Epidemic and endemic seroprevalence of antibodies to Cryptosporidium and Giardia in residents of three communities with different drinking water supplies

A scoping review of risk factors and transmission routes associated with human giardiasis outbreaks in high-income settings

The flagellated pathogen Giardia duodenalis is one of the leading causes of parasitic gastrointestinal illness worldwide. In many higher income countries, such as the United Kingdom, the disease is often perceived as being travel-related, likely leading to the under-reporting of sporadic cases and outbreaks. A summary of the literature describing outbreaks and risk factors in higher income countries is necessary to improve our understanding of this pathogen and identify existing knowledge gaps. Initial literature searches were carried out in September 2016 and updated at regular intervals until November 2021, using appropriate search terms in Medline, Embase and PubMed databases. A total of 75 papers met the inclusion criteria, revealing that the consumption of contaminated water and contact with young children of diaper-wearing age were the most common transmission routes leading to outbreaks of giardiasis. Of the ten studies where food was primarily associated with outbreaks, food handlers accounted for eight of these. Another reported transmission route was direct contact with fecal material, which was reported in six studies as the primary transmission route. Travel-associated giardiasis was considered the sole transmission route in two studies, whereas multiple transmission routes contributed to giardiasis outbreaks in eleven studies. The evidence around zoonotic transmission was less clear and hampered by the lack of robust and regularly applied parasite molecular typing techniques. This literature review summarizes the findings of Giardia outbreak investigations and epidemiological studies in high-income countries. Transmission routes are identified and discussed to highlight the associated risk factors. These data also indicate gaps in our current knowledge that include the need for robust, in-depth molecular studies and have underscored the importance of water as a transmission route for Giardia cysts. These future molecular studies will improve our understanding of Giardia epidemiology and transmission pathways in higher income countries to prevent spread of this significantly under-reported pathogen.

Persistent Iron Deficiency Anemia in Patients with Celiac Disease Despite a Gluten-Free Diet

Celiac disease (CD) is an autoimmune disorder characterized by intolerance to dietary gluten in genetically predisposed subjects. Iron deficiency anemia (IDA) is a common sign in CD, being the only abnormality in approximately 40% of celiac patients. A multifactorial etiology leads to IDA in CD. The two main causes are the villous atrophy of the mucosa at the site of iron absorption (the duodenum) and the resulting inflammation, which triggers the mechanism that leads to the anemia of chronic disease. Until now, it has been unclear why some patients with CD continue to have IDA despite a careful gluten-free diet (GFD) and the normalization of villous atrophy. Furthermore, some celiac patients are refractory to oral iron supplementation despite the healing of the mucosa, and they thus require periodic intravenous iron administration. The Marsh classification evaluates the degree of inflammation and villous atrophy, but it does not assess the possible persistence of ultrastructural and molecular alterations in enterocytes. The latter was found in CD in remission after adopting a GFD and could be responsible for the persistently reduced absorption of iron and IDA. Even in non-celiac gluten sensitivity, anemia is present in 18.5-22% of patients and appears to be related to ultrastructural and molecular alterations in intestinal microvilli. It is possible that a genetic component may also play a role in IDA. In this review, we evaluate and discuss the main mechanisms of IDA in CD and the possible causes of its persistence after adopting a GFD, as well as their therapeutic implications.

High serological response to Cryptosporidium-specific antigens in the Czech Republic and its association with water supply

A survey was conducted in the Czech Republic to determine whether serological responses to the 15/17-kDa and 27-kDa Cryptosporidium antigens had changed since the end of the communist era and if these responses were associated with drinking water sources. Sera from 301 blood donors residing in six areas served by various sources of drinking water were analysed by Western Blot (mini-immunoblots) to measure the IgG response. The intensity of response and percentage of persons with a strong response to the 27-kDa, but not the 15/17-kDa, antigen were higher than found 20 years earlier. A strong response to both the 15/17- and 27-kDa-antigens was higher than reported in other countries, and the probability of persons having a strong response was greater in areas with surface water sources than river-bank infiltration. Few cases of cryptosporidiosis were reported in spite of these high responses to Cryptosporidium antigens. These responses suggest a chronic low-level exposure from several sources that may be affording protection against symptoms and illness. Although strong serological responses were associated with surface water sources, drinking water is not likely to be the most important exposure for Cryptosporidium in the Czech Republic.

