Molecular variation in Giardia

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

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

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.

Multi-locus analysis of Giardia duodenalis intra-Assemblage B substitution patterns in cloned culture isolates suggests sub-Assemblage B analyses will require multi-locus genotyping with conserved and variable genes

Recent research concerning Giardia duodenalis has focused on resolving possible sub-assemblages within Assemblages A and B to better understand host-specific and zoonotic relationships. In the present study nine cloned, cultured, Assemblage B isolates were used to investigate the intra-Assemblage B substitution patterns of conserved (ssrDNA, ef, h2b, h4) and variable (tpi, gdh, bg) genes to assess their suitability for further application to sub-assemblage analyses. The resolution of each gene was found to be proportional to its substitution rate and for the genetically narrow sample set examined, the variable genes best represented the consensus phylogeny while the conserved genes only established fractions. However it was demonstrated that the spectra of conserved and variable genes were required to ensure accuracy of inferred phylogeny and it was therefore concluded that further research into sub-Assemblage B groups would require a mixture of conserved and variable genes for the multi-locus analyses of this genetically broad assemblage.

In vitro resistance to 5-nitroimidazoles and benzimidazoles in Giardia duodenalis: variability and variation in gene expression

The susceptibility of Giardia duodenalis trophozoites exposed in vitro to sublethal concentrations of metronidazole (MTZ) and albendazole (ABZ) may exhibit inter-culture (variability) and intra-culture (variation) differences in drug susceptibility. It was previously reported that MTZ-resistant trophozoites may display changes in pyruvate:ferredoxin oxidoreductase (PFOR) expression while changes at the beta-tubulin molecule are apparently absent in ABZ-resistant cultures. To assess the levels of gene expression of these molecules, we obtained cloned cultures growing at concentrations up to 23 microM MTZ (WBRM23) and up to 8muM ABZ (WBRA8) and gene sequence and expression of pfor and beta-tubulin loci were compared with these of drug-susceptible clone WB1. Neither the pfor nor the beta-tubulin genes showed changes at sequence level but the MTZ-resistant clones WBRM21 and WBRM23 showed up-regulation of the pfor RNA using the gdh gene as reference. By using WB1 and WBRA8 clones in representational difference analyses of gene expression (RDA) an insert referred to as ARR-VSP was selected and sequenced. It showed the highest homology to one VSP molecule in the Giardia Genome Database (orf GL50803_101765). This isogene was up-regulated in five ABZ-resistant clones and the clone WBRA8 exhibited the highest RNA expression level. When successive progenies of clones WB1, WBRM23 and WBRA8 were analyzed in Northern blot assays to detect pfor and ARR-VSP RNAs respectively, the expression patterns showed variation for both genes but it was much lower in the clone WBRA8. These results suggest that G. duodenalis cultures either susceptible or resistant to MTZ and ABZ may display variability and variation at RNA expression levels albeit these were more marked in the MTZ-resistant parasites. These data might have further implications defining major mechanisms involved in drug resistance of Giardia.

Genetic variability in parasites and host—parasite interactions

We have examined genetic variability in parasites in the context of ecological interactions with the host. Recent research onEchinococcus, GiardiaandCryptosporidiumhas been used to illustrate: (i) the problems that parasite variability and species recognition pose for understanding the complex and often controversial relationship between parasite and host occurrence; (ii) the need for accurate parasite characterization and the application of appropriate molecular techniques to studies on parasite transmission if fundamental questions about zoonotic relationships and risk factors are to be answered; (iii) our lack of understanding about within-host interactions between genetically heterogeneous parasites at the inter-and intraspecific levels, and the significance of such interactions with respect to evolutionary considerations and the clinical outcome of parasite infections. If advances in molecular biology and mathematical ecology are to be realized, we need to give serious consideration to the development of appropriate species concepts and in vivo systems for testing the predictions and assumptions of theoretical models.

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.

