An outbreak of waterborne cryptosporidiosis caused by post-treatment contamination

Infectious Diseases Associated with Hydrometeorological Hazards in Europe: Disaster Risk Reduction in the Context of the Climate Crisis and the Ongoing COVID-19 Pandemic

Hydrometeorological hazards comprise a wide range of events, mainly floods, storms, droughts, and temperature extremes. Floods account for the majority of the related disasters in both developed and developing countries. Flooding alters the natural balance of the environment and frequently establish a favorable habitat for pathogens and vectors to thrive. Diseases caused by pathogens that require vehicle transmission from host to host (waterborne) or a host/vector as part of their life cycle (vector-borne) are those most likely to be affected by flooding. Considering the most notable recent destructive floods events of July 2021 that affected several Central Europe countries, we conducted a systematic literature review in order to identify documented sporadic cases and outbreaks of infectious diseases in humans in Europe, where hydrometeorological hazards, mainly floods, were thought to have been involved. The occurrence of water-, rodent-, and vector-borne diseases in several European countries is highlighted, as flooding and the harsh post-flood conditions favor their emergence and transmission. In this context, strategies for prevention and management of infectious disease outbreaks in flood-prone and flood-affected areas are also proposed and comprise pre- and post-flood prevention measures, pre- and post-outbreak prevention measures, as well as mitigation actions when an infectious disease outbreak finally occurs. Emphasis is also placed on the collision of floods, flood-related infectious disease outbreaks, and the evolving COVID-19 pandemic, which may result in unprecedented multi-hazard conditions and requires a multi-hazard approach for the effective disaster management and risk reduction.

Associations between High Temperature, Heavy Rainfall, and Diarrhea among Young Children in Rural Tamil Nadu, India: A Prospective Cohort Study

BACKGROUND

The effects of weather on diarrhea could influence the health impacts of climate change. Children have the highest diarrhea incidence, especially in India, where many lack safe water and sanitation.

OBJECTIVES

In a prospective cohort of 1,284 children under 5 y of age from 900 households across 25 villages in rural Tamil Nadu, India, we examined whether high temperature and heavy rainfall was associated with increased all-cause diarrhea and water contamination.

METHODS

Seven-day prevalence of diarrhea was assessed monthly for up to 12 visits from January 2008 to April 2009, and hydrogen sulfide ([Formula: see text]) presence in drinking water, a fecal contamination indicator, was tested in a subset of households. We estimated associations between temperature and rainfall exposures and diarrhea and [Formula: see text] using binomial regressions, adjusting for potential confounders, random effects for village, and autoregressive-1 error terms for study week.

RESULTS

There were 259 cases of diarrhea. The prevalence of diarrhea during the 7 d before visits was 2.95 times higher (95% CI: 1.99, 4.39) when mean temperature in the week before the 7-d recall was in the hottest versus the coolest quartile of weekly mean temperature during 1 December 2007 to 15 April 2009. Diarrhea prevalence was 1.50 times higher when the 3 weeks before the diarrhea recall period included [Formula: see text] (vs. 0 d) with rainfall of [Formula: see text] (95% CI: 1.12, 2.02), and 2.60 times higher (95% CI: 1.55, 4.36) for heavy rain weeks following a 60-d dry period. The [Formula: see text] prevalence in household water was not associated with heavy rain prior to sample collection.

CONCLUSIONS

The results suggest that, in rural Tamil Nadu, heavy rainfall may wash pathogens that accumulate during dry weather into child contact. Higher temperatures were positively associated with diarrhea 1-3 weeks later. Our findings suggest that diarrhea morbidity could worsen under climate change without interventions to reduce enteric pathogen transmission through multiple pathways. https://doi.org/10.1289/EHP3711.

Validation of Quantitative Microbial Risk Assessment Using Epidemiological Data from Outbreaks of Waterborne Gastrointestinal Disease

The assumptions underlying quantitative microbial risk assessment (QMRA) are simple and biologically plausible, but QMRA predictions have never been validated for many pathogens. The objective of this study was to validate QMRA predictions against epidemiological measurements from outbreaks of waterborne gastrointestinal disease. I screened 2,000 papers and identified 12 outbreaks with the necessary data: disease rates measured using epidemiological methods and pathogen concentrations measured in the source water. Eight of the 12 outbreaks were caused by Cryptosporidium, three by Giardia, and one by norovirus. Disease rates varied from 5.5 × 10^-6 to 1.1 × 10^-2 cases/person-day, and reported pathogen concentrations varied from 1.2 × 10^-4 to 8.6 × 10² per liter. I used these concentrations with single-hit dose-response models for all three pathogens to conduct QMRA, producing both point and interval predictions of disease rates for each outbreak. Comparison of QMRA predictions to epidemiological measurements showed good agreement; interval predictions contained measured disease rates for 9 of 12 outbreaks, with point predictions off by factors of 1.0-120 (median = 4.8). Furthermore, 11 outbreaks occurred at mean doses of less than 1 pathogen per exposure. Measured disease rates for these outbreaks were clearly consistent with a single-hit model, and not with a "two-hit" threshold model. These results demonstrate the validity of QMRA for predicting disease rates due to Cryptosporidium and Giardia.

