Population-based laboratory surveillance for Giardia sp. and Cryptosporidium sp. infections in a large Canadian health region

BACKGROUND

Giardia lamblia (intestinalis) and Cryptosporidium parvum are the two most important intestinal parasites infecting North Americans but there is a paucity of active population-based surveillance data from Canada. This study determined the incidence of and demographic risk factors for developing Giardia sp. and Cryptosporidium sp. infections in a general Canadian population.

METHODS

Population-based laboratory surveillance was conducted among all residents of the Calgary Health Region (CHR; population approximately = 1 million) during May 1, 1999 and April 30, 2002.

RESULTS

Giardia sp. infection occurred at a rate of 19.6 per 100,000 populations per year. Although the yearly incidence was stable, a significant seasonal variation was observed with a peak in late summer to early fall. Males were at higher risk for development of this infection as compared to females (21.2 vs. 17.9 per 100,000/yr; relative risk (RR) 1.19; 95% confidence interval (CI), 1.00-1.40, p = 0.047), and there was a significant decrease in risk associated with an increasing age. Cryptosporidium sp. infection occurred at an overall rate of 6.0 per 100,000 populations per year although a large outbreak of Cryptosporidium sp. infections occurred in the second half of the summer of 2001. During August and September of 2001, the incidence of cryptosporidiosis was 55.1 per 100,000 per year as compared to 3.1 per 100,000 per year for the remainder of the surveillance period (p < 0.0001). Cryptosporidiosis was largely a disease of children with an incidence of 17.8 per 100,000 per year occurring among those aged < 20 years of age compared to 1.25 per 100,000 per year for adults > or = 20 years of age (RR 14.19; 95% CI, 9.77-21.11; p < 0.0001).

CONCLUSION

This study provides important information on the occurrence and demographic risk groups for acquisition of giardiasis and cryptosporidiosis in a non-selected Canadian population.

Giardia lamblia infection induces different secretory and systemic antibody responses in mice

The adult mouse model of Giardia lamblia infection serves as an excellent animal model to understand the immunological mechanisms involved in the control and clearance of Giardia infection. Little is known about the G. lamblia-specific antigens that stimulate the humoral immune response in this model of giardiasis. We analysed the secretory and systemic antibody responses to G. lamblia during primary and secondary infection in C3H/HeJ adult mice. Faecal IgA and Serum IgG anti-G. lamblia antibodies were observed at week 2 post-infection. Serum IgG responses remained constant over the next several weeks, whereas faecal IgA titres continued to rise from weeks 2-6 post-infection. Western blot analysis revealed that intestinal IgA and serum IgG antibody responses were directed toward several distinct proteins of G. lamblia. Certain proteins appeared to be recognized by both faecal IgA and serum IgG, whereas other antigens were specific for either the secretory or systemic antibody responses. G. lamblia primary and secondary infections were associated with differences in the antibody recognition pattern. The biochemical and immunological characterization of these antigens will help us to better understand the immunobiology of the G. lamblia-host interaction.

Identification of variant-specific surface proteins in Giardia muris trophozoites

Giardia lamblia undergoes antigenic variation, a process that might allow the parasite to evade the host's immune response and adapt to different environments. Here we show that Giardia muris, a related species that naturally infects rodents, possesses multiple variant-specific surface proteins (VSPs) and expresses VSPs on its surface, suggesting that it undergoes antigenic variation similar to that of G. lamblia.

Recent insights into the mucosal reactions associated with Giardia lamblia infections

Giardia lamblia is an intestinal protozoan parasite infecting humans and various other mammalian hosts. The most important clinical signs of giardiasis are diarrhoea and malabsorption. Giardia lamblia is able to undergo continuous antigenic variation of its major surface antigen, named VSP (variant surface protein). While intestinal antibodies, and more specifically anti-VSP IgA antibodies, were proven to be involved in modulating antigenic variation of the parasite the participation of the local antibody response in control of the parasite infection is still controversial. Conversely, previous studies based on experimental infections in mice showed that cellular immune mechanisms are essential for elimination of the parasite from its intestinal habitat. Furthermore, recent data indicated that inflammatory mast cells have a potential to directly, or indirectly, interfere in duodenal growth of G. lamblia trophozoites. However, this finding was challenged by other reports, which did not find a correlation between intestinal inflammation and resistance to infection. Since intestinal infiltration of inflammatory cells and/or CD8+T-cells were demonstrated to coincide with villus-shortening and crypt hyperplasia immunological reactions were considered to be a potential factor of pathogenesis in giardiasis. The contribution of physiological factors to pathogenesis was essentially assessed in vitro by co-cultivation of G. lamblia trophozoites with epithelial cell lines. By using this in vitro model, molecular (through surface lectins) and mechanical (through ventral disk) adhesion of trophozoites to the epithelium was shown to be crucial for increased epithelial permeability. This phenomenon as well as other Giardia-induced intestinal abnormalities such as loss of intestinal brush border surface area, villus flattening, inhibition of disaccharidase activities, and eventually also overgrowth of the enteric bacterial flora seem to be involved in the pathophysiology of giardiasis. However, it remains to be elucidated whether at least part of these pathological effects are causatively linked to the clinical manifestation of the disease.

Secretory antibodies against Giardia intestinalis in lactating Nicaraguan women

Secretory IgA (sIgA) antibodies are important in the host defence against the intestinal protozoan parasite Giardia intestinalis. However, few antigens have been identified. In this study 100 milk and saliva samples from lactating women, living in an endemic region (León, Nicaragua), were screened for the presence of antibodies against G. intestinalis. Most milk and saliva samples contained anti-Giardia antibodies (59% and 52%, respectively), with a mean sIgA content 50 times higher in milk than in saliva. The positive samples reacted with trophozoite membrane, flagella and cytoplasmic antigens. Western blot analysis showed that milk and saliva anti-Giardia sIgA recognized up to 16 different Giardia proteins in the molecular weight region 20-165 kDa. Two-dimensional Western blotting showed that the major immunoreactive proteins were the same as the immunoreactive proteins identified by serum from acute giardiasis patients in a non-endemic country. The major difference was a stronger reactivity against the variant surface proteins (VSPs) in the milk samples. Milk sIgAs also recognized recombinant Giardia proteins such as alpha-1 giardin, ornithine carbamoyl transferase, VSP-4EX, arginine deaminase and alpha-enolase. These antigens will be important targets in the development of new immunodiagnostic tools and vaccines.

