Giardia lamblia infections in Mongolian gerbils: an animal model

Detection of viable Giardia cysts by amplification of heat shock-induced mRNA

Primers obtained from gene sequences coding for heat shock proteins (HSP) were used to specifically detect enteric protozoans of the genus Giardia. The HSP primers amplified Giardia DNA or the corresponding RNA sequences obtained from lysed cysts and gave a 163-bp product. Since the presence of the product did not indicate whether the cysts were viable, these amplifications are a presence/absence test only. In contrast, amplification of heat shock-induced mRNA utilizing the same HSP primers was indicative of viable Giardia cysts. The limit of sensitivity of the presence/absence test was 1 cyst, whereas for the viability test it was 10 cysts. Thus, viable Giardia cysts can be rapidly and specifically detected with great sensitivity through the use of PCR amplifications.

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

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

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

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

Nucleic acid stains as indicators of Giardia muris viability following cyst inactivation

A reliable viability assay for Giardia is required for the development of disinfection process design criteria and pathogen monitoring by water treatment utilities. Surveys of single-staining nucleic acid dyes (stain dead parasites only), and double-staining vital dye kits from Molecular Probes (stain live and dead parasites) were conducted to assess the viability of untreated, heat-killed, and chemically inactivated Giardia muris cysts. Nucleic acid staining results were compared to those of in vitro excystation and animal infectivity. Nucleic acid stain, designated as SYTO-9, was considered the best among the single-staining dyes for its ability to stain dead cysts brightly and its relatively slow decay rate of visible light emission following DNA binding. SYTO-9 staining was correlated to animal infectivity. A Live/Dead BacLight was found to be the better of 2 double-staining viability kits tested. Logarithmic survival ratios based on SYTO-9 and Live/Dead BacLight were compared to excystation and infectivity results for G. muris cysts exposed to ozone or free chlorine. The results indicate that SYTO-9 and Live/Dead BacLight staining is stable following treatment of cysts with chemical disinfectants.

The immune response to Giardia

The flagellate Giardia duodenalis has been considered for many years to be a commensal living in the lumen of the small intestine of its host. It is only 25 years ago that it was accepted that Giardia is a significant pathogen of humans. Knowledge that Giardia can elicit an immune response that would probably contribute to the onset or absence of symptoms is not much older. The use of animal models to study the disease in the laboratory, together with the production of the whole life cycle in a test tube, have contributed greatly to our present knowledge of the immune responses to Giardia and of antigens that are specific to the trophozoite or cyst stages. In this review, Gaétan Faubert focuses on studies published since the last review in Parasitology Today in 1988, and examines the roles played by the humoral and cell-mediated immune responses in the control of the infection. It also covers the immunodiagnostic assays that have been recently developed on the basis of advances in our knowledge of the antigens of Giardia.

Longitudinal studies of Giardia contamination in two community drinking water supplies: cyst levels, parasite viability, and health impact

Giardia cyst concentrations were determined in an inventory of 153 raw and 91 chlorinated drinking water samples collected at 86 sites from throughout the western Canadian province of British Columbia. Sixty-four percent of raw water samples were cyst positive (69% of sites). Cyst concentrations were lower in chlorinated than in raw water. The viability of cysts in drinking water samples assessed by infectivity in Mongolian gerbils (Meriones unguiculatus) was decreased in chlorinated water. Two rural communities using Giardia-contaminated surface drinking water sources were selected for longitudinal studies including drinking water testing and serological studies of residents. Three hundred thirty-six raw and treated samples from these communities were collected over 24 months. Cyst concentrations and viability were assessed in a 12-month study of each community. Parasite concentrations were lower in chlorinated water than in raw water in both communities. Cyst concentrations were lower in reservoir-settled water than in raw water. Viability, assessed by animal infectivity and corrected for inoculum, decreased following reservoir settling as well as after chlorination. A bolus or spiking phenomenon of cysts was observed in both community drinking water systems and deserves further study. A striking seasonal pattern was seen in one community but not in the second. The seroprevalence data and number of laboratory-confirmed cases identified in each year-long community study are consistent with the possibility that low-level endemic transmission is occurring.

Disaccharidase deficiencies in Mongolian gerbils (Meriones unguiculatus) protected against Giardia lamblia

The activities of the disaccharidases lactase, maltase, sucrase and trehalase were examined in gerbils during Giardia lamblia infections. In a primary infection with trophozoites, the activities of all four enzymes were reduced from day 10 post-infection (p.i.) and remained at low levels well past the elimination phase of the infection. However, during a challenge infection, the disaccharidase decreases were short-lived, with impairments being seen only on days 2 and/or 4 post-challenge (p.c.). Sucrase activity was not affected by a challenge infection. When 0.1 mg of a soluble extract of G. lamblia trophozoites was used to challenge gerbils previously exposed to the live parasite, the pattern and duration of enzyme deficiencies were comparable with those observed after the challenge with the live parasite. In addition, decreasing the extract dose used to challenge the gerbils led to smaller disaccharidase deficiencies. G. lamblia-infected gerbils were also challenged with a soluble extract of Entamoeba histolytica trophozoites, and this had no effect on the disaccharidase activities. Therefore, the presence of the intact parasite was not necessary to induce enzyme reductions in immune animals. In addition, the effects seen during the secondary infection were parasite-specific and may have involved the host's immune response to Giardia antigens. Immune gerbils were further challenged with the in vitro-released excretory/secretory products of G. lamblia. Under our experimental conditions, disaccharidase activities were found to be affected by these products in a manner that was inconsistent with the results of the live parasite challenge, and this merits further study.

