Emerging Human Babesiosis with "Ground Zero" in North America

Abstract

The first case of human babesiosis was reported in the literature in 1957. The clinical disease has sporadically occurred as rare case reports in North America and Europe in the subsequent decades. Since the new millennium, especially in the last decade, many more cases have apparently appeared not only in these regions but also in Asia, South America, and Africa. More than 20,000 cases of human babesiosis have been reported in North America alone. In several cross-sectional surveys, exposure to Babesia spp. has been demonstrated within urban and rural human populations with clinical babesiosis reported in both immunocompromised and immunocompetent humans. This review serves to highlight the widespread distribution of these tick-borne pathogens in humans, their tick vectors in readily accessible environments such as parks and recreational areas, and their phylogenetic relationships.

Keywords: Babesia crassa; Babesia divergens; Babesia duncani; Babesia microti; Babesia spp.; Babesia venatorum; human babesiosis.

Figure 1

Geographical distribution of human babesiosis. The darker the color, the more numerous cases there are. There are no reported cases in unfilled countries or regions.

Figure 2

Phylogenetic analysis of 18S rRNA sequences of Babesia spp. found in human and tick vectors. The Maximum Likelihood method was performed in a default setting of the Jukes–Cantor model, uniform rates, and complete depletion with 1000 bootstrap replications. The trees were rooted with Toxoplasma gondii. Two species of piroplasms, one each in the closely related genera of Cytauxzoon (C. felis) and Theileria (T. parva) were also included. Scale bar indicates nucleotide substitutions per site. Numbers at the horizontal lines represent the percentage of replicates of 1000 repeats. The Neighbor-jointing method in the default setting yielded almost identical results as Maximum Likelihood did (Not shown). Each entry was identified in the order of Babesia sp., host, geographical region, and Accession number.