Mongolian gerbils were susceptible to infection with Giardia lamblia cysts from patients. Inoculation of gerbils with 5 x 10(3) cysts each resulted in an infection characterized by the intermittent release of cysts for up to 39 days. The mean number of cysts released per gerbil in a 2-hr period was 8.8 x 10(2) (range, 0-5 x 10(3)). The highest number of trophozoites found in the intestine was on day 15 after infection, when the mean number of trophozoites per gerbil was 6.36 x 10(6). Administration of cysts from different patients to gerbils resulted in a similar pattern of cyst release during the first 30 days of infection. Mongolian gerbils were also susceptible to infection with cultured trophozoites (Portland 1 strain). The pattern of cyst release and the number of trophozoites in the intestines of orally and duodenally inoculated gerbils were similar. Gerbils were protected against reinfection with G. lamblia for up to eight months after primary infection.

SUMMARY 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.Various abnormalities of small bowel pathology have been identified consistently in human giardiasis and these include disaccharidase deficiencies,' 2 increased intraepithelial lymphocyte counts'4 and, in patients with malabsorption crypt hyperplasia with short villi and increased lamina propria cellularity.) Low serum calcium and folate concentrations were consistent features in elderly people having giardiasis and aroused suspicion of underlying malabsorption." A decrease in the disaccharidase activity has been observed in vitro. Mouse mucosal cells incubated with G lamblia trophozoites showed a reduction in the activities of lactase, sucrase, and maltase.7We have recently described an animal model for giardiasis using gerbils and G lamblia isolated from humans.' In this study, we examined the progression

The susceptibility and resistance of inbred mice to Giardia muris was studied during the acute and elimination phases of infection. The infection in susceptible A/J and C3H/He mice was characterized by a short latent period, high cyst output during the acute phase of infection, and prolonged periods of cyst release. In contrast, resistant B1O.A and DBA/2 mice had a longer latent period, a lower cyst output during the acute phase, and relatively rapid resolution of infection. The trait of susceptibility and resistance during both acute and elimination phases of the infection was found to be under complex multigenic control as determined by examination of the response of F1 hybrid mice and backcross analyses. The genes controlling this trait did not appear to be linked to the H-2 locus. In addition, the control of the response of mice to G. muris during the acute phase of infection was probably mediated by mechanisms independent from those controlling the response during the elimination phase of infection.

Mongolian gerbils (Meriones unguiculatus) were inoculated with known numbers of Giardia cysts isolated from humans, beavers and mice. The pattern of cyst release in the feces was studied for a period of 35 days. After a latent period of 5 days, animals infected with G. muris release cysts in their feces every day until day 14. Gerbils infected with human or beaver isolates released cysts in their feces intermittently for 30 days. These results indicated that the mode of cyst release in these animals was characteristic of the parasite, and was independent of the host. Mongolian gerbils acquire complete resistance upon homologous species challenge but demonstrate only partial protection when challenged with a different species of Giardia. We concluded that the Mongolian gerbil model could be useful in epidemiological studies for two reasons: it can be used for determination of cyst viability, and for the identification of the etiological agent.

The kinetics of anti-sheep erythrocyte (SRBC) response were studied in susceptible (A/J) and resistant (B10.A) mice during infection with Giardia muris. Mice infected with G. muris were found to be less responsive to either intraperitoneally or intraduodenally administered SRBC. Immunodepression was of relatively short duration, occurring during the period of highest trophozoite density in the small intestine, and was present in both spleen and, in particular, mesenteric lymph node cell populations. The main difference in the kinetics of anti-SRBC responses between A/J and B10.A mice was that susceptible mice were significantly less responsive to SRBCs than were the resistant B10.A animals. The difference in the kinetics of the anti-SRBC response between A/J and B10.A mice was not due to T-suppressor cell activity. Mesenteric lymph node cell transfers but not spleen cell transfers from infected mice to syngeneic recipients caused depressed normal anti-SRBC response. Furthermore, administration of the soluble extract of the trophozoites to uninfected mice resulted in a depressed response against SRBCs. Pronounced immunodepression in gut-associated lymphoid tissues may be more relevant than systemic immunodepression to survival and reproduction of trophozoites in murine giardiasis.

