Experimental studies on bionomics of giardia infection
Giardia lamblia stiles, 1915 is one of the important pathogenic protozoa among Korean, and is the only species of protozoa which inhabits in the small intestine. A considerable reports have been reported concerning the locality in digestive tract, mechanism of living habits and pathogenicity, though none of them were conclusive.
The present study has aimed to clarify several unknown bionomical characteristics of the parasite.
Ⅰ. Localization and morphological variallon of genus Giardia in various parts of the small intestine of laboratory mice and rats.
Concerning the localization of Giardia in the small intestine, contradictory results have been reported : Hegner(1923), Thomson & Robertson(1929), chu(1930), Lavier(1935) and Craig &Faust(1949), stated duodenum was the optimum site of the
parasite, while Wenyon(1926) and Glukhowtzev(1935) pointed the upper part of the small intestine, and Armagham(1937), Hegner & Eskridge(1937) reported the lower part of small intestine was the optimum site of the parasite.
Morphological variation of Giardia in the various part of the small intestine in some host has not been studied.
The present study attempted to elucidate the localization of the parasite in the small intestine of naturally infected or experimentally infected hosts by quantitative examination. Related with the localization of Giardia, morphological
differences of the parasite and hydrogenion concentration in different part of the small intestine and histological changes of intestine were also studied.
Materials and Methods:
The small intestines of both mice and rats were divided into eight sections(from pylorus to cecal junction, Sect. Ⅰ, Ⅱ, ……Ⅷ).
The experimental animals were treated with 5cc of 1% atabrine solution before the experiment in order to eliminate the natural infection of Giardia. Collection of cysts were carried on by Faust's and Gate' method. The number of trophozoites found
in 100 microscopical fields in specimens prepared from the suspension of 0.02ml. of the intestinal content in each of various section of the small intestine was used for the quantitative comparison. trophozoites were stained by Iron-Hematoxylin method and measured the size with micrometer(Bausch & Lomb. Optical Co.).
Hydrogen ion concentration of intestinal contents which were diluted by normal saline(pH7.0) was measured by Beckman's pH meter.
Histological finding of different part of the small intestine of the infected rats was examined after staining with Hematoxylin-Eoain.
1. The localization of Giardia muris(natural infection).
Among eight Giardia-infected laboratory mice the trophozoites were concentrated mainly at the portion between Sect. Ⅳ to Ⅴ., and gradually decreased to bard the anterior(proximal) or the posterior part(distal), and no trophozoite was found from large intestine and the bile duct. The cysts were found mainly from the lower part of Sect.Ⅶ. The tendency of distribution was different between trophozoite and cyst. Generally trophozoites were distributed densely in the upper part, mainly sect. Ⅳ-Ⅴ, though cysts were found exclusively from lower part of the small intestine.
2. The localization of Giardia duodenalis(experimental infection).
Among 16 giardia-infected lavoratory rats the trophozoites were found densely at the portion between Sect. Ⅳ to Ⅵ and the highest concentration was observed at Sect. Ⅴ.
3. Average body length and breadth of Giardia muris drawn at random from different parts of the small intestine of 8 mice were as follows:
Maximum average of the body length of the trophozoite was found at the part of Sect. Ⅳ and minimum average value was observe at the part of Sect.Ⅶ. The average dimension of the breadth of trophozoite from Sect. Ⅱ, Ⅳ, Ⅵ showed no significant differences but small dimension value was observed at Sect. Ⅷ.
The portion where the maximum distribution rate and where the maximum average dimension of the body length of the trophozoite were shown was considered as an indication of the optimum site of the parasite.
4. Hydrogen ion concentration of various part of the small intestine of 4 Giardia-infected rats and 4 control rats revealed 6.20-6.98 without significant difference among them, and the pH value was increased toward the lower part of the intestine. The pH was 6.41 in the portions of Sect. Ⅳ, Ⅴ, and Ⅵ where the
Giardia duodenalis were concentrated.
5. Histologically, lymphocytic hyperplasia was observed in submucosa, especially at the portion of densely distributed area, and it was presumed that such an irritatory reaction would be due to the continuous irritation by the trophozoite of Giardia duodenalis.
Ⅱ. Studies on the factors effecting Giardia infection.
As a part of the life history of genus Giardia, the mechanism of excystment in vitro with diluted feces, intestinal and stomach enzymes, or varying pH, Bemrick(1933) indicated that bile might influence on the survival of Giardia, but he missed to examine whether it effected the excystment. It is presumed that age,
diet and bile might participate as further factors for the excystment and the survival of giardia. with these in mind, the present studies were initiated to clarify the following subjects.
(1) duration from ingestion of the cyst and to parasitism in the small intestine.
(2) Infectivity of Giardia in related with the age group and different diet.
(3) Influence of bile on the excystment and the survival of Giardia.
Materials and Methods:
For experiment 1, rats were sacrificed at the time of 24, 48, 72, 96, 120 hours after feeding with the cyst of Giardia duodenalis and the intestinal content in various part were examined by the direct smear and concentration method.
For experiment 2, rats were divided into 4 groups : adult(over 150gm body weight) and the immatured (under 70gm body weight) and each two groups were also divided into cereal and milk diet group.
For experiment 3, the bile duct was cannulated with intramedic No. 10 polyethylene tubing. The cannule was inserted at the anterior one third of the duct and another end of cannule in the caecum and then, purse string suture was applied.
1. No trophozoite of Giardia duodenalis was found in the small intestine of 4 rats sacrificed at 24 hours after feeding with the cysts, and in 2 out of 5 rats after 48 hours a few trophozoites were found from only one section each(Sect. Ⅳ, Sect.Ⅴ) of the small intestine. In 16 out of 17 rats sacrificed at 72, 96, 120
hours in minimum base.
2. In adult group, trophozoites were found sect. Ⅱ-Ⅷ without showing any difference regardless cereal or milk. In immatured group, trophozoites were found through Sect. Ⅲ-Ⅷ in the cereal group and sect. Ⅳ-Ⅶ in the milk group. This difference of age(body weight) or diet gave no significant influence for
infectivity of Giardia.
3. Even though the bile flow was led from liver to the caecum directly, trophozoites of Giardia duodenalis were found abundantly from the small intestine in 4 out of 5 operated rats as in 4 rats in control group. Thus it was assumed that bile itself was not indispensable factor for excystment and survival of Giardia duodenalis in the intestine.