Climate Change Contribution to the Emergence or Re-Emergence of Parasitic Diseases

The connection between our environment and parasitic diseases may not always be straightforward, but it exists nonetheless. This article highlights how climate as a component of our environment, or more specifically climate change, has the capability to drive parasitic disease incidence and prevalence worldwide. There are both direct and indirect implications of climate change on the scope and distribution of parasitic organisms and their associated vectors and host species. We aim to encompass a large body of literature to demonstrate how a changing climate will perpetuate, or perhaps exacerbate, public health issues and economic stagnation due to parasitic diseases. The diseases examined include those caused by ingested protozoa and soil helminths, malaria, lymphatic filariasis, Chagas disease, human African trypanosomiasis, leishmaniasis, babesiosis, schistosomiasis, and echinococcus, as well as parasites affecting livestock. It is our goal to impress on the scientific community the magnitude a changing climate can have on public health in relation to parasitic disease burden. Once impending climate changes are now upon us, and as we see these events unfold, it is critical to create management plans that will protect the health and quality of life of the people living in the communities that will be significantly affected.

Cryptosporidium and Giardia in Africa: current and future challenges

Cryptosporidium and Giardia are important causes of diarrhoeal illness. Adequate knowledge of the molecular diversity and geographical distribution of these parasites and the environmental and climatic variables that influence their prevalence is important for effective control of infection in at-risk populations, yet relatively little is known about the epidemiology of these parasites in Africa. Cryptosporidium is associated with moderate to severe diarrhoea and increased mortality in African countries and both parasites negatively affect child growth and development. Malnutrition and HIV status are also important contributors to the prevalence of Cryptosporidium and Giardia in African countries. Molecular typing of both parasites in humans, domestic animals and wildlife to date indicates a complex picture of both anthroponotic, zoonotic and spill-back transmission cycles that requires further investigation. For Cryptosporidium, the only available drug (nitazoxanide) is ineffective in HIV and malnourished individuals and therefore more effective drugs are a high priority. Several classes of drugs with good efficacy exist for Giardia, but dosing regimens are suboptimal and emerging resistance threatens clinical utility. Climate change and population growth are also predicted to increase both malnutrition and the prevalence of these parasites in water sources. Dedicated and co-ordinated commitments from African governments involving "One Health" initiatives with multidisciplinary teams of veterinarians, medical workers, relevant government authorities, and public health specialists working together are essential to control and prevent the burden of disease caused by these parasites.

Untangling the Impacts of Climate Change on Waterborne Diseases: a Systematic Review of Relationships between Diarrheal Diseases and Temperature, Rainfall, Flooding, and Drought

Global climate change is expected to affect waterborne enteric diseases, yet to date there has been no comprehensive, systematic review of the epidemiological literature examining the relationship between meteorological conditions and diarrheal diseases. We searched PubMed, Embase, Web of Science, and the Cochrane Collection for studies describing the relationship between diarrheal diseases and four meteorological conditions that are expected to increase with climate change: ambient temperature, heavy rainfall, drought, and flooding. We synthesized key areas of agreement and evaluated the biological plausibility of these findings, drawing from a diverse, multidisciplinary evidence base. We identified 141 articles that met our inclusion criteria. Key areas of agreement include a positive association between ambient temperature and diarrheal diseases, with the exception of viral diarrhea and an increase in diarrheal disease following heavy rainfall and flooding events. Insufficient evidence was available to evaluate the effects of drought on diarrhea. There is evidence to support the biological plausibility of these associations, but publication bias is an ongoing concern. Future research evaluating whether interventions, such as improved water and sanitation access, modify risk would further our understanding of the potential impacts of climate change on diarrheal diseases and aid in the prioritization of adaptation measures.

A Bibliometric and Trend Analysis on the Water-Related Risk Assessment Studies for Cryptosporidium Pathogen

BACKGROUND

The bibliometric methods have been used in many disciplines of sciences to study the scientific production and research trends. In this study, they were used to investigate research trends related to the risk assessment of Cryptosporidium pathogen in water field.

METHODS

Data were obtained on the Scopus database from 1993 to 2013. Research tendency was investigated by analyzing the distribution of languages, countries, journals, author keywords, authorship pattern and co-authorship relations.

RESULTS

The English language was dominant language of all publications (96.36%). Number of articles in this field increased from 2 in 1993 to 29 papers in 2007 and then received to 19 at the end of 2013. United States produced 35.41% of all pertinent articles followed by United Kingdom with 10.76% and Australia with 9.92%. Water Research Journal published the most papers in this field, taking 11.62% of all, followed by Journal of Water and Health (10.92%) and Water Science and Technology (10.21%). The most productive authors were Ashbolt NJ form Canada that accounts about 1.51% of the total publications followed by Rose JB and Haas CN from United States. Authorship pattern analysis results show that literature does follow Lotka's law (P=0.627).

CONCLUSION

A downward trend in the number of publications is likely to occur in future. The results of this bibliometric analysis may help relevant researchers realize the scope of the microbial risk assessment research of Cryptosporidium, and establish the further research direction.

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.

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.

Cryptosporidiosis in Farmed Animals

Cryptosporidiosis was first identified as a disease of veterinary, rather than human medical, importance, and infection of farmed animals with different species of Cryptosporidium continues to be of veterinary clinical concern. This chapter provides insights into Cryptosporidium infection in a range of farmed animals – cattle, sheep, goats, pigs, cervids, camelids, rabbits, water buffalo and poultry – presenting not only an updated overview of the infection in these animals, but also information on clinical disease, infection dynamics and zoonotic potential. Although extensive data have been accrued on, for example, Cryptosporidium parvum infection in calves, and calf cryptosporidiosis continues to be a major veterinary concern especially in temperate regions, there remains a paucity of data for other farmed animals, despite Cryptosporidium infection causing significant clinical disease and also, for some species, with the potential for transmission of infection to people, either directly or indirectly.