Giardia lamblia infections in adult mice

An adult mouse-Giardia lamblia model was developed and used to study host-parasite interactions, including antigenic variation. The H7/1 clone of isolate GS infected mice consistently and produced infections in 14 mouse strains tested. Infection patterns were mouse strain and Giardia isolate dependent. Antigenic variation occurred in immunocompetent mice but not in mice with severe combined immunodeficiency.

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

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

Successful experimental infections of a human volunteer and Mongolian gerbils with Giardia of animal origin

A human volunteer and Mongolian gerbils were shown to be susceptible to infection with Giardia from a Gambian giant pouched rat. The course of infection and the pattern of cyst excretion, as well as the number of cysts in gerbils which were given the same inocula of Giardia, differed from the course of infection in humans. The latent period in gerbils was longer and the gerbils continually excreted numerous cysts, whereas excretion of cysts, in smaller numbers, by the volunteer was intermittent. Moderate clinical symptoms were noted in the volunteer, and the infection was confirmed by the development of anti-Giardia antibodies. The study demonstrated the zoonotic character of giardiasis and has important implications for the epidemiology of Giardia.

Comparison of Giardia lamblia and Giardia muris cyst inactivation by ozone

Inactivation of Giardia lamblia and Giardia muris cysts was compared by using an ozone demand-free 0.05 M phosphate buffer in bench-scale batch reactors at 22 degrees C. Ozone was added to each trial from a concentrated stock solution for contact times of 2 and 5 min. The viability of the control and treated cysts was evaluated by using the C3H/HeN mouse and Mongolian gerbil models for G. muris and G. lamblia, respectively. The resistance of G. lamblia to ozone was not significantly different from that of G. muris under the study conditions, contrary to previously reported data that suggested G. lamblia was significantly more sensitive to ozone than G. muris was. The simple Ct value for 2 log unit inactivation of G. lamblia was 2.4 times higher than the Ct value recommended by the Surface Water Treatment Rule.

Effects of protein malnutrition on experimental giardiasis in the Mongolian gerbil

To determine the effects of protein malnutrition on the severity and duration of infection with Giardia lamblia, Mongolian gerbils were pair-fed a pelleted control (C) diet (20% protein) and a low-protein (5%; LP) diet for 3 weeks before and after being infected with 100,000 cysts orally. Weight loss, fecal fat, enteropooling, and the duration of cyst excretion were all greater in the infected LP than in the infected C animals. During peak infection the upper intestinal intraepithelial lymphocyte infiltration, crypt enlargement, and villus enterocyte migration were greater in C than in LP animals, as was the villus mast cell number at the end of the infection. It is concluded that in the protein-malnourished host the increased severity of Giardia infection correlates with a reduction in enterocyte production and migration, probably secondary to a reduced lymphocyte infiltration, and the increased infection duration correlates with blunted mast cell migration into affected villi.

Molecular variation in Giardia

Molecular characterisation of species within the genus Giardia has revealed that much of the phenotypic heterogeneity, particularly within the species G. duodenalis, has a genetic basis. The source of this genetic variation appears to arise from predominantly asexual, clonal reproduction, although occasional bouts of sexual reproduction cannot be ruled out. Genetic variation is extensive with some clones widely distributed and others seemingly unique and localised to a particular endemic focus. Little attention has been given to the molecular epidemiology of Giardia infections. Future studies should be directed at studying the ecology and dynamics of transmission of Giardia clones, particularly in localised areas, and to evaluating the factors that serve to maintain genetic diversity between clones, especially the role of inter-clonal competition. Future research using molecular techniques should aim to identify and follow Giardia clones in nature and correlate genetic typing with important clinical and epidemiological characteristics such as virulence, drug sensitivity and zoonotic potential.

Oxygen uptake in cysts and trophozoites of Giardia lamblia

Oxygen uptake in cysts and trophozoites of the parasitic protozoan Giardia lamblia was examined. Both showed oxygen uptake activity, but that of cysts was only 10% to 20% that of trophozoites. Oxygen dependence of oxygen uptake in cysts and trophozoites showed oxygen maxima above which oxygen uptake decreased. The oxygen concentration at which the oxygen uptake rate was greatest was higher for trophozoites than for cysts. The effect of various inhibitors on cyst and trophozoite oxygen uptake suggested that flavoproteins and quinones play some role in oxygen uptake. The substrate specificities and the effect of inhibitors on G. lamblia trophozoites were similar to those observed for G. muris. Metronidazole, the drug most commonly used in treatment of giardiasis, inhibited oxygen uptake and motility in trophozoites; however, it had no obvious effect on either oxygen uptake or excystation in cysts. Menadione, a redox cycling naphthaquinone, first stimulated, then completely inhibited, oxygen uptake in cysts and trophozoites; a complete loss of cyst viability and trophozoite motility was also observed. The effect of menadione on G. lamblia may indicate that redox cycling compounds have potential as chemotherapeutic agents for the treatment of giardiasis.