Giardia duodenalis: adhesion-deficient clones have reduced ability to establish infection in Mongolian gerbils

The role of Giardia duodenalis surface molecules in the attachment of trophozoites to epithelial cells has been established through the dual strategies of characterizing G. duodenalis clones with deficient adhesion and blocking experiments with surface-specific monoclonal antibodies. Also, the infectivity of the analyzed clones was tested using Mongolian gerbils as experimental model. Two adhesion-deficient G. duodenalis clones, C6 and C7, were isolated from the wild type C5 clone which in turn was obtained from the WB strain. The adhesion efficiencies of C6 and C7 clones (48.2+/-4.9 and 32.6+/-2.4, respectively) were significantly lower as compared with WB strain or C5 clone (82.8+/-6.4 and 79.9+/-7.9). Analysis of radiolabel surface proteins by 1D and 2D SDS-PAGE revealed prominently labelled 28 and 88 kDa components in C6 and C7 clones and a major 200 kDa protein in the C5 clone and the WB strain. The 88 and 200 kDa components are acidic proteins by two-dimensional electrophoretic analyses. The most striking difference between wild-type and adhesion-deficient Giardia trophozoites was the reduced expression of a 200 kDa surface protein in the latter. Significantly, a mAb (IG3) specific for the 200 kDa protein that reacted with more than 99% of WB and C5 trophozoites and less than 1% of C6 and C7 trophozoites as determined by indirect immunofluorescence inhibited the adhesion of trophozoites from WB and C5 clone to Madin Darby Canine Kidney cells by 52% and 40.9%, respectively, suggesting a participation of this antigen in adherence. Finally, the functional relevance of trophozoite adhesion to epithelial cells was indicated by the reduced capacity of the adhesion-deficient clones to establish the infection in Mongolian gerbils.

Unusually low levels of genetic variation among Giardia lamblia isolates

Giardia lamblia, an intestinal pathogen of mammals, including humans, is a significant cause of diarrheal disease around the world. Additionally, the parasite is found on a lineage which separated early from the main branch in eukaryotic evolution. The extent of genetic diversity among G. lamblia isolates is insufficiently understood, but this knowledge is a prerequisite to better understand the role of parasite variation in disease etiology and to examine the evolution of mechanisms of genetic exchange among eukaryotes. Intraisolate genetic variation in G. lamblia has never been estimated, and previous studies on interisolate genetic variation have included a limited sample of loci. Here we report a population genetics study of intra- and interisolate genetic diversity based on six coding and four noncoding regions from nine G. lamblia isolates. Our results indicate exceedingly low levels of genetic variation in two out of three G. lamblia groups that infect humans; this variation is sufficient to allow identification of isolate-specific markers. Low genetic diversity at both coding and noncoding regions, with an overall bias towards synonymous substitutions, was discovered. Surprisingly, we found a dichotomous haplotype structure in the third, more variable G. lamblia group, represented by a haplotype shared with one of the homogenous groups and an additional group-specific haplotype. We propose that the distinct patterns of genetic-variation distribution among lineages are a consequence of the presence of genetic exchange. More broadly, our findings have implications for the regulation of gene expression, as well as the mode of reproduction in the parasite.

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.

The zoonotic significance and molecular epidemiology of Giardia and giardiasis

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

Variability and variation in drug susceptibility among Giardia duodenalis isolates and clones exposed to 5-nitroimidazoles and benzimidazoles in vitro

OBJECTIVES

We analysed, in a cell-by-cell study, the in vitro susceptibility of Giardia duodenalis strains, including Mexican isolates and their clones to 5-nitroimidazoles and benzimidazoles.

METHODS

Fluorogenic dye staining (FDA-PI) and cell morphology (CM) assays, two fast and direct techniques, replaced the indirect 'gold standard' method (subculture in liquid medium) in the evaluation of 5-nitroimidazoles and benzimidazoles, respectively.