Stool microscopy as performed in clinical parasitology laboratories is a complex procedure with subjective interpretation. Quality assurance (QA) programs often emphasize proficiency testing as an assessment tool. We describe a result reproducibility assessment tool, which can form part of a broader QA program, and which is based on the blinded resubmission of selected clinical samples, using concordance between the reports of the initial and resubmitted specimen as an indicator. Specimens preserved in sodium acetate-acetic acid-formalin can be stored for several months for use in such a program. The presence of multiple protozoa in one specimen does not affect concordance. Some dilution of specimens occurs in this process, and this may explain poor concordance when specimens with low protozoal concentrations are resubmitted. Evaluation of this tool in a large parasitology laboratory revealed concordance rates for pathogenic protozoa (Entamoeba histolytica/Entamoeba dispar, Giardia lamblia, and Dientamoeba fragilis) of about 80%, which may be considered for use as a benchmark value. We also used this tool to demonstrate that when pairs of specimens from one patient are pooled to create a single specimen, concordance between the results of the individual and pooled specimens is high.Clinical parasitology laboratories, in contrast to most other diagnostic laboratories, utilize many complex manual technical procedures which are subject to individual variation and subjective interpretations (8). As a result, quality assurance (QA) programs are crucial for maintaining confidence in the accuracy of test results. Meaningful QA programs can be difficult to design and expensive to implement. In addition, indicators of diagnostic accuracy can be difficult to assess given the inherent variability among testing procedures (19) and technologists (11). Therefore, not only does the routine testing of stool specimens for intestinal protozoa by microscopy remain a challenge for the modern diagnostic laboratory (3, 19), but so does the assessment of the accuracy of this testing.To date, no studies have been published on the value of a QA program undertaken to directly evaluate the quality of microscopy in the detection of intestinal protozoa, although several have reviewed this for other types of procedures and microorganisms (e.g., bacterial counts [2]; human immunodeficiency virus [4]). QA programs, such as that undertaken by the College of American Pathologists, have typically relied on results from proficiency tests (17). In some areas of clinical microbiology, proficiency testing has been used to evaluate multiple steps in a complex process and reveal widespread systematic problems (e.g., for Streptococcus pneumoniae antimicrobial susceptibility testing [5]). In the parasitology laboratory, proficiency tests are based on sending "unknowns" to each participating laboratory, and the evaluation is based on the number of parasite species correctly identified. A potential weakness of proficiency testing is the possibility for the...

MA BEHR, E KOKOSKIN, TW GYORKOS, L CÉDILOTTE, GM FAUBERT, JD MACLEAN. Laboratory diagnosis for MAIN RESULTS:For 152 previously collected stools, copro-antigen detection had a sensitivity of 73 of 74 (98.6%) and a specificity of 78 of 78 (100%). In clinical samples of 62 patients, eight of the 62 patients (13%) were diagnosed with G lamblia infection on microscopy. Copro-antigen diagnosis was accurate in symptomatic patients, with sensitivity of seven of eight (87.5%) and specificity of 52 of 54 (96.8%). Serology was less accurate. IgG response to G lamblia had sensitivity of four of seven and specificity of 24 of 50 (48%), and IgM response had sensitivity of three of six and specificity 27 of 48 (56%). Western blot had a sensitivity of five of seven and a specificity of 38 of 49 (78%). CONCLUSIONS: Copro-antigen diagnosis of G lamblia is highly accurate in patients with chronic gastrointestinal complaints, while serology is less accurate and appears to be less useful diagnostically.

Abstract. The protozoan parasite Giardia lamblia is a major cause of waterborne enteric disease worldwide. Lectins are proteins that bind to carbohydrate (sugar) moieties. Potential targets for lectins are found on the surface of most single-celled organisms. Modest concentrations of wheat germ agglutinin (WGA) have been shown to inhibit G. lamblia excystation and trophozoite growth in vitro and can reduce cyst passage in mice infected with the closely related protozoan parasite, G. muris. Commercial preparations of wheat germ (WG) contain 13-53 g of WGA per gram. We performed a double-masked, placebo-controlled study of dietary supplementation with WG in 63 subjects with giardiasis in Montreal and Lima (25 asymptomatic patients passing cysts; 38 patients with symptoms). Asymptomatic subjects received WG (2 g, 3 times a day) or placebo (cornstarch, 2 g, 3 times a day) for 10 days, followed by metronidazole (250 mg 3 times a day) for 7 days. Symptomatic subjects received metronidazole (250 mg 3 times a day) plus either WG or placebo for 7 days. Stool specimens were collected every day (Montreal) or every other day (Lima) for 10 days and on Day 35 for microscopic examination and coproantigen determination. Subjects kept a diary of symptoms for 10 days after recruitment. In asymptomatic subjects, both cyst passage and coproantigen levels were reduced by ϳ 50% in those taking WG compared with the placebo group (P Ͻ 0.01 and P ϭ 0.06, respectively). In symptomatic subjects, cyst passage and coproantigen levels fell precipitously in response to metronidazole therapy, and there were no clinically important differences between those receiving supplemental WG or placebo. However, symptoms appear to have resolved more rapidly in the subjects taking WG in addition to metronidazole. The WG supplement was well tolerated in both symptomatic and asymptomatic subjects. These data suggest that components of WG, possibly WGA, either alone or in combination with antiprotozoal agents, can influence the course of human giardiasis.