Antibody-magnetite method for selective concentration of Giardia lamblia cysts from water samples

An antibody-magnetite method was developed in order to selectively concentrate Giardia cysts from water samples. The indirect technique employed a mouse immunoglobulin G anti-Giardia antibody as a primary antibody and an anti-mouse immunoglobulin G antibody-coated magnetite particle as a secondary labeling reagent. The magnetically labeled cysts were then concentrated by high-gradient magnetic separation. Ninety percent of the seeded cysts were recovered from buffer when this method was employed. An average of 82% of the seeded cysts were recovered from water samples with various turbidities. Significantly higher cyst recoveries were obtained from water samples with turbidities below 600 nephelometric turbidity units.

Degradation of Giardia lamblia cysts in mixed human and swine wastes

This study was conducted to determine the persistence of Giardia lamblia cysts in mixed septic tank effluent and swine manure slurry and to correlate fluorescein diacetate-propidium iodide staining of G. lamblia cysts with their morphology under low-voltage scanning electron microscopy. Under field conditions, G. lamblia cysts were degraded more rapidly in the mixed waste than in the control Dulbecco's phosphate-buffered saline (PBS). For total and viable cysts, the mixed waste had D values (time for a 90% reduction in number of cysts) of 18.3 and 15.5 days, and the Dulbecco's PBS control had D values of 41.6 and 26.8 days. The rates of cyst degradation in septic tank effluent and in Dulbecco's PBS were similar. Increasing the proportion of swine manure slurry in the mixed waste favored degradation of the parasite. These results indicate that the mixed waste treatment was the predominant factor affecting the cyst persistence and that it was swine manure slurry that played the role of degrading the parasite. Visualization of viable and nonviable Giardia cysts with low-voltage scanning electron microscopy revealed an excellent correlation between the viability of the cysts determined by fluorescein diacetate-propidium iodide staining and their electron microscopic morphology.

Isolation of two Giardia lamblia (WB strain) clones with distinct surface protein and antigenic profiles and differing infectivity and virulence

To determine the relationship between antigenic profiles and pathogenicity among Giardia lamblia clones (WB strain), trophozoites were cloned by the technique of limiting dilution. The phenotype of each clone was determined by an indirect immunofluorescence test using a polyclonal rabbit anti-G. lamblia trophozoite serum made against the parent strain. Two clones were chosen for further studies: a highly fluorescent clone, F+, in which more than 95% of the trophozoites fluoresced, and a low-fluorescence clone, F-, in which fewer than 5% fluoresced. Sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis and enzyme-linked immunotransfer blot studies of the membrane fractions of the two clones and parent strain revealed differences in both the total protein and antigenic profiles. A serum cytotoxicity test with the polyclonal serum showed that the F+ clones were more susceptible to immobilization and killing, while the majority of cells of the F- clones were resistant to such killing. Assessment of the infectivity of the two clones in the Mongolian gerbil animal model indicated that the F- clone more readily initiated infections, produced more cysts, had a higher intestinal trophozoite load, and produced a more severe clinical syndrome, while the F+ clone was less phenotypically stable in vivo and in some cases took longer to be cleared from the intestine.

Comparison of an in vitro method and an in vivo method of Giardia excystation

An in vitro method and an in vivo method of excystation were compared to determine the most useful method for the retrieval of Giardia duodenalis isolates. Cysts from 11 Giardia strains were used. In vitro excystation produced motile trophozoites in 16 sets, while in vivo excystation produced trophozoites in all of the 21 comparative sets of excystations. Few cultures were lost because of contamination by either method (17% of in vitro-derived trophozoites versus 23% of in vivo-derived trophozoites; P greater than 0.05). Both methods demonstrated comparable isolate retrieval rates (15% of in vitro-derived trophozoites adapting to culture compared with 29% of in vivo-derived trophozoites; P greater than 0.05), although analysis of the strains retrieved showed that two isolates were retrieved from in vitro excystation alone, compared with four from in vivo excystation. Analysis that included results of extra in vivo cultures showed that a total of nine isolates were retrieved by using this type of excystation. Despite the disadvantages of cost and labor, in vivo excystation appears to be more useful than in vitro excystation for isolate retrieval at the present time.

Phagocytosis of Giardia lamblia trophozoites by cytokine-activated macrophages

Phagocytosis of Giardia lamblia trophozoites by cytokine-activated and non-activated bone marrow-derived macrophages was examined in vitro. Macrophages treated with recombinant interferon-gamma (IFN-gamma) and bacterial lipopolysaccharide (LPS) ingested a significantly higher number of in vitro-grown trophozoites than untreated macrophages. Maximal uptake of parasites occurred after 4 h and 6 h of incubation where 81.4% and 79.1% of macrophages were positive for trophozoites. Other cytokines tested, IL-2, IL-3, IL-4, IL-5, GM-CSF, CSF-1 and tumour necrosis factor-alpha (TNF-alpha) either alone or in combination with LPS, failed to activate macrophages to phagocytose G. lamblia. The induction of this activated macrophage anti-microbial function was achieved pharmacologically using phorbol myristate acetate (PMA) and ionophore A23187. The giardicidal activity of macrophages activated with IFN-gamma and LPS or that induced by PMA and A23187 was inhibited by H-7, indicating the role for protein kinase C in the intracellular events following activation.

