BABESIOSIS IN WASHINGTON-STATE - A NEW SPECIES OF BABESIA

Objective; To,characterize the etiologic agent (WA1) of the first repo rted case of babesiosis acquired in Washington State. Design: Case rep ort, and serologic, molecular, and epizootiologic studies. Setting: So uth-central Washington State. Patient: A 41-year-old immunocompetent m an with an intact spleen who developed a moderately severe case of bab esiosis. Measurements: Serum specimens from the patient were assayed b y indirect immunofluorescent antibody (IFA) testing for reactivity wit h seven Babesia species and with WA1, which was propagated in hamsters inoculated with his blood. A Babesia-specific, ribosomal-DNA (rDNA) p robe was hybridized to Southern blots of restriction-endonuclease-dige sted preparations of DNA from WA1, Babesia microti, and Babesia gibson i. Serum specimens from 83 family members and neighbors were assayed f or IFA reactivity with WA1 and B. microti. Small mammals and ticks wer e examined for Babesia infection. Results: The patient's serum had ver y strong IFA reactivity with WA1, strong reactivity with B. gibsoni (w hich infects dogs), but only weak reactivity with B. microti. DNA hybr idization patterns with the rDNA probe clearly differentiated WA1 from B. gibsoni and B. microti. Four of the patient's neighbors had IFA ti ters to WA1 of 256. The tick vector and animal reservoir of WA1 have n ot yet been identified, despite trapping 83 mammals and collecting 235 ticks. Conclusions: WA1 is morphologically indistinguishable but anti genically and genotypically distinct from B. microti. Some patients el sewhere who were assumed to have been infected with B. microti may hav e been infected with WA1. Improved serodiagnostic and molecular techni ques are needed for characterizing Babesia species and elucidating the epidemiology of babesiosis, an emergent zoonosis.