Characterization of Giardia duodenalis isolates from a waterborne outbreak

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.

Isoenzyme profiles and phylogenetic analysis of Giardia duodenalis isolates from Iranian patients

The main objective of this study was to characterize the Giardia duodenalis isolates from Iranian patients in Fars Province, south of Iran by biochemical and molecular methods. Fifteen mass cultivated of G. duodenalis isolates in modified TYI-S-33 medium were analyzed using isoenzyme electrophoresis and PCR genotyping. Polyacrylamide gel electrophoresis (PAGE) of five different enzyme systems was used to characterize isolates: (i) glucose-6-phosphate dehydrogenase, (ii) glucose phosphate isomerase, (iii) malate dehydrogenase, (iv) malic enzyme, and (v) phosphoglucomutase. As well, a fragment of the SSU-rDNA (292 bp) gene was amplified by PCR using the primers RH11 and RH4. The sequencing of the PCR products and phylogenetic tree were performed. The isoenzyme electrophoretic profiles divided fifteen G. duodenalis isolates into four zymodemes. G6PD, GPI, MDH, ME, and PGM enzyme systems showed 1, 2, 2, 3, and 3 enzyme pattern, respectively. G6PD isoenzyme pattern had the most homogeneity, while isoenzyme patterns of ME and PGM had the most heterogeneity in our study. Genotyping results indicated that the zymodemes 1-4 were categorized in assemblage A based on the SSU-rDNA gene. Phylogenetic analysis showed that all four zymodemes were distributed within the cluster of assemblage A. Our results indicated that both isoenzyme and DNA analyses were useful to characterize the isolates of Giardia and distinguishing various zymodemes and assemblages. It could be suggested that the genetic diversity among isoenzymes profiles of G. duodenalis may explain the variable clinical manifestations, pathogenicity, host response, drug susceptibility, and treatment efficacy of human giardiasis.

Beaver Fever: Whole-Genome Characterization of Waterborne Outbreak and Sporadic Isolates To Study the Zoonotic Transmission of Giardiasis

Giardia duodenalis causes large numbers of gastrointestinal illness in humans. Its transmission through the contaminated surface water/wildlife intersect is significant, and the water-dwelling rodents beavers have been implicated as one important reservoir. To trace human infections to their source, we used genome techniques to characterize genetic relationships among 89 Giardia isolates from surface water, humans, and animals. Our study showed the presence of two previously described genetic assemblages, A and B, with mixed infections detected from isolates collected during outbreaks. Study findings also showed that while assemblage A could be divided into A1 and A2, A1 showed little genetic variation among animal and human hosts in isolates collected from across the globe. Assemblage B, the most common type found in the study surface water samples, was shown to be highly variable. Our study demonstrates that the beaver is a possible source of human infections from contaminated surface water, while acknowledging that theirs is only one role in the complex cycle of zoonotic spread. Mixes of parasite groups have been detected in waterborne outbreaks. More information on Giardia diversity and its evolution using genomics will further the understanding of the epidemiology of spread of this disease-causing protozoan.

Giardia causes the diarrheal disease known as giardiasis; transmission through contaminated surface water is common. The protozoan parasite’s genetic diversity has major implications for human health and epidemiology. To determine the extent of transmission from wildlife through surface water, we performed whole-genome sequencing (WGS) to characterize 89 Giardia duodenalis isolates from both outbreak and sporadic infections: 29 isolates from raw surface water, 38 from humans, and 22 from veterinary sources. Using single nucleotide variants (SNVs), combined with epidemiological data, relationships contributing to zoonotic transmission were described. Two assemblages, A and B, were identified in surface water, human, and veterinary isolates. Mixes of zoonotic assemblages A and B were seen in all the community waterborne outbreaks in British Columbia (BC), Canada, studied. Assemblage A was further subdivided into assemblages A1 and A2 based on the genetic variation observed. The A1 assemblage was highly clonal; isolates of surface water, human, and veterinary origins from Canada, United States, and New Zealand clustered together with minor variation, consistent with this being a panglobal zoonotic lineage. In contrast, assemblage B isolates were variable and consisted of several clonal lineages relating to waterborne outbreaks and geographic locations. Most human infection isolates in waterborne outbreaks clustered with isolates from surface water and beavers implicated to be outbreak sources by public health. In-depth outbreak analysis demonstrated that beavers can act as amplification hosts for human infections and can act as sources of surface water contamination. It is also known that other wild and domesticated animals, as well as humans, can be sources of waterborne giardiasis. This study demonstrates the utility of WGS in furthering our understanding of Giardia transmission dynamics at the water-human-animal interface.

IMPORTANCEGiardia duodenalis causes large numbers of gastrointestinal illness in humans. Its transmission through the contaminated surface water/wildlife intersect is significant, and the water-dwelling rodents beavers have been implicated as one important reservoir. To trace human infections to their source, we used genome techniques to characterize genetic relationships among 89 Giardia isolates from surface water, humans, and animals. Our study showed the presence of two previously described genetic assemblages, A and B, with mixed infections detected from isolates collected during outbreaks. Study findings also showed that while assemblage A could be divided into A1 and A2, A1 showed little genetic variation among animal and human hosts in isolates collected from across the globe. Assemblage B, the most common type found in the study surface water samples, was shown to be highly variable. Our study demonstrates that the beaver is a possible source of human infections from contaminated surface water, while acknowledging that theirs is only one role in the complex cycle of zoonotic spread. Mixes of parasite groups have been detected in waterborne outbreaks. More information on Giardia diversity and its evolution using genomics will further the understanding of the epidemiology of spread of this disease-causing protozoan.