The biology of Giardia spp

Gardia spp. are flagellated protozoans that parasitize the small intestines of mammals, birds, reptiles, and amphibians. The infectious cysts begin excysting in the acidic environment of the stomach and become trophozoites (the vegetative form). The trophozoites attach to the intestinal mucosa through the suction generated by a ventral disk and cause diarrhea and malabsorption by mechanisms that are not well understood. Giardia spp. have a number of unique features, including a predominantly anaerobic metabolism, complete dependence on salvage of exogenous nucleotides, a limited ability to synthesize and degrade carbohydrates and lipids, and two nuclei that are equal by all criteria that have been tested. The small size and unique sequence of G. lamblia rRNA molecules have led to the proposal that Giardia is the most primitive eukaryotic organism. Three Giardia spp. have been identified by light lamblia, G. muris, and G. agilis, but electron microscopy has allowed further species to be described within the G. lamblia group, some of which have been substantiated by differences in the rDNA. Animal models and human infections have led to the conclusion that intestinal infection is controlled primarily through the humoral immune system (T-cell dependent in the mouse model). A major immunogenic cysteine-rich surface antigen is able to vary in vitro and in vivo in the course of an infection and may provide a means of evading the host immune response or perhaps a means of adapting to different intestinal environments.

Comparison of animal infectivity, excystation, and fluorogenic dye as measures of Giardia muris cyst inactivation by ozone

Giardia muris cyst viability after ozonation was compared by using fluorescein diacetate-ethidium bromide staining, the C3H/HeN mouse-G. muris model, and in vitro excystation. Bench-scale batch experiments were conducted under laboratory conditions (pH 6.7, 22 degrees C) in ozone-demand-free phosphate buffer. There was a significant difference between fluorogenic staining and infectivity (P less than or equal to 0.05), with fluorogenic staining overestimating viability compared with infectivity estimates of viability. This suggests that viable cysts as indicated by fluorogenic dyes may not be able to complete the life cycle and produce an infection. No significant differences between infectivity and excystation and between fluorogenic staining and excystation (P less than or equal to 0.05) were detected for inactivations up to 99.9%. Only animal infectivity had the sensitivity to detect inactivations greater than 99.9%. Therefore, the animal model is the best method currently available for detecting high levels of G. muris cyst inactivation.

Propidium iodide as an indicator of Giardia cyst viability

The use of propidium iodide, whose uptake indicates cell death or damage, was investigated to assess the viability of heat-inactivated and chemically inactivated Giardia muris cysts. This was done by comparing propidium iodide staining with excystation. We first determined that propidium iodide could be used with an immunofluorescence detection procedure by showing that the percentages of Giardia lamblia cysts stained with this dye before and after subjecting them to a fluorescence detection method were similar. G. muris cysts were then exposed to heat (56 degrees C), 0.5 to 4 mg of chlorine per liter (pH 7.0, 5 degrees C), 0.1 to 10 mg of a quaternary ammonium compound per liter, or 2 mg of preformed and forming monochloramine per liter (pH 7.2, 18 to 20 degrees C). A good positive correlation between percent propidium iodide-stained cysts and lack of excystation was demonstrated for G. muris cysts exposed either to heat or to the quaternary ammonium compound. However, no significant correlation between absence of excystation and propidium iodide staining was found for cysts exposed to chlorine or monochloramines. These results demonstrate that the propidium iodide staining procedure is not satisfactory for determining the viability of G. muris cysts exposed to these two commonly used drinking water disinfectants.

Determination of Giardia lamblia cyst infective dose for the Mongolian gerbil (Meriones unguiculatus)

The purpose of this study was to determine the 50% infective dose for Giardia lamblia (CDC:0284:1) cysts in Mongolian gerbils (Meriones unguiculatus). The log10 50% infective dose results calculated by probit analysis and the Spearman-Karber method were 2.45 and 2.50, respectively.

Immunofluorescence and morphology of Giardia lamblia cysts exposed to chlorine

Giardia cyst-like objects detected by immunofluorescence in chlorinated water samples often cannot be positively identified by their morphological appearance. To determine the effect of chlorine on cyst immunofluorescence and morphology, Giardia lamblia cysts were exposed to chlorine for 48 h. The majority of cysts exposed to chlorine concentrations of 1 to 11 mg/liter at 5 and 15 degrees C lost their internal morphological characteristics necessary for identification, but most of them were still detectable by immunofluorescence.

Modification of RPMI 1640 for use in vitro immunological studies of host-parasite interactions in giardiasis

Incubation of trophozoites for 6 h in RPMI 1640 affected the viability of the parasite; however, RPMI 1640 supplemented with L-cysteine did not affect trophozoite viability, ability to grow when transferred to fresh TYI-S-33, or ability to infect gerbils. Similarly, incubation of murine spleen cells in modified medium did not affect the viability of the cells or proliferative responses to mitogens. RPMI 1640 supplemented with 11.4 mM L-cysteine is a suitable maintenance medium for in vitro studies in immunoparasitology because it maintains viability as well as some of the physiological functions of both trophozoites and lymphocytes.