Giardia and Cryptosporidium antibody prevalence and correlates of exposure among Alaska residents, 2007-2008

Giardia duodenalis and Cryptosporidium spp. are common intestinal protozoa that can cause diarrhoeal disease. Although cases of infection with Giardia and Cryptosporidium have been reported in Alaska, the seroprevalence and correlates of exposure to these parasites have not been characterised. We conducted a seroprevalence survey among 887 residents of Alaska, including sport hunters, wildlife biologists, subsistence bird hunters and their families and non-exposed persons. We tested serum using a multiplex bead assay to evaluate antibodies to the Giardia duodenalis variant-specific surface protein conserved structural regions and to the Cryptosporidium parvum 17- and 27-kDa antigens. Approximately one third of participants in each group had evidence of exposure to Cryptosporidium. Prevalence of Giardia antibody was highest among subsistence hunters and their families (30%), among whom positivity was associated with lack of community access to in-home running water (adjusted prevalence ratio [aPR] 1.15, 95% confidence interval (CI) 1.02-1.28) or collecting rain, ice, or snow to use as drinking water (aPR 1.09, 95% CI 1.01-1.18). Improving in-home water access for entire communities could decrease the risk of exposure to Giardia.

Estimating the burden of acute gastrointestinal illness due to Giardia, Cryptosporidium, Campylobacter, E. coli O157 and norovirus associated with private wells and small water systems in Canada

Waterborne illness related to the consumption of contaminated or inadequately treated water is a global public health concern. Although the magnitude of drinking water-related illnesses in developed countries is lower than that observed in developing regions of the world, drinking water is still responsible for a proportion of all cases of acute gastrointestinal illness (AGI) in Canada. The estimated burden of endemic AGI in Canada is 20·5 million cases annually – this estimate accounts for under-reporting and under-diagnosis. About 4 million of these cases are domestically acquired and foodborne, yet the proportion of waterborne cases is unknown. There is evidence that individuals served by private systems and small community systems may be more at risk of waterborne illness than those served by municipal drinking water systems in Canada. However, little is known regarding the contribution of these systems to the overall drinking water-related AGI burden in Canada. Private water supplies serve an estimated 12% of the Canadian population, or ~4·1 million people. An estimated 1·4 million (4·1%) people in Canada are served by small groundwater (2·6%) and surface water (1·5%) supplies. The objective of this research is to estimate the number of AGI cases attributable to water consumption from these supplies in Canada using a quantitative microbial risk assessment (QMRA) approach. This provides a framework for others to develop burden of waterborne illness estimates for small water supplies. A multi-pathogen QMRA of Giardia, Cryptosporidium, Campylobacter, E. coli O157 and norovirus, chosen as index waterborne pathogens, for various source water and treatment combinations was performed. It is estimated that 103 230 AGI cases per year are due to the presence of these five pathogens in drinking water from private and small community water systems in Canada. In addition to providing a mechanism to assess the potential burden of AGI attributed to small systems and private well water in Canada, this research supports the use of QMRA as an effective source attribution tool when there is a lack of randomized controlled trial data to evaluate the public health risk of an exposure source. QMRA is also a powerful tool for identifying existing knowledge gaps on the national scale to inform future surveillance and research efforts.

Human parasitic protozoa in drinking water sources in rural Zimbabwe and their link to HIV infection

OBJECTIVE

We aimed to perform a risk assessment in a rural setting, where drinking water is obtained from both protected and unprotected deep or shallow wells, boreholes and springs. Water is consumed untreated and this poses a risk of acquiring waterborne infections that may cause diarrhea.

METHODS

The study included 113 study participants who volunteered in Chiweshe rural community (Musarara village) in Mashonaland Central Province in Zimbabwe. There were 34 (30%) males and 79 (70%) females with ages ranging from 2 to 89 years. HIV counseling was carried out at the communal meeting and testing was done at home visits. Stool and drinking water samples were collected from 104 subjects. Routine laboratory methods were used to examine for parasitic infections.

