Selection of specific genotypes of Giardia intestinalis by growth in vitro and in vivo

The Exosome-like Vesicles of Giardia Assemblages A, B, and E Are Involved in the Delivering of Distinct Small RNA from Parasite to Parasite

The genetically related assemblages of the intestinal protozoa parasite Giardia lamblia are morphologically indistinguishable and are often derived from specific hosts. The Giardia assemblages are separated by large genetic distances, which might account for their relevant biological and pathogenic differences. In this work, we analyzed the RNAs cargo released into exosomal-like vesicles (ElVs) by the assemblages A and B, which differentially infect humans, and the assemblage E, which infects hoofed animals. The RNA sequencing analysis revealed that the ElVs of each assemblage contained distinct small RNA (sRNA) biotypes, suggesting a preference for specific packaging in each assemblage. These sRNAs were classified into three categories, ribosomal-small RNAs (rsRNAs), messenger-small RNAs (msRNAs), and transfer-small RNAs (tsRNAs), which may play a regulatory role in parasite communication and contribute to host-specificity and pathogenesis. Uptake experiments showed, for the first time, that ElVs were successfully internalized by the parasite trophozoites. Furthermore, we observed that the sRNAs contained inside these ElVs were first located below the plasma membrane but then distributed along the cytoplasm. Overall, the study provides new insights into the molecular mechanisms underlying the host-specificity and pathogenesis of G. lamblia and highlights the potential role of sRNAs in parasite communication and regulation.

Treatment-refractory giardiasis: challenges and solutions

Giardia is the commonest parasitic diarrheal pathogen affecting humans and a frequent cause of waterborne/foodborne parasitic diseases worldwide. Prevalence of giardiasis is higher in children, living in poor, low hygiene settings in developing countries, and in travelers returning from highly endemic areas. The clinical picture of giardiasis is heterogeneous, with high variability in severity of clinical disease. It can become chronic or be followed by post-infectious sequelae. An alarming increase in cases refractory to the conventional treatment with nitroimidazoles (ie, metronidazole) has been reported in low prevalence settings, such as European Union countries, especially in patients returning from Asia. In view of its relevance, we aim in this review to recapitulate present clinical knowledge about Giardia, with a special focus on the challenge of treatment-refractory giardiasis. We propose a working definition of clinically drug-resistant giardiasis, summarize knowledge regarding resistance mechanisms, and discuss its clinical management according to research-based evidence and medical practice. Advances in development and identification of novel drugs and potential non-pharmacological alternatives are also reviewed with the overall aim to define knowledge gaps and suggest future directions for research.

Host specificity in the Giardia duodenalis species complex

Giardia duodenalis is a unicellular flagellated parasite that infects the gastrointestinal tract of a wide range of mammalian species, including humans. Investigations of protein and DNA polymorphisms revealed that G. duodenalis should be considered as a species complex, whose members, despite being morphologically indistinguishable, can be classified into eight groups, or Assemblages, separated by large genetic distances. Assemblages display various degree of host specificity, with Assemblages A and B occurring in humans and many other hosts, Assemblage C and D in canids, Assemblage E in hoofed animals, Assemblage F in cats, Assemblage G in rodents, and Assemblage H in pinnipeds. The factors determining host specificity are only partially understood, and clearly involve both the host and the parasite. Here, we review the results of in vitro and in vivo experiments, and clinical observations to highlight relevant biological and genetic differences between Assemblages, with a focus on human infection.

Positive correlation of HIV infection with Giardia intestinalis assemblage B but not with assemblage A in asymptomatic Kenyan children

A cross-sectional molecular epidemiological study of Giardia intestinalis infection was conducted among asymptomatic Kenyan children with (n = 123) and without (n = 111) HIV infection. G. intestinalis assemblage B infection was positively correlated with HIV infection [HIV (+), 18.7% vs. HIV (-), 11.7%; P = 0.013], whereas assemblage A infection was not [HIV (+), 4.1% vs. HIV (-), 6.3%; P = 0.510]. Thus, HIV infection is a risk factor for G. intestinalis assemblage B infection but not for assemblage A infection.

Giardia spp. Are Commonly Found in Mixed Assemblages in Surface Water, as Revealed by Molecular and Whole-Genome Characterization

Giardia is the most common parasitic cause of gastrointestinal infections worldwide, with transmission through surface water playing an important role in various parts of the world. Giardia duodenalis (synonyms: G. intestinalis and G. lamblia), a multispecies complex, has two zoonotic subtypes, assemblages A and B. When British Columbia (BC), a western Canadian province, experienced several waterborne giardiasis outbreaks due to unfiltered surface drinking water in the late 1980s, collection of isolates from surface water, as well as from humans and beavers (Castor canadensis), throughout the province was carried out. To better understand Giardia in surface water, 71 isolates, including 29 from raw surface water samples, 29 from human giardiasis cases, and 13 from beavers in watersheds from this historical library were characterized by PCR. Study isolates also included isolates from waterborne giardiasis outbreaks. Both assemblages A and B were identified in surface water, human, and beavers samples, including a mixture of both assemblages A and B in waterborne outbreaks. PCR results were confirmed by whole-genome sequencing (WGS) for one waterborne outbreak and supported the clustering of human, water, and beaver isolates within both assemblages. We concluded that contamination of surface water by Giardia is complex, that the majority of our surface water isolates were assemblage B, and that both assemblages A and B may cause waterborne outbreaks. The higher-resolution data provided by WGS warrants further study to better understand the spread of Giardia.