Growth, activities of enzymes in the small intestine, and ultrastructure of microvillous border in gerbils infected with Giardia duodenalis

The aim of this study was to assess and correlate changes in weight gain, food intake, small intestinal disaccharidase activities and microvillous border surface area over the course of a primary Giardia duodenalis infection in weanling Mongolian gerbils (Meriones unguiculatus). Weight gain in infected animals was significantly impaired between days 8 and 20 postinoculation when compared to age- and weight-matched controls. No difference in food intake was observed between groups. Trophozoite population in the small intestine was maximal on day 4 and 6 of infection, and colonization persisted in the duodenum throughout the experiment (30 days). In infected gerbils, mucosal sucrase and maltase activities were significantly depressed in the duodenum and jejunum on day 4 and in all areas of the small intestine by day 6. Eight and 25 days postinoculation, disaccharidase activities had recovered in the jejunum and distal small intestine but remained depressed in the duodenum, the area where trophozoite colonization persisted. Diffuse loss of microvillous border surface area was observed in the duodenum and jejunum after 6 days of infection. Eight days postinoculation, microvillus surface area had returned to normal in the jejunum, but not in the duodenum. Our findings demonstrate that acute giardiasis in weanling gerbils impairs weight gain, depresses disaccharidase activities, and diffusely reduces mucosal microvillous border surface area.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of developmentally regulated Giardia lamblia cyst antigens using GCSA-1, a cyst-specific monoclonal antibody

GCSA-1, a monoclonal antibody raised against cysts generated in vitro was shown to be Giardia cyst-specific by immunoblot analysis and immunofluorescence. GCSA-1 recognized four polypeptides ranging from 29-45 kD present in the cyst wall. These antigens appeared within eight hours of exposure of trophozoites to encystation medium and were shown to be synthesized by encysting parasites by means of metabolic labelling with [35S]-cysteine. Trophozoites were not stained by the antibody. GCSA-1 also reacted with in vivo cysts obtained from faeces of infected humans, gerbils and mice. These data demonstrate that the determinants recognized by GCSA-1 are early cyst antigens which are developmentally regulated and conserved components of the cyst wall. The actual role of the antigens detected by GCSA-1 in encystation are unknown, but they represent a potential target for strategies directed at inhibiting this process.

Identification of Giardia lamblia-specific antigens in infected human and gerbil feces by western immunoblotting

Western immunoblot analysis of aqueous extracts of feces obtained from five giardiasis patients and from experimentally infected gerbils (Meriones unguiculatus) with rabbit antiserum to Giardia lamblia cysts has revealed antigens of three molecular weight groups. A stepladderlike, evenly-spaced set of strongly reactive antigens (darkest at a molecular weight [m.w.] of 55,000 to 70,000) appeared in the gerbil feces from day 4 (first experiment) or day 2 (second experiment) and lasted to about day 7 but disappeared completely by day 8 and did not reappear later. These antigenic bands were seen in gerbils infected with two isolates of G. lamblia. These bands were not revealed when antiserum to trophozoites was used as the probe, nor were they evident in specimens from the patients or in a preparation of sonicated cysts. A second group of antigens, represented by two to three low-m.w. bands of approximately 15,000 to 20,000, was evident in both the blots of gerbil feces after approximately day 8 and the specimens from the giardiasis patients. The third group of antigens revealed by blotting experiments was a high-m.w. band (approximately 110,000) which appeared on a number of days (beginning of day 8 of gerbil infection), but this band was not seen in the human specimens. A clear band corresponding to the previously reported GSA-65 antigen was not seen in either the gerbil or the human samples. Some low- and high-m.w. bands were also detected by antitrophozoite serum in the gerbil samples, but these were weak and unimpressive compared with those visualized using anticyst serum. A monoclonal antibody-based antigen capture enzyme-linked immunosorbent assay revealed that Giardia spp.-specific stool antigen rose suddenly at day 3 of gerbil infection, at the time when fecal cyst numbers began to rise rapidly.

Induction of a phosphomannosyl binding lectin activity in Giardia

Giardia lamblia, a protozoan parasite that causes widespread diarrheal disease, expresses a surface membrane associated lectin, taglin, which is specifically activated by limited proteolysis with trypsin, a protease that is present in abundance at the site of infection. When activated, taglin agglutinates enterocytes which are the cells to which the parasite adheres in vivo, and in addition, binds to isolated brush border membranes of these cells. These findings suggest that this lectin may be involved in the host-parasite interaction. Taglin is most specific for terminal phosphomannosyl residues and its binding to red cells is mediated by cell surface phosphate residues. Hemagglutinating activity induced by taglin is most active at pH 6.5 and is dependent on divalent cations. A monoclonal antibody to taglin reacts with the surface membrane of live trophozoites and recognizes a protein of 28/30 kDa in lysates of Giardia trophozoites, by immunoblotting. This finding is confirmed by direct demonstration of lectin activity by erythrocyte binding to proteins electroblotted to nitrocellulose, which revealed specific red cell binding to giardial protein bands in the same molecular weight range as those recognized by the monoclonal antibody.

Inactivation of gerbil-cultured Giardia lamblia cysts by free chlorine

Giardia lamblia cysts were harvested from Mongolian gerbils and exposed to free chlorine in buffered water at pH 5, 7, and 9 at 15 degrees C. The contact times required to obtain a 2-log reduction in cyst survival (i.e., a 99% kill) were interpolated from survival curves generated at fixed concentrations of chlorine in the range of 0.25 to about 16 mg/liter. Concentration-time (C.t') products for 99% inactivation ranged from about 120 to nearly 1,500 mg.min/liter. These values are higher than those reported previously for free chlorine using G. lamblia cysts from infected humans. The cysts isolated from gerbils, as with other Giardia cysts, were unusually sensitive to chlorine in alkaline solutions.