Leaching of Cryptosporidium parvum oocysts, Escherichia coli, and a Salmonella enterica serovar Typhimurium bacteriophage through intact soil cores following surface application and injection of slurry

Increasing amounts of livestock manure are being applied to agricultural soil, but it is unknown to what extent this may be associated with contamination of aquatic recipients and groundwater if microorganisms are transported through the soil under natural weather conditions. The objective of this study was therefore to evaluate how injection and surface application of pig slurry on intact sandy clay loam soil cores influenced the leaching of Salmonella enterica serovar Typhimurium bacteriophage 28B, Escherichia coli, and Cryptosporidium parvum oocysts. All three microbial tracers were detected in the leachate on day 1, and the highest relative concentration was detected on the fourth day (0.1 pore volume). Although the concentration of the phage 28B declined over time, the phage was still found in leachate at day 148. C. parvum oocysts and chloride had an additional rise in the relative concentration at a 0.5 pore volume, corresponding to the exchange of the total pore volume. The leaching of E. coli was delayed compared with that of the added microbial tracers, indicating a stronger attachment to slurry particles, but E. coli could be detected up to 3 months. Significantly enhanced leaching of phage 28B and oocysts by the injection method was seen, whereas leaching of the indigenous E. coli was not affected by the application method. Preferential flow was the primary transport vehicle, and the diameter of the fractures in the intact soil cores facilitated transport of all sizes of microbial tracers under natural weather conditions.

Quantitative health risk assessment of Cryptosporidium in rivers of southern China based on continuous monitoring

The concentrations of Cryptosporidium in the source water of several cities of Zhejiang Province, China were determined to be in the range of 0-17 oocysts/10 L in the rainy season in 2008, with a mean value of 7 oocysts/10 L. Based on the investigation data, comprehensive risk assessment of Cryptosporidium infection was performed by considering different water intake routes as well as water consumption. Intakes of unboiled tapwater (including drinking and tooth-brushing and food and dish washing) and source water (through swimming in rivers) were estimated to be 2.59-25.9 and 0.32-0.74 L/year-person, respectively. The mortality due to Cryptosporidium infection for people in this region, excluding HIV-infected patients, was calculated as 0-0.0146 per 10(5) persons using a conditional probability formula. Disability-adjusted life years (DALYs) were used to quantify the risk of Cryptosporidium infection, for which uncertainty was analyzed. For people who consumed conventionally treated water, the DALYs due to Cryptosporidium infection were 6.51 per 10(5) (95% CI: 2.16 × 10(-5)-22.35 × 10(-5)) persons, which were higher than a risk judged acceptable by some (1.97 × 10(-5) DALYs per year), and the risk for those consuming ozone-treated water became 0.0689 × 10(-5) DALYs per year. The major risk of infection resulted from swimming in the river. This study provides a method to establish the risk of Cryptosporidium infection and optimize the scheme for reducing the risk effectively, which is useful for the modification of water quality standards based on cost utility analysis given use of DALYs.

Symptomatic and asymptomatic cryptosporidiosis in young children in Iran

The present study was conducted during the period May 2003 to October 2003 in 616 children less than three years of age with and without diarrheal disease presenting at the pediatric clinic of teaching hospitals in Kermanshah, Iran. Single stool specimens were collected from 515 diarrheic and 99 non-diarrheic children. Two smears were made from each stool samples and were stained by a modified Ziehl Neelsen technique. Cryptosporidium parvum (C. parvum) were detected in 10.4% of children. The C. parvum infection rate was significantly higher in diarrheic children (11.6%) than in non-diarrheic children (4.0%). C. parvum was observed more frequently in stool samples of children who lived in rural areas (15.2%) than those who lived in urban areas (7.2%). In regard to the presence of animals, the infection rate was 18.5% among children who lived in association with animals in comparison with 8.2% among those who lived in compounds with no animals. The majority of C. parvum cases occurred in children between the ages of 0-12 months (11.9%), followed by in children between the ages of 13-24 months (9.2%) and in children between the ages of 25-36 months (3.0%). The data suggest that C. parvum is relatively endemic in young children and that Cryptosporidium may be an important pathogen associated with diarrhea in young children.

Cryptosporidiosis and filtration of water from Loch Lomond, Scotland

Coagulation and rapid gravity filtration coincided with a significant reduction in cryptosporidiosis cases.

Previous evidence has suggested an association between consumption of unfiltered water from Loch Lomond, Scotland, and cryptosporidiosis. Before November 1999, this water had been only microstrained and disinfected with chlorine; however, since that time, physical treatment of the water (coagulation, rapid gravity filtration) has been added. To determine risk factors, including drinking water, for cryptosporidiosis, we analyzed data on laboratory-confirmed cases of cryptosporidiosis collected from 1997 through 2003. We identified an association between the incidence of cryptosporidiosis and unfiltered drinking water supplied to the home. The association supports the view that adding a filtration system to minimally treated water can substantially reduce the number of confirmed cryptosporidiosis cases.