Axenic in vitro culture and molecular characterization of Giardia duodenalis from red deer (Cervus elaphus) and Thomson's gazelle (Gazella thomsonii)

Giardia duodenalis is an ubiquitous flagellate that infects humans and many species of animals. This species exhibits great biotypic and genetic diversity. In the present study, we established short- and long-term in vitro cultures of G. duodenalis trophozoites originating from red deer and Thomson's gazelle (artiodactyls) and genetically characterised the isolates by their glutamate dehydrogenase and triose phosphate isomerase gene sequences. The G. duodenalis isolates from red deer and the gazelle represented assemblages A (AIII sub-assemblage) and B. In conclusion, G. duodenalis assemblages and sub-assemblages can be associated with differences in growth rate in vitro cultures.

Giardia--from genome to proteome

In this review, the current status of genomic and proteomic research on Giardia is examined in terms of evolutionary biology, phylogenetic relationships and taxonomy. The review also describes how characterising genetic variation in Giardia from numerous hosts and endemic areas has provided a better understanding of life cycle patterns, transmission and the epidemiology of Giardia infections in humans, domestic animals and wildlife. Some progress has been made in relating genomic information to the phenotype of Giardia, and as a consequence, new information has been obtained on aspects of developmental biology and the host-parasite relationship. However, deficiencies remain in our understanding of pathogenesis and host specificity, highlighting the limitations of currently available genomic datasets.

Quantification of Giardia transcripts during in vitro excystation: interest for the estimation of cyst viability

The aim of the present study was to evaluate the potential of transcript quantification as an indicator of Giardia cyst viability. The variations of beta-giardin, EF1A and ADHE mRNAs were quantified during excystation by real-time RT-PCR assays and compared with the percentages of viability estimated using propidium iodide staining and in vitro excystation. The first experiments were performed with purified G. duodenalis assemblage B cysts. When 55% of excysting protozoa were observed, the increase of the selected transcripts ranged from 0.40+/-0.13 to 0.97+/-0.11 log10 after 1h of incubation in excystation medium. Purified cysts were also stored at 4 degrees C for up to 56 days and analysed at several sampling times. Significant correlations were observed between the variations of the selected mRNAs and the percentages of viability estimated with staining and excystation methods. Among the three transcripts, beta-giardin appeared to be the most appropriate to study the viability of Giardia cysts concentrated from wastewater samples.

Frequency of Giardia intestinalis assemblages isolated from dogs and humans in a community from Culiacan, Sinaloa, Mexico using beta-giardin restriction gene

The assemblage of 37 Giardia intestinalis samples was determined, 19 obtained from puppy feces, 12 from stools of different human subjects under 3 years of age and 6 from axenic culture. The assemblages were classified according to the restriction pattern of beta-giardin gene with Hae III enzyme. Results showed that dog assemblages were grouped AI (52.6%) and AII (47.4%), while 41.7% human samples belonged to genotype AI and 58.3% to genotype AII. All axenic cultures belonged to assemblage AI; types AI and AII were both found in dog and human feces by Hae III restriction enzyme assay, suggesting a similarity between human and dog parasites. These results suggest that domestic animals infected with Giardia could produce cysts potentially infective for humans.

Classification of Giardia intestinalis isolates by multiple polymerase chain reaction (multiplex)

Agarose gel electrophoresis of gdh gene fragments, amplified by Multiplex, was used to classify the assemblage of 24 Giardia isolates obtained from axenic cultures, children's stools, and feces of puppies from different dog breeds. Isolates were compared with seven reference strains of Giardia intestinalis. The results showed that 22/24 isolates (91%) belonged to assemblage A and could be further subclassified as assemblage A1 (18/22, 81%) and assemblage A2 (4/22, 19%). One sample revealed a mixture of A1/A2 genotypes, and another was assemblage G, indicating mixed infections by different strains in the same host, and an association with the assemblage reported in animals. The procedure described is useful to determine the Giardia genotype that parasitizes each host to conduct epidemiological studies assessing the close association between human- and animal-infecting strains and to monitor the adaptability of animal strains to humans.

Genotyping of Giardia duodenalis from human and animal samples from Brazil using beta-giardin gene: a phylogenetic analysis

Giardia duodenalis is one of the major diarrhea agents in human and animals distributed worldwide, and present high levels of genetic diversity, showing seven genotypes: A, B, C, D, E, F, and G. Only Assemblages A and B have been detected in humans and in a wide range of other mammalians hosts, whereas the remaining Assemblages (C-G) are host-specific. Molecular characterization of cysts of human and animal origin are useful to address the co-circulate isolates between these host, and represents an objective means to evaluate zoonotic infection hypothesis. In the present work the G. duodenalis genotypes were characterized by restriction fragment length polymorphisms and DNA sequencing analysis of PCR products of the beta-giardin gene. The cysts were collected in the city of Rio de Janeiro, in Brazil, from a population composed by humans (n=366, 310 children and 56 adults), domestic animals (n=11) from a municipal daycare center in the surroundings of a slum and neighborhood medium-high class domestic animals (n=18). Parasitological exams were developed in human fecal samples. Parasites were found in 60% (186/310) and 66% (37/56) of the samples from children and adults, respectively. Among children's samples, 27.7% (86/310) were positive for G. duodenalis. Only 1.7% (1/56) of the adults was positive for this parasite. In general a total of 87 fecal samples (86 from children and 1 from adult) from all population studied were positive for G. duodenalis, and 62 of these were subjected to molecular analysis using a PCR that amplified a fragment of the beta-giardin gene. Sixty samples were typed as genotype A1, two as genotype A2 and genotype B was not encountered. Among domestic animals samples (n=29), eight (seven dogs and one cat) from the slum community were identified as genotype A1, and all control samples (n=18) were negative in the molecular assay. The host-specific genotypes C, D and, F were not found. In this study we described single case of G. duodenalis infection associated with a child and her dog and both isolates characterized as genotype A1. Despite the low incidence, this data suggest the putative existence of a zoonotic cycle of G. duodenalis in the studied population.

