Ecology and Epidemiology of Lyme Disease in Western North America.

Simple Summary: Lyme disease affects about half a million Americans every year, and cases in Canada are rising. However, the number of studies focusing on the epidemiology of Lyme disease in western North America has been relatively low compared to that of eastern North America. Here, we aim to summarize the current state of knowledge regarding Lyme disease epidemiology in western North America, which includes current surveillance efforts tracking Lyme disease cases, modelling studies clarifying the geographic distributions of vectors for Borrelia burgdorferi, and the dynamics required to maintain and transmit B. burgdorferi in the natural environment. In providing a comprehensive picture of the state of Lyme disease in western North America, this review may be particularly helpful for future studies in the region. Lyme disease is the most common vector-borne disease in the United States and Canada. The causative agent of Lyme disease in North America is the spirochete Borrelia burgdorferi. In western North America, the primary vector of Borrelia burgdorferi is the western black-legged tick, Ixodes pacificus. Surveillance and modelling efforts indicate that I. pacificus is primarily found in coastal California, Oregon, Washington and the southern coastal regions of British Columbia However, infection rates with B. burgdorferi among I. pacificus ticks remain low, ranging from 0.6% to 9.9%. Lyme disease case numbers in western North America are also relatively low compared to eastern North America. Enzootic maintenance of B. burgdorferi by hosts in natural environments and climatic factors may influence Lyme disease risk. The borreliacidal western fence lizard, Sceloporus occidentalis, may contribute to the low infection rates observed in I. pacificus ticks, while the migratory nature of avian hosts can allow for long-distance tick dispersal. Moderately warm and moist environments and protection from sunlight define the suitable habitats of I. pacificus ticks. In this review, we discuss the ecology and epidemiology of Lyme disease in relation to I. pacificus, as well as the need for more studies in western North America. [ABSTRACT FROM AUTHOR]