Serum and intestinal fluid immunoglobulins in patients with giardiasis

Effect of dexamethasone on experimental enteritis produced by Giardia lamblia in a Meriones unguiculatus model

Our aim was to evaluate the impact of immunosuppression on the development of giardiasis. Thirty-six gerbils (4-6 weeks old) were distributed in four groups containing nine animals each: Control (CT); Control-Infected by Giardia lamblia (CTIn), Immunosuppressed (IS), and Immunosuppressed-Infected by G. lamblia (ISIn). Animals in the IS and ISIn groups received intramuscular dexamethasone solution for 25 days. On the 11th day, the animals in the CTIn and ISIn groups were inoculated with G. lamblia. After 14 days of infection, the 25th day of the experiment, all groups were euthanized. Four hours after euthanasia, the intestinal permeability was evaluated and sections of the duodenum and spleen were harvested for morphometric and histopathological analyses. Immunosuppressed groups showed a significant increase in intestinal permeability compared to control and infected groups. Considering that the infection can become chronic in immunosuppressed groups, we should be alert to the possibilities of chronic inflammatory changes, both locally and systemically, due to the loss of the intestinal barrier. Lesions were observed in the duodenal mucosa of the gerbils of the CTIn group, with reduced villi size, crypt hyperplasia, edema, and the presence of inflammatory infiltrate in the lamina propria. In the ISIn group, we observed no inflammation, long and intact villi, and a significant increase in the area of intestinal mucins, despite the large number of trophozoites identified. Our results suggest that exacerbation of the immune response has a direct relationship with the appearance of lesions during enteritis produced by G. lamblia in the assessed model.

Immune response to Giardia duodenalis

The intestinal protozoan Giardia duodenalis is a widespread opportunistic parasite of humans and animals. This parasite inhabits the upper part of the small intestine and has a direct life cycle. After ingestion of cysts, which are the infective stage, the trophozoites emerge from the cysts in the duodenum and attach to the small intestinal mucosa of the host. Since the migration of trophozoites from the lumen of the intestine into surrounding tissues is an unusual occurrence, the immune response to Giardia remains localized. The identification of antigens that play a role in acquired immunity has been difficult because of the occurrence of antigenic variation and because, Giardia being an ubiquitous organism, it is possible that the antigenic profiles of isolates from different geographic areas will vary. Innate-immunity mechanisms play a role in the control and/or severity of the infection. Both humoral and cell-mediated immune responses play a role in acquired immunity, but the mechanisms involved are unknown. A variety of serological assays have been used to detect circulating antibodies in serum. Because of the biological characteristics of the parasite and the lack of suitable antigens, the sensitivity of serological assays remains poor. On the other hand, detection of antigens in feces of infected patients has met with success. Commercial kits are available, and they are reported to be more sensitive than microscopic examination for the detection of giardiasis on a single specimen.

Immune response to Giardia duodenalis

The intestinal protozoan Giardia duodenalis is a widespread opportunistic parasite of humans and animals. This parasite inhabits the upper part of the small intestine and has a direct life cycle. After ingestion of cysts, which are the infective stage, the trophozoites emerge from the cysts in the duodenum and attach to the small intestinal mucosa of the host. Since the migration of trophozoites from the lumen of the intestine into surrounding tissues is an unusual occurrence, the immune response to Giardia remains localized. The identification of antigens that play a role in acquired immunity has been difficult because of the occurrence of antigenic variation and because, Giardia being an ubiquitous organism, it is possible that the antigenic profiles of isolates from different geographic areas will vary. Innate-immunity mechanisms play a role in the control and/or severity of the infection. Both humoral and cell-mediated immune responses play a role in acquired immunity, but the mechanisms involved are unknown. A variety of serological assays have been used to detect circulating antibodies in serum. Because of the biological characteristics of the parasite and the lack of suitable antigens, the sensitivity of serological assays remains poor. On the other hand, detection of antigens in feces of infected patients has met with success. Commercial kits are available, and they are reported to be more sensitive than microscopic examination for the detection of giardiasis on a single specimen.

Secretory immune response to membrane antigens during Giardia lamblia infection in humans

The secretory immune response in humans infected with Giardia lamblia was studied by using saliva samples and a membrane-rich protein fraction. The membrane fraction, studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, showed 24 antigen bands, ranging from 170 to 14 kDa. Saliva samples from giardiasis patients showed a heterogeneous response against the membrane fraction when they were assayed by immunoblotting. Among the antigens recognized by patient saliva samples, those of 170, 105, 92, 66, 32, 29, and 14 kDa stood out. These antigens were not recognized by saliva samples from healthy individuals. They may be of importance in future studies of protection from or diagnosis of G. lamblia infections.

Intestinal coinfection with numerous Giardia trophozoites and Vibrio cholerae in hospitalized children with watery diarrhea

During the recent cholera epidemic which affected Peru and other Latin American countries, fresh stool samples of 100 hospitalized children were assessed February through April 1991. The children had been admitted because of profuse watery diarrhea. The microbiologic study of wet mount preparations showed curved bacteria suspicious for cholera agent and confirmed afterward to be Vibrio cholerae 01 scrotype Inaba. In 30% of such cases, besides the curved bacteria, a strikingly large number of trophozoites of Giardia intestinalis were observed. The same samples studied by permanent stains confirmed the presence of Giardia trophozoites. To our knowledge, the association of Giardia with serious epidemic cholera infection has not been previously described. All patients were admitted because of severe dehydration requiring intravenous fluid replacement, which might suggest a synergistic role for the above-noted coinfection. Adequately designed case-control studies are needed to ascertain the frequency and the pathophysiologic and clinical significance of such an unusual association.

