**Meriem Braiki**

**1**

Section 1

Introduction

Sidi Bouzid Regional Hospital, Tunisia

Section 1 Introduction

**3**

**Chapter 1**

**1. Introduction**

**2. Parasitology**

host [3].

the disease [3].

genus *Echinococcus* [1].

Introductory Chapter: Overview

Echinococcosis is considered the most common parasitic disease and the most widespread zoonotic infection caused by several cestode species belonging to the

The parasitic life cycle involves two mammalian hosts. The intermediate hosts include members of the ungulates such as sheep, goats, and pigs. The definitive host

The adult parasite inhabits the small intestine of a definitive host and eggs, containing infective oncospheres, are produced. Subsequently, free eggs as well as cestode segments are excreted through the stool of the host into the environment [1]. Following an oral uptake of eggs by an intermediate host, a larval stage (metacestode) develops in several internal organs, mainly the liver and lungs, after a larval migration through the blood and lymph vessels. Typically, numerous protoscoleces are produced by the mature metacestode, each with the potential to develop into an adult cestode after oral ingestion by a suitable definitive

Humans are accidental or aberrant hosts that are not essential to the natural *Echinococcus* life-cycle. The eggs, after being ingested, develop as a cyst (hydatid cyst) inside the accidental host organs. Larval infection leading to the hydatid disease is characterized by metacestode long-term growth in the intermediate host. The parasitic cystic structure is typically filled with a clear hydatid fluid [4]. The inner germinating membrane of the cyst provides germination and the outer cystic layer features a laminated part. A granulomatous inflammatory reaction leads to a

Developing cysts are responsible for the morbidity and the mortality related to

Cystic echinococcosis (CE) occurs worldwide. *E. granulosus* is known to occur on all continents but high parasite prevalences are found in endemic areas such as central Asia, the Mediterranean Basin, the Russian Federation, Africa (northern

This parasite has 12 different genus types, though four major species are known to cause human parasitic disease: *Echinococcus granulosus* (*E. granulosus*), *Echinococcus multilocularis*, *Echinococcus vogeli*, and *Echinococcus oligarthrus* [2]. *E. granulosus* is the causative organism of cystic echinococcosis, a small-sized tapeworm measuring approximately 2–7 mm in length with at least 10 different

*Meriem Braiki, Azzaza Mohamed and Fethi Derbel*

on Echinococcosis

genome patterns and distinct genetic markers [1].

of this parasite is the dog and other members of canids.

fibrous tissue constitution walling the cyst [5].

and eastern regions), Australia, and South America [1, 3].
