Variation in Giardia: implications for taxonomy and epidemiology

Prevalence of Giardia duodenalis assemblages in weaned cattle on cow-calf operations in the United States

To determine the prevalence of Giardia duodenalis in weaned beef calves on cow-calf operations in the United States, fecal specimens were collected from 819 calves (6-18 months of age) from 49 operations. After cleaning and concentration procedures to maximize recovery of cysts from feces, DNA was extracted from each of the 819 specimens. The presence of G. duodenalis was determined by nested PCR of a fragment of the SSU rRNA gene. All positive PCR products were subjected to sequence analysis. The overall sample level prevalence of Giardia was 33.5% with prevalence ranging from 0 to 100% among operations. The highest within herd prevalence of infected beef calves was found in one cow-calf operation from the South region (100%), followed by a cow-calf operation from the West region (90%), and three cow-calf operations from the Midwest region (87.5, 85, and 85%). Giardia was not detected in samples from 7 operations including 5 cow-calf operations from the South region, and 1 cow-calf operation each from the Midwest and West regions. Molecular analysis of the Giardia-positive samples identified assemblage E (or E-like) in 31.7% of all samples (260/819) and assemblage A in 1.2% (10/819). A mixed infection with assemblages A and E was observed in four calves from an operation in Midwest region. The potentially zoonotic assemblage A was detected in specimens from four operations in Midwest region. These findings indicate that most G. duodenalis found in weaned beef calves was assemblage E which represents no known zoonotic threat. However, the presence of assemblage A in a small number of animals poses a potential risk of infection to humans.

Zoonotic enteric protozoa

A growing number of enteric protozoan species are considered to have zoonotic potential. Their clinical impact varies and in many cases is poorly defined. Similarly, the epidemiology of infections, particularly the role of non-human hosts, requires further study. In this review, new information on the life cycles and transmission of Giardia, Cryptosporidium, Entamoeba, Blastocystis and Balantidium are examined in the context of zoonotic potential, as well as polyparasitism and clinical significance.

Host parasite interactions and pathophysiology in Giardia infections

Giardia is a protozoan parasite of the small intestine, and a leading cause of diarrhoeal disease worldwide in a variety of animals, including humans. The host-parasite interaction and pathophysiological processes of giardiasis remain incompletely understood. Current research suggests that Giardia-induced diarrhoeal disease is mediated by small intestinal malabsorption and maldigestion, chloride hypersecretion and increased rates of small intestinal transit. Small intestinal malabsorption and maldigestion results from the CD8+ lymphocyte-induced diffuse shortening of brush border microvilli. Activation of CD8+ lymphocytes occurs secondary to small intestinal barrier dysfunction, which results from heightened rates of enterocyte apoptosis and disruption of epithelial tight junctions. Both host and parasite factors contribute to the pathogenesis of giardiasis and ongoing research in this field may elucidate genotype/assemblage-specific pathogenic mechanisms. Giardia infections can result in chronic gastrointestinal disorders such as post-infectious Irritable Bowel Syndrome and symptoms may manifest at extra-intestinal sites, even though the parasite does not disseminate beyond the gastrointestinal tract. The infection can cause failure to thrive in children. Furthermore, there is now evidence suggesting that Giardia symptoms may vary between industrialised and developing areas of the world, for reasons that remain obscure. More research is needed to improve our understanding of this parasitic infection which was recently included in the World Health Organisation "Neglected Disease Initiative".

Zoonotic potential and molecular epidemiology of Giardia species and giardiasis

Molecular diagnostic tools have been used recently in assessing the taxonomy, zoonotic potential, and transmission of Giardia species and giardiasis in humans and animals. The results of these studies have firmly established giardiasis as a zoonotic disease, although host adaptation at the genotype and subtype levels has reduced the likelihood of zoonotic transmission. These studies have also identified variations in the distribution of Giardia duodenalis genotypes among geographic areas and between domestic and wild ruminants and differences in clinical manifestations and outbreak potentials of assemblages A and B. Nevertheless, our efforts in characterizing the molecular epidemiology of giardiasis and the roles of various animals in the transmission of human giardiasis are compromised by the lack of case-control and longitudinal cohort studies and the sampling and testing of humans and animals living in the same community, the frequent occurrence of infections with mixed genotypes and subtypes, and the apparent heterozygosity at some genetic loci for some G. duodenalis genotypes. With the increased usage of multilocus genotyping tools, the development of next-generation subtyping tools, the integration of molecular analysis in epidemiological studies, and an improved understanding of the population genetics of G. duodenalis in humans and animals, we should soon have a better appreciation of the molecular epidemiology of giardiasis, the disease burden of zoonotic transmission, the taxonomy status and virulences of various G. duodenalis genotypes, and the ecology of environmental contamination.

Genotyping of Giardia duodenalis among children and dogs in a closed socially deprived community from Italy

Molecular characterization of Giardia duodenalis cysts from humans and animals living in well-defined contexts is useful to study the circulation of isolates and represents a tool to evaluate zoonotic infection risk. The presence of giardiasis in children living in a disadvantaged and socially deprived small Rom community, as well in dogs roaming freely in the same context was carried out by microscopic analysis and beta-giardin gene amplification. Five out of 14 children were found positive at microscopic examination for G. duodenalis and six positive at PCR, while eight out of 14 dogs tested both microscopically and molecularly positive for G. duodenalis. Moreover, most of the children and dogs were symptomatic. Molecular characterization of Giardia positive samples from children and dogs showed 99.5% identity with Giardia Assemblage A1. The dog-specific genotypes C and D were not found. The findings of this survey provide the first European evidence to support the possible role of dogs in zoonotic transmission involving children and stray dogs in a closed context with very low standards of hygiene (i.e. Rom community), and these results show the need to monitor the health of marginal populations to safeguard ethnic minority groups.

