**1. Introduction**

With the exception of *Trypanosoma brucei*, the etiological agent of African trypanosomiasis (sleeping sickness), pathogenic protists of Kinetoplastida and Apicomplexa lineages are intracellular pathogens causing broadly disseminated diseases: malaria (caused by species of the genus *Plasmodium spp*.), Chagas disease (caused by *Trypanosoma cruzi*), leishmaniasis (caused by species of *Leishmania spp*.), and toxoplasmosis (caused by *Toxoplasma gondii*). These illnesses kill millions of people worldwide; have a significant economic impact, and cause public health issues everywhere.

In the following paragraphs, we present the diseases caused by these pathogens as well as the life cycles they go through in order to adapt to the hosts in which they live.
