Sessions

Infectious diseases present an increasing threat to wildlife populations worldwide. The spread of infections is influenced by individual traits, population characteristics and environmental factors, such as the condition of individuals, population density and human-modified habitats. Ophidiomyces ophidiicola is the fungal pathogen causing snake fungal disease, to which aquatic and semi-aquatic species are highly susceptible.

Our study’s primary aim was the detection of O. ophidiicola in the dice snake (Natrix tessellata) populations of Lake Balaton. Furthermore we aimed to investigate how individual (sex, body size, condition) and population (density) characteristics, local variables, proximity of roads and landscape variables affect the probability of infection.

During our survey we designated 23 study sites around Lake Balaton. To determine population density we counted the snakes along a 250 metre transect on every site. Afterwards, in order to detect the fungal infection, we collected samples from the surface of the skin of six snakes per site using sterile swabs. We recorded the sex, body weight and body size of each snake as individual variables. In the laboratory, we isolated the DNA from the collected samples and used quantitative PCR to detect the pathogen. On a local level, we characterised our study sites by the percentage of vegetation cover as well as the area of artificial lakeside paving. To estimate the effect of road proximity, we measured the distance of the site’s transect from the nearest road and the main road. We used the extent of urban areas, paved surfaces, roads and aquatic vegetation cover together with the inner area of the settlements to characterise our study sites on a landscape level.

Out of the 136 sampled dice snakes from around Lake Balaton, 21 proved to be positive for O. ophidiicola infection. On a local scale, the area of artificial shoreline paving had a positive effect on the probability of infection, meaning that the likelihood of infection was higher on the habitats with larger extent of artificial paving. Presumably, this is the result of dice snakes particularly liking the artificial lakeside paving where they occur in large numbers during their mating period in the spring, which increases the chance of infection. In addition, the proximity of the nearest road also had a positive effect on the probability of infection, meaning that areas further away from the road had higher chances of infection. This can presumably be explained by the microclimate in the vicinity of the road, which is less favourable for the fungal infection.

Our study is the first to detect O. ophidiicola, the causative agent of snake fungal disease in dice snake populations around Lake Balaton. Our results also indicate that human induced habitat modifications – namely the extent of artificial shoreline paving and the presence of roads – considerably affect the probability of infection.