| Emerging vector-borne zoonotic diseases arise from complex interactions among pathogens, bridge vectors, wildlife hosts, and humans. Ixodes scapularis - the blacklegged tick --- hosts a suite of zoonotic pathogens it in the Midwestern United States, including the agents of Lyme disease, human granulocytic anaplasmosis, and babesiosis. Risk of these diseases is increasing due in part to spread of I. scapularis. Over six years, I have investigated hypothesized co-invasion of I. scapularis and pathogens in the Midwest by tracking the spatial and temporal dynamics of invasion using of wild bird, mammal, pet dog, and vegetation drag surveys, with subsequent genetic analyses of pathogens. My studies operated not only where I. scapularis is readily found, but also in zones beyond its detected distribution yet susceptible to establishment.;In Michigan, I have documented in real-time a northward invasion of blacklegged ticks from a focal area of recent blacklegged tick detection on the west coast. White- footed mouse surveillance was most sensitive method for detection of low-density tick populations due to their importance for feeding immature ticks as well as the ease with which large sample sizes are acquired. Invasion was not as apparent in the eastward, inland direction, and future studies will address ecological parameters that may explain the differential distribution. Compared to the wildlife studies, surveillance of pet dogs was less sensitive for detection of blacklegged tick distribution, likely because of the common practice of canine tick chemoprophylaxis.;While the detected distribution of blacklegged ticks was focal and expanding, I detected a wider distribution of the Lyme disease pathogen, Borrelia burgdorferi, in alternative tick species and wildlife hosts. This pattern was most evident in bird-associated ticks at a focal site 90 km to the east of I. scapularis invasion front, where I. dentatus ticks removed from birds harbored 3.5% infection prevalence with B. burgdorferi, and no I. scapularis ticks were found. The B. burgdorferi strains found in this scenario of 'cryptic' transmission were comprised of many novel types not previously described from Lyme disease endemic areas, and also at least three strains previously associated with disseminated human Lyme disease. I hypothesize that cryptic cycles reduce the time lag between I. scapularis invasion and the build-up of infection prevalence, and may result in the introduction of novel strains to human and canines.;Across five states of the Midwest that represent a continuum of establishment of I. scapularis, I hypothesized that patterns of diversity of pathogens within I. scapularis may be useful in elucidating the broad-scale tick invasion and subsequent disease emergence. Analysis of 1565 adult I. scapularis ticks from 13 sites across five Midwestern states revealed that tick density, infection prevalence with multiple microbial agents, co-infections, and strain diversity of B. burgdorferi were positively correlated with the duration of establishment of tick populations, though observed differences were subtle. Cumulatively, these data suggest that the invasion of ticks and emergence of various tick-borne diseases may be more complex than the traditional scenario whereby infected, invading ticks are the only means of introduction of pathogens to naive communities. |
