Evolutionary history, molecular phylogeny and taxonomy of Babesia parasites

SCHNITTGER L; RODRIGUEZ AE; FLORIN-CHRISTENSEN M; MORRISON DA

Conferencia; Joint Conference on Emerging and Re-emerging Epidemics Affecting global Health; 2012

Babesia are tick-transmitted hemoprotozooans that infect mammals and birds, and that are acknowledged for their major impact on farm and pet animal health and associated economic costs worldwide. Additionally, Babesia infections of wildlife can be fatal if associated with stressful management practices, and human babesiosis, also transmitted by blood transfusion, is an increasing public-health concern. Due to the huge diversity of species reported to serve as Babesia hosts, all vertebrates might be potential carriers, as long as they are adequate hosts for Babesia-vector ticks. Babesia, Cytauxzoon and Theileria parasites are closely related and collectively referred to as piroplasmids. Based on a phylogenetic tree of all currently available 18S rRNA genes, we present a thoroughly revised molecular classification, comprising five monophyletic Babesia lineages, one Cytauxzoon clade, and one Theileria clade. Importantly, previously unresolved tree placement of piroplasmids T. equi, and B. bicornis could be established, and the relationship between T. youngi, T. bicornis, and Cytauxzoon spp. inferred. The recently described monoxenous apicomplexa Cardiosporidium and Nephromyces as a closely related sister taxon of piroplasmids suggests that a monoxenous lifecycle in an invertebrate host was an ancient feature of their last common ancestor. To reconcile estimates on the origin of piroplasmids and ticks (~300 Ma, respectively), and mammalian radiation (60 Ma), we hypothesize that the dixenous piroplasmid life cycle evolved with the origin of ticks. Thus, the observed time gap between tick origin and mammalian radiation indicates the existence of hitherto unknown piroplasmid lineages and/or species in extant vertebrate taxa, including reptiles and possibly amphibians. A more widespread taxon sampling across all potential vertebrate and tick hosts as well as the construction of trees using multiple genes will allow to further advance Babesia phylogeny and taxonomy.Financed by CONICET, INTA (AESA 203961 and AERG 232152), and the European Commission (INCO 245145, PIROVAC).