Association between potential zoonotic enteric infections in children and environmental risk factors in Quebec, 1999-2006

This study was designed to evaluate the association of potential zoonotic gastroenteritis in children, and specifically giardiasis, salmonellosis and campylobacteriosis, with environmental risk factors in rural areas of Quebec. Notified cases of gastroenteritis in children of 0-4 years of age reported in the period of 1999 through 2006 from municipalities in southern Quebec with <100,000 inhabitants were investigated. Negative binomial regression models accounting for overdispersion and adjusted for clustering were used to estimate relative risks (RR) associated with livestock densities and drinking water quality. Analyses revealed that, during this period, 2500 cases of gastroenteritis were reported in children of 0-4 years, including 819 cases of giardiasis, 690 of salmonellosis and 852 of campylobacteriosis. The incidence rate associated with all potential zoonotic agents reported was 163 cases/100,000 children-years and this was statistically associated with cattle density: RR Quartile 4/Quartile 1 (Q4/Q1) = 1.92, 95% CI = 1.43-2.58. When estimated specifically for each pathogen, incidence rates of giardiasis (RR Q4/Q1 = 1.79, 95% CI = 1.11-2.87), salmonellosis (RR Q4/Q1 = 1.64, 95% CI = 1.15-2.33) and campylobacteriosis (RR Q4/Q1 = 2.43, 95% CI = 1.60-3.68) were also associated with cattle density, with a monotonic increase of RR with increasing animal density. Giardiasis incidence was also positively associated with a poor drinking water quality, although no statistically significant association was found. Our results suggest that, in rural Quebec, bacterial and parasitic enteric infections in young children may be zoonoses related to environmental risk factors and especially cattle production.

First genetic classification of Cryptosporidium and Giardia from HIV/AIDS patients in Malaysia

Given the HIV epidemic in Malaysia, genetic information on opportunistic pathogens, such as Cryptosporidium and Giardia, in HIV/AIDS patients is pivotal to enhance our understanding of epidemiology, patient care, management and disease surveillance. In the present study, 122 faecal samples from HIV/AIDS patients were examined for the presence of Cryptosporidium oocysts and Giardia cysts using a conventional coproscopic approach. Such oocysts and cysts were detected in 22.1% and 5.7% of the 122 faecal samples, respectively. Genomic DNAs from selected samples were tested in a nested-PCR, targeting regions of the small subunit (SSU) of nuclear ribosomal RNA and the 60kDa glycoprotein (gp60) genes (for Cryptosporidium), and the triose-phosphate isomerase (tpi) gene (for Giardia), followed by direct sequencing. The sequencing of amplicons derived from SSU revealed that Cryptosporidium parvum was the most frequently detected species (64% of 25 samples tested), followed by C. hominis (24%), C. meleagridis (8%) and C. felis (4%). Sequencing of a region of gp60 identified C. parvum subgenotype IIdA15G2R1 and C. hominis subgenotypes IaA14R1, IbA10G2R2, IdA15R2, IeA11G2T3R1 and IfA11G1R2. Sequencing of amplicons derived from tpi revealed G. duodenalis assemblage A, which is of zoonotic importance. This is the first report of C. hominis, C. meleagridis and C. felis from Malaysian HIV/AIDS patients. Future work should focus on an extensive analysis of Cryptosporidium and Giardia in such patients as well as in domestic and wild animals, in order to improve the understanding of transmission patterns and dynamics in Malaysia. It would also be particularly interesting to establish the relationship among clinical manifestation, CD4 cell counts and genotypes/subgenotypes of Cryptosporidium and Giardia in HIV/AIDS patients. Such insights would assist in a better management of clinical disease in immuno-deficient patients as well as improved preventive and control strategies.

High-throughput Giardia lamblia viability assay using bioluminescent ATP content measurements

The human pathogen Giardia lamblia is an anaerobic protozoan parasite that causes giardiasis, one of the most common diarrheal diseases worldwide. Although several drugs are available for the treatment of giardiasis, drug resistance has been reported and is likely to increase, and recurrent infections are common. The search for new drugs that can overcome the drug-resistant strains of Giardia is an unmet medical need. New drug screen methods can facilitate the drug discovery process and aid with the identification of new drug targets. Using a bioluminescent ATP content assay, we have developed a phenotypic drug screen method to identify compounds that act against the actively growing trophozoite stage of the parasite. This assay is homogeneous, robust, and suitable for high-throughput screening of large compound collections. A screen of 4,096 pharmacologically active small molecules and approved drugs revealed 43 compounds with selective anti-Giardia properties, including 32 previously reported and 11 novel anti-Giardia agents. The most potent novel compound was fumagillin, which showed 50% inhibitory concentrations of 10 nM against the WB isolate and 2 nM against the GS isolate.

Genome analysis and comparative genomics of a Giardia intestinalis assemblage E isolate

Background

Giardia intestinalis is a protozoan parasite that causes diarrhea in a wide range of mammalian species. To further understand the genetic diversity between the Giardia intestinalis species, we have performed genome sequencing and analysis of a wild-type Giardia intestinalis sample from the assemblage E group, isolated from a pig.

Results

We identified 5012 protein coding genes, the majority of which are conserved compared to the previously sequenced genomes of the WB and GS strains in terms of microsynteny and sequence identity. Despite this, there is an unexpectedly large number of chromosomal rearrangements and several smaller structural changes that are present in all chromosomes. Novel members of the VSP, NEK Kinase and HCMP gene families were identified, which may reveal possible mechanisms for host specificity and new avenues for antigenic variation. We used comparative genomics of the three diverse Giardia intestinalis isolates P15, GS and WB to define a core proteome for this species complex and to identify lineage-specific genes. Extensive analyses of polymorphisms in the core proteome of Giardia revealed differential rates of divergence among cellular processes.

Conclusions

Our results indicate that despite a well conserved core of genes there is significant genome variation between Giardia isolates, both in terms of gene content, gene polymorphisms, structural chromosomal variations and surface molecule repertoires. This study improves the annotation of the Giardia genomes and enables the identification of functionally important variation.

Molecular epidemiology of Giardia duodenalis in an endangered carnivore--the African painted dog

The African painted dog (Lycaon pictus) is an endangered carnivore of sub-Saharan Africa. To assist in conservation efforts a parasitological survey was conducted on wild and captive populations. Faecal samples were collected and examined for the presence of parasites using traditional microscopy techniques. The protozoan Giardia duodenalis was identified at a prevalence of approximately 26% in the wild populations and 62% in the captive population. Molecular characterisation of these isolates using three loci, 18S rRNA, β-giardin and the glutamate dehydrogenase gene revealed the zoonotic assemblages A and B existed in high proportions in both populations. The dog assemblages C and D were rarely observed. The identification of the zoonotic genotype suggests this species has the potential to act as a reservoir for human infections. Zoonotic transmission may be possible in captive populations due to the close interaction with humans however, in wild populations anthropozoonotic transmission seems more likely. This study is the first to observe G. duodenalis in the African painted dog and to identify a possible emerging disease in this wild carnivore.

