Abstract
California, with 13 chipmunk (Tamias) species, has more than any other state or country, occupying habitats ranging from chaparral to the high peaks of the Sierra Nevada. Chipmunks host zoonotic pathogens including Yersinia pestis, Anaplasma phagocytophilum, relapsing fever (RF) Borrelia spp., Borrelia burgdorferi, and spotted fever group (SFG) Rickettsia species. Chipmunk species are often not differentiated by public health workers, yet different species utilize different ecological niches and may have intrinsically different capacities for maintaining vector-borne pathogens and infecting vectors. We surveyed over 700 individuals from nine species of chipmunks throughout California for exposure to and infection by Y. pestis, A. phagocytophilum, RF Borrelia spp., Borrelia burgdorferi, and SFG Rickettsia species. DNA of all five pathogens was found and all chipmunks except Merriam’s chipmunk (T. merriami) were PCR-positive for at least one of the pathogens. Anaplasma phagocytophilum was most common (40.0%, 2/5) in Sonoma chipmunks (T. sonomae) from Marin county and B. burgdorferi most common (37.5%, 27/72) in redwood chipmunks (T. ochrogenys) from Mendocino county. RF Borrelia spp. was detected in 2% (6/297) of redwood chipmunks in Mendocino county and 10% (1/10) of both least (T. minimus) and lodgepole (T. speciosus) chipmunks in the western Sierra. Exposure to SFG Rickettsia spp. was found in the Northern Coastal region (Del Norte, Humboldt and Mendocino counties) and in the northern and western Sierra in several species of chipmunks. Y. pestis infection was found only in the western Sierra—in a yellow-pine (T. amoenus) and a long-eared (T. quadrimaculatus) chipmunk. Though more data are needed to thoroughly understand the roles that different chipmunk species play in disease transmission, our findings suggest that some chipmunk species may be more important to the maintenance of vector-borne diseases than others within each geographic area.
Highlights
Chipmunks (Tamias spp.) are small, terrestrial, diurnal mammals characterized as a genus by rapid reproductive rates and high population densities [1]
We surveyed over 700 individuals from nine species of chipmunks throughout California for exposure to and infection by Y. pestis, A. phagocytophilum, relapsing fever (RF) Borrelia spp., Borrelia burgdorferi, and spotted fever group (SFG) Rickettsia species
Y. pestis is potentially fatal in chipmunks as well as humans [9], while A. phagocytophilum, RF Borrelia spp., B. burgdorferi and SFG Rickettsia spp. are zoonoses but not known to cause clinical disease in chipmunks [10,11,12,13]
Summary
Chipmunks (Tamias spp.) are small, terrestrial, diurnal mammals characterized as a genus by rapid reproductive rates and high population densities [1]. Chipmunks host important zoonotic pathogens in the western United States including Yersinia pestis, the causative agent of plague, Anaplasma phagocytophilum, which causes granulocytic anaplasmosis, relapsing fever (RF) Borrelia spp., Borrelia burgdorferi, the agent of Lyme disease, and spotted fever group (SFG) Rickettsia species [4,5,6,7,8]. In the eastern-central Sierra Nevada, ranges of the lodgepole (T. speciosus), least (T. minimus), yellow-pine (T. amoenus), Allen’s (T. senex), and Uinta chipmunks (T. umbrinus) overlap at elevations between approximately 1800 and 2700m. On the western slope of the central Sierra Nevada, the long-eared (T. quadrimaculatus), lodgepole, Allen’s and Merriam’s chipmunk are found at elevations close to 1800m [14, 15]. On the western slope of the central Sierra Nevada, the long-eared (T. quadrimaculatus), lodgepole, Allen’s and Merriam’s chipmunk are found at elevations close to 1800m [14, 15]. (For distribution maps for all California chipmunk species, see pages 210–225 of [15] and for maps depicting the overlaps of Sierra Nevada chipmunk species, see pages 315–317 of [14].) Chipmunks share vector-borne pathogens with woodrats (Neotoma spp.), deer mice (Peromyscus spp.), and other sciurids such as the western grey squirrel (Sciurus griseus), California ground squirrel (Otospermophilus beecheyi), and Douglas squirrel (Tamiasciurus douglasii) [4, 16,17,18,19,20,21,22,23]
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