ABSTRACT
A fundamental feature of Echinococcus granulosus infection is its chronicity. There are many reasons for this; including weak natural immunity and the ability of the larval stages to evade or resist elimination by the hosts' specific immune responses. To identify the types of hosts' cellular immune response; a series of ultrastructral studies of hydatid cysts surgically removed from Turkana patients was conducted based on transmission electron microscopy. Ultrastructurally; the ectocyst (adventitial layer) is organised into three layers; an inner layer containing mainly the infiltrating mononuclear leukocytes; a middle; loose connective tissue layer with inflammatory cells mainly plasma cells; fibroblasts; scant neutrophils; eosinophils and lymphocytes; and an outer loose connective tissue layer that blends with the surrounding host tissue. The mast cells and basophils were not observed. This study has showm that the adventitial layer of hydatid cysts infiltrated by leukocytes; principally by macrophages and plasma cells