Enterococcus faecium SF68 enhances the immune response to Giardia intestinalis in mice

We studied the ability of the probiotic organism Enterococcus faecium SF68 to antagonize Giardia intestinalis infection in mice. Oral feeding of E. faecium strain SF68 starting 7 d before inoculation with Giardia trophozoites significantly increased the production of specific anti-Giardia intestinal IgA and blood IgG. This humoral response was mirrored at the cellular level by an increased percentage of CD4(+) T cells in the Peyer's patches and in the spleens of SF68-fed mice. The improvement of specific immune responses in probiotic-fed mice was associated with a diminution in the number of active trophozoites in the small intestine as well as decreased shedding of fecal Giardia antigens (GSA65 protein). The ability of SF68 to stimulate the immune system at both mucosal and systemic levels highlights mechanisms by which this probiotic might antagonize pathogens in vivo. Taken together, the data demonstrate the strong potential of strain SF68 to prevent protozoa from causing intestinal infections.

Immunopathology of giardiasis: the role of lymphocytes in intestinal epithelial injury and malfunction

T lymphocyte-mediated pathogenesis is common to a variety of enteropathies, including giardiasis, cryptosporidiosis, bacterial enteritis, celiac's disease, food anaphylaxis, and Crohn's disease. In giardiasis as well as in these other disorders, a diffuse loss of microvillous brush border, combined or not with villus atrophy, is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water, which ultimately cause diarrheal symptoms. Other mucosal changes may include crypt hyperplasia and increased infiltration of intra-epithelial lymphocytes. Recent studies using models of giardiasis have shed new light on the immune regulation of these abnormalities. Indeed, experiments using an athymic mouse model of infection have found that these epithelial injuries were T cell-dependent. Findings from further research indicate that that the loss of brush border surface area, reduced disaccharidase activities, and increase crypt-villus ratios are mediated by CD8+ T cells, whereas both CD8+ and CD4+ small mesenteric lymph node T cells regulate the influx of intra-epithelial lymphocytes. Future investigations need to characterize the CD8+ T cell signaling cascades that ultimately lead to epithelial injury and malfunction in giardiasis and other malabsorptive disorders of the intestine.

Quantitative assessment of sense and antisense transcripts from genes involved in antigenic variation (vsp genes) and encystation (cwp 1 gene) of Giardia lamblia clone GS/M-83-H7

Antigenic variation of the intestinal protozoan parasite Giardia lamblia is caused by an exchange of the parasite's variant surface protein (VSP) coat. Many investigations on antigenic variation were performed with G. lamblia clone GS/M-83-H7 which produces surface antigen VSP H7. To generate novel information on giardial vsp gene transcription, vsp RNA levels were assessed by quantitative reverse transcription-(RT)-PCR in both axenic VSP H7-type trophozoites and subvariants obtained after negative selection of GS/M-83-H7 trophozoites by treatment with a cytotoxic, VSP H7-specific monoclonal antibody. Our investigation was not restricted to the assessment of the sense vsp transcript levels but also included an approach aimed at the detection of complementary antisense vsp transcripts within the two trophozoite populations. We found that sense vsp H7 RNA predominated in VSP H7-type trophozoites while sense RNA from only one (vsp IVg) of 8 subvariant vsp genes totally analysed predominated in subvariant-type trophozoites. Interestingly, the two trophozoite populations exhibited a similar relative distribution regarding the vsp H7 and vsp IVg antisense RNA molecules. An analogous sense versus antisense RNA pattern was also observed when the transcripts of gene cwp 1 (encoding cyst wall protein 1) were investigated. Here, both types of RNA molecules only appeared after cwp 1 had been induced through in vitro encystation of the parasite. These findings for the first time demonstrated that giardial antisense RNA production did not occur in a constitutive manner but was directly linked to complementary sense RNA production after activation of the respective gene systems.

In vivo killing of Giardia trophozoites harbouring bacterial endosymbionts by intestinal Paneth cells: an ultrastructural study

To date Paneth cells have not previously been reported to kill Giardia trophozoites and other protozoa in vivo. Here we report the first evidence for in vivo killing of Giardia trophozoites by intestinal Paneth cells. Transmission electron microscopic (TEM) examination of duodenal specimens taken from naturally infected mice revealed that only Giardia trophozoites harbouring peripheral bacterial endosymbionts were destroyed and lysed in the vicinity of the activated Paneth cells. Additionally, intestinal epithelium was more affected by Giardia harbouring bacterial endosymbionts than Giardia with no endosymbionts. Our findings imply that the bacterial endosymbionts within Giardia trophozoites have a role in both host protective and pathological mechanisms, probably through altering the trophozoite antigencity. These observations might shed light on the diversity in infectivity and host specificity of Giardia species.

Lactobacillus johnsonii La1 antagonizes Giardia intestinalis in vivo

This study describes the in vivo activity of Lactobacillus johnsonii La1 (NCC533) in Giardia intestinalis-infected gerbils (Meriones unguiculatus). Daily administration of lactobacilli in the drinking water from 7 days before inoculation with Giardia trophozoites efficiently prevented G. intestinalis strain WB clone C6 from infecting gerbils. More specifically, shedding of fecal Giardia antigens (GSA65 protein) was diminished in the La1-treated group, and resolution of infection was observed by 21 days postinoculation. Histology and analysis of enzymatic markers of microvillus membrane integrity revealed that probiotic administration also protected against parasite-induced mucosal damage. In addition, a cellular response to Giardia antigens was stimulated in spleen cells from La1-treated gerbils. Results show for the first time the antigiardial effect of probiotic lactobacilli in vivo and provide further insight into the antagonistic properties of lactic acid bacteria against protozoa involved in intestinal infections.

Mast cell-dependent control of Giardia lamblia infections in mice

Mast cells are important for protective immunity to intestinal helminth infections and as mediators of allergic disease. Their role in protozoan infections is less well described. We have therefore analyzed mast cell responses and parasite control in mice infected with the protozoan Giardia lamblia. We also measured immunoglobulin A (IgA) responses to the parasite, as IgA can have a protective role in this model. c-kit w/wv mice failed to make parasite-specific IgA, mount a mast cell response, or eliminate the infection. Anti-c-kit-treated C57BL/6 mice had normal IgA responses, lacked mast cell responses, had reduced interleukin-6 (IL-6) mRNA in the small intestine, and failed to control the infection within 10 days. IL-9-deficient mice had a significant but reduced mast cell response and still controlled the infection within 2 weeks. Interestingly, IL-6-deficient mice had enhanced mast cell responses yet failed to rapidly control the infection. However, prevention of mast cell responses in IL-6-deficient mice by anti-c-kit treatment did not lead to parasite elimination. Both IL-6- and IL-9-deficient mice had normal IgA production. IL-6-deficient mice had significant serum levels of mast cell mediators, histamine and mast cell protease 1, following infection. Together, these results show that mast cells are important for the rapid control of Giardia infections in mice. Furthermore, they show that IL-6 is not necessary for these mast cell responses. Instead, they suggest that mast cell production of IL-6 appears to be important for control of this infection.

