Distribution and prevalence of vector-borne diseases in California chipmunks (Tamias spp.)

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.加利福尼亚州拥有13种花栗鼠（Tamias属）物种，数量多于全美任意一州乃至全球其他国家，其栖息生境涵盖灌丛地带至内华达山脉的高海拔峰巅。花栗鼠可携带多种人兽共患病病原体，包括鼠疫耶尔森菌（Yersinia pestis）、嗜吞噬细胞无形体（Anaplasma phagocytophilum）、回归热疏螺旋体（RF Borrelia spp.）、伯氏疏螺旋体（Borrelia burgdorferi）以及斑点热群立克次体（SFG Rickettsia species）。公共卫生从业者通常难以区分不同花栗鼠物种，但不同物种占据的生态位各不相同，其维持虫媒病原体以及感染媒介昆虫的内在能力或存在本质差异。我们对加利福尼亚州全域范围内9种花栗鼠的700余只个体开展了采样调查，以检测其是否暴露于或感染上述5种病原体。所有5种病原体的DNA均被检出，除梅里亚姆花栗鼠（T. merriami）外，其余所有花栗鼠样本均至少对一种病原体呈PCR阳性反应。嗜吞噬细胞无形体在马林县的索诺马花栗鼠（T. sonomae）中检出率最高（40.0%，2/5），而伯氏疏螺旋体在门多西诺县的红杉花栗鼠（T. ochrogenys）中检出率最高（37.5%，27/72）。回归热疏螺旋体在门多西诺县的红杉花栗鼠中检出率为2%（6/297）；在西内华达山区的最小花栗鼠（T. minimus）与黑松花栗鼠（T. speciosus）中，检出率均为10%（1/10）。针对斑点热群立克次体的暴露情况在北海岸地区（德尔诺特县、洪堡县及门多西诺县）以及内华达山脉北部与西部的多种花栗鼠中均有发现。鼠疫耶尔森菌感染仅在西内华达山区被检出，分别采自一只黄松花栗鼠（T. amoenus）与一只长耳花栗鼠（T. quadrimaculatus）。尽管需要更多数据以全面阐明不同花栗鼠物种在疾病传播中所扮演的角色，但本研究结果表明，在每个地理区域内，部分花栗鼠物种在维持虫媒疾病的传播循环方面可能比其他物种更为关键。