Babesia divergens host cell egress is mediated by essential and druggable kinases and proteases.

Egress from host cells is fundamental for the spread of infection by apicomplexan parasites, including Babesia species. These tick-borne pathogens represent emerging zoonoses, but treatment options are limited. Here, using microscopy, transcriptomics and chemical genetics, we identified signalling, proteases and gliding motility as key drivers of egress by Babesia divergens. We developed reverse genetic tools in B. divergens to perform a knockdown screen of putative mediators of egress, identifying kinases and proteases involved in distinct steps of egress (aspartyl protease (ASP) 3 and kinases cGMP-dependent protein kinase (PKG) and calcium-dependent protein kinase (CDPK4)) and invasion (ASP2, ASP3 and PKG) of red blood cells. Inhibition of egress stimulates additional rounds of intracellular replication, indicating that exit from the replication cycle is uncoupled from egress. Chemical genetics validated PKG, CDPK4, ASP2 and ASP3 as druggable targets in Babesia spp. and identified promising compounds for babesiosis treatment. Taken together, egress in B. divergens more closely resembles egress in Toxoplasma gondii than in the more evolutionarily related Plasmodium spp.