Published case studies of waterborne disease outbreaks--evidence of a recurrent threat

Residents of affluent nations are remarkably lucky to have high-quality, safe drinking water supplies that most residents of modem cities enjoy, particularly when considered in contrast to the toll of death and misery that unsafe drinking water causes for most of the world's population. Some may presume that drinking-water disease outbreaks are a thing of the past, but complacency can easily arise. A review of drinking water outbreaks in developed countries over the past 3 decades reveals some of the reasons why drinking water outbreaks keep occurring when society clearly has the means to prevent them. Prevention of future outbreaks does not demand perfection, only a commitment to learn from past mistakes and to act on what has been learned.

Infectious diseases of severe weather-related and flood-related natural disasters

PURPOSE OF REVIEW

The present review will focus on some of the possible infectious disease consequences of disastrous natural phenomena and severe weather, with a particular emphasis on infections associated with floods and the destruction of infrastructure.

RECENT FINDINGS

The risk of infectious diseases after weather or flood-related natural disasters is often specific to the event itself and is dependent on a number of factors, including the endemicity of specific pathogens in the affected region before the disaster, the type of disaster itself, the impact of the disaster on water and sanitation systems, the availability of shelter, the congregating of displaced persons, the functionality of the surviving public health infrastructure, the availability of healthcare services, and the rapidity, extent, and sustainability of the response after the disaster. Weather events and floods may also impact disease vectors and animal hosts in a complex system.

SUMMARY

Weather or flood-related natural disasters may be associated with an increased risk of soft tissue, respiratory, diarrheal, and vector-borne infectious diseases among survivors and responders.

Survival of Cryptosporidium parvum oocysts after prolonged exposure to still natural mineral waters

The survival kinetics of purified Cryptosporidium parvum oocysts of both human and ovine origin, immersed in four still natural mineral waters (total dissolved salts ranging from 91 mg/liter to 430 mg/liter) and reverse osmosis water was assessed by inclusion or exclusion of the fluorogenic vital dyes 4',6-diamidino-2-phenylindole and propidium iodide over a 12-week period. Semipermeable chambers were used to contain the oocysts while immersed in each mineral water type, permitting both intimate interactions between oocysts and matrices and straightforward sampling for viability assessments. The viability of both oocyst types, assessed at weekly intervals, remained unaltered after 12 weeks at 4 degrees C, whereas a progressive decline in the viability of both oocyst isolates was observed when immersed in mineral waters at 20 degrees C. At 20 degrees C, approximately 30% of oocysts remained viable after 12 weeks incubation. Here, temperature was the major factor that adversely affected oocyst survival, although higher mineral content was also proportionally and significantly associated with this increased oocyst inactivation. The prolonged survival of oocysts at 4 degrees C in our studies indicates that they could survive for prolonged periods of time in U.K. groundwaters (average temperature approximately 10 degrees C) and thus represent a potential public health hazard if contamination of mineral water sources by viable oocysts were to occur.

Climate change and waterborne and vector-borne disease

This paper considers the potential impact on human health from waterborne and vector-borne infections. It concentrates on the impact of two possible changes to climate; increased frequency of heavy rainfall events, with associated flooding and increased temperature. Flooding is associated with increased risk of infection in developing nations but not in the West unless water sources are compromised. There have been numerous reported of outbreaks that followed flooding that led to contamination of underground sources of drinking water. Heavy rainfall also leads to deterioration in the quality of surface waters that could adversely affect the health of those engaged in recreational water contact. It is also concluded that there may be an increase in the number of cyanobacterial blooms because of a combination of increased nutrient concentrations and water temperature. It is considered unlikely that climate change will lead to an increase in disease linked to mains drinking water, although private supplies would be at risk from increased heavy rainfall events. Although increased temperature could lead to climatic conditions favourable to increases in certain vector-borne diseases such as malaria, the infrastructure in the UK would prevent the indigenous spread of malaria.

Prevalence of Giardia spp. and Cryptosporidium spp. on dairy farms in southeastern New York state

A prevalence study was designed to determine the presence of Cryptosporidium spp. and Giardia spp. in the soil of 37 dairy farms in southeastern New York state. A sampling design was developed and used to collect soil samples from these farms. Areas on the farms which were considered to be potential sources of contamination to the environment were evaluated quantitatively using a multidimensional scale. This scale included factors which could have the potential to contribute to the risk of contamination of the environment with Giardia or Cryptosporidium. In addition, the runoff pathway from these areas was identified and sampling points along that pathway were determined. Using a sampling grid, sampling sites were determined and soil samples collected and analyzed individually for the following: presence of Giardia and Cryptosporidium, pH, gravimetric moisture content, and volumetric moisture content. Out of 782 soil samples, 17% were positive for Cryptosporidium and 4% were positive for Giardia. The pH of the soil ranged from 3.7 to 9.8 with a mean of 7.0. There was a significant association between the pH and the likelihood of detecting Cryptosporidium spp. As the pH increased, the likelihood of detecting an oocyst decreased. Gravimetric moisture content had a mean of 40% and a range from 7 to 86%. There was a significant association between the gravimetric moisture content and the likelihood of detecting Giardia in soil samples.

