Theileria haneyi: An Emerging Equids Hemoparasite with Milder Virulence but Major Diagnostic and Therapeutic Implications

<i>Theileria haneyi</i>, a recently discovered tick-borne hemoparasite infecting equids globally, has significant implications for equine health. Although it is closely related to <i>T. equi</i> (sharing 23% genomic divergence), it establishes an asymptomatic carrier state in persistently infected horses, creating a silent transmission reservoir. Its discovery and unique genetics justify its classification as a new taxon. A critical diagnostic challenge is that the lack of the <i>ema-1</i> gene in <i>T. haneyi</i> prevents its detection by the standard <i>T. equi</i> cELISA, emphasizing the need for species-specific tools. Although species-specific PCR assays, including PCR and qPCR targeting genes like <i>chr1sco</i> or <i>ema-11</i>, respectively, and an indirect ELISA targeting the EMA-11 recombinant protein, have been developed, global genetic variations may limit their serological utility. Therapeutically, <i>T. haneyi</i> exhibits resistance to the key antiparasitic drug, imidocarb dipropionate (ID), and interferes with the clearance of co-infecting <i>T. equi</i>. Major knowledge gaps persist, particularly regarding the identification of its competent vector. The current work presents an overview of <i>T. haneyi</i> virulence, transmission, diagnostics, and therapeutic gaps while pinpointing the deficits in current information necessary for advancing our understanding of the parasite's biology. Finally, the review discusses and recommends further studies to develop effective control and surveillance strategies for <i>T. haneyi</i> infection.