Genotypes of Giardia intestinalis clinical isolates of gastrointestinal symptomatic and asymptomatic Saudi children

Giardiasis is the most worldwide parasitic disease with the major clinical impact on infant and children. Two genotypes were reported commonly among humans (assemblage A and B). In this study, genotypes of Giardia intestinalis clinical isolates obtaining from 24 gastrointestinal symptomatic Saudi primary school children and 16 asymptomatic ones were explored by real-time polymerase chain reaction using the high resolution melting curve analysis targeting intergenic spacer (IGS) region rDNA of G. intestinalis. Children having acute, intermittent, and chronic diarrhea were 14, 5, and 5, respectively. Among all the giardiasis subjects, assemblage B was 37.5% followed by both of assemblages AI and AII with 30% and 27.5%, respectively. Mixed infection with the three previous assemblages was present in 5% of cases. Among symptomatic children, the prevalence of assemblage B was 62.5% then followed by assemblage AI (16.7%) and assemblage AII with 12.5%. All of the children who harbored G. intestinalis assemblages B were symptomatic, while asymptomatic ones had only assemblage AI and AII with 50% each. The difference was statistically highly significant. In symptomatic patients having acute diarrhea, assemblage B was present in 71.5%, while assemblage AI and AII were equal with 7.1%. All of the patients (14.3%) with mixed infection had acute diarrhea. In intermittent diarrhea, assemblage AI and B were equally distributed with 40% each. In chronic diarrhea, assemblage AI and AII were equal with 20% each, while assemblage B was found in 60%. The difference was statistically not significant. In conclusion, assemblage B is the commonest, while assemblage A is a predominant in symptomatic and asymptomatic giardiasis Saudi children, respectively. So human transmission is the common risk factor among symptomatic, while zoonotic transmission is a common risk factor in asymptomatic ones. On the other hand, a strong correlation between assemblage B and symptoms and no relation between genotypes and types of diarrhea are found. Also, PCR with HRM in one-step closed-tube methods is able to genotype G. intestinalis IGS rDNA without using the sequencing methods or the electrophoresis.

Prevalence, molecular typing and risk factor analysis for Giardia duodenalis infections in dogs in a central London rescue shelter

A cross-sectional survey to investigate canine infections with Giardia duodenalis was undertaken at a central London rescue shelter between October 2006 and March 2007. The objectives of the study were to (i) estimate the prevalence of infection in dogs admitted to a London dog shelter using a commercially available ELISA-based test kit; (ii) identify the relative importance of potential dog level risk factors for infection; and (iii) identify the occurrence of different G. duodenalis assemblages present in this population in order to identify presence of any potentially zoonotic assemblages. A faecal sample was collected from each dog entering the shelter within 1 day of arrival. Each sample was tested for the presence of parasite cyst wall protein using the Giardia SNAP test kit (Idexx Laboratories). Samples were graded for faecal consistency on a standard scale and data on age, breed, categorized breed group, sex and neutered status were collected for each dog. Associations between infection status and each dog level variable were investigated using univariable and multivariable logistic regression. Selected G. duodenalis-positive samples were genotyped using previously described primers targeting the 18S rDNA gene and the beta-giardin gene. Samples from a total of 878 dogs were collected and the true prevalence found to be 21.0% (95% CI 16.7-25.4%). In the present study, the odds of infection decreased with increasing age (adjusted odds ratio 0.66, 95% CI 0.54-0.80, p<0.0001) and was increased for Rottweilers (adjusted odds ratio 2.12, 95% CI 1.03-4.34, p=0.04). Of the 51 samples selected for genotyping, 41 samples yielded a good amplification at one or both of the targeted genes, demonstrating the occurrence of mainly dog-specific assemblages C and D. The potentially zoonotic assemblage A and a mixed template C/D were found in two individual dogs. The results of the present study illustrate the high prevalence of G. duodenalis in shelter dogs. Although predominantly infected with dog-specific assemblages, the identification of assemblage A suggests that appropriate precautions should be taken to minimize the risk of transmission to staff.

Parasites, emerging disease and wildlife conservation

In this review some emerging issues of parasite infections in wildlife, particularly in Australia, are considered. We discuss the importance of understanding parasite biodiversity in wildlife in terms of conservation, the role of wildlife as reservoirs of parasite infection, and the role of parasites within the broader context of the ecosystem. Using a number of parasite species, the value of undertaking longitudinal surveillance in natural systems using non-invasive sampling and molecular tools to characterise infectious agents is illustrated in terms of wildlife health, parasite biodiversity and ecology.

Molecular characterization of Giardia duodenalis isolates from domestic ferrets

Giardia duodenalis is a pathogen that has been found in a variety of mammals, including humans, and consists of host-specific (assemblages C, D, E, F, and G) and zoonotic (assemblages A, B) genetic groups. Ferrets are popular pets, and they, like humans, are hosts to this pathogen. The genetic characteristics of the Giardia population in ferrets are unclear because only one ferret isolate has been genotyped. To develop a more complete picture of the genetic characteristics of the Giardia population in domestic ferrets two additional Giardia isolates, recovered independently from two ferrets suffering from intestinal or hepatic giardiasis, were analyzed genetically. The sequences of both isolates at three loci, small subunit ribosomal RNA (SSUrDNA, 292 bp), beta-giardin (734 bp), and glutamate dehydrogenase (GDH, 713 bp) were identical to each other, but the sequences of triosephosphate isomerase locus (TPI, 512 bp) had five substitutions between isolates. Sequence homology and phylogenetic analyses at four loci identified both isolates as members of the assemblage A. Moreover, the sequences of SSUrDNA, beta-giardin, and GDH from both isolates were identical to those of the previous ferret isolate genotyped as assemblage A within the regions of overlap. The result obtained in the present study indicates that at least two genetically different types in assemblage A exist in domestic ferrets. In addition, there have been no reported human and animal isolates with the same sequence as those from ferret isolates at all four loci examined, suggesting that the present ferret isolates might be host-specific.

