CULTIVATION AND PHYLOGENETIC CHARACTERIZATION OF A NEWLY RECOGNIZED HUMAN PATHOGENIC PROTOZOAN

An intraerythrocytic protozoan (WA1) recently isolated from a patient in Washington State was shown to be morphologically identical to Babes ia microti but biologically and genetically distinct. Continuous growt h of WA1 was established in stationary erythrocyte cultures. Hybridiza tion of a chemiluminescent Babesia-specific DNA probe to Southern blot s of restriction enzyme-digested genomic DNA showed that WA1 could be distinguished from other Babesia species that were antigenically cross -reactive (Babesia gibsoni and babesial parasites from desert bighorn sheep, Ovis canadensis nelsoni) or known to infect humans (B. microti, Babesia divergens, and Babesia equi), or both. A 1436-bp portion of t he nuclear small subunit rRNA gene of WA1 was sequenced and analyzed. Genetic distance analysis showed that WA1 is most closely related to t he canine pathogen B. gibsoni and lies within a phylogenetic cluster w ith Theileria species and B. equi. The methodology described will be u seful for improved diagnosis and identification of human protozoal pat hogens.