Immunopathology of giardiasis

Conclusions G. lamblia continues to be the most common human intestinal protozoan parasite worldwide and still poses a major health problem to infants and young children particularly those in the developing world, to travellers in endemic areas, to immunodeficient individuals and communities exposed to waterborne outbreaks. Despite the availability of effective anti-giardial drugs, it is unlikely that these will eradicate the parasite from the environment particularly as there is increasing evidence that there are domestic and wild animal reservoirs of human infection and that giardiasis is likely to be a zoonosis. Understanding the interaction between Giardia and the host immune system may have important implications not only for the biological control of this parasite in the environment but for improving our understanding of the mechanism(s) by which it causes intestinal disease. Despite the fact that Giardia is essentially a luminal pathogen in the gut it does evoke both systemic and local immune responses. Current evidence emphasises the importance of secretory antibody for clearance of the pathogen, although other cell-mediated effector mechanisms are also likely to be involved. The relationship between serum and secretory antibody responses is not clear, particularly as to whether the presence of anti-Giardia antibodies in serum is in any way indicative of the development of protective immunity. The possibility that cell-mediated immune responses in the mucosa could account for the structural and functional abnormalities sometimes observed in human and experimental giardiasis in animals is an intriguing possibility and awaits further experimental verification. The apparent delay in the development of protective immunity despite continuing exposure to the parasite represents a major challenge for clinicians and biologists. It may relate to there being many antigenically diverse strains of the parasite, possibly due to the ability of a single strain to vary its surface antigens. Passage of the parasite through other mammalian hosts and exposure to bacterial endosymbionts and RNA viruses may also result in phenotypic changes sufficient to nullify a previous immune response to the parasite. These challenging questions await further investigation.     

Epidemiology of giardiasis

Prevalence analysis in the Gard; fluctuations according to seasons, age and sex. Statement a excystation method after passage in a induction solution; observations and excystation rate. Cysts resistance study in exterior middle at various temperature: at dry from -5 degrees C to 40 degrees C, in fresh water from -5 degrees C to 20 degrees C and in sea water at 10 degrees and 20 degrees C. Epidemiologic consequences.     

Gastric giardiasis.

AIMS: To assess the prevalence of gastric giardiasis in patients undergoing upper gastrointestinal endoscopy, and to define the clinicopathological correlates of gastric Giardia lamblia infection. METHODS: Consecutive gastric biopsy specimens (n = 15,023) from 11,085 patients, taken at Feltre City Hospital (north eastern Italy) from January 1986 to December 1991, were histologically and immunocytochemically examined for the occurrence of G lamblia trophozoites. Three gastric biopsy specimens from patients harbouring G lamblia infection, who repeated endoscopy before treatment, were also examined electron microscopically. RESULTS: Forty one patients (0.37% of the population study) harboured gastric giardiasis. All patients underwent upper gastrointestinal endoscopy because of dyspepsia, epigastric pain, or abdominal distension. Only two patients had diarrhoea at the time of investigation. Giardiasis was clinically unsuspected in all cases, although the nine patients who also had duodenal biopsies performed had concomitant intestinal giardiasis. Gastric giardiasis was invariably associated with chronic atrophic gastritis. Intestinal metaplasia of the gastric mucosa and Helicobacter pylori infection were found in 32 and 37 of the 41 patients with gastric giardiasis, respectively. CONCLUSIONS: The invariable association of gastric giardiasis with chronic atrophic gastritis, most often showing intestinal metaplasia and H pylori infection, indicates that a decreased gastric acidity is a prerequisite for localisation of G lamblia to the gastric mucosa. Though its possible role as a gastric pathogen remains to be elucidated, these findings suggest that trophozoites should be carefully searched for when examining gastric biopsy specimens showing chronic atrophic gastritis.     

Molecular epidemiology of giardiasis

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

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.     

Chronic giardiasis of the stomach.

Two cases of chronic giardiasis of the stomach diagnosed from gastric mucosal biopsy specimens are reported. The first case was associated with an acute-on-chronic gastritis and Helicobacter-like organisms, and the second with an adenocarcinoma of the stomach. In both cases the trophozoites had been missed in earlier biopsy specimens. As far as is known this is the first report of giardiasis of the stomach.     