Factors associated with the likelihood of Giardia spp. and Cryptosporidium spp. in soil from dairy farms

A study was conducted to identify factors associated with the likelihood of detecting Giardia spp. and Cryptosporidium spp. in the soil of dairy farms in a watershed area. A total of 37 farms were visited, and 782 soil samples were collected from targeted areas on these farms. The samples were analyzed for the presence of Cryptosporidium spp. oocysts, Giardia spp. cysts, percent moisture content, and pH. Logistic regression analysis was used to identify risk factors associated with the likelihood of the presence of these organisms. The use of the land at the sampling site was associated with the likelihood of environmental contamination with Cryptosporidium spp. Barn cleaner equipment area and agricultural fields were associated with increased likelihood of environmental contamination with Cryptosporidium spp. The risk of environmental contamination decreased with the pH of the soil and with the score of the potential likelihood of Cryptosporidium spp. The size of the sampling site, as determined by the sampling design, in square feet, was associated nonlinearly with the risk of detecting Cryptosporidium spp. The likelihood of the Giardia cyst in the soil increased with the prevalence of Giardia spp. in animals (i.e., 18 to 39%). As the size of the farm increased, there was decreased risk of Giardia spp. in the soil, and sampling sites which were covered with brush or bare soil showed a decrease in likelihood of detecting Giardia spp. when compared to land which had managed grass. The number of cattle on the farm less than 6 mo of age was negatively associated with the risk of detecting Giardia spp. in the soil, and the percent moisture content was positively associated with the risk of detecting Giardia spp. Our study showed that these two protozoan exist in dairy farm soil at different rates, and this risk could be modified by manipulating the pH of the soil.

Epidemiology of Cryptosporidium: transmission, detection and identification

There are 10 valid species of Cryptosporidium and perhaps other cryptic species hidden under the umbrella of Cryptosporidium parvum. The oocyst stage is of primary importance for the dispersal, survival, and infectivity of the parasite and is of major importance for detection and identification. Because most oocysts measure 4-6 microm, appear nearly spherical, and have obscure internal structures, there are few or no morphometric features to differentiate species and in vitro cultivation does not provide differential data as for bacteria. Consequently, we rely on a combination of data from three tools: morphometrics, molecular techniques, and host specificity. Of 152 species of mammals reported to be infected with C. parvum or an indistinguishable organism, very few oocysts have ever been examined using more than one of these tools. This paper reviews the valid species of Cryptosporidium, their hosts and morphometrics; the reported hosts for the human pathogen, C. parvum; the mechanisms of transmission; the drinking water, recreational water, and food-borne outbreaks resulting from infection with C. parvum; and the microscopic, immunological, and molecular methods used to detect and identify species and genotypes.

Cryptosporidia and microsporidia--waterborne diseases in the immunocompromised host

Cryptosporidia and microsporidia are emerging parasitic pathogens in immunocompetent and immunocompromised individuals. Cryptosporidium infects several wild and domestic animals that excrete oocysts into the environment and contaminated water represents the major source of infection for humans. Waterborne transmission of Cryptosporidium is a major risk for humans and appropriate measures have to be taken to protect immunocompetent and immunocompromised individuals to become infected. For microsporidia, the sources and ways of transmission are not well documented. Although several animal hosts have been identified recently, the relevant reservoirs of human microsporidia are still unknown. Also, the routes of spreading are unknown. Is microsporidiosis a zoonotic disease that will be transmitted through close contact with infected animals or is contaminated surface water responsible for transmission and represents a relevant reservoir? This review is designed to give information on these two emerging intestinal parasites in a format that will be useful to clinical microbiologists, physicians interested in infectious diseases, and public health personnel.

DNA sequence similarity between California isolates of Cryptosporidium parvum

We evaluated whether nucleic acid amplification with primers specific for Cryptosporidium parvum followed by automated DNA sequence analysis of the PCR amplicons could differentiate between California isolates of C. parvum obtained from livestock, humans, and feral pigs. Almost complete sequence identity existed among the livestock isolates and between the livestock and human isolates. DNA sequences from feral pig isolates differed from those from livestock and humans by 1.0 to 1.2%. The reference sequence obtained by Laxer et al. (M. A. Laxer, B. K. Timblin, and R. J. Patel, Am. J. Trop. Med. Hyg. 45:688-694, 1991.) differed from California isolates of C. parvum by 1.8 to 3.2%. These data suggest that DNA sequence analysis of the amplicon of Laxer et al. does not allow for differentiation between various strains of C. parvum or that our collection of isolates obtained from various hosts from across California was limited to one strain of C. parvum.

Prevalence of and associated risk factors for shedding Cryptosporidium parvum oocysts and Giardia cysts within feral pig populations in California

Populations of feral pigs (Sus scrofa) may serve as an environmental reservoir of Cryptosporidium parvum oocysts and Giardia sp. cysts for source water. We conducted a cross-sectional study to determine the prevalence of and associated demographic and environmental risk factors for the shedding of C. parvum oocysts and Giardia sp. cysts. Feral pigs were either live-trapped or dispatched from 10 populations located along the coastal mountains of western California, and fecal samples were obtained for immunofluorescence detection of C. parvum oocysts and Giardia sp. cysts. We found that 12 (5.4%) and 17 (7.6%) of 221 feral pigs were shedding C. parvum oocysts and Giardia sp. cysts, respectively. The pig's sex and body condition and the presence of cattle were not associated with the probability of the shedding of C. parvum oocysts. However, younger pigs (< or = 8 months) and pigs from high-density populations (> 2.0 feral pigs/km2) were significantly more likely to shed oocysts compared to older pigs (> 8 months) and pigs from low-density populations (< or = 1.9 feral pigs/km2). In contrast, none of these demographic and environmental variables were associated with the probability of the shedding of Giardia sp. cysts among feral pigs. These results suggest that given the propensity for feral pigs to focus their activity in riparian areas, feral pigs may serve as a source of protozoal contamination for surface water.

