The Effects of Latent Infection of Toxoplasma gondii on the Domestic Cat

Domestic cats have a worldwide T. gondii seroprevalence of 30-40% and play pivotal roles in this parasite’s transmission: it reproduces sexually only in felid intestines, after which it is shed in their feces. Asymptomatic T. gondii infection is associated with bradyzoite-containing brain cysts that produce tyrosine hydroxylase. Elevated dopaminergic tone is thought to underlie increased locomotor, risk-averse, and exploratory behavior in many infected animals. However, the effect on cat behavior is unknown. We propose that latent T. gondii infection in domestic cats similarly alters their behavior to increase its spread. This follows from the well-supported ‘fecal-exposure’ hypothesis: if T. gondii mediates the size of a cat’s home range characteristics, then it will direct where soil is contaminated with T. gondii and influence parasite exposure in intermediate hosts and in cats with overlapping home ranges. Since many species have subtle behavior alterations following T. gondii infection, we are testing whether T. gondii alters behavioral characteristics of its definitive host. Specifically, we hypothesize that chronic T. gondii infection in domestic cats decreases their risk-averse behavior and leads to increased locomotor activity. We have built an on-line survey to assess understanding of T. gondii infection and risks and recruited owners of pet cats from the participants. We then cross-sectionally evaluated whether risk-aversion and locomotory activity in their pets differ by seropositive status. In one behavioral paradigm, cat behavior is recorded over a series of episodes with and without the owner. When the owner is present, s/he sits and interacts with their cat. After an initial set of familiarization episodes, a balanced scent-based paradigm is used to evaluate a risk-averse response. We demonstrate that this least-invasive paradigm is useful to infer behavioral changes that may result from alteration of dopamine tone via T. gondii infection. This work provides an understanding of how T. gondii infection impacts cat behaviors to influence parasite spread. It also contributes to a theoretical framework to understand the impact of the risk of infection by fecal-transmitted parasites in an ecologically relevant setting.