The identification of a new Giardia duodenalis assemblage in marine vertebrates and a preliminary analysis of G. duodenalis population biology in marine systems

Giardia duodenalis is an intestinal parasite of many vertebrates. The presence of G. duodenalis in the marine environment due to anthropogenic and wildlife activity is well documented, including the contributions from untreated sewage and storm water, agricultural run-off and droppings from terrestrial animals. Recently, studies have detected this protistan parasite in the faeces of marine vertebrates such as whales, dolphins, seals and shore birds. To explore the population biology of G. duodenalis in marine life, we determined the prevalence of G. duodenalis in two species of seal (Halichoerus grypus, Phoca vitulina vitulina and Phoca vitulina richardsi) from the east and west coasts of the USA, sequenced two loci from G. duodenalis-positive samples to assess molecular diversity and examined G. duodenalis distribution amongst these seals and other marine vertebrates along the east coast. We found a significant difference in the presence of G. duodenalis between east and west coast seal species. Only the zoonotic lineages of G. duodenalis, Assemblages A and B and a novel lineage, which we designated as Assemblage H, were identified in marine vertebrates. Assemblages A and B are broadly distributed geographically and show a lack of host specificity. Only grey seal (Halichoerus grypus) samples and one gull sample (Larus argentatus) from a northern location of Cape Cod, Massachusetts, USA, showed the presence of Assemblage H haplotypes; only one other study of harbour seals from the Puget Sound region of Washington, USA previously recorded the presence of an Assemblage H haplotype. Assemblage H sequences form a monophyletic clade that appears as divergent from the other seven Assemblages of G. duodenalis as these assemblages are from each other. The discovery of a previously uncharacterised lineage of G. duodenalis suggests that this parasite has more genetic diversity and perhaps a larger host range than previously believed.

Giardia in Western Australian wildlife

Giardia has been found in numerous species of mammalian wildlife but very little information is available on the species and strains/genotypes that occur naturally in mammals in the wild. Recently, a novel genotype of Giardia was described in Western Australia, in the Southern brown bandicoot, or quenda (Isoodon obesulus). In order to determine the host range, distribution and prevalence of this novel 'quenda' 'genotype of Giardia, a comprehensive survey of this marsupial and cohabiting mammalian species was undertaken throughout the mainland and some off-shore islands of Western Australia, including urban areas. The overall prevalence of Giardia in 351 wildlife samples was low, with only 4.8% (17) samples testing positive. Amongst the 51 quenda samples, 11.8% (6) were positive for the 'quenda' genotype, 5.9% (3) for assemblage C/D and 2% (1) for assemblages A and E. This study has demonstrated that Giardia is a remarkably rare parasite in native wildlife in Western Australia, raising questions about the ecology of Giardia infections in wildlife.

Genotyping of Giardia duodenalis cysts by new real-time PCR assays for detection of mixed infections in human samples

Of the seven genetic groups, or assemblages, currently recognized in the Giardia duodenalis species complex, only assemblages A and B are associated with human infection, but they also infect other mammals. Recent investigations have suggested the occurrence of genetic exchanges among isolates of G. duodenalis, and the application of assemblage-specific PCR has shown both assemblages A and B in a significant number of human infections. In this work, three real-time quantitative (qPCR) assays were developed to target the G. duodenalis triose phosphate isomerase, glutamate dehydrogenase, and open reading frame C4 sequences. Primers were designed to allow the specific amplification of the DNA of assemblage A or B and to generate products distinguishable by their melting curves or, after qPCR, by their sequences, sizes, or restriction patterns. The assays showed full specificity and detected DNA from a single trophozoite (4 to 8 target copies). We applied these assays, as well as a TaqMan assay that targets the beta-giardin gene, to genomic DNA extracted from 30 human stools and to Giardia cysts purified by immunomagnetic capture from the same samples. Simultaneous detection of both assemblages was observed in a large number of DNAs extracted from stools, and experiments on the cysts purified from the same samples showed that this was essentially attributable to mixed infections, as only one assemblage was detected when dilutions of cysts were tested. In a few cases, detection of both assemblages was observed even when single cysts were tested. This result, which suggests the presence of recombinants, needs to be confirmed using more accurate methods for cyst separation and enumeration. The assays described in this study can be used to detect Giardia cysts infectious to humans in samples from animals and in water and food.

Inactivation of Cryptosporidium by ozone and cell ultrastructures

The fluorescence staining method and scanning electron microscopy (SEM) were used to study the effect of ozone (O3) inactivating Cryptosporidium in water and cell ultrastructures variation to shed light on the mechanism of inactivation preliminarily. Results indicated that O3 had a stronger inactivating capability. When the concentration of O3 was above 3.0 mg/L and the contact time was up to 7 min, a significant inactivating effect could be achieved. The turbidity on inactivation effects was also found to be statistically significant in artificial water. With increases in turbidity, the inactivating effect decreased. Inactivation rate improved with a temperature increase from 5 to 25 degrees C, but decreased beyond this. The inactivating capability of O3 was found to be stronger under acidic than that under alkalic conditions. When the concentration of organic matter in the reaction system was increased, the competition between Cryptosporidium and organics with O3 probably took place, thereby reducing the inactivation rate. In addition, the cellular morphology of Cryptosporidium varied with different contact times. At zero contact time, cells were rotundity and sphericity, at 60 sec they became folded, underwent emboly, and burst at 480 sec, the cell membrane of Cryptosporidium shrinked and collapsed completely.

Molecular detection of Giardia contamination in water bodies in a zoo

We used a combined microscopy-molecular approach to determine the occurrence and identities of waterborne Giardia sp. cysts isolated from 18 separate, 10l grab samples collected from a Malaysian zoo. Microscopy revealed that 17 of 18 samples were Giardia cyst positive with concentrations ranging from 1 to 120 cysts/l. Nine (52.9%) of the 17 cyst positive samples produced amplicons of which 7 (77.8%) could be sequenced. Giardia duodenalis assemblage A (6 of 7) and assemblage B (1 of 7), both infectious to humans, were identified at all sampling sites at the zoo. The presence of human infectious cysts raises public health issues, and their occurrence, abundance and sources should be investigated further. In this zoo setting, our data highlight the importance of incorporating environmental sampling (monitoring) in addition to routine faecal examinations to determine veterinary and public health risks, and water monitoring should be considered for inclusion as a separate element in hazard analysis, as it often has a historical (accumulative) connotation.

