Online

Looney, Raymond M.

Biology

2023

M.S.

Amphibian populations are declining globally and are seriously threatened by emerging infectious diseases. Most local amphibian die-offs are caused by Ranavirus (Family: Iridoviridae), and these die-offs can contribute to the risk of local population extinction. Ranaviruses are not particularly well studied, specifically, not much is known about their transmission dynamics and the impact that different transmission routes may have on amphibian population dynamics. The primary pathways for Ranavirus transmission are direct contact, necrophagy (consumption of dead individuals), and transmission through contact with virions in the water. My work specifically focuses on transmission through water and through contact with bird feathers, and its consequences for Ranavirus transmission to amphibian populations throughout the state of Vermont. I also investigated whether natural bodies of water that contain amphibian populations can test positive for Ranavirus and at what rate the virus persists across years. I investigated the ability for avian species to host Ranavirus on their wetted feathers by using the Canada goose (Branta canadensis) as a model study species. In the summer of 2019, 192 individuals of B. canadensis were swabbed along their wet abdomens to test for Ranavirus presence. To identify whether Ranavirus could be detected in natural bodies of water throughout Vermont, environmental DNA (eDNA) was collected from geese feathers and water sources at sites that had been previously tested for Ranavirus presence in amphibian populations. With quantitative PCR, viral DNA was extracted and amplified to test for the presence of Ranavirus. 13.9% of swab samples and 4.5% of filter samples tested positive for Ranavirus. Swab samples detected significantly more virus than filter samples (P<0.0005). Average viral load between samples was significantly higher in swab samples among sites (P<0.05). Ranavirus prevalence was estimated from a beta distribution and was significantly higher in swab samples (0.139, 95% CI [0.191, 0.094]) when compared to filters (0.045, 95% CI [0.082,0.018]). Building on the key result that that avian species can carry Ranavirus on their wetted feathers, I constructed a compartmental ordinary differential equation (ODE) model of the population dynamics of susceptible, infected, and dead amphibians. Although this initial model is too basic to accurately predict amphibian disease dynamics, it will be useful to understand whether geese are potential vectors of transmission of Ranavirus. In this paper I describe the structure of the model and how I will modify it to create a spatially explicit network model that predicts transmission through space and time and uses mark-recapture data to visualize how geese may visit different areas. This thesis documents the first reports of Ranavirus being detected on the feathers of waterbirds and the first reports of Ranavirus being detected in natural bodies of water in Vermont.