Human giardiasis as an etiology of skin allergy: the role of adhesion molecules and interleukin-6

The role of adhesion molecules; the intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) as mediators in development of skin allergy caused by giardiasis and the controlling role of the cytokine interleukin (IL)-6 over these adhesion molecules were studied. The work included 25 symptomatic giardiasis patients with skin allergy manifested by diffuse urticaria, pruritus, wheal and erythema, and had positive serum anti-Giardia immunoglobulin (Ig) E measured as mean optical density (OD) value by enzyme linked immunosorbent assay (ELISA), employed as an evidence of allergic sensitization (G.I). They were compared with 30 symptomatic giardiasis patients (G.II) and 20 apparently healthy control subjects (G.III), both latter groups had negative serum anti-Giardia IgE. The mean OD value of anti-Giardia IgE was significantly increased in G.I (P < 0.01) & insignificantly different in GIII (P > 0.05) compared with G.III. Serum levels of soluble forms of adhesion molecules; sICAM-1 & sVCAM-1, and IL-6 were determined by ELISA. sICAM-1 & sVCAM-1 serum levels were significantly increased (P < 0.001) in G.I compared with G.III and showed insignificant difference (P > 0.05) between Gs. II & III. Serum IL-6 significantly increased in G.I (P < 0.001) & G.II (P < 0.05) compared with G.III, and was significantly higher (P < 0.001) in G.I than G.II. Serum IL-6 correlated positively with serum sICAM-1 (P < 0.01) and sVCAM-1 (P < 0.001) in G.I. The results are discussed.

Genotyping of human giardiasis in relation to anti-Giardia secretory IgA and mucosal histopathology

Comparative study between the prevalence of pathological grading and Giardia genotypes revealed that, in patients infected with Giardia group I and II, out of patients having Giardia genotype I the prevalence of grade 0 was 13.16%, grade I was 21.05%, grade II was 47.37%, grade III was 13.16% and grade IV was 2.26% in comparison to 0%, 30.77%, 46.15%, 7.69% and 15.38% in genotype II (13 patients) and 10%, 40%, 20%, 20% and 10% in group III (10 patients) also in relation to 25%, 43.75%, 18.75%, 6.25% and 6.25% in mixed genotype infections group (16 patients) and 25%, 25%, 35.71%, 10.71% and 3.57% in undetermined infection group (28 patients) for grade 0, I, II, III & IV pathology respectively. There was no statistically significant difference regarding the prevalence of pathological grading in different Giardia genotypes in Gs I & II (P > 0.05). The mean OD of anti-Giardia secretory IgA in relation to Giardia genotypes in patients infected with Giardia Gs I & II was significantly different in the mean OD values of anti-Giardia secretory IgA in patients with different Giardia genotypes which were 1.091 +/- 0.377, 1.079 +/- 0.474, 1.524 +/- 0.503, 1.292 +/- 0.472 & 1.004 +/- 0.31 groups of genotype I, II, III, mixed genotypes infection and undetermined infection group respecttively (P > 0.05), being more increased in patients infected with Giardia genotype III and in mixed genotype infection.

Role of CD8+ and CD4+ T lymphocytes in jejunal mucosal injury during murine giardiasis

T-cell-mediated pathogenesis has been documented in various idiopathic and microbially induced intestinal disorders. Diffuse microvillous shortening seen in giardiasis is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water. Other mucosal changes include crypt hyperplasia and increased numbers of intraepithelial lymphocytes (IEL). A recent report using an athymic mouse model of infection showed that these epithelial injuries were dependent on T cells. The aim of the present study was to identify which subset of superior mesenteric lymph node (SMLN) T cells were responsible for mucosal alterations in giardiasis. CD4+ and CD8+ T cells, as well as whole lymphocyte populations, were isolated from SMLN of Giardia muris-infected mice for adoptive transfer. Jejunal segments of recipient mice were assessed for brush border ultrastructure, sucrase activity, crypt/villus ratio, and IEL numbers. Mice that received enriched CD8+ and whole SMLN lymphocytes, but not CD4+ T cells, from infected donors showed diffuse shortening of microvilli, loss of brush border surface area, impaired sucrase activity, and increased crypt/villus ratios compared to respective controls. Transfer of whole SMLN lymphocytes, as well as enriched CD4+ or CD8+ T cells, from infected donors led to increased IEL numbers in the recipient jejunum. The findings indicate that loss of intestinal brush border surface area, reduced disaccharidase activities, and increased crypt/villus ratios in giardiasis are mediated by CD8+ T cells, whereas both CD8+ and CD4+ SMLN T cells regulate the influx of IEL.

A 63 kDa VSP9B10A-like protein expressed in a C-8 Giardia duodenalis Mexican clone

BACKGROUND

It is well documented that Giardia duodenalis undergoes surface antigenic variation both in vivo and in vitro. Proteins involved have been characterized and referred to as VSP (variable surface protein).

METHODS

Two cloned cDNA inserts of 0.45 and 1.95 kb were obtained from G. duodenalis expression library and sequenced. Comparison sequence analyses were made against Genbank. PCR analysis was performed on G. duodenalis isolates to identify isolates bearing genes encoding such a peptide. Specific antiserum was prepared against 450-bp encoded peptide and tested by Western blot, immunofluorescence, and inhibition of adhesion of G. duodenalis to target cells.

RESULTS

We cloned and characterized a G. duodenalis 450-bp DNA fragment; its DNA sequence analysis revealed that this fragment displayed 99% identity with vsp9B10A gene. Predicted amino acid sequence for this fragment also had significant (99%) identity to VSP9B10A. A second 1.95-kb insert, which encompassed the 450-bp cDNA fragment, was also isolated; its DNA and amino acid sequence displayed 99.5% identity with vsp9B10A gene and 99.2% with the corresponding inferred protein, respectively. This inferred protein contained 24 Cys-X-X-Cys motifs and long ORF of 642 aminoacids. PCR analysis showed that DNA sequence encoding a fragment of this gene was present in P1, CIEA:0487:2-C-8 clone and in INP:180800-B2 G. duodenalis human isolates, while it was absent in sheep isolate of G. duodenalis INP:150593-J10.

CONCLUSIONS

Immunofluorescence analysis using antibodies raised against the peptide encoded by 450-bp fragment showed that expression of this epitope varies on trophozoite surface of the C-8 Mexican clone and is involved in parasite adhesion to target epithelial cells.