Genotyping of Giardia duodenalis from humans and dogs from Mexico using a beta-giardin nested polymerase chain reaction assay

Cysts of Giardia duodenalis were collected in Mexico from symptomatic children (n = 9) and from pet dogs (n = 5), and they were directly characterized by nested polymerase chain reaction (PCR) amplification of the beta-giardin gene. Eight isolates of human origin established as in vitro cultures and 2 reference strains, representing assemblages A and B of G. duodenalis, were also analyzed. PCR-restriction fragment length polymorphism showed that all isolates belonged to assemblage A. Sequence analyses indicated that the large majority of isolates were of the A1 genotype; interestingly, 2 human isolates displayed the A3 genotype, which has been previously identified in human isolates from Italy. The presence of cysts of the A1 and A3 genotypes in isolates from pet dogs is consistent with their role as reservoirs for human infection, although further studies are needed to confirm the occurrence of zoonotic transmission. Remarkably, cysts of assemblage B have not been found in any of the Mexican isolates studied to date.

Variation in Giardia: implications for taxonomy and epidemiology

The taxonomy, life cycle patterns and zoonotic potential of Giardia infecting mammals and birds have been poorly understood and controversial for many years. The development of molecular tools for characterising isolates of Giardia directly from faeces or environmental samples has made an enormous contribution to resolving these issues. It is now clear that the G. duodenalis morphological group is a species complex comprising a series of what appear to be largely host-adapted species, and at least two zoonotic species for which humans are the major host, but which are also capable of infecting other mammals. It is proposed that this new information be reflected in the redesignation of several species of Giardia described previously. The molecular epidemiological tools that are now available need to be applied in different endemic foci of Giardia transmission, as well as in outbreak situations, in order to understand better the frequency of zoonotic transmission as well as to develop more effective approaches to controlling giardiasis.

Discrimination of all genotypes of Giardia duodenalis at the glutamate dehydrogenase locus using PCR-RFLP

A PCR-RFLP genotyping tool was developed and used to characterise morphologically identical isolates of Giardia duodenalis from a variety of host species. Primers were designed to amplify a 432bp region of the glutamate dehydrogenase gene (gdh) from genetic Assemblages AI, AII, BIII, BIV, C, D and E of G. duodenalis. DNA extracted from cultured Giardia trophozoites, Giardia cysts purified from faeces and directly from whole faeces was amplified and sequenced at the gdh and 18SrDNA loci. The gdh sequences were identical with published gdh sequences for each assemblage with a few exceptions. However, in some cases genotyping results obtained using gdh differed from 18SrDNA genotyping results. From gdh sequence information a PCR-RFLP profile was identified for each of the genetic assemblages. PCR-RFLP is a reproducible, reliable and sensitive method for genotyping Giardia. Eight human, 12 cat, 9 dog and 16 cattle faecal isolates were genotyped using PCR-RFLP. This method allows G. duodenalis isolates from human-beings, their companion animals and livestock to be genotyped directly from faeces, leading to valuable information about Giardia genotypes in population without the need for in vitro/in vivo amplification.

Triosephosphate isomerase gene characterization and potential zoonotic transmission of Giardia duodenalis

To address the source of infection in humans and public health importance of Giardia duodenalis parasites from animals, nucleotide sequences of the triosephosphate isomerase (TPI) gene were generated for 37 human isolates, 15 dog isolates, 8 muskrat isolates, 7 isolates each from cattle and beavers, and 1 isolate each from a rat and a rabbit. Distinct genotypes were found in humans, cattle, beavers, dogs, muskrats, and rats. TPI and small subunit ribosomal RNA (SSU rRNA) gene sequences of G. microti from muskrats were also generated and analyzed. Phylogenetic analysis on the TPI sequences confirmed the formation of distinct groups. Nevertheless, a major group (assemblage B) contained most of the human and muskrat isolates, all beaver isolates, and the rabbit isolate. These data confirm that G. duodenalis from certain animals can potentially infect humans and should be useful in the detection, differentiation, and taxonomy of Giardia spp.

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.

Genetic homogeneity of axenic isolates of Giardia intestinalis derived from acute and chronically infected individuals in Mexico

Twenty-six axenic isolates of Giardia intestinalis, established in Mexico City over an 11-year period from symptomatic and asymptomatic individuals with acute or chronic infections, were typed genetically. A segment of the glutamate dehydrogenase gene was amplified by PCR and examined by restriction analysis using BspH1 and ApaI to determine the major genetic assemblages to which the isolates belonged. This was coupled with the amplification and analysis of segments of variant-specific surface protein genes to determine genetic subgroupings. Despite their heterogeneous clinical backgrounds, the isolates were found to be genetically homogeneous-all belonging to genetic group I of assemblage A. The results show that type A-I G. intestinalis is ubiquitous in Mexico City and that host factors play an important, if not dominant, role in determining the clinical outcome of Giardia infections in humans.

Genetic diversity within the morphological species Giardia intestinalis and its relationship to host origin

A genetic analysis of Giardia intestinalis, a parasitic protozoan species that is ubiquitous in mammals worldwide, was undertaken using organisms derived from a variety of mammalian hosts in different geographical locations. The test panel of 53 Giardia isolates comprised 48 samples of G. intestinalis, including representatives of all known genetic subgroups, plus an isolate of G. ardeae and four isolates of G. muris. The isolates were compared by allozymic analysis of electrophoretic data obtained for 21 cytosolic enzymes, representing 23 gene loci. Neighbour Joining analysis of the allelic profiles supported the monophyly of G. intestinalis but showed that the species encompasses a rich population substructure. Seven major clusters were evident within G. intestinalis, corresponding to lineages designated previously as genetic assemblages A-G. Some genotypes, e.g. those defining assemblage A, are found in divergent host species and may be zoonotic. However other genotypes, e.g. those defining assemblages C-G, appear to be confined to particular hosts or host groups. The findings reinforce other evidence that G. intestinalis, which was defined on the basis of morphological criteria only, is a species complex.

