Doctoral Dissertations

Orcid ID

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Comparative and Experimental Medicine

Major Professor

Richard W. Gerhold Jr.

Committee Members

Debra L. Miller, Marcy J. Souza, Mary Katherine Tolbert


Understanding the role of bird baths and shared water sources in the ecology and epidemiology of the deadly protozoan parasite Trichomonas gallinae is crucial to identify mitigation strategies for population-limiting epidemics. We evaluated multiple factors that influence the transmission of this pathogen including characterizing persistence in simulated bird baths, evaluating potential effects persistence may have on virulence, and investigating the molecular epidemiology of a concurrent outbreak. Trichomonads were thought to be extremely labile in the environment since their discovery over 200 years ago to 5 years ago when maximum recorded persistence in water was 20 min. We show that trichomonads persist up to 48 hr in simulated bird baths at 37°C with organic material (OM). We also measured persistence in a variety of conditions including, with and without organic material (4 and 16 hr, respectively), with artificially decreased dissolved oxygen (30 hr), and with exposure to UV light (4hr). Moreover, when cytopathic effect (CPE) of post-persistence trichomonads on cultured avian cells was compared to non-persistence control isolates, virulence changed significantly by treatment or persistence time. Post-UV treated persistence broad-winged hawk isolate destroyed significantly more of the cell monolayer than those from the OM treatment illustrating that persistence type can alter virulence. Currently, live animal or cell culture infection trials are the only tool to define virulence of an isolate; however, the more we understand the phylogenetics and epidemiology of Trichomonas spp, the better we can contribute phenotypic differences to genetic data. Using molecular techniques, we showed that circulating genotypes in subclinical hunter-killed doves differ from birds with lesions consistent with trichomonosis. Therefore, hunter-killed doves may not be the source of deadly strains circulating in other sympatric species. Combining laboratory work with the parasite, assessment of virulence on cell culture, and molecular techniques we have shown that the role of bird baths and water sources in transmission cannot be underestimated when addressing outbreaks and that molecular information will continue to improve our effects to mitigate the disease in wild birds.


A version of Chapter 2 was previously published by Kathryn E. Purple, Jacob M. Humm, R. Brian Kirby, Christina G. Saidak and Richard Gerhold: Purple, K., Humm, J.M., Kirby, R.B., Saidak, C.G., and Gerhold, R. 2015. Trichomonas gallinae persistence in four water treatments. J. Wildl. Dis. 51, 739– 742. A version of Chapter 3 was published by Kathryn E. Purple and Richard Gerhold: Purple, K.E., Gerhold, R.W., 2015. Persistence of Two Isolates of Trichomonas gallinae in Simulated Bird Baths With and Without Organic Material. Avian Dis 59, 472-474. A version of Chapter 4, Artificially decreased dissolved oxygen increases the persistence of Trichomonas gallinae in water, has been submitted for publication by Kathryn E. Purple, Todd Amacker, Chauntelle Williams, and Richard Gerhold to the American Society of Microbiologists Journal of Applied and Environmental Microbiology.

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