Disaccharidase activity in the small intestine of gerbils (Meriones unguiculatus) during primary and challenge infections with Giardia lamblia

The sequence of changes in the activity of six disaccharidases in the small intestine of gerbils during primary and secondary G lamblia infections was examined. The primary G lamblia infection induced a transient reduction in disaccharidase activity which was related to the highest trophozoite burden in the small intestine. During the primary exposure, a 30% to 85% decrease in the activity of enzymes was observed on days 10 and 20 after infection. Secondary exposure of gerbils to G lamblia caused a sharp decrease in disaccharidase activity as early as 24 h after challenge. The reduction in the enzyme activity was not influenced by the size of the challenge inoculum and occurred even when there were no live trophozoites in the small intestine. Disaccharidase deficiency could also be induced by challenge with the soluble extract of the trophozoites. Multiple challenge administrations of G lamblia trophozoites to gerbils induced a persistent disaccharidase deficiency. The results indicate that disaccharidase deficiency associated with the primary G lamblia infection probably represents a direct effect of the parasite on the brush border of the small intestine. On the other hand, the observed disaccharidase deficiency in the secondary G lamblia infection appears to be induced by the local immune responses of the host.

Zoonotic aspects of giardiasis: a review

Several studies suggested that some water-borne epidemics of giardiasis in the U.S.A. were of zoonotic origin. Also, cats and dogs were suspected of being sources of giardiasis for man. These observations have been partly supported by experimental cross-transmissions. However, there are also some indications that zoonotic giardiasis may not be common. The host-specificity of Giardia spp. is still controversial. To date, morphological characteristics can only differentiate three very basic types of Giardia: G. intestinalis, G. muris and G. agilis. Host-specific and morphometric criteria resulted in the description of more than 40 species of Giardia; many of them probably invalid. Only a few subtle antigenic differences among G. intestinalis (lamblia) strains have been observed. The comparison of isoenzymes and DNA banding patterns revealed 3 basic groups, not necessarily related to host origin. Further biochemical, immunological, genetic and cross-transmission studies in host and parasite populations are needed to better understand host-specificity of various Giardia isolates. At the present time one may only conclude that although mammals and man do not seem to possess their own unique species of Giardia, in reality the major methods of transmission of giardiasis probably remain basically host-specific.

Sequential changes of lamina propria immunoglobulin-containing cells in immune intact and immunosuppressed mice infected with Giardia lamblia

Following Giardia lamblia infection in immune intact NMRI mice, increased numbers of IgM-containing cells and decreased numbers of IgA containing cells were noticed in the lamina propria during the establishment (3-5 days) and acute (9-11 days) phases of infection. The decline in IgM-containing cells during the clearance phase of infection (17-21 days post-infection) was accompanied by an increase in IgA and IgG-containing cells. Our data suggest that the locally synthesized antibodies, especially of the IgA class, play a significant immunodulatory role in the clearance of G. lamblia infection from the gut. Mice immunosuppressed using rabbit anti-mouse lymphocyte serum or dexamethasone had significantly reduced numbers of IgA and IgG-containing cells during all phases of infection and higher parasite loads in their jejunum. It appears that one of the reasons for increased severity and chronicity of G. lamblia infection is the decrease in immunoglobulin-containing cells in the gut.

Giardia cyst wall-specific carbohydrate: evidence for the presence of galactosamine

Gas chromatographic (GC), mass spectrometric (MS), lectin binding and enzymatic analyses of the carbohydrates from Giardia cyst walls, intact cysts and trophozoites were performed to investigate the carbohydrate composition of Giardia cyst walls and to test the hypothesis that the Giardia cyst wall is composed largely of chitin. Galactosamine, verified by MS, was present in Giardia cyst walls and intact cysts (ca. 47 nmol 10(-6) cysts). Since not even trace amounts of it were detected in trophozoites by either GC or lectin binding, galactosamine is hypothesized to be a cyst wall-specific amino hexose. Based on the putative binding affinity of Phaseolus limensis lectin, galactosamine may be present in cyst walls as N-acetylgalactosamine. Neither glucosamine nor sialic acid were detected in as much as 11 mg dry weight of cysts, cyst walls, or trophozoites. Glucose, the most abundant carbohydrate, and ribose were detected in Giardia cysts and trophozoites. Galactose (ca. 10 nmol 10(-6) cysts) was detected in cysts but not in trophozoites. The lack of detectable levels of (1) glucosamine in cyst wall hydrolysates, (2) cyst staining by Calcofluor M2R, (3) endogenous chitinase activity and (4) N-acetylglucosamine when cysts served as a substrate for exogenous chitinase suggests that the Giardia cyst wall is not composed largely of chitin as previously reported. beta-N-Acetylgalactosaminidase, EC 3.2.1.32, activity was detected in cysts and trophozoites and represents the first carbohydrate splitting hydrolase detected in Giardia.