Giardia duodenalis genetic assemblages and hosts

Techniques for sub-classifying morphologically identical Giardia duodenalis trophozoites have included comparisons of the electrophoretic mobility of enzymes and of chromosomes, and sequencing of genes encoding β-giardin, triose phosphate isomerase, the small subunit of ribosomal RNA and glutamate dehydrogenase. To date, G. duodenalis organisms have been sub-classified into eight genetic assemblages (designated A–H). Genotyping of G. duodenalis organisms isolated from various hosts has shown that assemblages A and B infect the largest range of host species, and appear to be the main (or possibly only) G. duodenalis assemblages that undeniably infect human subjects. In at least some cases of assemblage A or B infection in wild mammals, there is suggestive evidence that the infection had resulted from environmental contamination by G. duodenalis cysts of human origin.

Environmentally Transmitted Pathogens

This chapter describes a variety of pathogens found in the environment that are capable of infecting humans and causing disease. Different classes of pathogens are discussed including bacteria, parasites and viruses. For each pathogen, data are provided on the incidence of the organism in a particular environmental matrix such as water, food or municipal waste. In addition, we discuss: the disease caused by the particular microbe; the mode of transmission; the incubation time needed within the host prior to the onset of disease; and the duration of illness. Fate and transport of pathogens in the environment are also described. A variety of bacterial pathogens are discussed including waterborne and waterbased bacteria. Parasites discussed include protozoa, nematodes, cestodes and trematodes. For viruses, both enteric and respiratory viruses are included.

Unraveling how Giardia infections cause disease

A 40-year-old NIH male scientist camped and fished in a remote lake in Alaska. On his return, he developed diarrhea, cramps, and loose stools without blood or mucus in the absence of fever and was diagnosed with giardiasis. A 3-year-old female living in the Florida Keys complained of intermittent stomachaches over a 2-month period. Her stools were variably loose. The patient was diagnosed with giardiasis, which led to examination of her mother, father, and brother, who were mildly symptomatic; all 3 were subsequently diagnosed with giardiasis. The child's only exposure was from swimming in a local community pool. A 40-year-old male from Mexico, who resided in Virginia and worked as a cook in a fast food restaurant, was diagnosed with giardiasis. He denied any symptoms and was not allowed to prepare food. Treatment with metronidazole, nitazoxanide, and albendazole failed to eradicate the infection. He was successfully treated with the combination of paromomycin and metronidazole.

Population-based analyses of Giardia duodenalis is consistent with the clonal assemblage structure

Background

Giardia duodenalis is a common protozoan parasite of humans and animals. Genetic characterization of single loci indicates the existence of eight groups called assemblages, which differ in their host distribution. Molecular analyses challenged the idea that G. duodenalis is a strictly clonal diplomonad by providing evidence of recombination within and between assemblages. Particularly, inter-assemblage recombination events would complicate the interpretation of multi-locus genotyping data from field isolates: where is a host infected with multiple Giardia genotypes or with a single, recombined Giardia genotype.

Methods

Population genetic analyses on the single and multiple-locus level on an extensive dataset of G. duodenalis isolates from humans and animals were performed.

Results

Our analyses indicate that recombination between isolates from different assemblages are apparently very rare or absent in the natural population of Giardia duodenalis. At the multi-locus level, our statistical analyses are more congruent with clonal reproduction and can equally well be explained with the presence of multiple G. duodenalis genotypes within one field isolate.

Conclusions

We conclude that recombination between G. duodenalis assemblages is either very rare or absent. Recombination between genotypes from the same assemblage and genetic exchange between the nuclei of a single cyst needs further investigation.

Rapid detection and enumeration of Giardia lamblia cysts in water samples by immunomagnetic separation and flow cytometric analysis

Giardia lamblia is an important waterborne pathogen and is among the most common intestinal parasites of humans worldwide. Its fecal-oral transmission leads to the presence of cysts of this pathogen in the environment, and so far, quantitative rapid screening methods are not available for various matrices, such as surface waters, wastewater, or food. Thus, it is necessary to establish methods that enable reliable rapid detection of a single cyst in 10 to 100 liters of drinking water. Conventional detection relies on cyst concentration, isolation, and confirmation by immunofluorescence microscopy (IFM), resulting in low recoveries and high detection limits. Many different immunomagnetic separation (IMS) procedures have been developed for separation and cyst purification, so far with variable but high losses of cysts. A method was developed that requires less than 100 min and consists of filtration, resuspension, IMS, and flow cytometric (FCM) detection. MACS MicroBeads were used for IMS, and a reliable flow cytometric detection approach was established employing 3 different parameters for discrimination from background signals, i.e., green and red fluorescence (resulting from the distinct pattern emitted by the fluorescein dye) and sideward scatter for size discrimination. With spiked samples, recoveries exceeding 90% were obtained, and false-positive results were never encountered for negative samples. Additionally, the method was applicable to naturally occurring cysts in wastewater and has the potential to be automated.

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.

Safe drinking water: critical components of effective inter-agency relationships

The paper supports the development of evidence-based emergency management frameworks of cooperation between agencies in the area of drinking water and public health, as part of developing the overall risk management culture within water utilities. We employed a qualitative research design to understand critical gaps in inter-agency relations that aggravated past drinking water and health incidents and from these identified determinants of effective relationships. We identified six critical institutional relationship components that were deficient in past incidents, namely proactivity, communication, training, sharing expertise, trust and regulation. We then analysed how these components are addressed by reputable water utilities and public health departments to develop positive examples of inter-agency cooperation. Control of different risks (e.g. public health, business, and reputation) resulting from drinking water incidents should employ a preventive framework similar to the multiple barrier approach for management of drinking water quality.