Human giardiasis: correlation of specific secretory IgA levels in duodenal fluid to the severity of disease and infestation by Giardia lamblia

Giardia lamblia specific secretory immunoglobulin A (sIgA) levels in the duodenal fluid of adult giardiasis cases are reported for the first time. The sIgA levels in the study group were found to be significantly higher (p less than 0.01) than in the 20 age- and sex-matched controls comprising cases classified as non-ulcerative dyspepsia who did nor reveal any G. lamblia in their stools and the duodenal fluid. An inverse relationship between the clinical severity of giardiasis and the level of sIgA in the duodenal fluid was noted. Cases with a higher trophozoite load in duodenal aspirate tended to be associated with envanescent G. lamblia-specific antibodies.

Giardiasis

Giardiasis is one of the most common pathogenic intestinal protozoal infections worldwide. Giardia lamblia is the most frequently identified etiologic agent in outbreaks associated with the ingestion of surface water, often due to ineffective filtration or pretreatment. In addition to humans, other sources of infection include beavers, perhaps muskrats, and possibly domestic animals. A low infecting dose (10 to 25 cysts) is reported to be sufficient to produce human infection. Clinical manifestations range from asymptomatic to a transient or persistent acute stage, with steatorrhea, intermittent diarrhea, and weight loss, or to a subacute or chronic stage that can mimic gallbladder or peptic ulcer disease. Diagnosis is usually based on repeated stool examinations but examination of duodenal fluid or biopsy material may also be necessary. Enzyme immunoassay or indirect immunofluorescence methods for direct detection of antigen or whole organisms in clinical specimens have also been developed. These tests are reported to be more sensitive than routine stool examination. Demonstration of serum immunoglobulin M and G antibodies may help differentiate recent from past infection or help detect recurrence in individuals who have been treated previously. Serum immunoglobulin A levels may be a useful indicator of exposure in waterborne outbreaks of diarrhea. Drugs available for treatment within the United States include metronidazole, quinacrine hydrochloride, and furazolidone.

Giardia lamblia

Giardia is the most frequently identified enteric parasite in the United States, but much is not known about host-parasite interaction. Advances using immunodiagnostic techniques, endonuclease restriction analysis, surface-antigen detection methods, and measuring homologous and heterologous antibody responses are beginning to clarify the biology of Giardia.

Clinical studies in adults presenting with giardiasis to a gastro-intestinal unit

Eight adults presenting with giardiasis to a gastrointestinal unit during a two year period were studied in detail. Symptoms were varied, diarrhoea occurring in only five patients. Four of the eight gave a history of travel to endemic zones, and three of those who gave no such history had possible predisposing conditions (gastric surgery (2), and borderline IgA deficiency (1]. Most patients exhibited mild malabsorption of fat and vitamin B12, and some abnormality of jejunal disaccharidases was usual. Jejunal histology varied from normal to partial villous atrophy, and the intraepithelial lymphocyte count was raised in those patients with the most marked histological abnormality. Treatment with metronidazole was uniformly successful, and most of the above abnormalities reverted to normal within a month of treatment.

Quantitative histological and immunohistochemical findings in jejunal biopsy specimens in giardiasis

Jejunal mucosa biopsies from non-immune deficient patients with Giardia lamblia infestation were examined and showed three different groups of mucosal changes, distinguishable on morphological and immunohistochemical grounds. In three patients no morphological or immunohistochemical abnormalities were found (group A). In five patients a normal villous architecture was seen. These biopsies had increased numbers of interepithelial lymphocytes and of immunoglobulin containing cells in the lamina propria, with a relative increase of the number of IgA and IgG containing cells (group B). Two patients with a malabsorption syndrome due to giardiasis had marked villous atrophy, documented by morphometric measurements and large numbers of interepithelial lymphocytes and of immunoglobulin containing cells in the lamina propria, especially IgA and IgG (group C). These findings differ considerably from those in patients with immunodeficiency or gluten sensitive enteropathy. This suggests that when villous atrophy of the jejunal mucosa is found immunohistochemistry of jejunal biopsy specimens may be helpful in the differential diagnosis between mere giardiasis and giardiasis superimposed on immunodeficiency or gluten sensitive enteropathy.

Immunoglobulin deficiency diseases of the intestine

Marshak has emphasized the role of the gastrointestinal tract as a major immunologic organ and described the radiologic findings of immunoglobulin deficiency diseases of the small intestine. According to his classification the radiologic findings include multiple nodular defects, edema and increased secretions associated with Giardiasis, a sprue-like pattern, and thickened folds. In this report, the role of the intestine in the immune response is briefly reviewed and several of the radiologic features of immune deficiency diseases and those of benign nodular lymphoid hyperplasia are illustrated.

Giardiasis: an overview for the clinician

Since the clinician confronting a case of giardiasis may find the current literature confusing and weighted towards rare immunoglobulin deficiency syndromes, a classification is proposed to answer questions pertinent to understanding and managing this infection. Current thinking of giardiasis must involve the realization that (1) asymptomatic carriers exist; (2) that the majority of symptomatic patients have no structural disease explaining their symptoms; and (3) that those patients with anatomic lesions and giardiasis probably have an underlying predisposing condition. A short review of the association of giardiasis and immunodeficiency will then be presented, along with current concepts of diagnosis and therapy.