Systemic and mucosal responses to oral administration of excretory and secretory antigens from Giardia intestinalis

Giardia, a flagellated protozoan that infects the upper small intestine of its vertebrate host, is the most common parasitic protist responsible for diarrhea worldwide. Molecules released by the parasite, particularly excretory and secretory antigens, seemed to be associated with pathogenesis as well as with the expression of Giardia virulence. In the present work, we examined the effect of oral administration of Giardia intestinalis excretory and secretory antigens on systemic and local antibody response as well as on mucosal injuries in BALB/c mice. Significant titers of serum-specific immunoglobulin G1 (IgG1) and specific IgG2a were observed. Systemic and mucosal specific IgA antibodies were also recorded. A transient production of serum-specific IgE antibody and high total IgE levels were also detected, suggesting the presence in excretory and secretory proteins of factors promoting a specific IgE response. The sera of excretory and secretory antigen-treated mice recognized proteins of 50 and 58 kDa as well as electrophoretic bands of 15, 63, and 72 kDa that could support a proteinase activity. The in vitro exposure of G. intestinalis trophozoites to heat-inactivated sera from mice orally inoculated with excretory and secretory antigens induced a decrease of growth, revealing a complement-independent inhibitory activity of specific serum antibodies. Furthermore, histological evaluation performed on the small and large intestines revealed moderate to acute histological changes comparable to those observed in natural or experimental Giardia infection characterized by eosinophilic infiltration, hypercellularity, and enterocytic desquamation. The present results suggested that Giardia excretory and secretory antigens stimulate a preferential Th2 response, which is probably involved in the intestinal alterations associated with giardiasis.

Secretory IgA antibody responses in Venezuelan children infected with Giardia duodenalis

We standardized and evaluated an ELISA technique for the detection of total and specific anti-Giardia duodenalis secretory IgA antibodies (sIgA). Samples of saliva and serum of 161 Venezuelan schoolchildren were analysed. After stool examination, 66 children were diagnosed to be infected with Giardia duodenalis, 22 with other protozoa, and 73 non-parasitized. The mean (+ 2 SD) values of secretory IgA in the non-parasitized group was considered as the criterion of positivity. The levels of total and specific anti-Giardia sIgA were significantly higher in children with Giardia compared with the group with other protozoa (p < 0.01) and the non-parasitized group (p < 0.001). The ELISA technique developed showed values of sensitivity and specificity of 74 and 94 per cent, respectively, a predictive value of 92 per cent for positive samples and 80 per cent for negative samples. Specific anti-Giardia IgA serum levels showed a low sensitivity (57 per cent) and a predictive value for negative samples (53 per cent). Our results suggest that secretory anti-Giardia IgA levels measured in saliva samples may reflect local intestinal IgA responses elicited by these parasites. Thus, determinations of the levels of sIgA anti-Giardia could be a useful diagnostic tool for giardiasis in children.

Paneth cell granule depletion in the human small intestine under infective and nutritional stress

Paneth cells are important contributors to the intestinal antimicrobial barrier through synthesis and release of antimicrobial peptides and proteins. Animal studies indicate that Paneth cell numbers, location and granule morphology are altered by infection and zinc status. We examined human tissue to determine whether Paneth cell numbers, distribution or granule morphology are altered in infective, inflammatory and nutritional disorders. Archival sections from infective disorders (giardiasis, cryptosporidiosis, HIV, helminth infection) were compared with active inflammatory conditions (coeliac, Crohn's and graft-versus-host diseases) and histologically normal tissues. A subset of tissues was studied by electron microscopy and TUNEL staining for apoptosis. Human defensin-5 (HD5) peptide and mRNA was analysed by immunohistochemistry, in situ hybridization and quantitative reverse transcription polymerase chain reaction. Sections from a tropical population cohort study were then analysed to determine the relationship of granule depletion to infection, nutritional status and plasma zinc concentration. In HIV-related cryptosporidiosis, but not other disorders, Paneth cells were reduced in number and markedly depleted of granules. Paneth cell granule depletion was associated with reduced HD5 immunoreactivity, but this was not due to apoptosis and there was no reduction in mRNA transcripts. In the tropical population studied, depletion of granules was associated with reduced body mass index, reduced plasma zinc levels and HIV infection. Paneth cell granules in human small intestine may be depleted in response to infective and nutritional stress. We postulate that this is one mechanism through which zinc status influences host susceptibility to intestinal infection.

Cellular immune response in giardiasis

There was statistically significant difference between all groups of giardiasis patients regarding the grade of CD4 lymphocyte infiltration (P<0.001), being more marked in symptomatic group. The prevalence of flatulence, anorexia and vomiting were more frequent in patients with heavy CD4 lymphocyte infiltration in duodenum. A high statistical significant increase was in the mean OD values of anti-Giardia duodenal secretory IgA in patients with marked CD4 infiltration in duodenum. But, a statistical insignificant difference in mean OD values of anti-Giardia total serum Ig in patients with different grades of CD4 infiltration in symptomatic group. There was statistically significant increased in the mean OD values of anti-Giardia total serum Ig in patients with marked intraepithelial CD8 lymphocyte Infiltration in the duodenum In the asymptomatic group, there was statistically insignificant difference in the mean OD values of anti-Giardia total serum Ig in patients with different grade of intra-epithelial CD8 infiltration in symptomatic group. There is statistically significant increased in the mean OD values of anti-Giardia total serum Ig in patients with marked intra-epithelial CD8 lymphocyte infiltration in the duodenum regarding immunohistochemical staining of Giardia antigen in duodenal biopsies. All the 61 symptomatic giardiasis patients revealed Giardia antigen stains in their duodenal biopsies with a sensitivity of 100% while asymptomatic group a sensitivity of 93.181%. None in the controls showed positive Giardia antigen in the duodenal biopsies with 100% specificity.

Oral immunization of BALB/c mice with Giardia duodenalis recombinant cyst wall protein inhibits shedding of cysts

The process of encystation is a key step in the Giardia duodenalis life cycle that allows this intestinal protozoan to survive between hosts during person-to-person, animal-to-person, waterborne, or food-borne transmission. The release of cysts from infected persons and animals is the main contributing factor to contamination of the environment. Genes coding for cyst wall proteins (CWPs), which could be used for developing a transmission-blocking vaccine, have been cloned. Since the immunogenicity of recombinant Giardia CWP is unknown, we have investigated the immunogenicity of recombinant CWP2 (rCWP2) and its efficacy in interfering with the phenomenon of encystation taking place in the small bowels of BALB/c mice vaccinated with the recombinant protein. Here we report that the immunization of BALB/c mice with rCWP2 stimulated the immune system in a manner comparable to that for a live infection with Giardia muris cysts. Fecal and serum anti-rCWP2 immunoglobulin A (IgA) antibodies were detected in the immunized mice. In addition, anti-rCWP2 IgG1 and IgG2a antibodies were detected in the serum. mRNAs coding for Th1 and Th2 types of cytokines were detected in spleen and Peyer's patch cells from immunized mice. When the vaccinated mice were challenged with live cysts, the animals shed fewer cysts. We conclude that rCWP2 is a possible candidate antigen for the development of a transmission-blocking vaccine.