Parasites and Diarrhea. I: Protozoans and Diarrhea

Intestinal parasitism is extremely common, with approximately 70% of all people harboring one or more intestinal parasite. Parasitism and diarrhea are both hyperendemic in areas where sanitation is suboptimal. Many clinicians assume that the identification of intestinal parasites in patients with diarrhea implies that the parasites are the cause. This approach is frequently misguided. Some intestinal parasites such as Giardia lamblia and Entamoeba histolytica certainly do cause diarrhea. Others, for example Entamoeba coli and Ascaris lumbricoides, almost certainly do not. In addition, there are a number of other organisms that have been associated with diarrheal illness in some cases, which may or may not be important pathogens. In this article, we will review the role of protozoans as definite and possible causes of diarrhea. In Part II, we review the role of helminths in diarrhea.

Cryptosporidiosis in Houston, Texas. A report of 95 cases

Cryptosporidiosis is an important cause of diarrhea. We identified 95 patients with cryptosporidiosis over a 6-year period in our county hospital system, including 9 children and 86 adults infected with the human immunodeficiency virus (HIV). Risk factors included male-to-male sexual practices and Hispanic race. Diarrhea, weight loss, and gastrointestinal complaints were the most common symptoms at presentation. Among the HIV-infected adults, 20 (23%) developed biliary tract disease. Biliary involvement was associated with low CD4 counts. Treatment with paromomycin and antimotility agents was effective in reducing diarrheal symptoms in 54 of 70 (77%) patients with the acquired immunodeficiency syndrome (AIDS), although there was a high rate of relapse. Paromomycin did not prevent the development of biliary disease. Biliary disease responded to cholecystectomy or sphincterotomy with stent placement. Though often a cause of morbidity, cryptosporidiosis was only rarely the cause of death, even among patients with HIV. Cryptosporidiosis continues to be an important medical problem even in developed-countries. Current methods of prevention and treatment are suboptimal.

Protozoal agents: what are the dangers for the public water supply?

Safe and efficient treatment of drinking water has been one of the major public health advances of the twentieth century. People in developed countries generally take for granted that their water is safe to drink, a luxury the majority of the world's population does not have. The leading cause of infant mortality in the developing world is infectious diarrhea, and the prevalence of diarrheal pathogens is largely influenced by the quality and quantity of clean water available for drinking and washing. Until recently, modern water treatment had all but eliminated these concerns in developed nations. Over the past two decades, however, the safety of our water supply has been threatened by the emergence of Cryptosporidium parvum, a protozoal pathogen. The hearty oocysts of this organism survive chlorination and filtration to cause a diarrheal illness that, while unpleasant enough in healthy people, is devastating in immunocompromised individuals. The 1993 Milwaukee outbreak, in which 403,000 people developed diarrhea from drinking water that met all the updated federal safety standards, demonstrated the tremendous public health importance of this organism. While earlier attention had focused on Giardia and amebic infections, the other "emerging" protozoan besides Cryptosporidium is Cyclospora. This review discusses the protozoal pathogens, including Cryptosporidium parvum, Giardia lamblia, Entamoeba histolytica, and Cyclospora cayetanensis, that cause waterborne diarrheal outbreaks and the threats they pose to the public.

Cryptosporidium sp. in children suffering from acute diarrhea at Uberlândia City, State of Minas Gerais, Brazil

This study's objective was to search for Cryptosporidium sp. in diarrheic feces from children aged zero to 12 years and cared for at medical units within Universidade Federal de Uberlândia or at a private practice in Uberlândia, State of Minas Gerais, Brazil, from September 1992 to August 1993. Three fecal samples preserved in 10% formalin, were collected from 94 children. Oocyst concentration was performed through Ritchie's (modified) method and staining of fecal smears for each sample (total of 1128 slides) was done by the "Safranin/Methylene Blue" and the "Kinyoun (modified)" techniques. The Hoffmann, Pons & Janer method was also employed to look for other enteroparasites. From 94 children, 4.26% excreted fecal Cryptosporidium oocysts. The infection seemed to vary according to age: 5.08% of patients aged zero to two years old; 33.33% of those aging eight to ten years (P > 0.05). Cryptosporidium appeared in November, December and March, during the rainy season. 20.21% of the children harbored at least one enteroparasite different from Cryptosporidium, mainly Giardia intestinalis (12.77%). From Cryptosporidium infected patients, two had only this kind, another harbored Giardia intestinalis; the last one hosted Strongyloides stercoralis.