Identification of zoonotic genotypes of Giardia duodenalis

Giardia duodenalis, originally regarded as a commensal organism, is the etiologic agent of giardiasis, a gastrointestinal disease of humans and animals. Giardiasis causes major public and veterinary health concerns worldwide. Transmission is either direct, through the faecal-oral route, or indirect, through ingestion of contaminated water or food. Genetic characterization of G. duodenalis isolates has revealed the existence of seven groups (assemblages A to G) which differ in their host distribution. Assemblages A and B are found in humans and in many other mammals, but the role of animals in the epidemiology of human infection is still unclear, despite the fact that the zoonotic potential of Giardia was recognised by the WHO some 30 years ago. Here, we performed an extensive genetic characterization of 978 human and 1440 animal isolates, which together comprise 3886 sequences from 4 genetic loci. The data were assembled into a molecular epidemiological database developed by a European network of public and veterinary health Institutions. Genotyping was performed at different levels of resolution (single and multiple loci on the same dataset). The zoonotic potential of both assemblages A and B is evident when studied at the level of assemblages, sub-assemblages, and even at each single locus. However, when genotypes are defined using a multi-locus sequence typing scheme, only 2 multi-locus genotypes (MLG) of assemblage A and none of assemblage B appear to have a zoonotic potential. Surprisingly, mixtures of genotypes in individual isolates were repeatedly observed. Possible explanations are the uptake of genetically different Giardia cysts by a host, or subsequent infection of an already infected host, likely without overt symptoms, with a different Giardia species, which may cause disease. Other explanations for mixed genotypes, particularly for assemblage B, are substantial allelic sequence heterogeneity and/or genetic recombination. Although the zoonotic potential of G. duodenalis is evident, evidence on the contribution and frequency is (still) lacking. This newly developed molecular database has the potential to tackle intricate epidemiological questions concerning protozoan diseases.

Giardia duodenalis is a parasite causing a gastrointestinal disease in humans, pets, livestock, and wildlife. The role of animals in human disease is unclear, because Giardia from humans and animals is morphologically indistinguishable. An international consortium of both veterinary and public health institutions built a web-based database, where molecular and epidemiological data are combined. After extensive genetic characterization, the zoonotic potential of Giardia became evident, but data on frequency and role in epidemiology is (still) lacking. Surprisingly, mixtures of Giardia genotypes in individual hosts were frequently observed, and have important implications for the etiology of Giardiasis. Possible explanations are the uptake of mixtures of Giardia genotypes by one host, or subsequent infection of an already infected host, likely without overt symptoms, with a different Giardia species, which may cause disease. We demonstrated that collaborative, human and veterinary health integrated databases have the potential to tackle intricate epidemiological questions concerning parasitic diseases, as was demonstrated for G. duodenalis in the present study.

Development of functional gastrointestinal disorders after Giardia lamblia infection

Background

Functional gastrointestinal disorders (FGID) may occur following acute gastroenteritis. This long-term complication has previously not been described after infection with the non-invasive protozoan Giardia lamblia. This study aims to characterize persistent abdominal symptoms elicited by Giardia infection according to Rome II criteria and symptoms scores.

Methods

Structured interview and questionnaires 12–30 months after the onset of Giardia infection, and at least 6 months after Giardia eradication, among 82 patients with persisting abdominal symptoms elicited by the Giardia infection. All had been evaluated to exclude other causes.

Results

We found that 66 (80.5%) of the 82 patients had symptoms consistent with irritable bowel syndrome (IBS) and 17 (24.3%) patients had functional dyspepsia (FD) according to Rome II criteria. IBS was sub classified into D-IBS (47.0%), A-IBS (45.5%) and C-IBS (7.6%). Bloating, diarrhoea and abdominal pain were reported to be most severe. Symptoms exacerbation related to specific foods were reported by 45 (57.7%) patients and to physical or mental stress by 34 (44.7%) patients.

Conclusion

In the presence of an IBS-subtype pattern consistent with post-infectious IBS (PI-IBS), and in the absence of any other plausible causes, we conclude that acute Giardia infection may elicit functional gastrointestinal diseases with food and stress related symptoms similar to FGID patients in general.

Environmentally Transmitted Pathogens

Pathogenic microorganisms usually originate from an infected host or directly from the environment; however, only a small proportion of these microbes cause infection. This chapter discusses the pathogens that are transmitted through the environment such as bacteria, viruses, and protozoa. Many human pathogens can be transmitted only by direct or close contact with an infected person or animal such as herpesvirus. Virus transmission by the airborne route may be both direct and indirect inhalation of infectious droplets or through contact with contaminated fomites. Water-borne diseases—such as yellow fever, dengue, filariasis, malaria, onchocerciasis, and sleeping sicknessare transmitted by insects that breed in water or live near water. The common bacterial pathogens transmitted through water include Salmonella, Escherichia coli, Shigella, Campylobacter, Yersinia, Vibrio, Helicobacter, and Legionella. Opportunistic pathogens are also numerous in the environment, and the most important opportunistic pathogen is Pseudomonas aeruginosa. Viruses are a leading cause of gastroenteritis and water-borne outbreaks may be caused by norovirus, hepatitis A virus, Coxsackie virus, echovirus, and adenoviruses. Respiratory diseases are also associated with a large number of viruses such as rhinoviruses, coronaviruses, parainfluenza viruses, respiratory syncytial virus (RSV), influenza virus, and adenovirus. Generally, viral and protozoan pathogens survive longer in the environment than enteric bacterial pathogens.

The role of birds in dissemination of human waterborne enteropathogens

Cryptosporidiosis, giardiasis and microsporidiosis are serious human diseases of waterborne origin; their etiologic agents and a substantial fecal coliform load can enter surface, drinking and recreational water resources from aquatic birds. The aim of this article is to present interactions between waterfowl and these waters that imply a negative public health impact, reinforcing the need for either better water-quality indicators or for water monitoring specifically for Cryptosporidium, Giardia and microsporidia. Where justifiable, the presence of waterfowl should be supported; however, management of drinking and recreational water resources needs to be improved by incorporating effective protection measures for pathogens linked to these birds.