Sequence analysis of the beta-giardin gene and development of a polymerase chain reaction-restriction fragment length polymorphism assay to genotype Giardia duodenalis cysts from human faecal samples

The flagellate parasite Giardia duodenalis is a major cause of diarrhoea in humans and in animals worldwide. Molecular techniques are particularly useful for studying the taxonomy, the population structure, the zoonotic potential of animal isolates, and the correlation between the genetic variability of the parasite and the range of clinical symptoms observed in humans. In this work, a new PCR assay that targets the beta-giardin gene was tested on 21 Giardia duodenalis reference strains representing Assemblages A, B and E, which are associated with infections of humans and other mammals. The assay was then applied to 30 faecal samples collected from Italian persons. The sequence analysis of 31 PCR products from both reference strains and clinical samples showed that each Assemblage is clearly distinct from the others on the basis of specific substitutions; the sequence diversity was approximately 5%, and all substitutions occurred at the third codon positions of the gene. The analysis of the intra-Assemblage variability allowed for the identification of three genotypes within Assemblage A, and of four genotypes within Assemblage B. Interestingly, two genotypes were identified only in the clinical samples and not in reference strains. Finally, a simple PCR-restriction fragment length polymorphism method was developed for the rapid discrimination of Assemblages and applied for the direct genetic analysis of cysts present in human faecal samples.

Human giardiasis: genotype linked differences in clinical symptomatology

Giardia duodenalis infection in humans can cause a variety of clinical symptoms. The relation between clinical symptomatology and the Giardia isolate genotype was studied in 18 Dutch patients infected with G. duodenalis who visited their general practitioner. Contrary to earlier studies, a 100% correlation between severity of diarrhoeal complaints and genotype was found: assemblage A isolates were solely detected in patients with intermittent diarrhoeal complaints, while assemblage B isolates were present in patients with persistent diarrhoeal complaints. These results are significant because they show for the first time that genetically linked features of G. duodenalis are major determinants in the severity of infection in human giardiasis.

Giardia lamblia: effect of infection with symptomatic and asymptomatic isolates on the growth of gerbils (Meriones unguiculatus)

Gerbils (Meriones unguiculatus) were intragastrically inoculated with axenic Giardia lamblia cultures from symptomatic and asymptomatic children. All isolates were able to colonize the duodenum. However, the colonization capacity of the symptomatic isolates was significantly higher compared to that of the asymptomatic ones. Despite the different colonization capacity of the isolates, the growth curves of infected animals were significantly lower than those of controls. The study demonstrates that acute giardia infections are capable of altering the corporal development of the host. These results may suggest that not only symptomatic, but also asymptomatic giardiasis in children, often unnoticed by parents and clinicians, could be causing a silent detriment in their nutritional status.

Isolation, propagation and characterisation of Cryptosporidium

This review consists of 11 papers presented at the Consensus Conference on Cryptosporidium in Water (Parasitology Stream), held in Melbourne, Australia, from 5 to 6th October 1998. The conference was sponsored by the Water Services Association of Australia, the Australian Water and Wastewater Association, and the Collaborative Research Centre for Water Quality and Treatment. The papers summarise the advantages and disadvantages of various contemporary technologies applicable to parasite propagation and biochemical/molecular characterisation. Studies have detected distinct genetic differences between clinical isolates from humans and animals, and it is hoped that comprehensive documentation studies will facilitate the identification of environmental isolates in the not too distant future.

The importance of systematics in parasitological research

The discipline of systematics plays a central role in all branches of biology. In today's technology-orientated research world, it is important to realise the continuing value of systematics, the basic tenet of which is to combine diverse types of data to produce classifications that reflect the natural history of living organisms. Accurate classification systems are crucial in the field of parasitology, not only because they provide the means to identify species and strains of parasites, but also because they provide a framework around which a parasite's biology can be studied. The construction of such a classification system is often hampered by the parasite's biology, which may preclude the application of traditional techniques or concepts (such as morphological differentiation or the biological species concept) to delineate species. It is often the case that these difficulties can be overcome by the use of molecular systematic techniques. In this paper, it is proposed that a detailed understanding of the phylogeny of a group of organisms can be used as a basis to examine other aspects of their systematics. This is illustrated using the protozoan parasite Giardia intestinalis. Data gathered using the complementary techniques of allozyme electrophoresis and nucleotide sequencing have been used to infer the phylogenetic relationships of G. intestinalis isolated from various host species. The results, supported by biological data, suggest that G. intestinalis is a species-complex. As we move towards the year 2000, molecular systematics will play an increasingly important role in elucidating host-parasite relationships. However, its use as a taxonomic tool will require a general acceptance by parasitologists and the adoption of formal procedures to allow the description of new species by these methods. The aim of this approach is not to dismiss traditional methods, but to use them in combination with contemporary methods in the true spirit of the discipline of systematics.

Multilocus enzyme electrophoresis: a valuable technique for providing answers to problems in parasite systematics

The aim of this review is to highlight the effectiveness of the technique of multilocus enzyme electrophoresis in answering questions relating to the systematics of parasites and to highlight errors in the way the technique has been used and the results interpreted. We have approached this topic by answering specific questions that we have been asked by colleagues and students not necessarily familiar with the technique, the method of data analysis and its application. Although the technique has been applied to provide answers for taxonomic and population genetics studies, it remains under-utilised, perhaps because of recent advances in newer molecular technology. Rather than not acknowledge or dismiss the value of more traditional technology, we suggest that researchers examine problems in the systematics of parasites by the comparison of data derived from morphological, biochemical and molecular techniques.