Giardia and Cryptosporidium in backwash water from rapid sand filters used for drinking water production

Backwash water from rapid sand filters of a treatment plant using surface water from small rivers for drinking water production was examined with the aim of determining the degree of their potential contamination with Giardia cysts and Cryptosporidium oocysts. Simultaneous investigations were carried out for both protozoans from November 1993 to February 1994. Water samples were concentrated by continuous flow centrifugation (11 backwash water samples) or by using polypropylene cartridge filters (12 raw water samples and 39 backwash water samples). Parasites were identified by the direct immunofluorescence assay. Ten out of 12 raw water samples tested were positive for Giardia (range: 2-103/ 100 L) and 8 out of 12 were positive for Cryptosporidium (range: 0.8-109/100L). Eight of 11 backwash water samples collected by continuous flow centrifugation were positive for Giardia (range: 3-86/100 L) or Cryptosporidium (range: 1-69/100 L). Out of 39 samples collected using cartridge filters, 34 were positive for Giardia (range: 1.4-374/100 L) and 33 for Cryptosporidium (range: 0.8-252/100 L). Overall, Giardia, Cryptosporidium, or both were detected in 92% of the backwash water samples. The results have clearly shown that backwash waters were contaminated with Giardia and Cryptosporidium and the supernatant returned to the raw water after the sedimentation process was not free from cysts and oocysts.

A mixed outbreak of cryptosporidium and campylobacter infection associated with a private water supply

In an outbreak of gastroenteritis affecting 43 people, cryptosporidium and campylobacter were isolated from stool specimens and in two cases dual infection was found. All the cases had drunk unboiled water from a private untreated water supply. Investigations revealed the carcasses of three lambs in a collection chamber connected with the water supply, and these, or run-off of slurry from surrounding fields, were the presumed source of contamination. Issues relating to the maintenance and monitoring of private water supplies are discussed. Problems with such supplies include old piping, proximity of livestock, inadequate knowledge of the layout and limited resources for monitoring and maintenance.

Differentiation of Cryptosporidium parvum, C. muris, and C. baileyi by PCR-RFLP analysis of the 18S rRNA gene

We have developed a combined polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) assay for the detection and differentiation of Cryptosporidium parvum, Cryptosporidium muris, and Cryptosporidium baileyi. The assay utilizes PCR to amplify an approximately 1750 basepair product of the Cryptosporidium 18S rRNA gene. Following double digestion with restriction endonucleases Dral and Vsp1, this PCR product yields DNA fragments that can be resolved electrophoretically into RFLP profiles that are distinct for C. parvum, C. muris, and C. baileyi. Previous PCR-restriction analyses could not simultaneously differentiate all three species. Future application of this technique could include predicting the disease-causing potential of oocyst-contaminated environmental specimens and helping to determine the source of oocyst contamination.

Simplified method for recovery and PCR detection of Cryptosporidium DNA from bovine feces

An assay to identify Cryptosporidium DNA in bovine feces has been developed emphasizing standardization of sample preparation and simplification of the DNA recovery process for PCR amplification and DNA hybridization detection. The Cryptosporidium DNA recovery-PCR detection procedure (CR-PCR) can recover DNA suitable for PCR amplification without using or generating hazardous chemicals or wastes. In comparisons with a commercial enzyme-linked immunoassay (Color Vue-Cryptosporidium; Seradyn, Indianapolis, Ind.), the CR-PCR could detect 10(3) to 10(4) times fewer purified oocysts diluted in solution (water or buffered saline) and 10(2) times fewer oocysts from diarrheic feces and showed earlier detectability from solid, nondiarrheic feces in an experimental infection. This assay may prove useful for detecting Cryptosporidium oocysts in feces and in clarifying the role of livestock in waterborne outbreaks of cryptosporidiosis.

Identification of genetic heterogeneity in the Cryptosporidium parvum ribosomal repeat

Oocysts of the protozoan parasite Cryptosporidium parvum are found in most surface waters and can contaminate municipal water supplies, as demonstrated by recent outbreaks of cryptosporidiosis. A method capable of fingerprinting C. parvum isolates from the environment would facilitate the study of epidemiology and transmission cycles and aid in the implementation of preventive measures to reduce water contamination by oocytes. In this study, we report polymorphism in C. parvum isolates on the basis of analysis of random amplified polymorphic DNA and nucleotide sequences in a region of the 18S rRNA and the internal transcribed spacer 1. Isolate-specific primers for these two regions were designed, and PCR tests capable of discriminating between isolates were developed. In both PCR assays, the five C. parvum isolates analyzed segregated into two subgroups. One group consisted of isolates that originated directly from human patients, and the other group had various host origins and had been propagated in laboratory animals. These results demonstrate the feasibility of distinguishing C. parvum isolates by sequence-specific PCR tests.

Outbreak of cryptosporidiosis associated with a disinfected groundwater supply

In an outbreak of cryptosporidiosis in Warrington, a town in North-West England, 47 cases were recorded between November 1992 and February 1993, most within the first month. There was a strong statistical association between cases and residence in an area supplied from two groundwater sources. In a case-control study, a strong association between having drunk unboiled tap water from these sources, and a dose-response relationship were found. Oocysts were not detected in the water supply. During very heavy rainfall one source of water was found to drain surface water directly from a field containing livestock faeces, thereby bypassing natural sandstone filtration. Exceptionally heavy rainfall occurred at the probable time of infection. After withdrawal of the original water supply, the outbreak rapidly subsided. It was concluded that there was very strong evidence that this outbreak was waterborne. This, the second documented outbreak of cryptosporidiosis attributable to a groundwater supply, demonstrates that infection can be transmitted from a disinfected groundwater source despite apparently satisfactory treated water quality. We recommended that guidelines for protection of groundwater are implemented, raw groundwater should be routinely monitored for microbiological contamination, and the structure of all sources and waterworks should be assessed in risk surveys of water catchment areas.

