Molecular Dialogue Between Parasites and Hosts: Interactions and Coevolution

Parasites and hosts continually adapt to one another, and the resulting selection leaves detectable signatures in both genomes. This review organizes host-parasite interaction into five mechanistic tiers-molecular recognition, invasion, immune coexistence, developmental regulation, and adaptive genomic imprint-and asks, for each tier, which parasite molecules act, how the host counters them, and what genomic signature the exchange leaves. Redundant ligand-receptor pathways determine host specificity; antigenic variation, molecular mimicry, tegumental masking, and extracellular-vesicle signalling sustain coexistence; transcription factors and epigenetic regulators time life-cycle transitions; and balancing and positive selection leave readable imprints. We close with five testable propositions and with the cross-cutting lessons that emerge from comparing Plasmodium, Schistosoma, Trypanosoma, and Toxoplasma rather than describing them in turn: functional constraint, not antigenic novelty, predicts vaccine durability.