Echinococcus, Giardia and Cryptosporidium: observational studies challenging accepted dogma

The development of in vitro culture systems that allow the maintenance, and support the development of Echinococcus, Giardia and Cryptosporidium in the laboratory have had a significant impact on their biology and taxonomy and the epidemiology of infections they cause. This short retrospective review demonstrates how radical shifts in our understanding have occurred as a result of being able to grow these organisms in culture, and how molecular tools have helped in the interpretation of such research that often reflects the observations of earlier workers.

The inadequacy of morphology for species and genus delineation in microbial eukaryotes: an example from the parabasalian termite symbiont coronympha

Background

For the majority of microbial eukaryotes (protists, algae), there is no clearly superior species concept that is consistently applied. In the absence of a practical biological species concept, most species and genus level delineations have historically been based on morphology, which may lead to an underestimate of the diversity of microbial eukaryotes. Indeed, a growing body of molecular evidence, such as barcoding surveys, is beginning to support the conclusion that significant cryptic species diversity exists. This underestimate of diversity appears to be due to a combination of using morphology as the sole basis for assessing diversity and our inability to culture the vast majority of microbial life. Here we have used molecular markers to assess the species delineations in two related but morphologically distinct genera of uncultivated symbionts found in the hindgut of termites.

Methodology/Principal Findings

Using single-cell isolation and environmental PCR, we have used a barcoding approach to characterize the diversity of Coronympha and Metacoronympha symbionts in four species of Incisitermes termites, which were also examined using scanning electron microscopy and light microcopy. Despite the fact that these genera are significantly different in morphological complexity and structural organisation, we find they are two life history stages of the same species. At the same time, we show that the symbionts from different termite hosts show an equal or greater level of sequence diversity than do the hosts, despite the fact that the symbionts are all classified as one species.

Conclusions/Significance

The morphological information used to describe the diversity of these microbial symbionts is misleading at both the genus and species levels, and led to an underestimate of species level diversity as well as an overestimate of genus level diversity. The genus ‘Metacoronympha’ is invalid and appears to be a life history stage of Coronympha, while the single recognized species of Coronympha octonaria inhabiting these four termites is better described as four distinct species.

Multilocus genotyping of Cryptosporidium and Giardia in non-outbreak related cases of diarrhoea in human patients in Belgium

Stool samples from Belgian patients suffering from abdominal pain and/or diarrhoea were examined for Cryptosporidium and Giardia. Cryptosporidium-positive samples were genotyped using the 70 kDa heat shock protein and the 60 kDa glycoprotein (GP60) genes: C. hominis was identified in 54.2% and C. parvum in 45.8% of the samples. Sequencing at the GP60 locus indicated that subgenotype IbA10G2 of C. hominis and subgenotype IIaA15G2R1 of C. parvum were the most prevalent, although several other subgenotypes were identified. For Giardia, sequencing at the beta-giardin, triose phosphate isomerase (TPI) and glutamate dehydrogenase (GDH) genes revealed assemblage B as the most prevalent (74.4%) in human patients. A high degree of heterogeneity was found, especially on the beta-giardin gene, and to a lesser extent on the GDH gene. Furthermore, using a novel species-specific PCR based on the TPI gene, mixed infections with both assemblage A and B were detected in a large number (32.4%) of human patients, which might have important epidemiological implications.

Molecular characterisation of Giardiaduodenalis in captive non-human primates reveals mixed assemblage A and B infections and novel polymorphisms

Giardia is frequently detected in stools of non-human primates (NHP). However, a molecular identification has been rarely applied to Giardia isolates from NHP, and the distribution of the zoonotic assemblages A and B remains unclear. Moreover, little is known about the genetic variability among the isolates, although this may contribute to the elucidation of the different transmission pathways, including the role of NHP as a reservoir for human giardiasis. Therefore, 258 Giardia samples from 31 NHP species housed in nine zoological gardens and one sanctuary in Belgium and The Netherlands were characterised based on an assemblage-specific PCR targeting the triose phosphate isomerase (tpi) gene to identify both assemblage A and B infections. In addition, a multi-locus sequencing approach based on the glutamate dehydrogenase, the tpi and the beta-giardin genes was used to examine both the genetic variability and the ability to allocate these isolates to different NHP groups. Overall, assemblage B was the most prevalent (78.6%), but mixed assemblage A and B infections occurred in 32.7% of the samples. Sequencing of the isolates revealed the presence of new polymorphisms for both assemblages and at the three loci examined. The majority of the assemblage B isolates could not be grouped into recently described sub-assemblages, particularly at the tpi gene. Isolates could only be allocated to a specific group when polymorphisms of the three loci were combined. The results confirm that NHP are a potential reservoir for zoonotic transmission and advocate the use of assemblage-specific primers in molecular epidemiological surveys, as mixed infections are likely to be underestimated. The high level of heterogeneity within assemblages indicates that a revised nomenclature of these sub-assemblages is needed, but points out the potency of a multi-locus sequencing approach to unravel the complex epidemiology of Giardia duodenalis.

High genetic polymorphism among Giardia duodenalis isolates from Sahrawi children

Human giardiasis, the gastrointestinal infection caused by two genetically different groups (or assemblages) of Giardia duodenalis, is very common worldwide, and its prevalence is higher in developing countries. However, few surveys in these regions have been performed to include a genetic characterization of the parasite, which is necessary to unravel the complex epidemiology of the infection. In this work, we screened 120 faecal samples collected from Sahrawi children in 2003-2005, and found 41 (34.2%) of them to be positive, using immunofluorescent microscopy, for the presence of G. duodenalis cysts. Molecular characterization of the isolates was performed by RFLP and/or sequence analysis of the triose phosphate isomerase (tpi) and the glutamate dehydrogenase (gdh) genes. The results disclosed an unexpectedly high genetic polymorphism among isolates of both assemblages A and B, and a large percentage of the sequences (50% for the tpi gene, and 90% for the gdh gene) from assemblage B isolates characterized by the presence of overlapping nucleotide peaks at specific positions in the chromatograms, which can be attributed to mixed infections or to allelic sequence heterozygosity of single cysts. Notably, this phenomenon was not observed in sequences from assemblage A isolates. These results suggest that the genetic structure is different in isolates of assemblages A and B.

