infection. Especially surfaces close to the patients’ environment may be touched at high frequencies, allowing transmission from animated sources to others via contaminated inanimate surfaces.

Therefore, the knowledge on the survival of bacteria, fungi, viruses and protozoa on surfaces, and hence, in a broader sense, in the human environment, is important for implementing tactics for prevention of Healthcare-acquired Infections (HAI). This chapter will elaborate the role of surfaces in the transmission of pathogens. Particular emphasis is laid on the current knowledge of the survival time and conditions favouring survival of the pathogens. Finally, mechanisms of transmission from inanimate surfaces to patients are highlighted.

Within the multi-barrier strategy of the prevention of HAI, environmental disinfection policies should be based on risk assessments for surfaces with different risks for cross contamination such as high- and low-touched surfaces with appropriate standards for adequate disinfection measures under consideration of the persistence and infectious dose of the pathogens. As a result, surface disinfection is indicated in the following situations:

Frequently touched surfaces adjacent to patients

Surfaces with assumed or visible contamination

Terminal disinfection in rooms or areas where infected or colonized patients with easily transferable nosocomial pathogens are cared for, and

in outbreak situations.

Furthermore, the knowledge of the persistence of pathogens will also support ensuring the biosafety in microbiological and biomedical laboratories, food-handling settings, and for hygienic behaviour in the everyday life to prevent transmission of infectious diseases.

Cryptosporidiosis in HIV/AIDS patients in Kenya: clinical features, epidemiology, molecular characterization and antibody responses

We investigated the epidemiological and clinical features of cryptosporidiosis, the molecular characteristics of infecting species and serum antibody responses to three Cryptosporidium-specific antigens in human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) patients in Kenya. Cryptosporidium was the most prevalent enteric pathogen and was identified in 56 of 164 (34%) of HIV/AIDS patients, including 25 of 70 (36%) with diarrhea and 31 of 94 (33%) without diarrhea. Diarrhea in patients exclusively infected with Cryptosporidium was significantly associated with the number of children per household, contact with animals, and water treatment. Cryptosporidium hominis was the most prevalent species and the most prevalent subtype family was Ib. Patients without diarrhea had significantly higher serum IgG levels to Chgp15, Chgp40 and Cp23, and higher fecal IgA levels to Chgp15 and Chgp40 than those with diarrhea suggesting that antibody responses to these antigens may be associated with protection from diarrhea and supporting further investigation of these antigens as vaccine candidates.

Prospects for immunotherapy and vaccines against Cryptosporidium

Cryptosporidium spp is a ubiquitous parasite that has long been recognized as a frequent cause of protozoal diarrhea in humans. While infections in immunocompetent hosts are usually self-limiting, immunocompromised individuals can develop severe, chronic, and life-threatening illness. Vaccine development or immunotherapy that prevents disease or reduces the severity of infection is a relevant option since efficacious drug treatments are lacking. In particular, children in developing countries might benefit the most from a vaccine since cryptosporidiosis in early childhood has been reported to be associated with subsequent impairment in growth, physical fitness, and intellectual capacity. In this review, immunotherapies that have been used clinically are described as well as experimental vaccines and their evaluation in vivo.

Reduction in cryptosporidiosis associated with introduction of enhanced filtration of drinking water at Loch Katrine, Scotland

Previous evidence has suggested an association between cryptosporidiosis and consumption of unfiltered drinking water from Loch Katrine in Scotland. Before September 2007, the water was only micro-strained and chlorinated; however, since that time, coagulation and rapid gravity filtration have been installed. In order to determine risk factors associated with cryptosporidiosis, including drinking water, we analysed data on microbiologically confirmed cases of cryptosporidiosis from 2004 to 2010. We identified an association between the incidence of cryptosporidiosis and unfiltered Loch Katrine drinking water supplied to the home (odds ratio 1.86, 95% confidence interval 1.11-3.11, P = 0.019). However, while filtration appears to be associated with initially reduced rates of cryptosporidiosis, evidence suggests it may paradoxically make those consumers more susceptible to other transmission routes in the long-term. These findings support implementation of similar treatment for other unfiltered drinking-water supplies, as a means of reducing cryptosporidiosis associated with drinking water.

