Giardia intestinalis
Systematic position
Phylum- Protozoa
Subphylum- Sarcomastigophora
Class- Mastigophora
Order- Polymastigina
Genus- Giardia
Species- intestinalis
History
— First seen by Leeuwenhoek in 1681
— Discovered in his own stool
Geographical distribution
— World-wide
Habitat
— Duodenum & upper part of jejunum of man
Morphology
— Exists in two phases :1.Trophozoite 2.Cyst
Trophozoite
— Looks like a tennis racket in flat view & like a split pear in longitudinal view
— Dorsal surface convex, ventral surface concave with a sucking disc
— 14 µm long & 7 µm broad
— Anterior end broad & rounded, posterior end tapers to a sharp point
— Bilaterally symmetrical
— All body organs paired
— Two axostyles, two nuclei & four pairs of flagella
Cyst
— Oval, 12 µm long, 7µm broad
— Axostyles lie more or less diagonally, forming a sort of dividing line within cyst wall
— 4 nuclei, clustered at one end/ lie in pairs at opposite poles
— Remains of flagella & margins of sucking disc may be seen inside cytoplasm
— Acid environment causes parasite to encyst
Life cycle
— In trophozoite stage parasite multiplies in man’s intestine by binary fission
— Under unfavourable conditions in duodenum parasite encysts, usually in large intestine
— In the cyst a thick resistant wall secreted by parasite, divides into two within cyst
— Man becomes infected by ingestion of cysts
— Just after 30 minutes of ingestion cyst hatches into 2 trophozoites & multiply in enormous numbers, colonize in duodenum
— To avoid high acidity of duodenum Giardia localises in biliary tract
Pathogenicity
— Sucking disc helps the parasite to attach from the convex surface to epithelial cells of intestine
— Causes disturbance in intestinal function, leading to malabsorption of fat
— Patient may complain looseness of bowels, mild steatorrhoea (passage of yellowish & greasy stools due to excess of fat)
— Parasite is also capable of causing harm by toxic effects (allergy), traumatic, irritative & spoilative action
Laboratory Diagnosis
— Microscopical examination of freshly passed stool for demonstration of trophozoites & cysts
— Trophozoites may be recovered both in bile A (aspirated from duodenum) & B (removed from bile duct) drawn by duodenal intubation
Treatment
— Atebrin & acranil- effective for giardiasis
— Schneider (1961) reported good results with a derivative of imidazole
— Chloroquine in doses of 300 mg base once daily for 5 days is also effective
