**Firas Alali**

**1**

**Chapter 1**

**1. Introduction**

**1.1** *Toxoplasma gondii* **and life cycle**

Introductory Chapter:

*Saeed El-Ashram, Gungor Cagdas Dincel,* 

*Mohammed Hamdy Farouk, Abdulaziz Alouffi,* 

*Billy M. Hargis, Víctor Manuel Petrone-García,* 

and Wild Animals

The Significance of *Toxoplasma* 

*gondii* in Humans, and in Domestic

*Hany M.R. Abdel-Latif, Shagufta Iqbal, Guillermo Tellez-Isaias,* 

Since 1908, when *Toxoplasma gondii* was isolated in a rodent (*Ctenodactylus gundi*), from which the parasite gained its name [1], more than a century has passed. Because of the crescent-shaped form of the parasite, the genus name was taken from the Greek word toxin, which means bow. It was not until 1970 that the entire life cycle of the parasite was revealed, considering cat (*Felis catus*) the only definitive host (DH) in which the parasite could complete its entire sexual life cycle [2]. *T. gondii* belongs to the *phylum Ampicomplexa*, which contains intercellular parasites with a polarized cell structure and an apical complex [3]. *T. gondii* life cycle is considered sexual and asexual with a characteristic complexity; it reproduces sexually in the DH and asexually in the intermediate hosts (IH) [4] with three distinct stages of reproduction: tachyzoites (replicating fast), bradyzoites (replicating slowly), and sporozoites (in sporulated oocysts). As described briefly, after consuming any of the three stages, wild and domestic cats are infected [5]; prepatent period typically lasts between 3 and 10 days until 19 days or more [6]. Digestive enzymes break down the cyst wall, releasing the bradyzoites [7] and allowing the infection of intestinal epithelial cells through

asexual reproduction (schizonts). Merozoites are discharged and reinvade the intestinal epithelium when the schizont reaches maturity. After this stage, sexual differentiation is observed [5, 8], rising to flagellated microgametes and macrogametes and beginning fertilization [6], resulting in the production of a zygote (diploid) and growing into an unsporulated oocyst, which is discharged into the intestinal lumen and expelled from the DH. Sporulation of the oocysts takes from 1 to 5 days, depending on environmental variables such as temperature and humidity [9, 10]. Oocysts

*Gabriela Aguilar-Tipacamú and Inkar Castellanos-Huerta*

Department of Veterinary Parasitology, College of Veterinary Medicine, University of Kerbala, Kerbala, Iraq
