New Insights into Protozoa Parasites: Essential Processes and Drug Targets

Dear Colleagues,

Protozoa are a polyphyletic group of unicellular eukaryotes, including free-living or parasitic organisms. Among 50,000 described species, the great majority comprehends free-living cells that colonize almost all kinds of habitats, mainly feeding on organic matter. However, some species are parasites, producing disease in their hosts. In nature, protozoa parasites can be found in different hosts, such as plants, insects and other arthropods, as well as in all kind of vertebrate animals, including mammals. Since most of these diseases present anthropozoonotic potential, completely eliminating them is almost impossible, especially in wild environments. Serious and regular surveillance actions are essential if we are to avoid increases in the number of cases. Among the most important protozoa diseases for humans are Chagas disease, sleeping sickness, and leishmaniasis, caused by trypanosomatids; malaria and toxoplasmosis, caused by apicomplexa; and giardiasis, trichomoniasis, and amebiasis, caused by anaerobic protozoa. Together, these diseases affect almost all populations across the world, posing risks of infection related to geographic areas and economic and social issues, among other features. The clinical drugs used to combat these diseases are unsatisfactory, showing limited efficacy and high toxicity in many cases. The parasites’ interactions with their hosts are very complex, based on the balance between pathogens’ virulence and the host immune response. The comprehension of crucial molecular, cellular, and biochemical mechanisms, identifying their checkpoints for the success of the infection, seems to be a very reasonable approach for the development of alternative anti-protozoan drugs in the near future. In this context, the involvement of oxidative stress in protozoan infections has been demonstrated, at times aiding in cell signaling and regulation, while, at other times, causing parasites’ death. The role of antioxidant enzymes as virulence factors highlights the significance of these molecular processes, as well as the adaptive strategies employed by protozoa parasites to survive in oxidative conditions within the host, impacting the success of the infection. Conversely, autophagy serves as a physiological mechanism in eukaryotes to maintain homeostasis by degrading nonfunctional cellular components, thus minimizing the accumulation of damaged organelles and macromolecules. The participation of the autophagic pathway in protozoa has been described, particularly in relation to chemotherapy, where it can counteract the effects of drugs. The scope of this Special Issue includes distinct aspects of the protozoa–host interactions, describing cellular, molecular, and biochemical processes that relate to survival mechanisms, antioxidant defenses, and redox metabolism. We will accept reviews or original contributions.

Dr. Rubem F. S. Menna-Barreto
Dr. Ana Cristina Souza Bombaça
Guest Editors

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• protozoa
• parasites
• trypanosomatids
• apicomplexan parasites
• anaerobic protozoa
• chemotherapy
• drug targets
• protozoa–host interactions
• autophagy
• oxidative stress