Research :: Microbial Community Ecology of Tick-Borne Human Pathogens
Summary
Tick Ovary with Eggs
Dog tick, Dermacentor variablis
Lone Star ticks, Amblyomma americanum
IU/BSU Tick Team - Spring 2004
Nate & Jeff
The goal of this research is to characterize the microbial communities of several common tick species using DNA sequence-based techniques, analyze patterns of co-occurrence among microbial taxa, and mathematically model the consequences of those patterns on epidemiological dynamics of tick-borne pathogens. In particular, tick-borne microbial communities will be analyzed for evidence of competitive exclusion or mutual facilitation among species. Ecological interactions among species are one of the most important factors shaping community structure. Much research has demonstrated that ticks may simultaneously harbor multiple bacterial species, including symbionts transmitted through eggs and pathogens transmitted through bites. Habitat alteration, expanding ranges of tick vectors, and increased populations of shared animal hosts make the movement of pathogenic microorganisms among tick species more likely.
On a worldwide basis, ticks serve as vectors for more human pathogens than any other arthropod. In the United States, the large majority of cases of vector-borne disease arise from tick bites (e.g. Lyme Disease), and new tick-borne pathogens are regularly being discovered. This research will contribute to our basic understanding of microbial communities of arthropods and the epidemiology of pathogen transmission. Further, this research will have a practical impact on management of tick-borne diseases and our understanding of the relationship between invasion of tick vectors and the emergence of novel, or more highly virulent, human pathogens.
Details
In collaboration with Clay Fuqua, Curt Lively, Mike Wade (all at Indiana University) and Bob Pinger (Ball State University), we are investigating the microbial community ecology of tick-borne human pathogens. We are characterizing the microbial communities of three local tick species to analyze patterns of co-occurrence among microbial taxa. In particular, we are interested in whether avirulent symbionts may exclude human pathogens from tick communities. Ticks carry a diversity of microbes acquired by feeding on infected hosts or by vertical transmission through eggs, and are the number one source of vector-borne disease in the US. In Indiana, the black-legged tick (Ixodes scapularis, vector of Lyme Disease) is invading from the north while the lone star tick (Amblyomma americanum, vector of human ehrlichiosis) is invading from the south. The dog tick (Dermacentor variablis, vector of Rocky Mountain Spotted Fever) is widely established throughout the state. This situation provides an opportunity to evaluate how changing tick distributions and overlapping host ranges, and microbial interactions within ticks, affect the prevalence of tick-borne human pathogens. Initial results have revealed a novel group of vertically-transmitted bacteria (Arsenophonus) in all tick species thus examined (Grindle et al. 2003). Microbial interactions within arthropod vectors represent a potential determinant of human disease. This project is funded by the NIH/NSF Ecology of Infectious Disease Program (EID).
In addition, with John Colbourne and Peter Cherbas (Indiana University Center for Genomics and Bioinformatics), we are constructing and analyzing a high density cDNA library and cDNA-based DNA microarrays to study the molecular biology of Amblyomma americanum, the lone star tick (http://cgb.indiana.edu/genomics/projects/11). The genomic resources developed during this project will be used in studying the developmental biology, cytology and host-microbe interaction for this important disease vector.
Further, in collaboration with John Colbourne (CGB), Clay Fuqua (Biology) and Frank Yang Indiana University Medical School, and with the support of the Indiana University METACyt Program, we intend to develop novel, critical experimental methodologies for studying polymicrobial infection in the Lone Star tick, Amblyomma americanum, and to assess influences of polymicrobial infection on tick vector-pathogen interactions, including changes in the tick transcriptome, proteome and metabolome. Establishing methodologies to study polymicrobial infection in tick vectors is critical for understanding tick-pathogen interactions and transmission to human hosts.