Giardia intestinalis

                                   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