Doctoral Dissertations

Date of Award

8-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Comparative and Experimental Medicine

Major Professor

Richard W. Gerhold

Committee Members

Chunlei Su, Agricola Odoi, John J. Schaefer

Abstract

Toxoplasma gondii is a single celled, apicomplexan parasite with a complicated life cycle. Felids are the definitive hosts, and shed oocysts in their feces, which are extremely hardy in the environment. Intermediate hosts maintain a life-long infection with the parasite encysted in tissues. Due to this phenomenon, being seropositive is indicative of infection. The transmission dynamics between cats and wildlife is not completely understood. With its zoonotic risk, it is important to understand how T. gondii is spreading between domestic and wild populations. We sought to deepen the understanding of the dynamics between free-roaming cat populations and select wildlife species. With the three R’s of animal research (Reduce, replace, refine) in mind, we developed an isolation technique that directly inoculates cell culture without the need for animal subjects. In order to develop a standardized procedure, the authors developed a protocol for this technique. Experimental in vitro isolation of the parasite was successful in 3/5 (60%) ducks, 4/4 (100%) turkeys, 1/6 (17%) white-tailed deer, and 4/6 (67%) kangaroos using Vero or Human Foreskin Fibroblast (HFF) cells. Isolation was successful in 5 (100%) duck samples using mouse bioassay. Isolates were confirmed using multiloculus PCR-RFLP markers. To investigate the presence of the parasite in different populations, blood samples were tested using the Modified Agglutination Test (MAT). Free-roaming domestic cats in East Tennessee showed 56.4% (2,757/4,863) seropositive. Age was determined as a significant (p=Toxoplasma gondii is emerging in many novel species and has unknown effects on naïve populations. Understanding these dynamics is important for mitigation of future infections in both humans and animals.

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