Comparison of the levels of intra-specific genetic variation within Giardia muris and Giardia intestinalis

The extent of intra-specific genetic variation between isolates of Giardia muris was assessed by allozyme electrophoresis. Additionally, the levels of allozymic variation detected within G. muris were compared with those observed between members of the two major assemblages of the morphologically distinct species Giardia intestinalis. Four isolates of G. muris were analysed. Three (Ad-120, -150, -151) were isolated from mice in Australia, while the fourth (R-T) was isolated from a golden hamster in North America. The 11 isolates of G. intestinalis (Ad-1, -12, -2, -62, representing genetic Groups I and II of Assemblage A and BAH-12, BRIS/87/HEPU/694, Ad-19, -22, -28, -45, -52, representing genetic Groups III and IV of Assemblage B) were from humans in Australia. Intra-specific genetic variation was detected between G. muris isolates at four of the 23 enzyme loci examined. Similar levels of variation were found within the genetic groups that comprise Assemblages A and B of G. intestinalis. These levels of intra-specific variation are similar to those observed within other morphologically-distinct species of protozoan parasites. We suggest that the magnitude of the genetic differences detected within G. muris provides an indication of the range of genetic variation within other species of Giardia and that this can be used as a model to delineate morphologically similar but genetically distinct (cryptic) species within this genus.

Multiparasite communities in animals and humans: frequency, structure and pathogenic significance

Individual humans and animals are subject to infection by a variety of parasites (broadly defined to include viruses, bacteria and other non-protozoan microparasites) at any one time. Multiple parasite infections occur frequently in populations of wild animals as well as in humans from developing countries. In some species and regions, hosts with multiple infections are more common than hosts with either no infection or a single infection. Studies, predominantly on animals, show that a wide variety of environmental and host-dependent factors can influence the structure and dynamics of the communities of parasites that make up these multiple infections. In addition, synergistic and competitive interactions can occur between parasite species, which can influence the likelihood of their successful transmission to other hosts and increase or decrease their overall pathogenic impact. This review summarises aspects of our current knowledge on the frequency of multiparasite infections, the factors which influence them, and their pathogenic significance.

Genetic analysis of Giardia from hoofed farm animals reveals artiodactyl-specific and potentially zoonotic genotypes

Thirty one Giardia isolates, established from six species of hoofed livestock by axenic culture or growth in suckling mice, were compared genetically by analysis of DNA amplified from loci encoding variant surface proteins or the enzyme glutamate dehydrogenase and by allozyme analysis. The isolates were heterogeneous, but all showed affinity with genetic Assemblage A--one of two major assemblages defined previously by analysis of Giardia from humans. Three distinct genotypes were evident. Ten isolates (eight axenic and two established in suckling mice) from an alpaca, pig, horse, cattle and sheep were indistinguishable from human-derived G. intestinalis belonging to a previously designated genetic group (Group I). This genotype seems to have broad host specificity, including a zoonotic potential for humans. Five isolates (two axenic and three established in suckling mice) from an alpaca, a horse and sheep had close affinity with human-derived Group I and Group II G. intestinalis genotypes. The other 16 isolates (comprising both axenic and suckling mouse-propagated cultures derived from cattle, sheep, alpaca, a goat and pigs in Australia and Europe) differed from all other Giardia with "duodenalis" morphology that have been examined by these methods and they segregated as a highly distinct sublineage (referred to herein as 'Novel livestock') within genetic Assemblage A. The predominance of 'Novel livestock' genotypes in the test panel and their apparent exclusive association with artiodactyl hosts indicates that they may be confined to this group of mammals. Assemblage B genotypes, which are prevalent in humans and some other animal species, were not detected.

First record of Giardia in cattle in Denmark

Faecal samples from asymptomatic dairy cows and calves from a farm on the Island Falster, Denmark, were examined by a sucrose gradient flotation technique. Giardia cysts were found in 7.6% of the 92 samples, and estimated cyst excretion rates ranged from 50-200 cysts per gram faeces. Given that Giardia has the potential to cause clinical disease in cattle and to be transmitted to other animal species and humans, finding the parasite in cattle may be of major epidemiological significance. Future work should focus on elucidating the pathogenicity, transmission patterns and the genetic structure of Giardia populations in cattle in Denmark.

Molecular genetic approaches to parasite identification: their value in diagnostic parasitology and systematics

A wide range of approaches is available to parasitologists to aid in specific parasite identification and to formulate phylogenetic relationships. This review emphasises the usefulness of molecular genetic techniques, especially DNA-based procedures, in addressing problems of identification, characterisation and phylogeny of parasites. It should be stressed that an understanding of the various DNA approaches, techniques and target genes most likely to be effective in addressing key issues in diagnostic parasitology and systematics is still developing. Nevertheless, DNA methods clearly have great potential with regard to specificity and sensitivity, and applications will increase further with technological advance. Indeed, because of the minimal requirements for material, PCR-based methods especially should prove of immense value in future studies with parasites.

The use of allozyme electrophoresis to assess genetic heterogeneity among previously subspeciated isolates of Fusobacterium nucleatum

Fusobacterium nucleatum has been implicated in the pathogenesis of periodontal diseases. Five subspecies have previously been proposed. The validity of these subdivisions was investigated using allozyme electrophoresis for 21 enzyme mobilities. The 18 F. nucleatum isolates tested had previously been subspeciated and included type strains as well as isolates from both oral and extraoral sites. The results showed 2 distinct genetic groups with fixed differences at 82.5% of the test loci, indicative of a species complex with a number of subspecies within each of the 2 groups. There was also evidence of a correlation between the 2 major groups of isolates and the site from which they were taken. It was concluded that there is a high degree of genetic heterogeneity within the species F. nucleatum and that its current subspeciation is of questionable validity.