Human waterborne trematode and protozoan infections

Waterborne trematode and protozoan infections inflict considerable morbidity on healthy, i.e., immunocompetent people, and may cause life-threatening diseases among immunocompromised and immunosuppressed populations. These infections are common, easily transmissible, and maintain a worldwide distribution, although waterborne trematode infections remain predominantly confined to the developing countries. Waterborne transmission of trematodes is enhanced by cultural practices of eating raw or inadequately cooked food, socio-economical factors, and wide zoonotic and sylvatic reservoirs of these helminths. Waterborne protozoan infections remain common in both developed and developing countries (although better statistics exist for developed countries), and their transmission is facilitated via contacts with recreational and surface waters, or via consumption of contaminated drinking water. The transmissive stages of human protozoan parasites are small, shed in large numbers in feces of infected people or animals, resistant to environmental stressors while in the environment, and few are (e.g., Cryptosporidium oocysts) able to resist standard disinfection applied to drinking water.

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.

Genotyping of Giardia in Dutch patients and animals: a phylogenetic analysis of human and animal isolates

Giardia duodenalis (syn. Giardia lamblia, Giardia intestinalis) is a protozoan organism that can infect the intestinal tract of many animal species including mammals. Genetic heterogeneity of G. duodenalis is well described but the zoonotic potential is still not clear. In this study, we analysed 100 Giardia DNA samples directly isolated from human stool specimens, to get more insight in the different G. duodenalis assemblages present in the Dutch human population. Results showed that these human isolates could be divided into two main Assemblages A and B within the G. duodenalis group on the basis of PCR assays specific for the Assemblages A and B and the DNA sequences of 18S ribosomal RNA and the glutamate dehydrogenase (gdh) genes. Genotyping results showed that G. duodenalis isolates originating from Dutch human patients belonged in 35% of the cases to Assemblage A (34/98) and in 65% of the cases to Assemblage B (64/98) whereas two human cases remained negative in all assays tested. In addition, we compared these human samples with animal samples from the Netherlands and human and animal samples from other countries. A phylogenetic analysis was carried out on the DNA sequences obtained from these Giardia and those available in GenBank. Using gdh DNA sequence analysis, human and animal Assemblage A and B Giardia isolates could be identified. However, phylogenetic analysis revealed different sub-clustering for human and animal isolates where host-species-specific assemblages (C, D, E, F and G) could be identified. The geographic origin of the human and animal samples was not a discriminating factor.

Foodborne protozoan parasites

This report addresses Cryptosporidium, Giardia, Cyclospora, and more briefly, Toxoplasma as the main parasitic protozoa of concern to food production worldwide. Other parasitic protozoa may be spread in food or water but are not considered as great a risk to food manufacture. The protozoan parasites Cryptosporidium, Giardia, and Cyclospora have proven potential to cause waterborne and foodborne disease. Toxoplasma gondii has been considered a risk in specific cases, but humans are not its primary host. Cryptosporidium and Giardia are widespread in the environment, particularly the aquatic environment, and major outbreaks of cryptosporidiosis and giardiasis have occurred as a result of contaminated drinking water. Large outbreaks of waterborne cyclosporiasis have not been identified. Cryptosporidium, Giardia, and Cyclospora have potential significance in the preparation and consumption of fresh produce and in catering practice, in which ready-to-eat foods may be served that have not received heat treatment. None of the three organisms Cryptosporidium, Giardia, and Cyclospora has been shown to be a problem for heat processed food or tap water that has undergone appropriate treatment at a water treatment works. All three are sensitive to standard pasteurisation techniques. Although humans are not a primary host for T. gondii, the potential exists for both waterborne and foodborne toxoplasmosis. Parasitic protozoa do not multiply in foods, but they may survive in or on moist foods for months in cool, damp environments. Their ecology makes control of these parasites difficult. For general control of parasitic protozoa in the food chain, the following steps are necessary: - Follow good hygienic practice in food service and catering industries.- Minimise dissemination of cysts and oocysts in the farming environment and via human waste management.- Include these microorganisms in Hazard Analysis Critical Control Point (HACCP) plans of water suppliers, industries or sectors that use fresh produce, and operations in which contaminated process or ingredient water could end up in the product (e.g., where water supplies may become contaminated).

Giardia infection in farm animals

Giardia infection is prevalent in farm animals from an early age. Despite the wide occurrence of the infection and recent understanding of its epidemiology, many aspects of giardiasis of farm animals remain unclear. In this article, Lihua Xiao discusses the prevalence, patterns, sources and clinical importance of Giardia infection in a variety of farm animals.

The zoonotic significance and molecular epidemiology of Giardia and giardiasis

The taxonomy and molecular epidemiology of Giardia and Giardia infections are reviewed in the context of zoonotic and waterborne transmission. Evidence to support the zoonotic transmission of Giardia is very strong, but how frequent such transmission occurs and under what circumstances, have yet to be determined. Zoonotic origin for waterborne outbreaks of Giardia infection appears to be uncommon. Similarly, livestock are unlikely to be an important source of infection in humans. The greatest risk of zoonotic transmission appears to be from companion animals such as dogs and cats, although further studies are required in different endemic foci in order to determine the frequency of such transmission.

Blastocystis in humans and animals: new insights using modern methodologies

Among the waterborne protozoan parasites of medical and veterinary importance, Blastocystis is perhaps one of the less well-understood. However, in recent years, there has been a surge of interest in the organism, fueled in part by the possible association of Blastocystis infection with intestinal disorders, and its unusual taxonomic affiliations. Although there is information on the parasite's morphology, taxonomy and mode of transmission, its pathogenicity, life cycle, and function of certain organelles continue to baffle investigators. The clinical relevance of Blastocystis will be better answered once an animal model is found. Blastocystis infections have a worldwide distribution but prevalence is highest in areas with poor hygiene and deficient sanitation services and facilities. Application of modern molecular tools has advanced knowledge of the organism's genetic diversity, taxonomy and zoonotic potential.