Multiple-subgenotype infections of Giardia intestinalis detected in Palestinian clinical cases using a subcloning approach

To evaluate the geographic distribution of Giardia intestinalis genotypes in Nablus, West Bank, Palestine, a genotyping study was performed using clinical fecal samples. Microscopic examination confirmed that 8 of 69 (11.6%) samples were G. intestinalis positive, and subsequent genotyping analyses targeting the small-subunit ribosomal RNA (18S rRNA) and glutamate dehydrogenase (GDH) genes revealed the G. intestinalis genotypes within the 8 samples. Of these 8 samples, 6 were clustered with assemblage A-II and the remaining 2 samples were clustered with assemblage B by 18S rRNA gene analysis; however, direct sequencing of the GDH gene segments from the latter 2 samples showed a mixed infection profile. To assess those samples, we employed a subcloning approach and successfully isolated 6 independent assemblage B subgenotypes. These partial GDH gene sequences (393 bp) had 15 single-nucleotide polymorphisms, all of which were synonymous transition substitutions at the third nucleotide position of codons. From the results, we concluded that the highly polymorphic gene loci such as GDH gene locus might provide us an opportunity to obtain a detailed molecular data even from the samples with multiple-subgenotype mixed infections. Therefore, subcloning approach is recommended in genotyping studies, especially in those conducted in giardiasis-endemic areas, where the repeated and cumulative infections could be commonly expected.

Human zoonotic enteropathogens in a constructed free-surface flow wetland

Effluents from a small-scale free-surface flow constructed wetland, used for polishing of secondary treated wastewater, contained significantly higher concentrations of potentially viable Giardia duodenalis cysts and Enterocytozoon bieneusi spores than did wetland influents consisting of secondary treated wastewater. Zoonotic Assemblage A of G. duodenalis cysts was identified in wetland inflows, while Assemblage A and two nonhuman infective Assemblages (i.e., C, and E) were present in wetland effluents. E. bieneusi spores represented genotype K based on DNA sequencing analysis of internal transcribed spacer. The study demonstrated that: (1) free-surface flow small-scale constructed wetlands may not provide sufficient remediation for human zoonotic protozoa and fungi present in secondary treated wastewater; (2) dogs and livestock can substantially contribute human-pathogenic protozoan and fungal microorganisms to engineered vegetated wetland systems; and (3) large volumes of wetland effluents can contribute to contamination of surface waters used for recreation and drinking water abstraction and therefore represent a serious public health threat.

Is Giardia a significant pathogen in production animals?

Although Giardia duodenalis is recognised worldwide as the most important parasitic cause of gastro-intestinal disorder in human patients, the relevance of infection in production animals is prone to debate. Since the 1980s, clinical disease has been associated with giardiasis in production animals, both in natural conditions and in experimental studies. However, most Giardia research is focussed on the relevance of production animals as a reservoir for zoonotic transmission. In this study, the current knowledge on clinical relevance of giardiasis in production animals is reviewed, along with the diagnosis, treatment and control of infection. Furthermore, future research objectives are discussed.

Giardia duodenalis: genetic recombination and its implications for taxonomy and molecular epidemiology

Traditionally, species within the Giardia genus have been considered as eukaryotic organisms that show an absence of sexual reproduction in their simple life cycles. This apparent lack of sex has been challenged by a number of studies that have demonstrated (i) the presence in the Giardia duodenalis genome of true homologs of genes specifically involved in meiosis in other eukaryotes, and their stage-specific expression; (ii) the exchange of genetic material in different chromosomal regions among human isolates of the parasite; (iii) the fusion between cyst nuclei (karyogamy) and the transfer of genetic material (episomal plasmids) between them. These results are pivotal for the existence of sexual recombination. However, many details of the process remain elusive, and experimental data are still scarce. This review summarizes the experimental approaches and the results obtained, and discusses the implications of recombination from the standpoint of the taxonomy and molecular epidemiology of this widespread pathogen.

A longitudinal study of Giardia duodenalis genotypes in dairy cows from birth to 2 years of age

Fecal specimens were collected from 30 calves from birth to 24 months of age at a dairy farm in Maryland to determine the prevalence of Giardia duodenalis genotypes in cattle of different ages. Fecal samples were subjected to density gradient centrifugation to remove debris and concentrate cysts. Specimens were analyzed by immunofluorescence microscopy and polymerase chain reaction (PCR). All PCR positive specimens were sequenced using the SSU-rRNA gene of Giardia. All 30 calves shed G. duodenalis cysts at some time during the study. Of 990 specimens, 312 were positive for G. duodenalis (31.5%). The highest prevalence of infection occurred at weeks 4 and 5 of age with 25 out of 30 calves shedding cysts at those sampling times. Overall, pre-weaned calves (<8 weeks of age) exhibited the highest prevalence (60.8%), followed by post-weaned calves (3-12 months of age) (32.1%) and heifers (12-24 months of age) (11.4%). Sequence analysis of the 312 PCR-positive samples revealed the presence of both Assemblages A and E, G. duodenalis, with cumulative prevalences of 70% and 100%, respectively. Assemblage A was not detected in pre-weaned calves, but was detected in 6.9% and 4.7% of post-weaned calves and heifers, respectively. These data indicate not only that calves are infected with both Assemblages A and E simultaneously, but also that infections with zoonotic Assemblage A, G. duodenalis are more common than previously reported. Thus, calves appear to be a more significant reservoir of human infectious G. duodenalis than previous data have suggested.

GiardiaDB and TrichDB: integrated genomic resources for the eukaryotic protist pathogens Giardia lamblia and Trichomonas vaginalis

GiardiaDB (http://GiardiaDB.org) and TrichDB (http://TrichDB.org) house the genome databases for Giardia lamblia and Trichomonas vaginalis, respectively, and represent the latest additions to the EuPathDB (http://EuPathDB.org) family of functional genomic databases. GiardiaDB and TrichDB employ the same framework as other EuPathDB sites (CryptoDB, PlasmoDB and ToxoDB), supporting fully integrated and searchable databases. Genomic-scale data available via these resources may be queried based on BLAST searches, annotation keywords and gene ID searches, GO terms, sequence motifs and other protein characteristics. Functional queries may also be formulated, based on transcript and protein expression data from a variety of platforms. Phylogenetic relationships may also be interrogated. The ability to combine the results from independent queries, and to store queries and query results for future use facilitates complex, genome-wide mining of functional genomic data.