Comparison of genetic groups determined by molecular and immunological analyses of Giardia isolated from animals and humans in Switzerland and Australia

Nine axenic isolates of Giardia originating from four different host species in Switzerland were subjected to genetic analysis using the polymerase chain reaction (PCR) to amplify segments of genes encoding different trophozoite variant surface proteins (VSPs). Three genotypes were identified on the basis of product yield, size, and restriction-fragment-length polymorphisms (RFLPs). Five G. duodenalis isolates (O1, B1, B2, B3-1A1 and C1--from a sheep, three calves and a dog, respectively) were classified as belonging to genetic group I of Andrews et al. (1989). DNA amplified from the VSP genes tsp11, tsa417 and vsp1267 of these isolates was indistinguishable in size and restriction characteristics from that amplified from group-I Giardia isolated from humans in Australia. One human-derived Swiss isolate (H2-17A1), typed as belonging to genetic group II, yielded a vsp1267-specific PCR product that was indistinguishable by size or restriction sites from the equivalent 1.6-kb product amplified from human-derived Australian group-II organisms. This isolate also yielded 1.8-kb tsp11 and 0.52-kb tsa417/tsp11-like PCR products possessing RFLPs typical of group-II organisms. Three isolates (O2-4A1, O3 and H3-15K2--originating from two sheep and a human, respectively) represent a novel genotype that is closely related to genetic groups I and II. These three isolates exhibited identical RFLPs in their tsp11 PCR products and failed to yield a vsp1267 PCR product. An antiserum specific for the 90-kDa VSP of the sheep-derived clone O2-4A1 reacted strongly by immunofluorescence and on Western blots with surface proteins from the O2, O3 and H3 isolates only--consistent with the genetic classification determined above. The data provide no evidence for the occurrence of host-specific genotypes.

Molecular genetic analysis of Giardia intestinalis isolates at the glutamate dehydrogenase locus

Samples of DNA from a panel of Giardia isolated from humans and animals in Europe and shown previously to consist of 2 major genotypes--'Polish' and 'Belgian'--have been compared with human-derived Australian isolates chosen to represent distinct genotypes (genetic groups I-IV) defined previously by allozymic analysis. Homologous 0.52 kilobase (kb) segments of 2 trophozoite surface protein genes (tsa417 and tsp11, both present in isolates belonging to genetic groups I and II) and a 1.2 kb segment of the glutamate dehydrogenase (gdh) gene were amplified by the polymerase chain reaction (PCR) and examined for restriction fragment length polymorphisms (RFLPs). Of 21 'Polish' isolates that were tested, all yielded tsa417-like and tsp11-like PCR products that are characteristic of genetic groups I or II (15 and 6 isolates respectively) in a distinct assemblage of G. intestinalis from Australia (Assemblage A). Conversely, most of the 19 'Belgian' isolates resembled a second assemblage of genotypes defined in Australia (Assemblage B) which contains genetic groups III and IV. RFLP analysis of gdh amplification products showed also that 'Polish' isolates were equivalent to Australian Assemblage A isolates (this analysis does not distinguish between genetic groups I and II) and that 'Belgian' isolates were equivalent to Australian Assemblage B isolates. Comparison of nucleotide sequences determined for a 690 base-pair portion of the gdh PCR products revealed > or = 99.0% identity between group I and group II (Assemblage A/'Polish') genotypes, 88.3-89.7% identity between Assemblage A and Assemblage B genotypes, and > or = 98.4% identity between various Assemblage B/'Belgian' genotypes. The results confirm that the G. duodenalis isolates examined in this study (inclusive of G. intestinalis from humans) can be divided into 2 major genetic clusters: Assemblage A (= 'Polish' genotype) containing allozymically defined groups I and II, and Assemblage B (= 'Belgian' genotype) containing allozymically defined groups III and IV and other related genotypes.

Minisatellites corresponding to the human polycore probes 33.6 and 33.15 in the genome of the most 'primitive' known eukaryote Giardia lamblia

DNA fingerprinting has been widely used for genetic characterization and individual recognition in a range of species, from man and other mammals down the evolutionary scale to some lower eukaryotic parasites. These techniques utilise repetitive elements first characterised in the human genome, known as minisatellites, which display extensive allelic variability. Few biological or biochemical characteristics have been found that distinguish isolates of Giardia lamblia (Gl), or their apparent variations in virulence. We have characterized 21 Gl isolates in axenic culture using DNA fingerprinting with the human minisatellite probes, 33.6 and 33.15. Up to 12 variable bands per isolate were recognized in the size range of 2.5 to 15 kb by Southern blot hybridization of restriction endonuclease-digested Gl DNA. Most isolates demonstrated a distinct banding pattern or DNA fingerprint. The results suggest that this method may provide a basis for the detailed genotypic characterization of Gl which will be amenable to computer and statistical analysis for use in studies of virulence and epidemiology. Also, as Gl occupies a unique phylogenetic position as a member of the earliest known divergence from the eukaryotic line of descent, this study may provide a useful model for the study of other important eukaryotic pathogens, as it is rapidly becoming apparent that minisatellites are ubiquitous components of eukaryotic genomes.

