Pathogenicity and antigenic components of excysted Giardia lamblia isolated from patients in Riyadh, Saudi Arabia.

Giardia lamblia cysts were isolated from patients in Riyadh, Saudi Arabia. Cysts and trophozoites (from axenically excysted cysts) were given orally by gavage to mice to establish the pathogenicity of the Riyadh isolate. There was no effect of varying the dose of administered parasite on parasite excretion or morbidity. A typical pathologic pattern of giardiasis was demonstrated by histologic methods and electron microscopy. Antigenic components of the Riyadh isolate were compared with the Portland strain and with Entamoeba histolytica by gel diffusion immunoprecipitation and immunoblotting. There were few antigens in common between Riyadh isolate and the Portland strain, and little cross-reactivity of the Riyadh isolate with Entamoeba histolytica was observed.

Enzyme-linked immunosorbent assay for the detection of anti-Giardia specific immunoglobulin G in filter paper blood samples.

Conventional diagnosis of infection with Giardia duodenalis is by faecal examination but the sensitivity of a single examination is low. Serological tests, although not always positive, are more acceptable to patients and are useful in determining the prevalence of giardiasis in large populations. We show here that blood collected on filter paper and dried provides an excellent source of material for enzyme-linked immunosorbent assays; using samples from a group of 88 stool-negative and 45 positive patients, the optimum results were obtained by taking the control mean optical density plus one standard deviation as the negative/positive cut-off value. The sensitivity was 91% (2/45 false negatives), and the specificity 95% (4/88 false positives). This method should be particularly useful for large-scale surveys in developing countries or wherever serological testing is done in central laboratories.

A simple method for excystation of Giardia lamblia cysts.

Fresh Giardia lamblia trophozoites were isolated by in vitro excystation of purified cysts from the faeces of Saudi patients. The method consisted of mixing one part of the cyst suspension with nine parts of 1 N hydrochloric acid, at pH 2, then culturing the excysted trophozoites in modified TYI-S-33 medium in sealed glass vials. During the excystation process most cysts developed a space between the trophozoite and the cyst wall, and after several steps of enlargement the trophozoite emerged at the posterior end of the cyst. Keeping the cysts at 4 degrees C for more than 10 days did not affect the excystation process. Trophozoites obtained by this method can be cryopreserved and recultured without significant loss of activity. This is a simple and rapid method of obtaining G. lamblia trophozoites from cysts in stools or from other sources.

ELISA for detection of anti-Giardia specific IgM: response in serum.

Infection with Giardia lamblia (G. duodenalis, G. intestinalis) is common all over the world, especially in children. Traditional diagnosis by faecal microscopy has only moderate sensitivity; serological tests, although not always positive, are acceptable to patients and useful in epidemiological studies. We show here that serum IgM separated by column chromatography and assayed by an indirect ELISA test can be a useful tool for the diagnosis of giardiasis. One hundred and thirty-nine positive sera (based on a single faecal examination), and 97 negative serum samples from Riyadh, Saudi Arabia, were examined. Taking positive results as being 2 s.d. above the mean of the controls, there were 117 positive results among the microscopically negative controls (3% false positives). The sensitivity of the test was 84% and the specificity 97%; the predictive value of a positive result is 97.5% and of a negative one 81%.