RESULTS

Only 29 (25.7%) of participants were confirmed HIV positive using 2 rapid serology tests; eighty-four (74.3%) were negative. Diarrheic stool samples were observed in 17 (16.3%) participants and of these 5 (29.4%) were HIV seropositive. Several parasites were isolated from stool samples: G. duodenalis 6 (5.7%), E. histolytica/dispar 19 (18.2%), C. parvum, 8 (7.6%) and C. cayetanensis 23 (22.1%). Eleven out of 30 (36.6%) water bodies had protozoan parasites: G. duodenalis 2 (6.6%), E. histolytica 4 (13.3%), C. parvum 1 (3.3%), C. cayetanensis 3 (10%), E. coli 1 (3.3%).

CONCLUSION

The water sources were being used without treatment and were shown to pose a risk for acquiring diarrheagenic protozoan parasites.

A large community outbreak of gastroenteritis associated with consumption of drinking water contaminated by river water, Belgium, 2010

On 6 December 2010 a fire in Hemiksem, Belgium, was extinguished by the fire brigade with both river water and tap water. Local physicians were asked to report all cases of gastroenteritis. We conducted a retrospective cohort study among 1000 randomly selected households. We performed a statistical and geospatial analysis. Human stool samples, tap water and river water were tested for pathogens. Of the 1185 persons living in the 528 responding households, 222 (18·7%) reported symptoms of gastroenteritis during the time period 6–13 December. Drinking tap water was significantly associated with an increased risk for gastroenteritis (relative risk 3·67, 95% confidence interval 2·86–4·70) as was place of residence. Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. Tap water samples tested positive for faecal indicator bacteria and protozoa. The results support the hypothesis that a point-source contamination of the tap water with river water was the cause of the multi-pathogen waterborne outbreak.

Microarray analysis of the human antibody response to synthetic Cryptosporidium glycopeptides

Glycoproteins expressed by Cryptosporidium parvum are immunogenic in infected individuals but the nature of the epitopes recognised in C. parvum glycoproteins is poorly understood. Since a known immunodominant antigen of Cryptosporidium, the 17kDa glycoprotein, has previously been shown to bind to lectins that recognise the Tn antigen (GalNAcα1-Ser/Thr-R), a large number of glycopeptides with different Tn valency and presentation were prepared. In addition, glycopeptides were synthesised based on a 40kDa cryptosporidial antigen, a polymorphic surface glycoprotein with varying numbers of serine residues, to determine the reactivity with sera from C. parvum-infected humans. These glycopeptides and non-glycosylated peptides were used to generate a glycopeptide microarray to allow screening of sera from C. parvum-infected individuals for the presence of IgM and IgG antibodies. IgG but not IgM in sera from C. parvum-infected individuals bound to multivalent Tn antigen epitopes presented on glycopeptides, suggesting that glycoproteins from C. parvum that contain the Tn antigen induce immune responses upon infection. In addition, molecular differences in glycosylated peptides (e.g. substituting Ser for Thr) as well as the site of glycosylation had a pronounced effect on reactivity. Lastly, pooled sera from individuals infected with either Toxoplasma or Plasmodium were also tested against the modified Cryptosporidium peptides and some sera showed specific binding to glycopeptide epitopes. These studies reveal that specific anti-glycopeptide antibodies that recognise the Tn antigen may be useful diagnostically and in defining the roles of parasite glycoconjugates in infections.

High anti-Cryptosporidium parvum IgG seroprevalence in HIV-infected adults in Limpopo, South Africa

A seroepidemiological study was performed to determine the seroprevalence of Cryptosporidium in human immunodeficiency virus (HIV)-infected adults and local university students in the Limpopo Province, South Africa. Using a custom anti-C. parvum immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA), the seroprevalence of Cryptosporidium was found to be significantly higher (75.3%; 146 of 193) in HIV-infected individuals compared with student volunteers (32.8%; 19 of 58) (P < 0.001). A more recent diagnosis of HIV was associated with anti-C. parvum IgG seropositivity, as was lower weight among HIV-infected women. This is the first seroepidemiologic study of Cryptosporidium in rural South Africa, and it shows high endemicity among the HIV-infected population. In addition to raising the possibility of significant Cryptosporidium-related morbidities, this finding reveals that in Limpopo and perhaps in other low-income, rural populations, interrupting waterborne pathogen transmission will require strategies effective against environmentally hardy parasites such as Cryptosporidium.