A three nucleotide signature sequence in small subunit rRNA divides human Giardia in two different genotypes

The nucleotide sequence of the 16S rRNA gene and the space DNA region was determined for Giardia duodenalis, obtained from humans in The Netherlands (AMC-4) and Washington State (CM). These rDNA sequences differ from other G. duodenalis isolates (Portland-1 and BRIS/83/HEPU/ 106) both of which have virtually identical rDNA sequences. The most characteristic feature was found close to the 5' end of the 16S rRNA. The Portland-1 -Bris/83/HEPU/ 106 type has GCG in position 22-24, while AMC-4 and CM have AUC in this position. These two sequences, present in an otherwise conserved region of the 16S rRNA, are "signature" sequences, which divide Giardia isolates into two different groups.

Division of Giardia isolates from humans into two genetically distinct assemblages by electrophoretic analysis of enzymes encoded at 27 loci and comparison with Giardia muris

Giardia that infect humans are known to be heterogeneous but they are assigned currently to a single species, Giardia intestinalis (syn. G. lamblia). The genetic differences that exist within G. intestinalis have not yet been assessed quantitatively and neither have they been compared in magnitude with those that exist between G. intestinalis and species that are morphologically similar (G. duodenalis) or morphologically distinct (e.g. G. muris). In this study, 60 Australian isolates of G. intestinalis were analysed electrophoretically at 27 enzyme loci and compared with G. muris and a feline isolate of G. duodenalis. Isolates of G. intestinalis were distinct genetically from both G. muris (approximately 80% fixed allelic differences) and the feline G. duodenalis isolate (approximately 75% fixed allelic differences). The G. intestinalis isolates were extremely heterogeneous but they fell into 2 major genetic assemblages, separated by fixed allelic differences at approximately 60% of loci examined. The magnitude of the genetic differences between the G. intestinalis assemblages approached the level that distinguished the G. duodenalis isolate from the morphologically distinct G. muris. This raises important questions about the evolutionary relationships of the assemblages with Homo sapiens, the possibility of ancient or contemporary transmission from animal hosts to humans and the biogeographical origins of the two clusters.

Genotypic heterogeneity within Giardia lamblia isolates demonstrated by M13 DNA fingerprinting

There has been considerable speculation regarding the possible relationship between the phenotypic and genotypic heterogeneity seen among human isolates of Giardia lamblia and the wide clinical spectrum of human giardiasis. Several workers have suggested that human giardiasis may be a mixed infection consisting of variant strains or subgroups which are present in the same infection and which are selectable, but it is not clear whether these apparent variant strains represent a truly heterogeneous infection or whether the genotypic heterogeneity observed is due to the susceptibility of the Giardia genome to a high rate of structural genetic rearrangement. We have therefore studied variation in Giardia intestinalis genotypes in 19 isolates in vitro and in vivo by using the technique of M13 DNA fingerprinting. Genotypes of isolates changed with time when cultured under standard conditions and when pressured with bile. Sequential isolates and their clones taken from a patient with chronic giardiasis both before and after several treatments with metronidazole had different genotypes. Finally, clones of isolate WB had different initial genotypes, which changed after 4 months in culture. These findings suggest that the apparent genotypic heterogeneity at least in these G. intestinalis isolates is more likely to be due to the plasticity of the Giardia genome than to the presence of a truly mixed population of strains within the same infection.

Giardia intestinalis: detection of major genotypes by restriction analysis of gene amplification products

The polymerase chain reaction (PCR) has been used to amplify a 0.52 kb segment of Giardia intestinalis DNA, using primers specific for nucleotide sequences conserved within two genes (tsp11 and tsa417) that encode homologous, cysteine-rich trophozoite surface proteins. Using products amplified from axenic isolates belonging to genetic groups I and II (defined on the basis of allozyme electrophoresis data), restriction endonuclease analysis revealed both tsp11-like and tsa417-like fragments within all samples. The study also identified among the amplification products of group II organisms an additional fragment, containing a novel PstI site, that is not detected in the reaction products of group I isolates. The recovery of three distinct PCR products from each group II isolate was verified by cloning the fragments into the plasmid vector pGEM-7. Fragments containing the new PstI site possess the ClaI site common to both tsp11 and tsa417-like fragments, but they lack the HindIII site which characterizes tsp11-like fragments and also lack the PstI and KpnI sites which characterize tsa417-like fragments. Spot-blot analyses using cloned fragments of all three types as probes showed strong homologous hybridization but weak heterologous hybridization, indicating that each type differs substantially in nucleotide sequence from the others. Because the samples of Giardia DNA used in the PCR were purified from cultures that had been established from single trophozoites, the data indicate that individual trophozoites belonging to genetic group II possess three homologous genes defined by these related fragments. The presence of a PstI site in the amplified segment of the newly-discovered third gene of group II organisms provides a simple diagnostic means of differentiating group I and II isolates.

Two genes encoding homologous 70-kDa surface proteins are present within individual trophozoites of the binucleate protozoan parasite Giardia intestinalis

A 0.52-kb DNA sequence encoding part of a major surface antigen of Giardia intestinalis trophozoites has been amplified by the polymerase chain reaction (PCR) using primers specific for nucleotide sequences that are conserved between two apparently related genes, tsp11 (cloned previously from the Australian G. intestinalis isolate, Ad-1) and tsa417 (cloned from the Afghanistani isolate, WB). Restriction analysis revealed that the DNA amplified from each of seven axenic isolates of G. intestinalis was not homogeneous, even though the template DNA had been purified from cultures that had been established from single trophozoites. Every isolate yielded two PCR products, whose respective cleavage fragments corresponded to tsp11 (HindIII+, PstI-, KpnI-) and to tsa417 (HindIII-, PstI+, KpnI+). This was confirmed by cloning individual amplification products into the plasmid vector, pGEM-7Zf(+). The sequence of one cloned fragment (1-P4), derived from the Ad-1 isolate, but possessing restriction sites characteristic of tsa417, exhibited 98.6% identity over 425 bp with tsa417 and only 63.8% identity with the corresponding region of tsp11. The data indicate that individual trophozoites of all the isolates examined contain a copy of each of these homologous genes.