RESULTS

Under these conditions, the activity of several 5-nitroimidazole and benzimidazole derivatives was consistent with their known efficacy, but parasite stocks exhibited a greater variability in response to 5-nitroimidazoles compared with benzimidazoles. Also, consecutive progenies from single stocks maintained in continuous subculture in drug-free media displayed changes (variations) in the proportions of drug resistant (R/T) subpopulations when exposed to sublethal concentrations of 5-nitroimidazoles and benzimidazoles. These were again more variable upon exposure to 5-nitroimidazoles than to benzimidazoles. Variations were not due to drug susceptibility shifts in parent trophozoites since analysis of cytokinetic processes showed a predominant pattern of susceptible/susceptible or resistant/resistant daughters, whereas susceptible/resistant daughters were scarce.

CONCLUSIONS

Our observations support the idea that G. duodenalis cultures exhibit variations in their response to 5-nitroimidazoles and benzimidazoles as a result of a drug-independent competition between drug-susceptible and drug-resistant subpopulations when parasites are subcultured.

The future impact of societal and cultural factors on parasitic disease -- some emerging issues

A variety of societal and cultural factors will increase host exposure or susceptibility to infectious agents, particularly parasites. Such factors have already had a major impact on the emergence of infectious diseases and the situation is likely to worsen further as we enter the new millennium. The changes that are enhancing the spread and transmission of parasitic diseases, as well as those which are adversely affecting host responsiveness, are examined with reference to specific parasites.

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

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

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.

Possible contamination of surface waters with Giardia spp. through muskrats

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

A comparison of phase contrast microscopy and an immunofluorescence test for the detection of Giardia spp. in faecal specimens from cattle and wild rodents

As part of a study on the presence of Giardia cysts in water, a commercial direct immunofluorescence (DIF) test for the cysts was evaluated and compared to phase contrast microscopy. Forty faecal samples were collected from cattle; 31 contained Giardia. All 31 samples were positive by DIF whereas only 17 were detected by microscopy. The detected Giardia cysts were identified as belonging to the G. duodenalis group. 216 faecal samples were collected from wild rodents (Apodemus flavicollis, A. sylvaticus and Clethrionomys glareolus); 103 contained Giardia. Cysts were detected in 97 samples by DIF and in 57 by microscopy; 51 samples were positive by both methods. Nineteen rodents harboured cysts which morphologically resembled G. duodenalis. Specific identification was possible only by phase contrast microscopy, but the results suggested that DIF was superior for the detection of Giardia cysts in faeces of the animals tested.

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.

In vitro drug susceptibility of 29 isolates of Giardia duodenalis from humans as assessed by an adhesion assay

Twelve isolates of Giardia duodenalis from Caucasian hosts in the Perth metropolitan area, along with 16 isolates from Aborigines in the north of Western Australia and the reference isolate P1C10 were examined for their in vitro drug sensitivity. Dose-response curves were constructed for each isolate for metronidazole, the most common clinically used antigiardial agent, as well as for the benzimidazole compound albendazole. Less than a 9-fold variation was found in the susceptibility of the isolates to albendazole, while for metronidazole there was well over a 16,000-fold variation between the same group of isolates. In addition, it was found that isolates of Giardia obtained from Aboriginal hosts were significantly less sensitive to albendazole than those obtained from Caucasians. The results of this study have important implications for the continued use of metronidazole and the potential use of albendazole for the treatment of giardiasis.

A DNA fingerprinting method for individual characterization of Toxoplasma gondii strains: combination with isoenzymatic characters for determination of linkage groups

The genetic polymorphism of Toxoplasma gondii was evaluated for 14 strains by isoenzyme and DNA analysis. The 14 strains belonged to 5 different zymodemes defined by the variable patterns of 6 enzyme systems. A restriction-fragment-length polymorphism analysis was carried out with two endonucleases (Sal I and Pst I) and two repetitive probes (TGR1E and TGR6). This kind of repetitive probe allowed an individual identification of strain, with 13 schizodemes being observed among 14 strains. Only two strains were found to be totally identical when DNA and isoenzyme characters were considered. The numerical taxonomy methods applied to the results obtained for both types of characters allowed determination of linkage groups. Strain clustering obtained by numerical analysis of DNA characters alone is similar to the clustering obtained by analysis of isoenzyme and DNA characters together. A relationship was observed between the defined groups and virulence in Swiss mice.