Detection of viable Cryptosporidium parvum oocysts by PCR

PCR was used to detect and specifically identify a gene fragment from Cryptosporidium parvum. An 873-bp region of a 2,359-bp DNA fragment encoding a repetitive oocyst protein of C. parvum was shown to be specifically amplified in C. parvum. An excystation protocol before DNA extraction allowed the differentiation between live and dead Cryptosporidium parvum oocysts.

An outbreak of waterborne cryptosporidiosis associated with a public water supply in the UK

In November and December 1992, an outbreak of waterborne cryptosporidiosis occurred in Bradford, a city in the North of England. In all 125 cases were involved, the majority of whom lived in part of the city which received its drinking water supply from a single water treatment works. A case control study demonstrated an association between illness and the consumption of tapwater from this source; those drinking large volumes being more likely to have been ill. Treated water from the defined source yielded cryptosporidial oocysts. Heavy rainfall was recorded in the catchment area of the reservoir supplying raw water to the treatment works, immediately prior to the probable time of infection, based on dates of onset of illness.

Comparison of four different methods for detection of Cryptosporidium species

Newly available assays offer alternatives to conventional microscopic examination for Cryptosporidium spp. We compared two enzyme immunoassays, ProSpect Cryptosporidium microtiter assay (Alexon, Inc., Mountain View, Calif.) and Color Vue Cryptosporidium assay (Serady, Indianapolis, Ind.), and a direct immunofluorescent assay, Merifluor Cryptosporidium kit (Meridian Diagnostics, Cincinnati, Ohio), with acid-fast Kinyoun-staining for the detection of Cryptosporidium spp. Examinations were performed on 129 stool specimens received from patients during a recent waterborne outbreak. A specimen was considered positive when organisms could be identified visually by acid-fast and immunofluorescent stains or if organisms could be visualized by either acid-fast or immunofluorescent stain and detected by both enzyme immunoassays. The final number of positive specimens was 55. No single procedure detected all 55 positive specimens. Of these, ProSpect and Color Vue detected 52 (sensitivity, 94.5%), and the Kinyoun stain and Merifluor detected 53 (sensitivity, 96.4%). The final number of negative specimens was 74. One false-positive result was seen with both the Kinyoun stain and the ProSpect assay. The Color Vue and ProSpect assays required the most hands-on technologist time. The ProSpect assay and Merifluor kit were easiest to perform. The acid-fast stain was difficult to interpret. The Merifluor kit was easiest to read and was adaptable to both batch and single testing. Overall, the Kinyoun stain and the Merifluor test were preferable to both of the enzyme immunoassays because of the high reagent cost and hands-on time required for the enzyme immunoassays. The difficult interpretation of the Kinyoun stain smears made the Merifluor a more desirable test despite its higher cost. We conclude that all methods tested were equally sensitive and specific for the detection of Cryptosporidium spp. Ease of use, adaptability to batch testing, and cost are important criteria in determining the method of choice.

Cryptosporidium oocysts in water for human consumption. Comparison of staining methods

A study was carried out on the presence of oocysts of Cryptosporidium spp. in water for human consumption in the Province of Salamanca, Spain, using four different staining techniques: Ziehl-Neelsen, auramine, indirect immunofluorescence with monoclonal antibodies (Meridian, USA) and direct immunofluorescence with monoclonal antibodies (Pasteur, France). The presence of oocysts was detected in the water used for the washing of sand filters in the four water purifying plants and in the drinking water of two of the six geographical areas studied. The Ziehl-Neelsen and auramine staining techniques were found to have excellent diagnostic correlation. Immunofluorescence stainings with monoclonal antibodies proved to be less sensitive.

An outbreak of cryptosporidiosis associated with a swimming pool

In August 1988 an increase was noted in the number of cases of cryptosporidiosis identified by the microbiology laboratory at Doncaster Royal Infirmary. By 31 October, 67 cases had been reported. Preliminary investigations implicated the use of one of two swimming pools at a local sports centre and oocysts were identified in the pool water. Inspection of the pool revealed significant plumbing defects which had allowed ingress of sewage from the main sewer into the circulating pool water. Epidemiological investigation confirmed an association between head immersion and illness. The pools were closed when oocysts were identified in the water and extensive cleaning and repair work was undertaken. The pool water was retested for cryptosporidial oocysts and found to be negative before the pool reopened.

An outbreak of waterborne cryptosporidiosis in Swindon and Oxfordshire

An outbreak of cryptosporidiosis resulted in 516 cases in Wiltshire and Oxfordshire. The outbreak caused widespread interest and led to an official inquiry. The majority of cases were in children; 8% of cases were admitted to hospital and the median duration of illness was 3 weeks. The geographical distribution of cases matched the distribution of water supplies from three treatment works and cryptosporidium oocysts were found at these works and in the treated water. Attack rates in electoral wards supplied by the three treatment works were significantly higher than in other wards. The cause of the outbreak appeared to be the failure of normal treatment to remove oocysts. Measures at the treatment works reduced the number of oocysts detected in treated water, after which the outbreak came to an end. The conclusion of the investigations was that cryptosporidiosis is a risk of conventionally treated public water supplies.