Molecular phylogenies of Blastocystis isolates from different hosts: implications for genetic diversity, identification of species, and zoonosis

Small-subunit (SSU) rRNA gene sequences were obtained by PCR from 12 Blastocystis isolates from humans, rats, and reptiles for which elongation factor 1alpha (EF-1alpha) gene sequences are already available. These new sequences were analyzed by the Bayesian method in a broad phylogeny including, for the first time, all Blastocystis sequences available in the databases. Phylogenetic trees identified seven well-resolved groups plus several discrete lineages that could represent newly defined clades. Comparative analysis of SSU rRNA- and EF-1alpha-based trees obtained by maximum-likelihood methods from a restricted sampling (13 isolates) revealed overall agreement between the two phylogenies. In spite of their morphological similarity, sequence divergence among Blastocystis isolates reflected considerable genetic diversity that could be correlated with the existence of potentially >/=12 different species within the genus. Based on this analysis and previous PCR-based genotype classification data, six of these major groups might consist of Blastocystis isolates from both humans and other animal hosts, confirming the low host specificity of Blastocystis. Our results also strongly suggest the existence of numerous zoonotic isolates with frequent animal-to-human and human-to-animal transmissions and of a large potential reservoir in animals for infections in humans.

Efficacy of antigiardial drugs

The flagellated protozoa Giardia duodenalis is the most commonly detected parasite in the intestinal tract of humans. Infections with the parasite result in diarrhoeal disease in humans and animals, with infants at risk from failure-to-thrive syndrome. The incidence of giardiasis worldwide may be as high as 1000 million cases. Current recommended treatments include the nitroheterocyclic drugs tinidazole, metronidazole and furazolidone, the substituted acridine, quinacrine, and the benzimidazole, albendazole. Paromomycin is also used in some situations, and nitazoxanide is proving to be useful. However, treatment failures have been reported with all of the common antigiardial agents, and drug resistance to all available drugs has been demonstrated in the laboratory. In addition, clinical resistance has been reported, including cases where patients failed both metronidazole and albendazole treatments. The identification of new antigiardial drugs is an important consideration for the future, but maintaining the usefulness of the existing drugs is the most cost-effective measure to ensure the continued availability of antigiardial drugs.

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.

Anthropozoonotic Giardia duodenalis genotype (assemblage) a infections in habitats of free-ranging human-habituated gorillas, Uganda

To facilitate ecotourism and research, free-ranging mountain gorillas of Uganda have been habituated to humans. Testing of fecal samples of gorillas (n = 100), people sharing gorilla habitats (n = 62). and local pre- and postweaned cattle (n = 50) having access to these habitats with fluorescein isothiocyanate-conjugated monoclonal antibodies revealed Giardia duodenalis cysts at prevalences of 2, 5, and 10%, respectively. The identification of G. duodenalis was confirmed by fluorescent in situ hybridization with 2 species-specific 18-bp oligonucleotide probes conjugated to hexachlorinated 6-carboxyfluorescein. The mean pathogen concentration was 2.5, 2.8, and 0.2 x 10(4) cysts/g of the gorilla, people, and cattle feces, respectively. All cyst isolates aligned with genotype (assemblage) A, as confirmed by polymerase chain reaction amplification and sequencing of a 130-bp region near the 5' end of the small subunit-ribosomal RNA gene. A single genotype (assemblage) A recovered from 3 genetically distant but geographically united host groups indicates anthropozoonotic transmission of G. duodenalis. A large percentage of the local community does not follow park regulations regarding the disposal of their fecal waste, as self-reported in a questionnaire. This genotype may have been introduced into gorilla populations through habituation activities and may have then been sustained in their habitats by anthropozoonotic transmission.

A descriptive analysis of giardiasis cases reported in Ontario, 1990-1998

Cases of giardiasis in Ontario were described using notifiable disease data from the Ontario Ministry of Health for the years 1990-1998 inclusive. The mean annual age- and sex-adjusted incidence rate was 25.77 cases per 100,000 population for the 25,289 cases reported. Children under five years of age had the highest incidence of disease. Males had a higher mean annual incidence in all age groups. Four deaths occurred among cases. The most frequently reported symptoms were loose stools or watery diarrhea (50.1%). A seasonal pattern was noted, peaking in late summer and early autumn. The most frequently reported probable risk settings were the home (40.1%) and travel (39.1%). The study findings suggest that a high proportion of cases occur in urban areas and spatial analysis showed the highest incidence around Lake Huron and Georgian Bay. Unfiltered water and person-to-person contact are believed to be important sources of infection.

Biology of Giardia lamblia

Giardia lamblia is a common cause of diarrhea in humans and other mammals throughout the world. It can be distinguished from other Giardia species by light or electron microscopy. The two major genotypes of G. lamblia that infect humans are so different genetically and biologically that they may warrant separate species or subspecies designations. Trophozoites have nuclei and a well-developed cytoskeleton but lack mitochondria, peroxisomes, and the components of oxidative phosphorylation. They have an endomembrane system with at least some characteristics of the Golgi complex and encoplasmic reticulum, which becomes more extensive in encysting organisms. The primitive nature of the organelles and metabolism, as well as small-subunit rRNA phylogeny, has led to the proposal that Giardia spp. are among the most primitive eukaryotes. G. lamblia probably has a ploidy of 4 and a genome size of approximately 10 to 12 Mb divided among five chromosomes. Most genes have short 5' and 3' untranslated regions and promoter regions that are near the initiation codon. Trophozoites exhibit antigenic variation of an extensive repertoire of cysteine-rich variant-specific surface proteins. Expression is allele specific, and changes in expression from one vsp gene to another have not been associated with sequence alterations or gene rearrangements. The Giardia genome project promises to greatly increase our understanding of this interesting and enigmatic organism.

