Borrelia miyamotoi is a relapsing fever spirochete transmitted by ticks in the Ixodes ricinus complex, which are known to vector many pathogens, including Borrelia burgdorferi sensu lato, the agents of Lyme borreliosis. Borrelia miyamotoi was first discovered in Japan in 1995, and then in 1999 it was detected in I. scapularis in the eastern United States. After being recognized as a human pathogen in Russia in 2011, human case of B. miyamotoi infection has been continuously reported in the United States and Eurasia. Despite being discovered more than 20 years ago, very little is known about how B. miyamotoi is maintained in nature. Most knowledge about the ecology of B. miyamotoi has been acquired incidentally from studies focused on B. burgdorferi sensu lato. My dissertation research, therefore, aimed to improve understanding about how B. miaymotoi is maintained among the vector and wildlife hosts. In each chapter of my dissertation, I investigated fundamental components of B. miyamotoi maintenance in the enzootic cycle and discussed potential implication of my finding for public health. In chapter 1, I estimated acarological risk of B. miyamotoi infection by investigating B. miyamotoi infection prevalence and density of infected ticks (DIT) from field collected larval, nymphal and adult I. scapularis from Wisconsin (WI) and Massachusetts (MA), where I. scapularis and associated pathogens are highly abundant, and where human cases of B. miyamotoi have been reported. I found that larvae and nymphs pose broadly similar B. miyamotoi acarological risk, and the two juvenile stages may pose greater risk than do the adults. Therefore, I suggested that estimates of acarological risk as well as the seasonality for I. scapularis-borne diseases should be expanded to incorporate larvae. Reservoir hosts of juvenile and adult ticks, small mammals and white-tailed deer (Odocoileus virginianus), respectively, were investigated for their roles in B. miyamotoi maintenance. Borrelia miyamotoi infection prevalence of small mammal hosts captured in Wisconsin was investigated to identify potential reservoir host species in chapter 2, and I compared the infection prevalence of B. miyamotoi in adult ticks removed from white-tailed deer with that in questing adults in chapter 3. The results showed potentially low or limited reservoir competence of white-footed mice for B. miyamotoi and highest infection prevalence from eastern chipmunks. Significantly higher infection prevalence of deer blood-fed females than that of questing females was observed, suggesting deer may be amplifying hosts for B. miyamotoi. Transovarial transmission (TOT) rate and filial infection prevalence (FIP) of B. miyamotoi were investigated from engorged females and their larval clutches, which were collected from hunter-harvested white-tailed deer in chapter 4. The result showed that TOT and FIP are high, but < 100%, which suggests that vertical transmission alone will be insufficient to support the enzootic maintenance of B. miyamotoi infection. In chapter 5, I used the next-generation matrix model to investigate the effects of systemic, non-systemic (co-feeding), and vertical transmission on B. miyamotoi maintenance by R0. Model results indicated potential significant contributions of non-systemic and vertical transmission on B. miyamotoi maintenance, whereas systemic transmission showed minimal effects on R0 of B. miyamotoi.
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