Detection of IgG antibodies in sera from patients with Cryptosporidium parvum and Cryptosporidium hominis

OBJECTIVES

Detection of anti-Cryptosporidium immunoglobulin G (IgG) antibodies in human sera has been used to demonstrate population exposure to this gastro-intestinal protozoan parasite. We characterised the dynamics of IgG antibody responses to two Cryptosporidium parvum (IOWA isolate) sporozoite antigens (15/17 kDa and 27 kDa) using longitudinal sera taken from laboratory-confirmed cryptosporidiosis cases in England and Wales. The effect of the infecting Cryptosporidium species was also investigated.

METHODS

A mini-gel Western blot was used to test sera from ten Cryptosporidium stool-positive diarrhoea patients, taken soon after diagnosis and at 3 month intervals.

RESULTS

Overall responses to the 15/17 kDa antigen complex were stronger and over a greater range than those to the 27 kDa antigen, but declined between 181 and 240 days and were barely detectable thereafter. Responses to the 27 kDa antigen were much weaker but remained detectable for a greater length of time. No differences were detected in either antibody response to infection with C. hominis or C. parvum.

CONCLUSIONS

The assay appears to be applicable for the study of recent exposure to C. parvum or C. hominis in the United Kingdom population, with strong responses to the 15/17 kDa antigen occurring within 6 months of infection.

Celiac disease and giardiasis: a case report

When investigating a patient with suspected celiac disease (CD), several other conditions must be considered, including potential infection with Giardia lamblia. Although giardiasis is rare, its histopathological and serological picture may resemble that of CD. We report the case of a young man with diabetes mellitus and a family history of CD referred to our hospital because of diarrhoea and weight loss. Investigation showed, among other factors, partial villous atrophy in duodenal biopsies and elevated immunoglobulin A antitissue transglutaminase antibodies. The patient was diagnosed with CD and recommended a gluten-free diet. At the same time, faecal tests were conducted, indicating the presence of G. lamblia. The patient was treated and improved, even after discontinuing the gluten-free diet. Subsequent follow-up after 6 months showed total regression of mucosal histopathology and a normal antitissue transglutaminase antibodies level.

Multiplex assay detection of immunoglobulin G antibodies that recognize Giardia intestinalis and Cryptosporidium parvum antigens

Giardiasis and cryptosporidiosis are common enteric parasitic diseases that have similar routes of transmission. In this work, we have identified epitopes within the Giardia variant-specific surface protein (VSP) sequences that are recognized by IgG antibodies from 13 of 14 (93%) sera from patients with stool-confirmed giardiasis. The conserved epitopes are shared among VSPs from both of the assemblages that commonly infect humans, and they are likely to be structural, as both sodium dodecyl sulfate treatment and dithiothreitol reduction decrease antibody recognition. In a multiplex bead assay (MBA), we used three VSP fragments from an assemblage A Giardia strain, three VSP fragments from assemblage B strains, and the α-1 giardin structural antigen to detect IgG antibodies to Giardia and used the recombinant 17- and 27-kDa antigens to simultaneously detect IgG antibodies to Cryptosporidium. The MBA differentiated between sera from Giardia and Cryptosporidium outbreaks and also identified a giardiasis outbreak that may have included cryptosporidiosis cases. Approximately 40% of cryptosporidiosis outbreak samples had high MBA responses for both the 27- and 17-kDa antigens, while <10% of nonoutbreak and giardiasis outbreak samples had high responses. At least 60% of giardiasis outbreak samples were positive for antibodies to multiple Giardia antigens, while ≤12% of nonoutbreak samples and samples from U.S. and British Columbia cryptosporidiosis outbreaks met our definition for Giardia seropositivity. A MBA using multiple parasite antigens may prove useful in the epidemiologic analysis of future waterborne or food-borne outbreaks of diarrheal disease.