Cross-species transmission of Giardia spp.: inoculation of beavers and muskrats with cysts of human, beaver, mouse, and muskrat origin

Giardia cysts isolated from humans, beavers, mice, and muskrats were tested in cross-species transmission experiments for their ability to infect either beavers or muskrats. Giardia cysts, derived from multiple symptomatic human donors and used for inoculation of beavers or muskrats, were shown to be viable by incorporation of fluorogenic dyes, excystation, and their ability to produce infections in the Mongolian gerbil model. Inoculation of beavers with 5 x 10(5) Giardia lamblia cysts resulted in the infection of 75% of the animals (n = 8), as judged by the presence of fecal cysts or intestinal trophozoites at necropsy. The mean prepatent period was 13.1 days. An infective dose experiment, using 5 x 10(1) to 5 x 10(5) viable G. lamblia cysts collected by fluorescence-activated cell sorting, demonstrated that doses of between, less than 50, and less than 500 viable cysts were required to produce infection in beavers. Scanning electron microscopy of beaver small intestine revealed that attachment of G. lamblia trophozoites produced lesions in the microvillous border. Inoculation of muskrats with G. lamblia cysts produced infections when the dose of cysts was equal to or greater than 1.25 x 10(5). The inoculation of beavers with Giardia ondatrae or Giardia muris cysts did not produce any infection; however, the administration to muskrats of Giardia cysts of beaver origin resulted in the infection of 62% of the animals (n = 8), with a prepatent period of 5 days. Our results demonstrated that beavers and muskrats could be infected with Giardia cysts derived from humans, but only by using large numbers of cysts.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of viable Giardia cysts in vitro: determination by fluorogenic dye staining, excystation, and animal infectivity in the mouse and Mongolian gerbil

The purpose of this research was to document the formation of viable Giardia cysts in vitro. Viability staining, using fluorogenic dyes that required metabolic conversion for detection, and immunocytochemistry at the light microscopic level provided information on viability and for the identification of formed in vitro. Analysis of cysts formed in vivo and in vitro showed similar morphologic appearances by both light and electron microscopy. Cysts formed in vitro were capable of establishing infections in both mouse and gerbil models for giardiasis. Trophozoites obtained from mice experimentally infected with in vitro-formed cysts could be maintained in culture and induced a second time to form cysts in vitro. This model for the production of viable Giardia cysts in vitro should facilitate research on controlling the complete life cycle of Giardia outside an animal host.

Antigenic variation of Giardia lamblia in vivo

A single Giardia lamblia trophozoite can give rise in vitro to G. lamblia with varying surface antigens. To determine whether antigenic variation also occurs in vivo, gerbils were inoculated with defined G. lamblia clones and the surface antigens of the intestinal trophozoites were studied at different times during the infection. The proportion of monoclonal antibody 6E7-reacting trophozoites from WB C1-6E7S-inoculated gerbils had decreased significantly by day 3 postinoculation, indicating the presence of a heterogeneous population. On day 7, the 170-kilodalton antigen was no longer present and was replaced by a variety of antigens, including a major protein of 92 kilodaltons. With the exception of isolates from gerbils inoculated with WB A6-6E7S, the banding patterns of G. lamblia isolated from gerbils on day 7 or later were the same regardless of the clones used for inoculation. These studies show that G. lamblia changes its surface antigen(s) in vivo within 7 days following inoculation and appears to maintain the same set of surface antigens during the course of infection.

Variable infectivity of human-derived Giardia lamblia cysts for Mongolian gerbils (Meriones unguiculatus)

To determine whether gerbils can be used as a suitable animal model for giardiasis, we attempted to infect Mongolian gerbils with cysts of Giardia lamblia isolated from the stools of 10 humans with symptomatic and asymptomatic giardiasis. We obtained 100% infection with one isolate (CDC:0284:1), as evidenced by the presence of numerous trophozoites in the intestines of the gerbil and cysts in the feces. Cysts from four patients were not infective, while cysts from the other five patients produced infections in 11 to 75% of the animals. On the basis of these and other experiments, we concluded that (i) only certain isolates of human G. lamblia infect gerbils, colonize the intestine, and complete their life cycle by undergoing differentiation into cysts; (ii) the infection could last for about 39 days, but the animals excreted maximum numbers of cysts on about day 13 postinfection; (iii) the pattern of cyst excretion was irregular, and some gerbils, like humans, excreted cysts intermittently; (iv) the minimum number of cysts needed to establish an infection in 50% of the gerbils was 100; and (v) only certain strains retained the ability to infect gerbils even after repeated animal passage.

Epidemic giardiasis caused by a contaminated public water supply

In the period November 1, 1985 to January 31, 1986, 703 cases of giardiasis were reported in Pittsfield, Massachusetts (population 50,265). The community obtained its water from two main reservoirs (A and B) and an auxiliary reservoir (C). Potable water was chlorinated but not filtered. The incidence of illness peaked approximately two weeks after the city began obtaining a major portion of its water from reservoir C, which had not been used for three years. The attack rate of giardiasis for residents of areas supplied by reservoir C was 14.3/1000, compared with 7.0/1000 in areas that received no water from reservoir C. A case-control study showed that persons with giardiasis were more likely to be older and to have drunk more municipal water than household controls. A community telephone survey indicated that over 3,800 people could have had diarrhea that might have been caused by Giardia, and 95 per cent of households were either using alternate sources of drinking water or boiling municipal water. Environmental studies identified Giardia cysts in the water of reservoir C. Cysts were also detected in the two other reservoirs supplying the city, but at lower concentrations. This investigation highlights the risk of giardiasis associated with unfiltered surface water systems.

