2.1.2. Babesia duncani A Babesia sp. (originally referred to as Babesia sp. WA1), morphologically indistinguishable from B. microti, was recognized in babesiosis patients from Washington and California in the early 1990s (Quick et al., 1993; Thomford et al., 1994). This parasite has been formally named B. duncani (Conrad et al., 2006). Although morphologically similar parasites have been reported from people in California previously, it is unknown if these were B. duncani or B. sp. CA type (Scholtens et al., 1968; Bredt et al., 1981). Importantly, cases have been documented in immunocompetent individuals with spleens as well as immunocompromised individuals and blood transfusion-acquired cases have been reported (Herwaldt et al., 2011; Bloch et al., 2012). Serological studies conducted near cases in California and Washington indicated that 3.5–16% of individuals were seropositive (Quick et al., 1993; Persing et al., 1995). Even higher seroprevalences have been reported among blood donors in several states outside the endemic range, which is likely due to movement of infected individuals or infection with one or more Babesia spp. that cross-react with B. duncani (Prince et al., 2010). Phylogenetic analysis of B. duncani indicated that it is in a separate clade from other Babesia species that includes B. conradae from dogs in California, a Babesia sp. from woodrats in Texas, B. lengau from cheetahs in Africa, and B. poelea and B. uriae from seabirds (Fig. 1) (Kjemtrup et al., 2000; Yabsley et al., 2005, 2006 a, 2009; Conrad et al., 2006; Bosman et al., 2010; Charles et al., 2012). This group was also related to Babesia sp. CA-type from humans in California and other Babesia from mule deer (Odocoileus hemionus) and bighorn sheep (Ovis canadensis) in California (Kjemtrup et al., 2000), Significantly, to date, neither a reservoir nor a tick vector has been identified. Testing of numerous rodent, insectivore, and lagomorph species in Washington was uniformly negative for B. duncani (Quick et al., 1993; Persing et al., 1995).

Published as part of Yabsley, Michael J. & Shock, Barbara C., 2013, Natural history of Zoonotic Babesia: Role of wildlife reservoirs, pp. 18-31 in International Journal for Parasitology: Parasites and Wildlife 2 on pages 22-23, DOI: 10.1016/j.ijppaw.2012.11.003, http://zenodo.org/record/10933713