Cryptosporidiosis: environmental, therapeutic, and preventive challenges

Cryptosporidium spp. are responsible for endemic and epidemic disease worldwide. Clinical manifestations may include acute, persistent, or chronic diarrhea, biliary, and pulmonary disease. Disease severity ranges from asymptomatic or mild to severe, intractable diarrhea with wasting depending on immune status, nutrition, and age. Transmission is fecal-oral with both human and animal reservoirs. Disease is often self limited in healthy individuals, but therapy remains a challenge in the immune-compromised. Prevention currently depends on appropriate hygiene and proper water management and treatment.

Serological responses to Cryptosporidium in human populations living in areas reporting high and low incidences of symptomatic cryptosporidiosis

One approach to investigating differences in the reported incidence of disease is to measure the extent of exposure to the organism in question by testing for a specific antibody response. IgG responses to Cryptosporidium sporozoite antigens of low molecular size in adults have been shown to be consistent and of sufficient intensity to act as reliable markers of exposure. This study used a western blot procedure to investigate the relative intensity of IgG antibody responses to the 15/17-kDa Cryptosporidium sporozoite antigen complex and the 27-kDa antigen in sera from two cities in north-west England: Liverpool (low numbers of clinical cases reported) and Preston (high numbers reported). The intensity of antibody response to the 15/17-kDa antigen complex was significantly greater in the Liverpool sera, but there was no significant difference in intensity of response to the 27-kDa antigen. The relationship between diagnosed and reported cryptosporidiosis infections and infections identified by serological testing is complex, but could indicate a protective effect resulting from either exposure to non-pathogenic strains or from repeated low-level exposure to pathogenic strains.

Longitudinal analysis of cryptosporidium species-specific immunoglobulin G antibody responses in Peruvian children

Cryptosporidium species are ubiquitous in the environment and are frequently detected in the stools of children who live where sanitation conditions are poor. To better characterize the immune response to these parasites, we monitored immunoglobulin G (IgG) antibody levels in a cohort of children from Lima, Peru. Two new enzyme-linked immunosorbent assays based on the C. parvum (bovine, subtype IIa) Iowa strain 17-kDa and 27-kDa antigens were used to measure IgG antibody levels in longitudinal serum samples. Antibody responses were detected during infections with C. parvum, C. felis, and C. meleagridis and with four different subtypes of C. hominis. We also noted that the magnitude of the antibody response was related to the number of previous infections and that older children generally had higher levels of antibodies to the two C. parvum antigens. Antibody responses were not associated with infections with either Cyclospora sp. or Giardia sp. We believe the antibody assays will be important tools for monitoring the success of future public health interventions.

Screening for Giardia/Cryptosporidium infections using an enzyme immunoassay in a centralized regional microbiology laboratory

CONTEXT

Stool parasitologic testing for Giardia and Cryptosporidium (G/C) previously relied on staining (ie, modified iron hematoxylin-kinyoun), ethyl acetate concentration procedures, and microscopy (the stool ova and parasite method). In April 1999, a microplate enzyme immunoassay (EIA) (ProSpecT G/C, Remel, Inc, Lenexa, Kan) for routine screening of all stool specimens was implemented.

OBJECTIVE

To determine the clinical and laboratory impact of this service change.

DESIGN

Changes were made to the regional microbiology requisition so that physicians could order either a G/ C EIA screen or stool ova and parasite examination. During a 3-year period (May 1999 through April 2002), changes in physician ordering practice, the rate of detection of G/ C infections, and test turnaround times were monitored. The economic outcomes have also been studied and compared annually since implementation and up to the current fiscal year (2004).

RESULTS

The following effects have been noted since G/ C EIA screening was implemented: (1) 70% of all stool parasite tests ordered were converted to G/C EIA screens versus stool ova and parasite tests, (2) stool parasitologic volumes decreased by up to 30% because of physicians ordering a single test per patient, (3) most stool parasite results (70%-80%) were reported within 24 hours of specimen receipt, and (4) the screening assay has improved detection of cryptosporidiosis cases. Although the G/C EIA tests cost more than stool ova and parasite examination, the equivalent of 1.8 full-time employees have been freed up to perform other duties.