Cross-reactivity among different Giardia lamblia isolates using immunofluorescent antibody and enzyme immunoassay techniques

Rabbit antisera to 11 Giardia lamblia isolates were reacted with 8 G. lamblia isolates using single antibody ELISA and indirect immunofluorescent antibody techniques (IFA). Using living trophozoite organisms, IFA showed marked surface fluorescence with homologous antisera-organism pairs while heterologous pairs showed reduced or no reactivity. Using formalin-fixed trophozoites, the pattern of fluorescence changed to include diffuse internal fluorescence with both homologous and heterologous pairs. In contrast to the variability in surface fluorescence, similar reactivity was noted for homologous and heterologous antisera-isolate pairs with the ELISA. In addition, a double antibody enzyme immunoassay using rabbit antisera prepared to 2 G. lamblia isolates was performed with 8 different isolates as test antigen. All 8 were equally well detected. These data confirm previous findings that G. lamblia isolates have both different and common antigens. The different antigens appear to be on the surface of the organism while the common antigens appear to be internal or somatic.

Presence of Giardia spp. and absence of Salmonella spp. in New Jersey muskrats (Ondatra zibethicus)

Of 220 muskrat fecal specimens collected from 12 sites in southwestern New Jersey, 154 (70%) were found to contain cysts of the protozoan parasite Giardia spp. Cysts from selected muskrat fecal specimens infected Mongolian gerbils, but attempts to cultivate trophozoites removed from these gerbils were unsuccessful. Salmonella spp. were not detected in any of the muskrat fecal specimens.

Small rodents and other mammals associated with mountain meadows as reservoirs of Giardia spp. and Campylobacter spp

Sixty-five percent (469 of 722) of the fecal samples collected from small rodents in the central Washington Cascade mountains were positive for Giardia spp. Trapping studies showed that microtines of the genus Microtus were heavily infected with the parasite. Morphologically the cysts and trophozoites were of the Giardia duodenalis type. Small-rodent populations appear to maintain their infection throughout the year. Our data suggest that there is no difference in the percentage of positive animals in areas receiving a lot of human use as opposed to animals in those areas receiving very little or no human use. Giardia spp. were also found in elk and beaver fecal samples. Campylobacter spp. were recovered infrequently from the small rodents inhabiting alpine meadows. Of 551 specimens cultured, less than 1% were positive for the bacterium, and the isolates were identified as Campylobacter coli. Water voles were susceptible to a human isolate of Campylobacter jejuni and shed the bacterium for several weeks. C. jejuni was also isolated from a bear fecal sample collected from a protected watershed. Our studies indicate that microtines and possibly other small rodents inhabiting mountain meadows have a potential to act as a reservoir for both Giardia spp. and Campylobacter spp. Because these animals may carry human pathogens, they should be included in animal surveys designed to assess the health risks associated with mountain watersheds.

Infectivity of Swiss Giardia isolates to jirds and mice, and in vitro cultivation of trophozoites originating from sheep

The susceptibility of Giardia-free jirds (Meriones unguiculatus) and AJ-strain mice to oral inoculation with cysts from Swiss Giardia isolates was assessed. Giardia cysts of human, dog, cat, and sheep origin produced infections in jirds (4-10 weeks old). AJ-strain mice (6 weeks old) were insusceptible to Giardia from man, dog, and cat. The number of Giardia cysts inoculated per rodent ranged from 5000 to 12,600. The course of infection was studied in jirds experimentally infected with a Giardia isolate of cat origin. After administration of 6300 cysts to each of 16 jirds, 5 (31%) started to excrete cysts 4-5 days post inoculation (p.i.). Cyst excretion patterns were mostly intermittent, patency periods lasted 5-28 days, and average cyst numbers per g feces of individual jirds varied between 118,500 and 835,200 (maximal number: 3216700). The parasites were eliminated spontaneously in all 5 jirds. The Giardia isolate of cat origin was passaged 4 times in the jird. A Giardia isolate obtained from sheep was transferred in the cyst stage to jirds. Giardia trophozoites isolated from one of these jirds have been axenically cultivated in vitro in a modified, filter-sterilized TYI-S-33 culture medium and successfully cryopreserved. To our knowledge, this is the first report on axenic cultivation of Giardia of sheep origin. Giardia from cats could not be cultivated in vitro under the same conditions. The fact that Swiss Giardia isolates from humans and various domestic animals are not strictly host-specific is in agreement with similar findings from other areas and suggests a zoonotic character for giardiasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Excystation and culturing of human and animal Giardia spp. by using gerbils and TYI-S-33 medium

Mongolian gerbils were used as an animal model to excyst and host Giardia spp. isolated from meadow voles, dogs, beavers, and humans. Both cysts and trophozoites were used to establish infections. Gerbils were infected with Giardia duodenalis from beaver, dog, and human sources, and the trophozoites were extracted and cultured in Diamond TYI-S-33 medium. The use of gentamicin and ampicillin in the medium, coupled with treatment of gerbils with gentamicin before they were sacrificed, permitted the elimination of trophozoite purification techniques before culturing. An extract of whole bovine calf blood, CLEX, was substituted for fetal bovine serum in TYI-S-33 medium and was found to be both adequate and less expensive.