Fate of Cryptosporidium parvum oocysts within soil, water, and plant environment

Vegetative Filter Strips (VFS) have long been used to control the movement of agricultural nutrients and prevent them from reaching receiving waters. Earlier studies have shown that VFS also dramatically reduce both the kinetics and extent of Cryptosporidium parvum (C. parvum) oocysts overland transport. In this study, we investigated possible mechanisms responsible for the ability of VFS to reduce oocyst overland transport. Measurement of the kinetics of C. parvum adhesion to individual sand, silt, and clay soil particles revealed that oocysts associate over time, albeit relatively slow, with clay but not silt or sand particles. Measurement of oocyst overland transport kinetics, soil infiltration depth, distance of travel, and adhesion to vegetation on bare and vegetated soil surfaces indicate that oocysts move more slowly, and penetrate the soil profile to a greater extent on a vegetated surface than on a bare soil surface. Furthermore, we demonstrate a small fraction of the oocysts become attached to vegetation at the soil-vegetation interface on VFS. These results suggest VFS function to reduce oocyst overland transport by primarily decreasing oocyst surface flow enough to allow penetration within the soil profile followed by subsequent adhesion to or entrapment within clay particle aggregates, and to a lesser extent, adhesion to the surface vegetation.

Life cycle ofCryptosporidium murisin two rodents with different responses to parasitization

This study focuses on mapping the life cycle ofCryptosporidium murisin two laboratory rodents; BALB/c mice and the southern multimammate ratMastomys coucha, differing in their prepatent and patent periods. Both rodents were simultaneously experimentally inoculated with viable oocysts ofC. muris(strain TS03). Animals were dissected and screened for the presence of the parasite using a combined morphological approach and nested PCR (SSU rRNA) at different times after inoculation. The occurrence of first developmental stages ofC. murisin stomach was detected at 2·5 days post-infection (dpi). The presence of Type II merogony, appearing 36 h later than Type I merogony, was confirmed in both rodents. Oocysts exhibiting different size and thickness of their wall were observed from 5 dpi onwards in stomachs of both host models. The early phase of parasitization in BALB/c mice progressed rapidly, with a prepatent period of 7·5–10 days; whereas inM. coucha, the developmental stages ofC. muriswere first observed 12 h later in comparison with BALB/c mice and prepatent period was longer (18–21 days). Similarly, the patent periods of BALB/c mice andM. couchadiffered considerably, i.e. 10–15 daysvschronic infection throughout the life of the host, respectively.

Cryptosporidium pathogenicity and virulence

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

Subclinical infection and asymptomatic carriage of gastrointestinal zoonoses: occupational exposure, environmental pathways, and the anonymous spread of disease

Asymptomatic carriage of gastrointestinal zoonoses is more common in people whose profession involves them working directly with domesticated animals. Subclinical infections (defined as an infection in which symptoms are either asymptomatic or sufficiently mild to escape diagnosis) are important within a community as unknowing (asymptomatic) carriers of pathogens do not change their behaviour to prevent the spread of disease; therefore the public health significance of asymptomatic human excretion of zoonoses should not be underestimated. However, optimal strategies for managing diseases where asymptomatic carriage instigates further infection remain unresolved, and the impact on disease management is unclear. In this review we consider the environmental pathways associated with prolonged antigenic exposure and critically assess the significance of asymptomatic carriage in disease outbreaks. Although screening high-risk groups for occupationally acquired diseases would be logistically problematical, there may be an economic case for identifying and treating asymptomatic carriage if the costs of screening and treatment are less than the costs of identifying and treating those individuals infected by asymptomatic hosts.

Intranasal vaccination in mice with an attenuated Salmonella enterica Serovar 908htr A expressing Cp15 of Cryptosporidium: impact of malnutrition with preservation of cytokine secretion