Drug targets and mechanisms of resistance in the anaerobic protozoa

The anaerobic protozoa Giardia duodenalis, Trichomonas vaginalis, and Entamoeba histolytica infect up to a billion people each year. G. duodenalis and E. histolytica are primarily pathogens of the intestinal tract, although E. histolytica can form abscesses and invade other organs, where it can be fatal if left untreated. T. vaginalis infection is a sexually transmitted infection causing vaginitis and acute inflammatory disease of the genital mucosa. T. vaginalis has also been reported in the urinary tract, fallopian tubes, and pelvis and can cause pneumonia, bronchitis, and oral lesions. Respiratory infections can be acquired perinatally. T. vaginalis infections have been associated with preterm delivery, low birth weight, and increased mortality as well as predisposing to human immunodeficiency virus infection, AIDS, and cervical cancer. All three organisms lack mitochondria and are susceptible to the nitroimidazole metronidazole because of similar low-redox-potential anaerobic metabolic pathways. Resistance to metronidazole and other drugs has been observed clinically and in the laboratory. Laboratory studies have identified the enzyme that activates metronidazole, pyruvate:ferredoxin oxidoreductase, to its nitroso form and distinct mechanisms of decreasing drug susceptibility that are induced in each organism. Although the nitroimidazoles have been the drug family of choice for treating the anaerobic protozoa, G. duodenalis is less susceptible to other antiparasitic drugs, such as furazolidone, albendazole, and quinacrine. Resistance has been demonstrated for each agent, and the mechanism of resistance has been investigated. Metronidazole resistance in T. vaginalis is well documented, and the principal mechanisms have been defined. Bypass metabolism, such as alternative oxidoreductases, have been discovered in both organisms. Aerobic versus anaerobic resistance in T. vaginalis is discussed. Mechanisms of metronidazole resistance in E. histolytica have recently been investigated using laboratory-induced resistant isolates. Instead of downregulation of the pyruvate:ferredoxin oxidoreductase and ferredoxin pathway as seen in G. duodenalis and T. vaginalis, E. histolytica induces oxidative stress mechanisms, including superoxide dismutase and peroxiredoxin. The review examines the value of investigating both clinical and laboratory-induced syngeneic drug-resistant isolates and dissection of the complementary data obtained. Comparison of resistance mechanisms in anaerobic bacteria and the parasitic protozoa is discussed as well as the value of studies of the epidemiology of resistance.

Emerging parasite zoonoses associated with water and food

The environmental route of transmission is important for many protozoan and helminth parasites, with water, soil and food being particularly significant. Both the potential for producing large numbers of transmissive stages and their environmental robustness, being able to survive in moist microclimates for prolonged periods of time, pose a persistent threat to public and veterinary health. The increased demands on natural resources increase the likelihood of encountering environments and produce contaminated with parasites. For waterborne diseases, the protozoa, Cryptosporidium, Giardia and Toxoplasma, are the most significant causes, yet, with the exception of Toxoplasma, the contribution of zoonotic transmission remains unclear due to the absence of 'standardised' methods. The microsporidia have been documented in one waterborne outbreak, but the role of animals as the cause of contamination was not elucidated. In foods, surface contamination is associated with the faecal-oral pathogens, and some data are available to indicate that animal wastes remain an important source of contamination (e.g. cattle faeces and apple cider outbreaks), however, further work should focus on examining the source of contamination on fruit and vegetables. Increasing recognition of the burden of human fascioliasis has occurred; it is now recognised as an emerging zoonosis by the WHO. Toxoplasma, Trichinella and Taenia spp. remain important meatborne parasites, however, others, including Pleistophora-like microsporidians may be acquired from raw or lightly cooked fish or crustaceans. With increased international travel, the public health importance of the foodborne trematodiases must also be realised. Global sourcing of food, coupled with changing consumer vogues, including the consumption of raw vegetables and undercooking to retain the natural taste and preserve heat-labile nutrients, can increase the risk of foodborne transmission. A greater awareness of parasite contamination of our environment and its impact on health has precipitated the development of better detection methods. Robust, efficient detection, viability and typing methods are required to assess risks and to further epidemiological understanding.

Giardiasis as a re-emerging infectious disease and its zoonotic potential

The reasons for considering giardiasis as a re-emerging infectious disease are presented, with emphasis on Giardia infections in child care centres, livestock and pets, and the role of zoonotic transmission. However, the aetiology and control of giardiasis is complicated by the genetic and phenotypic variability of Giardia species infective to mammals. Of particular significance has been the uncertainty about host specificity and the question of zoonotic transmission. The recent application of molecular characterisation procedures based on PCR has made an enormous contribution to an understanding of the genetic structure of Giardia populations, and this is reviewed in the context of the zoonotic transmission and molecular epidemiology of Giardia infections.

Prevalence and genotypic characterisation of Giardia in dairy calves from Western Australia and Western Canada

In this study, the prevalence of Giardia duodenalis infections was determined in Western Canadian and Western Australian dairy calves. Faecal samples were collected from Holstein calves located on a commercial dairy near Lethbridge, Alta., Canada (N=28) and from calves located on two commercial dairies located near Perth, WA, Australia (N=36). Faecal samples were examined for the presence of Giardia cysts using sucrose gradient centrifugation, followed by immunofluoresence microscopy. DNA was then extracted from Giardia isolates obtained from positive samples. A PCR based method was employed to amplify and sequence a 292bp region of the 16S-rRNA gene. Genetic sequences obtained from Giardia isolates were compared to each other and to previously sequenced isolates. Following a single faecal sample, 58% of Western Australian calves and 57% of Western Canadian calves were positive for Giardia. Geometric mean cyst counts/g of faeces were 839 for Western Australian calves and 3475 for Western Canadian calves, but these values did not differ significantly. Genetic sequences were obtained from 10 calves from Western Canada, while six sequences were obtained from Western Australian calves. Of the Western Canadian isolates, eight aligned with the proposed 'Hoofed livestock' genotype. Of the five isolates obtained from Western Australian calves, four sequences were identical to the 'Hoofed livestock' genotype. Two isolates from the Western Canadian calves and one isolate from the Western Australian calves had the identical genetic sequence to the Genotype (Assemblage) A sequence, a common human genotype. The results of this study demonstrate, for the first time, that Giardia infections occur in Western Australian calves. Also, calves from different geographical locations appear to be primarily infected with a Giardia genotype unique to hoofed livestock. However, calves can shed Giardia cysts potentially infective for humans. Thus, Giardia infections should be considered important to Australian dairy producers, and infections in calves may pose a risk to public health regardless of geographical location.

