Infection Dynamics In A Host-Pathogen System: House Finches (Carpodacus Mexicanus) And Mycoplasma Gallisepticum

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The transmission of parasites and pathogens among hosts remains an essential question in disease ecology. Transmission is rarely a simple process: variation among hosts, pathogens, the environment, and interactions of these factors can be crucial components in disease epidemics. In order to better understand the probability and rate that a pathogen spreads through a population, it is necessary to account for these multiple heterogeneities. House finches (Carpodacus mexicanus) are susceptible to a novel strain of the bacteria Mycoplasma gallisepticum, which causes conjunctivitis in the finches and other passerine species. I use both experimental work and long-term datasets on this host-pathogen system to better understand how both host and pathogen heterogeneities influence infection dynamics. I find that individual behaviors can influence the risk of infection. Behaviors associated with indirect transmission, rather than direct transmission, increase infection risk. Also, the risk of infection is lower for socially dominant birds, but highly social infected birds can increase infection risk for susceptibles. However, the relative importance of indirect and direct transmission of M. gallisepticum is not yet clear. Viability of M. gallisepticum on antimicrobial feeders designed to kill the bacteria is not significantly different than viability on standard feeders, preventing a true exclusion of indirect transmission from this system. This demonstrates that bacterial viability lasts longer than previously thought, further supporting feeders as an important source of M. gallisepticum. Bacterial load and distribution within and among house finch groups can predict infection probabilities, and these probabilities also show sex-based differences. Individual variation may also be responsible for the seasonal cycles of conjunctivitis: the introduction of naïve juveniles to a group of recovered adults causes an outbreak of M. gallisepticum, and reintroducing infected individuals to a group of multi-age, recovered individuals can also initiate a new wave of infections. Finally, community structure influences patterns of disease prevalence within house finches. Higher abundances of northern cardinals and American goldfinches were associated with higher disease prevalence in house finches. Taken together, these results show that heterogeneities within a host-pathogen system are essential to understanding how variation in infection patterns may influence disease dynamics.

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Dhondt, Andre Alfons

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Schat, Karel Antoni
Lovette, John I
Zamudio, Kelly

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Ph. D., Ecology

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Doctor of Philosophy

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dissertation or thesis

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