Intracellular Parasitic Infections Caused by Plasmodium falciparum, Leishmania spp., Toxoplasma gondii, Echinococcus multilocularis, Among Key Pathogens: Global Burden, Transmission Dynamics, and Vaccine Advances—A Narrative Review with Contextual Insights from Armenia

Intracellular parasitic infections continue to pose significant public health and veterinary challenges globally, driven by their ability to evade immune responses, persist within host cells, and spread through complex transmission pathways. Caused by a diverse array of protozoan, helminthic, and arthropod-borne parasites, these infections, such as toxoplasmosis, leishmaniasis, and tick-borne diseases, remain prevalent across many regions, often exacerbated by environmental, socio-economic, and ecological factors. This review explores the current knowledge on intracellular parasitic diseases, outlining parasite classification, immune evasion mechanisms, diagnostic difficulties, and control strategies. Special attention is given to recent advancements in vaccine development, with a focus on experimental and licensed vaccines targeting intracellular pathogens. Additionally, the review highlights the importance of a 'One Health' approach, integrating human, animal, and environmental health efforts to address the multifaceted nature of parasitic transmission and control. Within this global context, Armenia serves as a case study, offering insight into how local ecological conditions, vector distribution, public health capacity, and social determinants shape the national burden of these infections. Challenges in Armenia, such as limited access to advanced diagnostics, underreporting, and the need for robust surveillance systems, underscore broader regional needs for investment in research, infrastructure, and cross-sectoral collaboration.