Nomenclature and genetic groupings of Giardia infecting mammals

Giardia is a ubiquitous and well-known enteric parasite affecting humans and a range of domestic and wild mammals. It is one of the most common parasites of domestic dogs and dairy cattle and a frequently recognized waterborne pathogen. Giardiasis is considered to be a re-emerging infection because of its association with outbreaks of diarrhoea in child-care centres. Although only a single species has been recognized as causing disease in humans and most other mammals, molecular characterization of morphologically identical isolates from humans and numerous other species of mammals has confirmed the heterogeneity of this parasite and provided a basis for a clearer understanding of the taxonomy and zoonotic potential of Giardia.

Effects of repeat fenbendazole treatment in dairy calves with giardiosis on cyst excretion, clinical signs and production

In this 90-day study, 60 male Holstein dairy calves were experimentally infected with Giardia duodenalis. Calves were randomly blocked by weight into treatment (N=30) and placebo (N=30) groups. Beginning on study Day 0, calves in the treatment group were administered an oral dose of 5mg/kg of fenbendazole once daily for three consecutive days. Calves in the placebo group received a daily oral treatment of 5 ml of saline for 3 days. These treatments were repeated on Days 30 and 60 of the study. Fecal samples were collected from calves once per week and examined for the presence of Giardia cysts. Calves were monitored daily for clinical signs of intestinal disease and all episodes of diarrhea recorded. Calves were weighed once per week and total feed intake, on a dry matter basis, was calculated daily. Following each treatment, the number of calves shedding Giardia cysts in the fenbendazole group was reduced (p<0.001) compared to the saline group. Also, calves in the fenbendazole group had fewer cysts (p<0.05) detected in their feces following treatment compared with calves that received saline. Within 2 weeks post treatment, the number of infected animals and fecal Giardia cysts returned to placebo levels. This pattern of reinfection was consistent after every treatment period. Calves receiving fenbendazole had fewer total days with diarrhea (p<0.01) and the average number of days each calf had diarrhea was reduced (p<0.05), compared to the placebo group. There were no differences in mean body weight, average daily gain, or feed intake between the treatment or placebo groups. This study demonstrates that fenbendazole is an effective treatment for giardiosis, resulting in a clinical benefit and reducing the number of infective cysts shed by calves. However, this treatment regime had no impact on production parameters and reinfection occurred rapidly in these calves.

The Giardia lamblia genome

Giardia lamblia is a protozoan parasite of humans and other mammals that is thought to be one of the most primitive extant eukaryotic organisms. Although distinctly eukaryotic, it is notable for its lack of mitochondria, nucleoli, and perixosomes. It has been suggested that Giardia spp. are pre-mitochondriate organisms, but the identification of genes in G. lamblia thought to be of mitochondrial origin has generated controversy regarding that designation. Giardi lamblia trophozoites have two nuclei that are identical in all ways that have been studied. They are polyploid with at least four, and perhaps eight or more, copies of each of five chromosomes per organism and have an estimated genome complexity of 1.2x10(7)bp of DNA, and GC content of 46%. There is evidence for recombination at the telomeres of some of the chromosomes, and multiple size variants of single chromosomes have been identified within cloned isolates. However, the internal regions of the chromosomes demonstrate no evidence of recombination. For example, there is no evidence for control of vsp gene expression by DNA recombination, and no evidence for rapid mutation in the vsp genes. Single pass sequences of approximately 9% of the G. lamblia genome have already been obtained. An ongoing genome project plans to obtain approximately 95% of the genome by a random approach, as well as a complete physical map using a bacterial artificial chromosome library. The results will facilitate a better understanding of the biology of Giardia spp. as well as their phylogenetic relationship to other primitive organisms.

Genomic polymorphism among Blastocystis hominis strains and development of subtype-specific diagnostic primers

Genomic polymorphisms among nine strains of Blastocystis hominis were examined by random amplified polymorphic DNA (RAPD) using four different arbitrary polymerase chain reaction (PCR) primers. Based on the RAPD patterns, nine strains were classified into three groups. The specific primers designed from the unique bands yielded a single band from within each same group, but did not amplify between all the groups examined. Specificity of these diagnostic primers was tested against several common intestinal parasites and a yeast, and no amplification was confirmed. Since the current criteria indicates that Blastocystis organisms isolated from humans are designated as B. hominis, the authors propose to classify several subtypes among B. hominis groups based on the difference of genomic DNA using three diagnostic primers.

Molecular epidemiology: assumptions and limitations of commonly applied methods

An understanding of the epidemiology of a disease (i.e. its aetiology, transmission patterns) is crucial for the development and implementation of effective management practices. This requires sound epidemiological data. It is therefore important that scientists understand the assumptions and limitations of the methods used to gather such data. The aim of this paper is to discuss some of the assumptions and limitations of PCR-based methods used in studies of epidemiology. Since its development, PCR has had a major impact in the biological sciences. The ability to selectively amplify a specific region of the genome from a small amount of DNA makes this technique particularly useful as a diagnostic tool. A variety of PCR-based methods are available which can be used to identify strains and species of parasites. Some of these methods, such as random amplification of polymorphic DNA, have intrinsic properties which can limit their application. Other methods, such as PCR-restriction fragment length polymorphism, require the availability of a sound taxonomic or genetic framework for the development of any diagnostic system for a particular organism. The problems encountered developing diagnostic probes in the absence of such a framework will be discussed using Giardia intestinalis as an example.