Variant cysteine-rich surface proteins of Giardia isolates from human and animal sources

Cloned Giardia isolates obtained from a sheep, a calf, and a human possessed a major membrane protein that showed marked intraspecific variations in size as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis following surface biotinylation and radioiodination. Metabolic labeling with [35S] cysteine and electrophoretic analysis also revealed for each cloned isolate a predominant protein that corresponded in size to the major surface protein demonstrated by surface labeling techniques. Immunoprecipitation studies with a polyclonal antiserum specifically directed against the 90-kDa major cysteine-rich protein purified from a subclone of the sheep isolate (O2-4A1) showed that the cysteine-rich protein and the major surface protein are identical. The surface location of the antigen was further corroborated by the reaction of fluorescence-labeled antibodies raised against the 90-kDa O2-4A1 cysteine-rich protein with the entire surface of live trophozoites of the homologous clone. The ability of the cloned Giardia isolates to undergo variations of their cysteine-rich surface protein (CRISP) was demonstrated by the spontaneous appearance of new CRISPs in clonally derived populations during prolonged in vitro culturing and in cultures of the O2-4A1 clone that had survived treatment with the cytotoxic anti-90-kDa CRISP antiserum specific for the surface antigen of this clone. The surviving progeny were devoid of the original CRISP, as judged by resistance to the immune serum. Subsequent cysteine metabolic labeling of the recloned surviving trophozoites demonstrated a large number of new variants, each expressing a single CRISP that varied significantly in molecular weight from those in the different cloned lines. These studies suggest that the presence of CRISPs and their variations are not restricted to Giardia isolates obtained from humans but are universal phenomena among the Giardia duodenalis types of organisms.

Differentiation of major genotypes of Giardia intestinalis by polymerase chain reaction analysis of a gene encoding a trophozoite surface antigen

The polymerase chain reaction (PCR) has been used to amplify in vitro a semi-conserved region of a gene encoding an M(r) 68-72,000 surface antigen of Giardia intestinalis trophozoites. Using primers specific for conserved nucleotide sequences identified within the promoter-distal portion of two homologous genes (tsp11 and tsa417) cloned previously from the G. intestinalis isolates Ad-1 (from Australia) and WB (from Afghanistan), a single PCR-amplified DNA fragment of the expected size (0.52 kilobases) was obtained in high yield from either purified DNA or whole trophozoites of the Ad-1 isolate and from every 1 to 9 other axenic G. intestinalis isolates belonging to genetic groups I and II (defined previously on the basis of allozyme electrophoresis data--Andrews et al. 1989). Discernible product was recovered from as few as 2-4 trophozoites. In contrast, 6 G. intestinalis isolates that were assigned by allozymic analysis to genetic groups III/IV yielded small amounts of a 0.37-kilobase (kb) amplification product (with evidence in some samples of an additional 0.4 or 0.18 kb fragment) but no 0.52 kb product. Two animal-derived isolates of G. duodenalis (one from an Australian native rodent, Notomys alexis, the other from a domestic cat) also yielded a single 0.37 kb PCR-amplified fragment, whereas an isolate from another cat produced a 0.34 kb fragment. No product was recovered from G. muris, a morphologically distinct species of Giardia. The results demonstrate that different genotypes of G. duodenalis can be distinguished using this assay and that it is diagnostic for isolates belonging to two major clusters (groups I/II and III/IV) of G. intestinalis. The amplified DNA segment appears to be relatively conserved among group I and group II isolates of G. intestinalis. A related but clearly distinct sequence seems to be conserved among group III/IV isolates of G. intestinalis and some isolates of G. duodenalis.

A gene encoding a 69-kilodalton major surface protein of Giardia intestinalis trophozoites

A gene encoding a 68.5-kDa trophozoite surface protein (TSP11) of the Australian Giardia intestinalis (syn. G. lamblia) isolate, Ad-1, has been cloned from a genomic expression library screened with an antiserum specific for 3 major surface antigens. Sequence analysis of two overlapping genomic fragments identified a single open reading frame that contained no introns and predicted a cysteine-rich, 667-residue polypeptide with features common to other trophozoite surface proteins. These include the presence of 27 copies of the 4-amino acid Cys-X-X-Cys motif, an N-terminal signal sequence and a highly conserved, hydrophobic C-terminal segment. Transcripts from the tsp11 gene were detected as a single band on Northern blots using total RNA extracted from Ad-1 trophozoites. Primer extension analysis indicated that the mRNA has a 5' untranslated region of only 5 nt, similar to the very short (1-6 nt) leader sequences reported for other Giardia mRNAs. A large portion of the promoter distal segment of tsp11 has homology with tsa417, a gene encoding a 72.5-kDa trophozoite surface antigen of the Afghanistan-derived G. intestinalis isolate, WB [13].

The use of suckling mice to isolate and grow Giardia from mammalian faecal specimens for genetic analysis

A simple technique is described for preparation of Giardia cysts from faecal samples, the growth of trophozoites in suckling mice and the isolation of trophozoites for genetic analysis by allozyme electrophoresis. In total, 125 new isolates of Giardia have been collected from human and animal sources over a wide geographical area of South Australia and the Northern Territory of Australia. A number of long-established axenized isolates of G. intestinalis belonging to Groups I and II also adapted to grow in suckling mice. These findings indicate that suckling mice are permissive hosts for a variety of genetically dissimilar but morphologically similar organisms of the G. duodenalis type and that this in vivo technique may be less selective than isolation by in vitro culture. The use of suckling mice has revealed that infections can be composed of mixed genotypes and that isolation and purification techniques can be selective. Allozymic interpretation is essential to reveal the genetic complexity of such mixtures.