Characterisation of alpha-1 giardin: an immunodominant Giardia lamblia annexin with glycosaminoglycan-binding activity

Alpha-1 giardin is an immunodominant protein in the intestinal protozoan parasite Giardia lamblia. The Triage((R)) parasite panel, used to detect copro-antigens in stool from giardiasis patients, reacts with an epitope between amino acids 160 and 200 in alpha-1 giardin. This region of the protein is also highly immunogenic during human infections. Alpha-1 giardin is related to annexins and like many other annexins it was shown to be plasma membrane associated. Immunoelectron and immunofluorescence microscopy revealed that some alpha-1 giardin are displayed on the surface of recently excysted cells. Recombinant alpha-1 giardin displayed a Ca(2+)-dependent binding to glycosaminoglycans (GAGs), in particular heparan sulphate, a common GAG in the intestinal tract. Recombinant alpha-1 giardin bound to thin sections of human small intestine, a binding which could be inhibited by adding increasing concentrations of sulphated sugars. A surface associated trypsin activated Giardia lectin (taglin) has been suggested to be important for G. lamblia attachment. In this study we show that a monoclonal antibody that inhibits taglin recognises alpha-1 and alpha-2 giardin. Thus, alpha-1 giardin is a highly immunoreactive GAG-binding protein, which may play a key role in the parasite-host interaction. Our results further show a conserved function of annexins from lower to higher eukaryotes.

Identification of immunoreactive proteins during acute human giardiasis

The protozoan Giardia lamblia is a major cause of parasite-induced diarrhea in humans. Humoral immunity has been shown to be important for clearance of the infection, but only a few antigens have been identified. In this study, we focused on the immunoreactivity of nonvariant antigens. Serum samples from 93 patients with acute giardiasis who were infected during a waterborne outbreak in a nonendemic country were screened on 1-dimensional Western blots. Representative serum samples that reacted strongly with proteins of different molecular weights were further analyzed on 2-dimensional Western blots. Sixteen immunoreactive proteins were identified using mass spectrometry analysis, among them variable surface proteins, alpha-giardins, arginine deiminase, ornithine carbamoyl transferase, and fructose-1,6-bisphosphate aldolase. Several of the identified proteins were immunoreactive in recombinant form, and they may be important in the development of new diagnostic tools and vaccines.

[The phagocytic activity of blood platelets in different parasitic diseases]

Blood platelets take part in immune reactions of the organism, especially in anti-parasitic immunity. We conducted the phagocytic activity of blood platelets. This experiments were done on 40 patients infected with Giardia intestinalis (26), Ascaris lumbricoides (8), Entamoeba histolytica/Entamoeba dispar (6). Blood for analysis was collected thrice, before treatment (P1), after two weeks (P2), and after two months treatment with anti-parasitic drugs (P3). Control group consisted of 32 healthy people. The evaluation of platelet phagocytic activity revealed that the mean percentage of phagocytizing platelets in patients was 2.87 (P1), 2.94 (P2), 2.86 (P3), being significantly lower in controls (mean 2.15), the difference was statistically significant (p < 0.05). No statistically significant difference was found in the mean phagocytic index between patients (P1, P2, P3) and controls. Our general conclusion is--parasites are able to stimulate phagocytic activity of blood platelets.

Mucosal defences against Giardia

Giardia lamblia (syn. G. duodenalis or G. intestinalis), the causative agent of giardiasis, is one of the most common causes worldwide of intestinal infections in humans. Symptomatic infection is characterized by diarrhoea, epigastric pain, nausea, vomiting, and weight loss, yet many infections are asymptomatic. The protozoan, unicellular parasite resides in the lumen and attaches to the epithelium and overlying mucus layers but does not invade the mucosa and causes little or no mucosal inflammation. Giardiasis is normally transient, indicating the existence of effective host defences, although re-infections can occur, which may be related to differences in infecting parasites and/or incomplete immune protection. Mucosal defences against Giardia must act in the small intestinal lumen in the absence of induction by classical inflammatory mediators. Secretory IgA antibodies have a central role in anti-giardial defence. B cell-independent mechanisms also exist and can contribute to eradication of the parasite, although their identity and physiological importance are poorly understood currently. Possible candidates are nitric oxide, antimicrobial peptides such as Paneth cell alpha-defensins, and lactoferrin. Elucidation of the key anti-giardial effector mechanisms will be important for selecting the best adjuvants in the rational development of vaccination strategies against Giardia.

Passive immunity and serological immune response in dairy calves associated with natural Giardia duodenalis infections

In a previous study, Giardia infection patterns were studied in newborn dairy calves over a 4-month period. Chronic Giardia infections were observed in all calves with initial cyst excretion occurring at approximately 1 month of age. In the work presented here, the passive immunity and serological immune response associated with these Giardia infections were examined. Colostrum and milk samples were collected from the dams of these calves, and monthly serum samples were collected from each calf. The colostrum, milk and sera samples were analyzed by ELISA and Western blot for the presence of anti-Giardia IgG antibodies. In addition, the in vitro anti-Giardia activity of milk and colostrum was examined using a miniculture adherence assay. When examined by ELISA, mean anti-Giardia antibody titres were found to be significantly higher in colostrum compared to milk. The monthly mean serum antibody titres in the calves were not found to differ significantly at any time point during the study. Western blot analysis revealed that colostrum from the dams reacted strongly with many different Giardia antigens between 205 and 7.5kDa, while milk reacted with few antigens in the same size range. Sera collected from the calves when 30 and 60 days of age reacted with few Giardia antigens, but as the calves aged, IgG antibodies in their sera began to react with antigens of 21, 50, 65, 73 and 79kDa. The miniculture adherence assay demonstrated that colostrum had significantly more anti-Giardia activity in vitro compared to milk. These results suggest that the calves in this dairy did not mount a significant humoral immune response against Giardia following infection. However, colostrum contained a high level of anti-Giardia antibodies and exhibited anti-Giardia activity in vitro. Therefore, colostrum may have the potential to provide initial protection against Giardia infections in calves, but the lack of a strong, specific humoral immune response by these calves could account for the high prevalence and chronic duration of the infections.