Cryptosporidium is a protozoan parasite associated with acute and persistent diarrhea that, even in asymptomatic persons, can impair normal growth and potentially cognitive and physical development in young children. The recent availability of the complete gene sequence for Cryptosporidium hominis antigen Cp15 allows examination of innovative vaccine regimens involving intra-nasal antigen priming with live bacterial vectors applicable to human populations. We used a recently described weaned mouse model of cryptosporidiosis, where nourished and malnourished vaccinated mice receive the Cp15 antigen recombinant with cytolysinA on a Salmonella serovar Typhi CVD 908-htr A vector, followed by parenteral exposure to antigen with adjuvant. After challenge with Cryptosporidium oocysts via gavage, parameters of infection and disease (stool shedding of parasites, growth rates) were quantified, and serum/lymphoid tissue harvested to elucidate the Cp15-specific adaptive immune response. In vaccinated nourished mice, the regimen was highly immunogenic, with strong antigen-specific IL-6 and IFN-γ secretion and robust Cp15-specific immunoglobulin titers. In vaccinated malnourished mice, secretion of cytokines, particularly IFN-γ, and antigen-specific humoral immunity were generally undiminished despite protein deprivation and stunted growth. In contrast, after natural (oral) challenge with an identical inoculum of Cryptosporidium oocysts, cytokine and humoral responses to Cp15 were less than one-fourth those in vaccinated mice. Nevertheless, vaccination resulted in only transient reduction in stool shedding of parasites and was not otherwise protective against disease. Overall, immunogenicity for a C. hominis antigen was documented in mice, even in the setting of prolonged malnutrition, using an innovative vaccine regimen involving intra-nasal antigen priming with a live enteric bacterial vector, that has potential applicability to vulnerable human populations irrespective of nutritional status.

Burden of disease from cryptosporidiosis

PURPOSE OF REVIEW

The global significance of cryptosporidiosis is widespread and far-reaching. In this review, we present recent data about strain diversity and the burden of disease, along with developments in therapeutic and preventive strategies.

RECENT FINDINGS

Cryptosporidium is an emerging pathogen that disproportionately affects children in developing countries and immunocompromised individuals. Without a diagnostic tool amenable for use in developing countries, the burden of infection and its relationship to growth faltering, malnutrition, and diarrheal mortality remain underappreciated. Disease incidence is also increasing in industrialized countries largely as a result of outbreaks in recreational water facilities. Advances in molecular methods, including subtyping analysis, have yielded new insights into the epidemiology of cryptosporidiosis. However, without practical point-of-care diagnostics, an effective treatment for immunocompromised patients, and a promising vaccine candidate, the ability to reduce the burden of disease in the near future is limited. This is compounded by inadequate coverage with antiretroviral therapy in developing countries, the only current means of managing HIV-infected patients with cryptosporidiosis.

SUMMARY

Cryptosporidiosis is one of the most important diarrheal pathogens affecting people worldwide. Effective methods to control and treat cryptosporidiosis among high-risk groups present an ongoing problem in need of attention.

Human cryptosporidiosis caused by Cryptosporidium tyzzeri and C. parvum isolates presumably transmitted from wild mice

We report a case of severe human cryptosporidiosis caused by Cryptosporidium tyzzeri and C. parvum with an unusually high frequency of liquid stools. Wild mice were the most likely source of infection, demonstrating the potential for wild-mouse-borne Cryptosporidium to infect humans and highlighting the health risks associated with synantropic rodents.

Social and gender determinants of risk of cryptosporidiosis, an emerging zoonosis, in Dagoretti, Nairobi, Kenya

The aim of the study was to investigate the social and gender determinants of the risk of exposure to Cryptosporidium from urban dairying in Dagoretti, Nairobi. Focus group discussions were held in six locations to obtain qualitative information on risk of exposure. A repeated cross-sectional descriptive study included participatory assessment and household questionnaires (300 randomly selected urban dairy farming households and 100 non-dairying neighbours). One-hundred dairy households randomly selected from the 300 dairy households participated in an additional economic survey along with 40 neighbouring non-dairy households. We found that exposure to Cryptosporidium was influenced by gender, age and role in the household. Farm workers and people aged 50 to 65 years had most contact with cattle, and women had greater contact with raw milk. However, children had relatively higher consumption of raw milk than other age groups. Adult women had more daily contact with cattle faeces than adult men, and older women had more contact than older men. Employees had greater contact with cattle than other groups and cattle faeces, and most (77 %) were male. Women took more care of sick people and were more at risk from exposure by this route. Poverty did not affect the level of exposure to cattle but did decrease consumption of milk. There was no significant difference between men and women as regards levels of knowledge on symptoms of cryptosporidiosis infections or other zoonotic diseases associated with dairy farming. Awareness of cryptosporidiosis and its transmission increased significantly with rising levels of education. Members of non-dairy households and children under the age of 12 years had significantly higher odds of reporting diarrhoea: gender, season and contact with cattle or cattle dung were not significantly linked with diarrhoea. In conclusion, social and gender factors are important determinants of exposure to zoonotic disease in Nairobi.