Page 15 - Medical Parasitology_ A Textbook ( PDFDrive )

Entamoeba histolytica 7

2
i d
Mature cysts
ingested

C d A d
B
d

i = Infective Stage i d
d = Diagnostic Stage 1 d
Cysts and trophozoites
A = Noninvasive Colonization passed in faeces
B = Intestinal Disease
C = Extraintestinal Disease
4 Trophozoites d

Exits host
Multiplication
Excystation Trophozoites
3 4 d
5 Cysts d d d d

Fig. 3.2 Life cycle of Entamoeba histolytica (Reproduced from https://www.cdc.gov/dpdx/ame-
biasis/index.html)

Pathogenesis and Clinical Features

Entamoeba histolytica causes intestinal and extraintestinal amoebiasis.
The lumen-dwelling amoebae do not cause any illness. They cause disease only
when trophozoites invade the intestinal tissues. The trophozoite penetrates the epi-
thelial cells in the colon, aided by its movement and histolysin, a tissue lytic enzyme,
which damages the mucosal epithelium. Amoebic lectin mediates adherence.