CONCLUSIONS

Routine stool G/C EIA screening in our region is not only clinically relevant but also improves the timeliness and efficiency of detection of these important enteric parasite infections.

Population-based laboratory surveillance for Giardia sp. and Cryptosporidium sp. infections in a large Canadian health region

BACKGROUND

Giardia lamblia (intestinalis) and Cryptosporidium parvum are the two most important intestinal parasites infecting North Americans but there is a paucity of active population-based surveillance data from Canada. This study determined the incidence of and demographic risk factors for developing Giardia sp. and Cryptosporidium sp. infections in a general Canadian population.

METHODS

Population-based laboratory surveillance was conducted among all residents of the Calgary Health Region (CHR; population approximately = 1 million) during May 1, 1999 and April 30, 2002.

RESULTS

Giardia sp. infection occurred at a rate of 19.6 per 100,000 populations per year. Although the yearly incidence was stable, a significant seasonal variation was observed with a peak in late summer to early fall. Males were at higher risk for development of this infection as compared to females (21.2 vs. 17.9 per 100,000/yr; relative risk (RR) 1.19; 95% confidence interval (CI), 1.00-1.40, p = 0.047), and there was a significant decrease in risk associated with an increasing age. Cryptosporidium sp. infection occurred at an overall rate of 6.0 per 100,000 populations per year although a large outbreak of Cryptosporidium sp. infections occurred in the second half of the summer of 2001. During August and September of 2001, the incidence of cryptosporidiosis was 55.1 per 100,000 per year as compared to 3.1 per 100,000 per year for the remainder of the surveillance period (p < 0.0001). Cryptosporidiosis was largely a disease of children with an incidence of 17.8 per 100,000 per year occurring among those aged < 20 years of age compared to 1.25 per 100,000 per year for adults > or = 20 years of age (RR 14.19; 95% CI, 9.77-21.11; p < 0.0001).

CONCLUSION

This study provides important information on the occurrence and demographic risk groups for acquisition of giardiasis and cryptosporidiosis in a non-selected Canadian population.

Characterization of a Low Molecular Weight Glycolipid Antigen from Cryptosporidium parvum

Cryptosporidium parvum, an Apicomplexan parasite of the mammalian gut epithelium, causes a diarrheal illness in a wide range of hosts and is transmitted by contamination of food or water with oocyst-laden feces from an infected animal. We have identified a glycosylinositol phospholipid from the sporozoite stage of the parasite that is frequently recognized by serum antibodies from human cryptosporidiosis patients. The humoral immune response is dominated by IgG1 subclass antibodies but can also include IgA and IgM antibodies. The glycosylinositol phospholipids were purified by butanol extraction of a Triton X-114-soluble fraction followed by octyl-Sepharose column chromatography and preparative high performance TLC and were shown to include at least 5 species. By using mass spectrometry and radiolabeled neutral glycan analysis, we found that the structure of the dominant glycosylinositol phospholipid antigen contained a C18:0 lyso-acylglycerol, a C16:0-acylated inositol, and an unsubstituted mannose3-glucosamine glycan core. Other diacyl species were also identified, most notably a series of glycosylinositol phospholipids having an acyl-linked C20:0 to C28:0 lipid on the inositol ring. Less abundant species having three acyl-linked fatty acids and species with an additional 1-3 hexoses linked to the mannose core were also observed. We are currently working to determine the role that these glycolipids may play in the development of disease and in the clearance of infection.

Cryptosporidium and Giardia-zoonoses: fact or fiction?

Giardia and Cryptosporidium are enteric protozoan parasites that infect a wide range of vertebrate hosts. Both are transmitted either by direct faecal/oral contact or by the ingestion of contaminated food or water. The discovery of morphologically similar organisms infecting humans and a variety of mammals and birds has led to the proposal that both Cryptosporidium and Giardia are zoonotic (i.e. transmitted in nature between humans and animals). Transmission between humans and animals has been supported by cross-infection studies. However, closer examination of many of these studies reveals limitations in the methodologies utilised. More recent molecular genetic studies have demonstrated considerable genetic diversity among isolates of the same species of Giardia and Cryptosporidium, suggesting that these species are in fact species complexes and that some of these novel species may be host-specific. This paper will critically examine the evidence for the zoonotic transmission of these parasites.