Serum IgE levels in giardiasis

Raised levels of serum immunoglobulin E are found in many parasitic diseases. In order to determine the influence of Giardia lamblia on IgE levels of clinically symptomatic patients, a controlled study was performed. There was no difference between the serum IgE values from Brazilian patients with giardiasis and those from normal Brazilian controls, although in both groups there were many individuals with values higher than the normal range reported from the northern hemisphere.     

Antibodies to cysts of Giardia lamblia in primary giardiasis and in the absence of giardiasis.

The significance of serum antibodies binding to cysts of Giardia lamblia was evaluated by indirect immunofluorescence. Titers of 10 or higher were found in 85.6% of adults, who had probably never had giardiasis. Titers in 118 adults (geometric mean, 29.9) were higher than in 35 children (16.4), and titers in women (42.3) were higher than in men (20.0). Titers in 150 patients with primary giardiasis (80.4) were higher than in control adults, but overlapping precluded serological diagnosis. Titers increased with the duration of infection. Female patients had higher titers (100.5) than did males (66.1), but men who had been infected longer than 45 days had high titers (132). Titers in second serum samples taken from 26 patients 2 weeks to 3 months after successful nitroimidazole treatment (58.1) were lower than before treatment (151.7) but higher than in 118 controls. We conclude that most people have antibodies which cross-react with G. lamblia but which are induced by other immunogens and that primary giardiasis induces protracted systemic antibody responses.     

Quantitative histology in giardiasis.

The Weibel graticule was used to assess quantitatively histological changes in proximal jejunal mucosal biopsies from patients with Giardia lamblia infections. Most had malabsorption. A group of patients who had mild abdominal symptoms but no intestinal infection and normal absorption were the controls. There were significant differences in mean surface area (SA) measurements between patients with giardiasis and severe malabsorption and controls (P less than 0.001) and infected patients with normal absorption (P less than 0.05). SA measurements correlated significantly with D-xylose excretion results (r = 0.55; P less than 0.01) and daily facal fat output (r = -0.61; P less than 0.001). Significant correlations between duration of symptoms and SA measurements (r = 0.43; P less than 0.05) and D-xylose excretion (r = 0.43; P less than 0.05) in giardiasis suggest that histological and functional impairment are maximal soon after infection and resolve in time. Treatment with metronidazole or mepacrine was associated with a significant increase in SA (P less than 0.05) in patients with severe malabsorption but there was little change in SA in a similar group of patients who received tetracycline. The Weibel graticule was found to be useful in assessing the severity of histological changes and in following changes after treatment.     

Electron microscopy in the diagnosis of giardiasis

Biopsy specimens of intestinal mucosa from two patients with malabsorption syndrome were examined with routine light and electron microscopy. Both showed intact intestinal mucosa, but by electron microscopy, the presence of Giardia lamblia in the intervillar spaces was identified. Electron microscopy is useful for the identification of this parasite, since the stool examinations in up to 50% may be negative. The parasites appear in light microscopy as cellular debris and can be easily overlooked, while by electron microscopy the typical morphologic features of the parasite are diagnostic.     

The course of experimental giardiasis in Mongolian gerbil

Parasitology Research - Fifteen Mongolian gerbils were inoculated with 10 × 106 viable trophozoites of Giardia intestinalis. Their faeces were examined daily by flotation method...     

A family cluster of giardiasis with variable treatment responses: refractory giardiasis in a family after a trip to India

Persistence of giardiasis after some of the recommended drugs is occurring with increasing frequency. We describe the follow-up of four members of a family with giardiasis through microscopic observation, immunochromatography and PCRs of tpi and β-giardin genes. Three patients did not respond to tinidazole but they were cured after quinacrine. However, PCR became negative at 2 months after negativization of stools in two patients and after 1 year in one patient. In all cases Giardia assemblage B was characterized with high homology between all isolates. Further studies are needed to determine the value of PCR in the diagnosis of Giardia infections.     

Immunological methods of diagnosis in giardiasis: an overview

The epidemiology and clinical presentations of giardiasis are reviewed to provide a basis of understanding the laboratory aspects of this parasitic infection. Diagnosis is then discussed in light of recent studies that challenge our overall approach to the diagnosis of enteric parasites and demonstrate the need for further evaluation on the basis of cost-effectiveness as well as reliability and clinical practicality. Overall effectiveness as well as the difficulties with present standard diagnostic methods in giardiasis are reviewed. This is followed by a discussion of the more recently developed immunological approaches to diagnosis. The role of these tests in the parasitology laboratory is also discussed.