| Summary: | Human babesiosis is a life-threatening infectious disease that causes societal and economic impact worldwide. Several species of <i>Babesia</i> cause babesiosis in terrestrial vertebrates, including humans. A one-day clinic was held in Ontario, Canada, to see if a red blood cell parasite, which is present in blacklegged ticks, <i>Ixodes scapularis</i>, is present in humans. Based on PCR testing and DNA sequencing of the 18S rRNA gene, we unveiled <i>B. odocoilei</i> in two of 19 participants. DNA amplicons from these two patients are almost identical matches with the type strains of <i>B. odocoilei</i> in GenBank. In addition, the same two human subjects had the hallmark symptoms of human babesiosis, including night sweats, chills, fevers, and profound fatigue. Based on symptoms and molecular identification, we provide substantive evidence that <i>B. odocoilei</i> is pathogenic to humans. Dataset reveals that <i>B. odocoilei</i> serologically cross-reacts with <i>Babesia duncani</i>. Clinicians must realize that there are more than two <i>Babesia</i> spp. in North America that cause human babesiosis. This discovery signifies the first report of <i>B. odocoilei</i> causing human babesiosis.
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