For many of the infections described in later chapters there is more than one reservoir species involved in maintaining the microparasite in nature, and the number of species recognized as reservoirs continues to increase. For example, while rodents have long been identified as reservoirs of numerous arthropod-borne infections, until recently relatively little was known about the role of shrews, despite them often sharing habitat and ectoparasites with rodents. Recent studies have suggested that shrews may play at least as important a role as rodents in maintaining B. burgdorferi and other tick-borne infections in both the USA and Europe. This highlights the fact that as continued ecological and epidemiological studies are conducted, the list of potential reservoir hosts will increase.