title: An Ixodes minor and Borrelia carolinensis enzootic cycle involving a critically endangered Mojave Desert rodent.
abstract: Microtus californicus scirpensis is an endangered, isolated subspecies of California vole. It requires water pools and riparian bulrush (Schoenoplectus americanus) and occupies some of the rarest habitat of any North American mammal. The minimally vegetated, extremely arid desert surrounding the pools is essentially uninhabitable for Ixodes species ticks. We describe an enzootic cycle of Borrelia carolinensis in Ixodes minor ticks at a site 3500 km distant from the region in which I. minor is known to occur in Tecopa Host Springs, Inyo County, eastern Mojave Desert, California. Voles were live-trapped, and ticks and blood samples queried by PCR and DNA sequencing for identification and determination of the presence of Borrelia spp. Between 2011-2013, we found 21 Ixodes minor ticks (prevalence 4-8%) on Amargosa voles and Reithrodontomys megalotis. DNA sequencing of 16S rRNA from ticks yielded 99% identity to I. minor. There was 92% identity with I. minor in the calreticulin gene fragment. Three ticks (23.1%), 15 (24%) voles, three (27%) house mice, and one (7%) harvest mice were PCR positive for Borrelia spp. Sequencing of the 5S-23S intergenic spacer region and flagellin gene assigned Amargosa vole Borrelia strains to B. carolinensis. Ixodes minor, first described in 1902 from a single Guatemalan record, reportedly occurs only in the southeast American on small mammals and birds. The source of this tick in the Mojave Desert and time scale for introduction is not known but likely via migratory birds. Borrelia strains in the Amargosa ecosystem most closely resemble B. carolinensis. B. carolinensis occurs in a rodent-I. minor enzootic cycle in the southeast U.S. although its epidemiological significance for people or rodents is unknown. The presence of a tick and Borrelia spp. only known from southeast U.S. in this extremely isolated habitat on the other side of the continent is of serious concern because it suggests that the animals in the ecosystem could be vulnerable to further incursions of pathogens and parasites.
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California 1320 Tupper Hall, Davis, California, 95616.
authors.forename: Janet
authors.initials: J
authors.lastname: Foley
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California 1320 Tupper Hall, Davis, California, 95616.
authors.forename: Caitlin
authors.initials: C
authors.lastname: Ott-Conn
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California 1320 Tupper Hall, Davis, California, 95616.
authors.forename: Joy
authors.initials: J
authors.lastname: Worth
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California 1320 Tupper Hall, Davis, California, 95616.
authors.forename: Amanda
authors.initials: A
authors.lastname: Poulsen
authors.affiliation: Wildlife Investigations Lab, California Department of Fish and Wildlife 1701 Nimbus Road, Rancho Cordova, California, 95670 ; Wildlife Health Center, University of California Davis, California, 95616.
authors.forename: Deana
authors.initials: D
authors.lastname: Clifford
keywords: 16S rRNA; Amargosa vole; Borrelia burgdorferi sensu lato; Microtus californicus scirpensis; Migration; calreticulin