Giardia and other intestinal parasites in different dog populations in Northern Belgium

The objectives of this study were to obtain data on the prevalence of intestinal parasites in different dog populations in northern Belgium, to estimate the zoonotic risk associated with these infections and to identify potential risk factors. Between 2004 and 2007 a total of 1159 faecal samples were collected from 451 household dogs, 357 dogs from breeding kennels and 351 dogs with gastrointestinal disorders. The samples from dogs with gastrointestinal disorders were sent to the diagnostic Laboratory for Parasitology at Ghent University by veterinary practitioners. In household dogs the prevalence of intestinal parasites was relatively low. Giardia was the most commonly found parasite (9.3%, CI 5.5-13.1), followed by Toxocara canis (4.4%, CI 2.7-6.8). Much higher infection rates were observed in kennel dogs, especially for Giardia spp. (43.9%, CI 37.8-50.0); T. canis (26.3%, CI 21.8-31.2) and Cystoisospora spp. (26.3%, CI 21.8-31.2). Also in dogs with gastrointestinal problems, Giardia spp. (18.1%, CI 13.1-23.1), Cystoisospora spp. (8.8%, CI 6.1-12.3) and T. canis (7.4%, CI 4.9-10.7) were the most frequently detected parasites. In all dog populations pups were more frequently infected with Cystoisospora (P<0.0001 to P<0.05), Giardia (P<0.001 to P<0.05), and T. canis (P<0.0001 to P<0.001) than adult dogs, except for T. canis in household dogs, where this correlation was not significant. A significant association of anthelmintic treatment with T. canis infections was only observed within the household population. Household dogs with a higher number of treatments per year were more frequently infected with T. canis (P<0.05). There was a significant difference between the different breeding kennels for the occurrence of Cystoisospora, Giardia and T. canis (P<0.0001) and large kennels harboured relatively more infected animals than smaller breeding facilities (P<0.05). However, this was not significant for Giardia spp. Breed and gender did not affect the risk of an infection in any of the study populations. Toxocara and Giardia present a zoonotic risk, especially in household dogs, where the majority of Giardia positive samples (80%) belonged to the zoonotic assemblage A. In kennel dogs and clinically affected dogs the host-specific Giardia assemblages C and D were most prevalent (94% and 80%, respectively).

The molecular epidemiology of Cryptosporidium and Giardia infections in coyotes from Alberta, Canada, and observations on some cohabiting parasites

Coyotes from southern Alberta and Saskatchewan, Canada, were examined for the presence of Giardia and Cryptosporidium and cohabiting helminths. Toxascaris was present in over 90% of the 70 animals examined, and Taenia sp. in 6.5-25% of the two groups of animals studied. Giardia (12.5-21.7%) and Cryptosporidium (0-17.4%) were also common and molecular characterisation revealed both zoonotic and host-adapted genotypes of Giardia, whereas the Cryptosporidium proved to be a variant of the canine species C. canis. The seasonal variation observed in the occurrence of Cryptosporidium may be related to stress-induced shedding of the parasite.

Genotyping of Giardia duodenalis from Southern Brown Howler Monkeys (Alouatta clamitans) from Brazil

Giardia duodenalis is a widespread intestinal protozoan that can infect humans and animals, both domestic and wild. Independent of host, infections present with the same symptoms. However, based on host specificity, Giardia isolates have been grouped into genotypes A to G. Parasites of assemblage A and B are known to infect humans, in addition to primates and a wide variety of mammals. In Brazil, hitherto Giardia genotypes were defined only for humans and domestic animals. To evaluate the genotypes of different Giardia present among other animals, fecal samples from 28 Southern Brown Howler Monkeys (Alouatta clamitans) kept in captivity from South Brazil were screened for G. duodenalis using parasitological methods. All of them were asymptomatic, but positive for Giardia. The genotype of the G. duodenalis circulating among these animals was ascertained by molecular typing, performed using amplification and sequencing of the beta-giardin gene. Sixteen of 28 samples were successfully amplified by PCR and sequencing of this gene s revealed that all of them were of the genotype A1. These findings suggest that A. clamitans represent a potential risk of environmental contamination of a G. duodenalis genotype that also infect humans, and therefore can be considered a potential reservoir for G. duodenalis of a genotype that can also infects humans. Therefore, these results highlight a potential public health problem due to the epidemiological and molecular evidence for anthropozoonotic transmission.

Identification of genotypes of Giardia intestinalis of human isolates in Egypt

In Egypt, the genotyping study of Giardia intestinalis in human is limited. To determine the prevalence of G. intestinalis, faecal samples were collected from Egypt. Samples were concentrated using density gradient centrifugation. The samples were subjected to PCR and DNA sequence analysis for TPI gene. Prevalence of Giardia infection was 34.6% of 52 examined. DNA sequence showed that the Assemblage B was the most prevalent (80%) genotype, the 15% of the positive samples belonged to Assemblage E, and the 5% of them belonged to Assemblage A. Certainly, both genotypes A and B are highly common in human worldwide. However, up to now, Assemblage E had not been known to be infectious for humans. Therefore, this is the first time that Assemblage E is reported in human. However, further analyses of a second locus are required to confirm this result. The extent to which Giardia-infected cattle in Egypt might pose a risk of human infection is unknown.

Detection and surveillance of waterborne protozoan parasites

The majority of the world's population still live without access to healthy water and the contamination of drinking water with protozoan pathogens poses a serious threat to millions of people in the developing world. Even in the developed world periodic outbreaks of diarrhoeal diseases are caused by the protozoan parasites Cryptosporidium sp., Giardia duodenalis and Entamoeba histolytica. Thus, surveillance of drinking water is imperative to minimize such contaminations and ensure continuous supplies of healthy water world-wide. This article reviews the progress in technology for detection and surveillance of these important waterborne parasites.