Interleukin-6-deficient mice are highly susceptible to Giardia lamblia infection but exhibit normal intestinal immunoglobulin A responses against the parasite

In the present study, interleukin-6 (IL-6)-deficient mice were infected with Giardia lamblia clone GS/M-83-H7. Murine IL-6 deficiency did not affect the synthesis of parasite-specific intestinal immunoglobulin A. However, in contrast to wild-type mice, IL-6-deficient animals were not able to control the acute phase of parasite infection. Reverse transcription-PCR-based quantitation of cytokine mRNA levels in peripheral lymph node cells exhibited a short-term up-regulation of IL-4 expression in IL-6-deficient mice that seemed to be associated with failure in controlling the parasite population. This observation suggests a further elucidation of IL-4-dependent, Th2-type regulatory processes regarding their potential to influence the course of G. lamblia infection in the experimental murine host.

Role of interleukin-6 in the control of acute and chronic Giardia lamblia infections in mice

In this study, we investigated the role of interleukin-6 (IL-6) in Giardia lamblia infections in mice. Elevated IL-6 expression was found in wild-type mice 15 days postinfection. Furthermore, IL-6-deficient mice controlled infections only slowly although normal immunoglobulin A production was observed. Thus, IL-6 is necessary for early control of acute G. lamblia infections.

[Eosinophil cationic protein in serum of children with food allergy]

The evaluation of eosinophil cationic protein (ECP) concentration--one of late allergy reaction markers was performed in serum of children with food allergy and children with food allergy and H. pylori or Giardia lamblia infection of the gastrointestinal tract. The ECP values were referred to the characteristics of histopathological changes in gastric mucosa and to the values of cytokines (IL-4, IL-5, IL-8) determined in biopsy specimens of gastric mucosa from these patients. The studies indicate that the exclusive evaluation of ECP concentration in serum does not reflect unequivocally the severity of pathological changes of gastric mucosa in children with food allergy.

Detection of Giardia duodenalis antigen in coprolites using a commercially available enzyme-linked immunosorbent assay

The objective of this experiment was to assess the utility of a commercially available enzyme-linked immunosorbent assay (ELISA) kit for diagnosis of giardiasis in archaeological human remains. The kit, a monoclonal antibody assay, is used to detect the presence of Giardia-specific antigen 65 (GSA65) in human faeces. We utilized the assay in ancient faecal material. The material included desiccated faeces found in mummies or in archaeological sites, and sediments from latrines. A total of 83 specimens, previously examined microscopically for parasites, were examined. The ELISA detected 3 positive samples, dated to about 1200 AD, 1600 AD and 1700 AD. The ELISA was superior to direct observation. It was possible to identify G. duodenalis cysts by direct microscopy in only one of these samples. The results did not show cross-reactivity between this protozoan and helminths. The use of ELISA to detect G. duodenalis coproantigen could help the diagnosis of giardiasis in ancient human remains.

[Beta-thromboglobulin concentration in chosen parasitic diseases]

Blood platelets are active elements in the body defense mechanisms, e.g. in antiparasitic immunology. A platelet stimulation may result from a direct contact with a parasite, increased IgG and/or IgE concentrations, the presence of complement, CRP or lymphokins. This study was aimed at establishing whether a parasitic infection could induce a platelet activation. The study involved 35 patients (30 patients were infected with Giardia intestinalis and 5 patients with Echinococcus granulosus). Blood for analysis was collected twice--before treatment (A1) and after treatment (A2). The concentrations of beta-thromboglobulin were assayed by means of the set of ASSERA-CHROM, according to the immuno-enzymatic method with labelled antibodies. The platelet count was determined with a haematologic analyser. Although platelets do not get into a direct contact with the parasite, an increase in the concentration of b-thromboglobulin is observed, and it may indicate the involvement of platelets in the parasitic disease.

Intestinal infection with Giardia spp. reduces epithelial barrier function in a myosin light chain kinase-dependent fashion

BACKGROUND & AIMS

Giardiasis causes malabsorptive diarrhea, and symptoms can be present in the absence of any significant morphologic injury to the intestinal mucosa. The effects of giardiasis on epithelial permeability in vivo remain unknown, and the role of T cells and myosin light chain kinase (MLCK) in altered intestinal barrier function is unclear. This study was conducted to determine whether Giardia spp. alters intestinal permeability in vivo, to assess whether these abnormalities are dependent on T cells, and to assess the role of MLCK in altered epithelial barrier function.

METHODS

Immunocompetent and isogenic athymic mice were inoculated with axenic Giardia muris trophozoites or sterile vehicle (control), then assessed for trophozoite colonization and gastrointestinal permeability. Mechanistic studies using nontransformed human duodenal epithelial monolayers (SCBN) determined the effects of Giardia on myosin light chain (MLC) phosphorylation, transepithelial fluorescein isothiocyanate-dextran fluxes, cytoskeletal F-actin, tight junctional zonula occludens-1 (ZO-1), and MLCK.

RESULTS

Giardia infection caused a significant increase in small intestinal, but not gastric or colonic, permeability that correlated with trophozoite colonization in both immunocompetent and athymic mice. In vitro, Giardia increased permeability and phosphorylation of MLC and reorganized F-actin and ZO-1. These alterations were abolished with an MLCK inhibitor.

CONCLUSIONS

Disruption of small intestinal barrier function is T cell independent, disappears on parasite clearance, and correlates with reorganization of cytoskeletal F-actin and tight junctional ZO-1 in an MLCK-dependent fashion.

Surface antigenic variation in Giardia lamblia

Giardia lamblia, a common intestinal dwelling protozoan and a cause of diarrhoea in humans and animals world-wide, undergoes surface antigenic variation. The variant-specific surface proteins (VSPs) are a family of related, highly unusual proteins that cover the entire surface of the parasite. VSPs are cysteine-rich proteins containing many CXXC motifs, one or two GGCY motifs, a conserved hydrophobic tail and a Zn finger motif. The biological role(s) of VSPs is unclear. As VSPs are resistant to the effects of intestinal proteases, they likely allow the organism to survive in the protease-rich small intestine. Although immune escape is commonly mentioned as the reason antigenic variation occurs, VSP expression changes in vivo even in the absence of an adaptive immune system suggesting the biological role of antigenic variation is more complex. The molecular mechanisms involved in antigenic variation are not known but appear to differ from those known to occur in other protozoa.

[Intestinal giardiasis. Mini-review]

Giardia intestinalis is a common parasite in our country and the rest of the world and is responsible for several clinical disturbances that include dysentery type diarrheas, recurrent abdominal pain, duodenitis, jejunitis, cholecystitis and in some cases toxemias and convulsions. In this paper we review recent concepts of intestinal giardiasis, considering the basic aspects of the biology and physiology of Giardia intestinalis, its morphology and its relationship the parasite pathogenicity. We detail the physiopathological mechanisms responsible for the different clinic manifestations of giardiasis, the specific laboratory and endoscopic methods of diagnosis and the most recent advances in the treatment and prophylaxis of this disease.