Prevalence of Giardia cysts and Cryptosporidium oocysts and characterization of Giardia spp. isolated from drinking water in Canada

This study was carried out to estimate the prevalence and potential for human infectivity of Giardia cysts in Canadian drinking water supplies. The presence of Cryptosporidium oocysts was also noted, but isolates were not collected for further study. A total of 1,760 raw water samples, treated water samples, and raw sewage samples were collected from 72 municipalities across Canada for analysis, 58 of which treat their water by chlorination alone. Giardia cysts were found in 73% of raw sewage samples, 21% of raw water samples, and 18.2% of treated water samples. There was a trend to higher concentration and more frequent incidence of Giardia cysts in the spring and fall, but positive samples were found in all seasons. Cryptosporidium oocysts were found in 6.1% of raw sewage samples, 4.5% of raw water samples, and 3.5% of treated water samples. Giardia cyst viability was assessed by infecting Mongolian gerbils (Meriones unguiculatus) and by use of a modified propidium iodide dye exclusion test, and the results were not always in agreement. No Cryptosporidium isolates were recovered from gerbils, but 8 of 276 (3%) water samples and 19 of 113 (17%) sewage samples resulted in positive Giardia infections. Most of the water samples contained a low number of cysts, and 12 Giardia isolates were successfully recovered from gerbils and cultured. Biotyping of these isolates by isoenzyme analysis and karyotyping by pulsed-field gel electrophoresis separated the isolates into the same three discrete groups. Karyotyping revealed four or five chromosomal bands ranging in size from 0.9 to 2 Mb, and four of the isolates had the same banding pattern as that of the WB strain. Analysis of the nucleotide sequences of the 16S DNA coding for rRNA divided the isolates into two distinct groups corresponding to the Polish and Belgian designations found by other investigators. The occurrence of these biotypes and karyotypes appeared to be random and was not related to geographic or other factors (e.g., different types were found in both drinking water and sewage from the same community). Biotyping and karyotyping showed that isolates from this study were genetically and biochemically similar to those found elsewhere, including well-described human source strains such as WB. We conclude that potentially human-infective Giardia cysts are commonly found in raw surface waters and sewage in Canada, although cyst viability is frequently low. Cryptosporidium oocysts are less common in Canada. An action level of three to five Giardia cysts per 100 liters in treated drinking water is proposed on the basis of the monitoring data from outbreak situations. This action level is lower than that proposed by Haas and Rose (C. N. Haas and J. B. Rose, J. Am. Water Works Assoc. 87(9):81-84, 1995) for Cryptosporidium spp. (10 to 30 oocysts per 100 liters).

Studies of Giardia spp. and Cryptosporidium spp. in two adjacent watersheds

Two adjacent British Columbia, Canada, watersheds with similar topographical features were studied. Both the Black Mountain Irrigation District (BMID) and the Vernon Irrigation District (VID) serve rural agricultural communities which are active in cattle ranching. The present study was carried out in five phases, during which a total of 249 surface water samples were tested in the study watersheds. The aims of these phases were to determine levels of parasite contamination in raw water samples collected from the intakes as well as from other sites in each watershed and to investigate cattle in the watersheds as potential sources of parasite contamination of surface drinking water supplies. Giardia cysts were not detected in the raw water samples collected from lake sources at the headwaters of both watersheds but were found in 100% (70 or 70) of water samples collected at the BMID intake and 97% (68 of 70) of water samples collected at the VID intake. Significantly higher levels (P < 0.05) of Giardia cysts were found at the BMID intake (phase 1, 7 to 2,215 cysts per 100 liters; phase 3, 4.6 to 1,880 cysts per 100 liters) when compared with that of the VID intake (2 to 114 cysts per 100 liters). The BMID watershed has a more complex system of surface water sources than the VID watershed. Cattle have access to creeks in the BMID watershed, whereas access is restricted in the VID watershed. Collection of raw water samples from a creek upstream and downstream of a cattle ranch in the BMID watershed showed that the downstream location had significantly higher (P < 0.05) levels (0.6 to 42.9 cysts per 100 liters and 1.4 to 300.0 oocysts per 100 liters) of both Giardia cysts and Cryptosporidium oocysts than those of the upstream location (0.5 to 34.4 cysts per 100 liters and 0.5 to 34.4 oocysts per 100 liters). Peak concentrations of both parasites coincided with calving activity. Fecal samples, collected from cattle in both watersheds, showed 10% (3 of 30) in the BMID and 50% (5 of 10) in the VID watersheds to be Giardia positive. No Cryptosporidium-positive fecal samples were found. Giardia cysts isolated from the BMID watershed were repeatedly infective to gerbils in contrast to those from the VID watershed. The 10 BMID drinking water Giardia isolates retrieved into culture and biotyped showed zymodeme and karyotype heterogeneity. The differences in patterns of parasite contamination and cattle management practices contribute to the unique watershed characteristics observed between two areas which are topographically similar and geographically adjacent.

Possible contamination of surface waters with Giardia spp. through muskrats

Muskrats were examined for Giardia infections. Collected faecal samples were processed by means of sucrose density gradient centrifugation, using a 1 M sucrose solution. Identification of cysts was done by phase contrast microscopy, by the immunofluorescence test, or by both methods. From July 1994 to September 1995, a total of 234 muskrats from two different geographical areas in western parts of Germany were examined for the presence of Giardia cysts. 176 animals (75.2%) were found to be Giardia-positive. This study corroborates the assumption that animals such as muskrats living close to surface water bodies could contaminate water bodies with parasites such as Giardia.

A second community outbreak of waterborne giardiasis in Canada and serological investigation of patients

A waterborne outbreak of giardiasis which occurred 5 years after another in the same town in Canada was investigated. Sera from residents defined as cases or non-cases were tested by enzyme-linked immunosorbent assay (ELISA) and compared with sera from symptomatic and asymptomatic control groups. The outbreak-associated Giardia isolate was retrieved from contaminated drinking water and antigen from this strain was used in the serological investigation. Up to 84% of cases were identified by ELISA. More cases were identified by elevated immunoglobulin (Ig) G than by either elevated anti-Giardia IgA or IgM levels. Residents of the community infected during the first outbreak were significantly less likely to have been reinfected during the second outbreak. This is the first report of a second waterborne outbreak occurring in a community and results of the investigations are consistent with an acquired, protective immunity lasting at least 5 years.