Medical parasites are diverse organisms that can cause significant morbidity and mortality worldwide. Understanding the pathophysiology of these parasites is crucial for developing effective treatment and prevention strategies. This review explores the mechanisms through which medical parasites induce disease and evade host immune responses. Key parasitic pathogens, including protozoa, helminths, and ectoparasites, employ various strategies to establish infection and promote survival within the host. Mechanisms of tissue invasion, such as the secretion of proteolytic enzymes and the alteration of host cell signaling pathways, are critical for establishing parasitic niches. Additionally, many parasites possess sophisticated immune evasion tactics, such as antigenic variation, secretion of immunomodulatory molecules, and the ability to mimic host antigens. These adaptations allow parasites to persist in hostile environments and evade detection by the host immune system. The interplay between the parasite's pathogenic mechanisms and the host's immune response is complex, leading to a range of clinical manifestations, from mild to severe disease. Understanding these interactions not only sheds light on the biology of these organisms but also highlights potential targets for therapeutic intervention. This review aims to provide a comprehensive overview of the pathophysiological processes underlying parasitic infections and their implications for public health.