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Int J Parasitol. 2019 Feb;49(2):95-103. doi: 10.1016/j.ijpara.2018.07.002. Epub 2018 Oct 25.

Evidence for transmission of the zoonotic apicomplexan parasite Babesia duncani by the tick Dermacentor albipictus.

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Department of Biology, San Francisco State University, 1600 Holloway Ave, San Francisco, CA 94132, USA. Electronic address:
Department of Biology, San Francisco State University, 1600 Holloway Ave, San Francisco, CA 94132, USA.
Section of Infectious Diseases, Department of Medicine and Microbial Pathogenesis, Yale University, New Haven, CT, USA.
Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
California Department of Public Health, Vector-Borne Disease Section, Sacramento, CA 95899, USA.
California Department of Fish and Wildlife, Wildlife Investigations Laboratory, Rancho Cordova, CA 94570, USA.
Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA.


Babesiosis is a potentially fatal tick-borne zoonotic disease caused by a species complex of blood parasites that can infect a variety of vertebrates, particularly dogs, cattle, and humans. In the United States, human babesiosis is caused by two distinct parasites, Babesia microti and Babesia duncani. The enzootic cycle of B. microti, endemic in the northeastern and upper midwestern regions, has been well characterised. In the western United States, however, the natural reservoir host and tick vector have not been identified for B. duncani, greatly impeding efforts to understand and manage this zoonotic disease. Two and a half decades after B. duncani was first described in a human patient in Washington State, USA, we provide evidence that the enzootic tick vector is the winter tick, Dermacentor albipictus, and the reservoir host is likely the mule deer, Odocoileus hemionus. The broad, overlapping ranges of these two species covers a large portion of far-western North America, and is consistent with confirmed cases of B. duncani in the far-western United States.


Babesia duncani; Babesiosis; Dermacentor albipictus; Odocoileus hemionus; Vector-borne zoonotic disease

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