Cross-species therapeutics in Plasmodium and Babesia: erythrocyte invasion and conserved drug targets.

The phylum Apicomplexa encompasses a diverse group of protozoan parasites of profound medical and veterinary importance, among which the genera Plasmodium and Babesia stand out because of their shared pathological niche within host erythrocytes. While Plasmodium spp., transmitted by anopheline mosquitoes, are the causative agents of human and zoonotic malaria, Babesia spp., transmitted by ixodid ticks, cause babesiosis, a burgeoning zoonosis and a significant cause of economic loss in the livestock industry. Globally, babesiosis is an emerging threat, with Babesia microti being the primary cause of human babesiosis in the USA and Europe, transmitted by Ixodes scapularis ticks. Although their life cycles diverge critically, most notably in the presence of an exo-erythrocytic hepatic stage in Plasmodium and its absence in Babesia, both parasites share a core pathogenic strategy. They invade, replicate within, and lyse red blood cells, leading to the clinical manifestations of haemolytic anaemia and fever. This review undertakes a comprehensive comparative analysis of Plasmodium and Babesia, leveraging the vast body of research on the former to illuminate the biology and vulnerabilities of the latter. We systematically dissected their parallel life cycles in both vertebrate and invertebrate hosts, elucidating the molecular mechanisms underlying their distinct developmental pathways and transmission strategies. A central focus is placed on the conserved machinery of erythrocyte invasion, a multi-step process mediated by an apical complex of secretory organelles (micronemes and rhoptries) and specific ligand-receptor interactions, which presents a prime target for intervention. Beyond cellular invasion, we delve into the shared metabolic architecture that constitutes the foundation for cross-species drug discovery. We critically evaluated high-value conserved targets, such as the mitochondrial cytochrome bc₁ complex, proteasomal protein degradation system, unique apicoplast organelle with its prokaryotic pathways, essential kinases, and folate biosynthesis pathway, dihydroorotate dehydrogenase (DHODH), ATP4, falcipain proteases, and the heme detoxification pathway. For each target, we discuss the mechanism of action of existing and experimental inhibitors, the evidence for their efficacy across both genera, and the emerging challenge of drug resistance. Ultimately, this synthesis argues that the deep evolutionary relationship between Plasmodium and Babesia has resulted in a core set of indispensable biological processes that are susceptible to parallel therapeutic interventions. By mapping the shared vulnerabilities within their erythrocytic pathogenesis, this review will be useful in designing novel, broad-spectrum antiprotozoal agents and strategic drug repurposing efforts, thereby advancing the fight against both malaria and babesiosis.