Detection of anti-Giardia lamblia serum antibody among children of day care centers

OBJECTIVES

To detect anti-Giardia lamblia serum antibodies in healthy children attending public day care centers and to assess serological tests as tools for estimating the prevalence of G. lamblia in endemic areas.

METHODS

Three separate stool specimens and filter paper blood samples were collected from 147 children ranging from 0 to 6 years old. Each stool sample was processed using spontaneous sedimentation and zinc sulfate flotation methods. Blood samples were tested by indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assay (ELISA) for Giardia IgG.

RESULTS AND CONCLUSIONS

Of 147 individuals tested, 93 (63.3%) showed Giardia cysts in their feces. Using IIF and ELISA, serum antibodies were detected in 93 (63.3%) and 100 (68%) samples, respectively. Sensitivity of IIF and ELISA was 82% and 72%, respectively. However, ELISA revealed to be less specific (39%) than IIF (70%). IIF also showed a higher concordance with microscopic examination than ELISA.

Central importance of immunoglobulin A in host defense against Giardia spp

The protozoan pathogen Giardia is an important cause of parasitic diarrheal disease worldwide. It colonizes the lumen of the small intestine, suggesting that effective host defenses must act luminally. Immunoglobulin A (IgA) antibodies are presumed to be important for controlling Giardia infection, but direct evidence for this function is lacking. B-cell-independent effector mechanisms also exist and may be equally important for antigiardial host defense. To determine the importance of the immunoglobulin isotypes that are transported into the intestinal lumen, IgA and IgM, for antigiardial host defense, we infected gene-targeted mice lacking IgA-expressing B-cells, IgM-secreting B-cells, or all B-cells as controls with Giardia muris or Giardia lamblia GS/M-83-H7. We found that IgA-deficient mice could not eradicate either G. muris or G. lamblia infection, demonstrating that IgA is required for their clearance. Furthermore, although neither B-cell-deficient nor IgA-deficient mice could clear G. muris infections, IgA-deficient mice controlled infection significantly better than B-cell-deficient mice, suggesting the existence of B-cell-dependent but IgA-independent antigiardial defenses. In contrast, mice deficient for secreted IgM antibodies cleared G. muris infection normally, indicating that they have no unique functions in antigiardial host defense. These data, together with the finding that B-cell-deficient mice have some, albeit limited, residual capacity to control G. muris infection, show that IgA-dependent host defenses are central for eradicating Giardia spp. Moreover, B-cell-dependent but IgA-independent and B-cell-independent antigiardial host defenses exist but are less important for controlling infection.

Advances and prospects for subunit vaccines against protozoa of veterinary importance

Protozoa are responsible for considerable morbidity and mortality in domestic and companion animals. Preventing infection may involve deliberate exposure to virulent or attenuated parasites so that immunity to natural infection is established early in life. This is the basis for vaccines against theilerosis and avian coccidiosis. Vaccination may not be effective or practical with diseases, such as cryptosporidiosis, that primarily afflict the immune-compromised or individuals with an incompletely developed immune system. Strategies for combating these diseases often rely on passive immunotherapy using serum or colostrums containing antibodies to parasite surface proteins. Subunit vaccines offer an attractive alternative to virulent or attenuated parasites for several reasons. These include the use of bacteria or lower eukaryotes to produce recombinant proteins in batch culture, the relative stability of recombinant proteins compared to live parasites, and the flexibility to incorporate only those antigens that elicit "protective" immune responses. Although subunit vaccines offer many theoretical advantages, our lack of understanding of immune mechanisms to primary and secondary infection and the capacity of many protozoa to evade host immunity remain obstacles to developing effective vaccines. This review examines the progress made on developing recombinant proteins of Eimeria, Giardia, Cryptosporidium, Toxoplasma, Neospora, Trypanosoma, Babesia, and Theileria and attempts to use these antigens for vaccinating animals against the associated diseases.

Identification and characterization of an excretory-secretory product from Giardia lamblia

A 58 kDa excretory-secretory product (ESP) of Giardia lamblia has been characterized. The ESP was purified over 508-fold by a combination of ammonium sulphate precipitation and sequential chromatography on affinity matrix and a gel filtration column. The homogeneity of the purified protein was established by sodium dodecyl sulphate polyacrylamide gel electrophoresis (Mr, 58 kDa) and analytical isoelectrophoresis (pI 4.75). The purified protein was recognized by the pooled sera of G. lamblia-positive patients as well as an antiserum raised against crude Giardia extract, thus indicating it to be an immunodominant parasite product. The ESP was found to agglutinate rabbit erythrocytes. The haemagglutinating activity of this protein was inhibited strongly by thyroglobulin, fetuin, asialofetuin and monosialoganglioside but not by simple sugars. The purified protein was characterized immunochemically and was found to be heat stable as well as protease sensitive. Lectin-binding studies of the purified ESP and its sensitivity to periodic-acid silver staining as well as to metaperiodate treatment clearly indicated its glycoprotein nature. The major localization site of the ESP was found to be on the surface of the parasite as revealed by flow cytometric analysis. Further, this glycoprotein induced fluid accumulation in ligated rabbit ileal loops and revealed a positive skin permeability reaction in the rabbit.

vsp gene expression by Giardia lamblia clone GS/M-83-H7 during antigenic variation in vivo and in vitro

Giardia lamblia infections are associated with antigenic variation of the parasite, which is generated by a continuous change of the variant-specific surface proteins (VSPs). Many investigations on the process of antigenic variation were based on the use of G. lamblia clone GS/M-83-H7, which expresses VSP H7 as its major surface antigen. In the present study, mice were infected with the aforementioned clonal line to investigate vsp gene expression during the complex process of antigenic variation of the parasite. Trophozoites collected from the intestines of individual animals at different time points postinfection (p.i.) were analyzed directly for their vsp gene expression patterns, i.e., without cultivating the recovered parasites in vitro. Because few trophozoites were recovered at late time points p.i., a combined 5' rapid amplification of cDNA ends-reverse transcription-PCR approach was utilized. This allowed detection and subsequent sequence analysis of vsp gene transcripts upon generation of amplified cDNA analogues. The same PCR approach was applied for analysis of vsp gene expression in variants obtained after negative selection of axenic GS/M-83-H7 trophozoites by treatment with a cytotoxic, VSP H7-specific monoclonal antibody. In an overall view of the entire panel of in vivo- and in vitro-derived parasite populations, expression of 29 different vsp gene sequences could be demonstrated. In vivo antigenic variation of G. lamblia clone GS/M-83-H7 was shown to be a continuous process involving the consecutive appearance of relatively distinct sets of vsp transcripts. During the 42-day infection period investigated, this process activated at least 22 different vsp genes. Comparative molecular analyses of the amino acid level demonstrated that all cDNA segments identified encode structural elements typical of the terminal segment of Giardia VSP. The similarity of most of the GS/M-83-H7 VSP sequences identified in the present study supports previous suggestions that vsp gene diversification in G. lamblia is the result of ancestral gene duplication, mutation, and/or recombination events.