Health and environmental policy issues in Canada: the role of watershed management in sustaining clean drinking water quality at surface sources

Sustaining clean and safe drinking water sources is increasingly becoming a priority because of global pollution. The means of attaining and maintaining clean drinking water sources requires effective policies that identify, document, and reduce watershed risks. These risks are defined by their potential impact to human health. Health and risk are, therefore, indelibly linked because they are in part defined by each other. Understanding pathogen ecology and identifying watershed sources remains a priority because of the associated acute risks. Surface water quality changes resulting from inputs of human waste, nutrients and chemicals are associated with higher drinking water risks. Nutrient input can increase primary production and the resulting increase of organic matter results in greater disinfection by-product formation or requires greater treatment intensity. Many drinking water disease outbreaks have resulted from breaches in treatment facilities, therefore, even with greater treatment intensity poor source water quality intrinsically has greater associated health risks. Government and international agencies play a critical role in developing policy. The goal of maintaining water supplies whose availability is maximized and risks are minimized (i.e. sustainable) should be a vital part of such policy. Health risks are discussed in the context of a multi-barrier perspective and it is concluded that both passive (protection) and active (prescriptive management) management is necessary for sustainability. Canadian aboriginal water systems, British Columbian water policy and US EPA policies are given as examples. The basis for developing effective policies includes a strong reliance on sound science and effective instrumentation with careful consideration of stakeholders' interests. Only with such directed policies can the future availability of clean drinking water sources be ensured.

Enzyme immunoassay detection of antigen-specific immunoglobulin g antibodies in longitudinal serum samples from patients with cryptosporidiosis

Cryptosporidium parvum is a protozoan parasite that causes diarrheal illness in a wide range of mammalian hosts, including humans. Characteristic serum immunoglobulin G (IgG) antibody responses to antigens in the 27- and 17-kDa size ranges have been shown to develop after infection, and several enzyme-linked immunosorbent assay (ELISA) and Western blot assay formats have been used to measure these IgG levels in human serum. Using a collection of serial samples from laboratory-confirmed cryptosporidiosis patients, we compared the results obtained by using two new ELISAs with those obtained with two different Western blot assays. When assayed with the large-format Western blot, 97% of the 67 patients had a demonstrable antibody response on at least one occasion. The Cp23 ELISA correctly identified 93% of the samples that had a 27-kDa response by Western blot and 100% of the negative samples. The Triton antigen ELISA detected 77% of the samples that had a 17-kDa response by Western blot and 88% of the negative samples. The sensitivity of the Triton antigen assay was higher for samples collected between 16 and 92 days after the onset of symptoms (96%). The minigel-format Western blot did not compare favorably with the large-format blot for the detection of antibodies to the 27-kDa antigen (71% sensitivity). A half-life of about 12 weeks was estimated for antibodies to both the 27- and 17-kDa antigens. We believe the Cp23 and Triton antigen ELISAs will be useful in epidemiologic studies of the prevalence of Cryptosporidium infection in the population.

Treatment of giardiasis

Giardia lamblia is both the most common intestinal parasite in the United States and a frequent cause of diarrheal illness throughout the world. In spite of its recognition as an important human pathogen, there have been relatively few agents used in therapy. This paper discusses each class of drugs used in treatment, along with their mechanism of action, in vitro and clinical efficacy, and side effects and contraindications. Recommendations are made for the preferred treatment in different clinical situations. The greatest clinical experience is with the nitroimidazole drugs, i.e., metronidazole, tinidazole, and ornidazole, which are highly effective. A 5- to 7-day course of metronidazole can be expected to cure over 90% of individuals, and a single dose of tinidazole or ornidazole will cure a similar number. Quinacrine, which is no longer produced in the United States, has excellent efficacy but may be poorly tolerated, especially in children. Furazolidone is an effective alternative but must be administered four times a day for 7 to 10 days. Paromomycin may be used during early pregnancy, because it is not systematically absorbed, but it is not always effective. Patients who have resistant infection can usually be cured by a prolonged course of treatment with a combination of a nitroimidazole with quinacrine.