Intestinal parasitism in the animals of the zoological garden "Peña Escrita" (Almuñecar, Spain)

Gastrointestinal parasites cause serious diarrhoea in captive animals. Therefore, we have undertaken this study to establish programmes to prevent, control, and treat intestinal parasitism in the animals of the zoological garden "Peña Escrita" of Almuñecar (Granada). An annual survey was conduced to estimate the occurrence of gastrointestinal parasites and the seasonality of this parasitism. Between June 2006 and May 2007, 432 samples were collected from primates, carnivores, perissoodactyla, artiodactyla, rodentia, diprotodontia, galliformes, anseriformes and struthioniformes. One or more intestinal parasites were identified in 72.5% of the animals. The most frequent pathogenic endoparasites were Eimeria spp. (17.3%), Trichuris spp. (5.1%), Strongyloides spp. (4.5%), Cyclospora spp. (4.5%), Cryptosporidium spp. (3.2%) and Isospora spp. (2.6%). Iodamoeba butschlii, Parascaris equorum and Trichuris spp. did not vary with season and Cryptosporidium spp., Dicrocoelium dendriticum, Metastrongylus spp. and Cylicospirura spp. appeared exclusively in Artiodactyla. Multiple parasitic infections were common, 70% of animals presented with at least two parasites (maximum=6). The most frequent cases of multiple parasitism were Eimeria spp. plus Blastocystis spp. and Eimeria spp. plus Nematodirus spp., in the last case the animals presented explosive diarrhoea. In accord with our results, after each sampling, some of the affected animals were treated and the corresponding programmes of prevention and control were designed.

Molecular epidemiology of giardiasis

Giardia duodenalis is a widespread parasite of mammalian species, including humans. Due to its invariant morphology, investigation on aspects such as host specificity and transmission patterns requires a direct genetic characterization of cysts/trophozoites from host samples. A number of molecular assays have been developed to help unravel the complex epidemiology of this infection. A coherent picture has emerged from those studies, indicating the existence of seven genetic groups (or assemblages), two of which (A and B) are found in both humans and animals, whereas the remaining five (C-G) are host-specific. Sequence-based surveys have identified a number of genotypes within assemblages A and B in animal species, some of which may have zoonotic potential. Recently, however, molecular approaches have been complicated by the recognition of intra-isolate sequence heterogeneity (i.e., "mixed templates", that affects identification of subtypes within each assemblage), and by the unreliable assignment of isolates to G. duodenalis assemblages generated by different genetic markers. This raises concerns about previous interpretation of genotyping data, especially when single genetic markers have been used. The mechanisms that may be responsible for these findings, including allelic sequence heterozygosity and meiotic recombination, are discussed.

Phylogenetic analysis of the SSU rRNA gene from the piscine diplomonad Spironucleus torosus (Diplomonadida: Hexamitinae)

Previous studies have recorded Spironucleus torosus Poynton et Morrison, 1990 from several species of gadoid fishes, including the only freshwater gadoid, the burbot Lota lota (L.). Two morphologically different isolates of S. torosus have been described (elongate and pyriform). Both have been found in saltwater, while only the elongate has been found in freshwater. To address the conspecificity of the two morphs of S. torosus, and to identify the source of S. torosus in burbot in Norway, we have sequenced the small subunit ribosomal RNA (SSU rRNA) gene from 43 isolates of S. torosus from six species of gadoid fishes sampled at 15 localities in Norway, Sweden and the Baltic Sea. Phylogenetic analyses of the SSU rRNA gene sequence data recovered two major clades, one containing mainly isolates from burbot, while the other contained isolates from marine gadoid fishes only. The genetic distance (based on 25 nucleotide substitutions in 789 base pairs) separating the two assemblages was not large enough to consider the two groups separate species. Spironucleus torosus isolated from burbot displayed limited genetic variation in the small subunit ribosomal RNA (SSU rRNA) gene along the post-Pleistocene migration route of its host. The present study is the first report of S. torosus in tusk Brosme brosme (Ascanius), whiting Merlangius merlangus (L.), and fourbeard rockling Enchelyopus cimbrius (L.).

The public health and clinical significance of Giardia and Cryptosporidium in domestic animals

Giardia and Cryptosporidium are common enteric parasites of domestic animals, particularly dogs, cats and livestock. Their occurrence is of potential significance from both clinical and public health perspectives yet, until recently, confusion over the taxonomy of these organisms prevented a clear understanding of the epidemiology of infections with both Giardia and Cryptosporidium. The recent application of molecular epidemiological tools has helped to resolve taxonomic issues, allowing cycles of transmission to be determined. In addition, advances have been made in elucidating mechanisms associated with pathogenesis, whereas only limited progress has been achieved in the areas of chemotherapy and prophylaxis.

Prevalence and molecular characterization of Giardia duodenalis and Cryptosporidium spp. in dairy cattle in Ontario, Canada

Giardia duodenalis and Cryptosporidium spp. are intestinal protozoan parasites that infect a wide range of host species, including humans. Molecular characterization of these parasites has demonstrated that a number of genotypes and species are common to both humans and animals, and that zoonotic transmission may occur. Numerous studies have reported a high prevalence of G. duodenalis and Cryptosporidium spp. in cattle, particularly calves, and these animals are frequently associated with zoonotic transmission. In the present study, a total of 143 faecal samples from adults, heifers and calves were collected from two dairy cattle farms in eastern Ontario, Canada. The prevalence and molecular characteristics of G. duodenalis and Cryptosporidium spp. in these animals were determined in order to investigate the potential for transmission between cattle and humans in this region. Following DNA extractions from faecal samples, nested-PCR protocols were used to amplify fragments of the 16S rRNA gene and the heat-shock protein 70 (HSP-70) gene for determining the prevalence of G. duodenalis and Cryptosporidium spp. infections, respectively. Genotypes of G. duodenalis, and species of Cryptosporidium, were determined by means of DNA sequencing of amplicons, and subsequent sequence alignment. Cattle on both farms showed a high prevalence of G. duodenalis (42.0%) and Cryptosporidium spp. (27.3%). G. duodenalis infections were more prevalent in calves and heifers than in adults, and Cryptosporidium spp. infections were only observed in calves and heifers. The zoonotic genotype, G. duodenalis Assemblage B was isolated from 24.5% of the cattle tested, while G. duodenalis Assemblage E was found in 17.5% of the cattle tested. The overall prevalence of the zoonotic species Cryptosporidium parvum in the animals tested was found to be 21.7%, while only 1.4% were infected with C. bovis. These findings suggest that there is a potential risk of zoonotic and/or zooanthroponotic transmission of G. duodenalis and C. parvum infections between cattle and humans in eastern Ontario, likely by means of contaminated water or food, or through direct faecal-oral transmission in the case of farmers and veterinary staff.