Treatment of giardiasis reverses "active" coeliac disease to "latent" coeliac disease

In patients with coeliac disease, a regression of intestinal damage without a gluten-free diet is a very rare event. We describe a young child with diarrhoea, intestinal mucosa atrophy and positive serum anti-endomysial and anti-tissue transglutaminase (anti-tTG) antibodies during intestinal giardiasis infection. He showed normal intestinal mucosa architecture and negative anti-endomysial and anti-tTG antibodies after his giardiasis was cured, although he continued to assume a normal diet. Re-evaluations on a 6-monthly basis showed that he was symptom free, and all haemato-chemical parameters were within normal limits. Three years after the initial diagnosis, a third intestinal biopsy showed: normal mucosa architecture; an increase in the intra-epithelial CD3+ and gamma/delta+ lymphocyte counts; and immunoglobulin-A anti-endomysial antibody detection in the supernatant of the intestinal mucosa culture incubated with gliadin. An active coeliac disease status, with intestinal mucosa atrophy, may regress to a latent coeliac disease status with normal intestinal mucosa histology after removal of the environmental factors that have presumably precipitated mucosa damage. Serum anti-endomysial and anti-tTG antibody behaviour is not a permanent, life-long feature and this must recommend the repetition of anti-endomysial or anti-tTG antibody assays in the same patient whenever coeliac disease diagnosis is again suspected, irrespective of previous negativity.

Detection of Giardia lamblia and Entamoeba histolytica in stool samples by two enzyme immunoassays

Two commercially produced enzyme immunoassays (EIAs) to detect antigens of Giardia lamblia and Entamoeba histolytica in stool specimens were evaluated. A total of 276 stool specimens were collected from patients who presented with various medical complaints in the outpatient clinic of the Department of Infectious Diseases and Tropical Medicine, University of Munich. Every specimen was examined by conventional microscopy and tested by both EIA kits. When microscopy was used as the reference standard, the EIA kit detecting Giardia lamblia showed a sensitivity of 100% and a specificity of 99.6%. The EIA kit detecting Entamoeba histolytica had a sensitivity of 81.8% and a specificity of 99.2%. Both tests showed no cross-reactivity with other intestinal protozoa. Antigen detection by EIA has the potential to become a valuable tool capable of making stool diagnostics more effective, although it should not be considered as a replacement for microscopic examination, since other potential pathogens could otherwise escape detection.

Successful treatment of metronidazole- and albendazole-resistant giardiasis with nitazoxanide in a patient with acquired immunodeficiency syndrome

A case of metronidazole- and albendazole-resistant giardiasis in a patient with the acquired immunodeficiency syndrome was successfully treated with nitazoxanide (1.5 g twice a day for 30 days). Animal studies and in vitro assays showed that the isolate was resistant to both metronidazole and albendazole and susceptible to nitazoxanide.

Microbes and microbial toxins: paradigms for microbial-mucosal interactions I. Pathophysiological aspects of enteric infections with the lumen-dwelling protozoan pathogen Giardia lamblia

Giardia lamblia is one of the most important causes of waterborne diarrheal disease worldwide, and giardiasis is the most common protozoan infection of the human small intestine. Symptomatic infection is characterized by diarrhea, abdominal pain, and malabsorption, leading to malnutrition and weight loss, particularly in children. The pathogen resides strictly in the lumen of the small intestine, and infection is typically not accompanied by significant mucosal inflammation. Clinical and experimental studies indicate that B cell-dependent host defenses, particularly IgA, are important for controlling and clearing Giardia infection, although B cell-independent mechanisms also contribute to this outcome. In contrast to antigiardial host defenses, much less is known about the pathophysiological mechanisms underlying the clinical symptoms of giardiasis, partly because of the current lack of suitable model systems. In addition to being an important human enteric pathogen, Giardia is an interesting model organism for gaining basic insights into genetic innovations that led to evolution of eukaryotic cells, since it belongs to the earliest diverging eukaryotic lineage known. The completion of the giardial genome project will increase understanding of the basic biology of the protozoan and will help us to better understand host pathogen-interactions as a basis for developing new vaccination and therapeutic strategies.

Jejunal brush border microvillous alterations in Giardia muris-infected mice: role of T lymphocytes and interleukin-6

Intestinal colonization with the protozoan Giardia causes diffuse brush border microvillous alterations and disaccharidase deficiencies, which in turn are responsible for intestinal malabsorption and maldigestion. The role of T cells and/or cytokines in the pathogenesis of Giardia-induced microvillous injury remains unclear. The aim of this study was to assess the role of T cells and interleukin-6 (IL-6) in the brush border pathophysiology of acute murine giardiasis in vivo. Athymic nude (nu(-)/nu(-)) CD-1 mice and isogenic immunocompetent (nu(+)/nu(+)) CD-1 mice (4 weeks old) received an axenic Giardia muris trophozoite inoculum or vehicle (control) via orogastric gavage. Weight gain and food intake were assessed daily. On day 6, segments of jejunum were assessed for parasite load, brush border ultrastructure, IL-6 content, maltase and sucrase activities, villus-crypt architecture, and intraepithelial lymphocyte (IEL) infiltration. Despite similar parasitic loads on day 6, infected immunocompetent animals, but not infected nude mice, showed a diffuse loss of brush border microvillous surface area, which was correlated with a significant reduction in maltase and sucrase activities and a decrease in jejunal IL-6 concentration. In both athymic control and infected mice, jejunal brush border surface area and disaccharidases were high, but levels of tissue IL-6 were low and comparable to the concentration measured in immunocompetent infected animals. In both immunocompetent and nude mice, infection caused a small but significant increase in the numbers of IELs. These findings suggest that the enterocyte brush border injury and malfunction seen in giardiasis is, at least in part, mediated by thymus-derived T lymphocytes and that suppressed jejunal IL-6 does not necessarily accompany microvillous shortening.

Giardia vaccination

Recently, a Giardia vaccine has become commercially available in the USA for prevention of clinical signs of giardiasis and reduction of cyst shedding in dogs and cats. The vaccine is based upon the current state of knowledge of Giardia antigenicity and immunology. Here, Merle Olson, Howard Ceri and Douglas Morck describe studies that led to the development of this vaccine and subsequent efficacy studies. Immunoprophylaxis and immunotherapeutic application of the vaccine are discussed.