Domaines de recherche

PhD Thesis

Lyme disease is the most common vector-borne disease in the temperate regions of the northern hemisphere. This multisystemic inflammatory disorder is caused by spirochete bacteria of the Borrelia burgdorferi sensu lato (sl) genospecies complex, which are transmitted among vertebrate hosts by the hard ticks of the genus Ixodes. In Europe, the main vector responsible for transmitting the disease to humans is the sheep tick, I. ricinus. Its distribution is wide across Europe, ranging from Ireland to the Urals, and from northern Sweden to North Africa. Abiotic factors such as climate and biotic factors such as the community of host species and vegetation structure affect the geographic distribution and seasonal abundance of I. ricinus ticks, and the prevalence of tick-borne diseases. For example, abiotic variables such as temperature, relative humidity, and saturation deficit are known to influence questing behavior and life history traits (development and mortality), and ultimately phenology and abundance. Climate change in Europe is believed to have increased the expansion of I. ricinus ticks towards northern latitudes in Scandinavia and towards higher altitudes in Central Europe. Given the importance of alpine tourism and leisure activities in Switzerland, changes in the altitudinal abundance of I. ricinus ticks may have important consequences for the risk of exposure to tick-borne pathogens. The dramatic variation in tick abundance across an altitudinal gradient is therefore an interesting system for studying how climate variables influence tick abundance and the prevalence of tick-borne pathogens. The aim of my PhD thesis is to better understand how climate and elevation influence the ecology of I. ricinus ticks and the prevalence of tick-borne pathogens at different elevations. We used data from a long-term study that had monitored the abundance of I. ricinus ticks at four different elevations (620, 740, 900, and 1073 m above sea level) on Chaumont Mountain, in Neuchatel, Switzerland. These four sites were sampled on a monthly basis over a period of 14 years from January 2004 to December 2017. We will use environmental variables such as air temperature, relative humidity, and saturation deficit to determine how climate and elevation affect the abundance of I. ricinus ticks and the prevalence of tick-borne pathogens.

Master Thesis

The fungal pathogen, Batrachochytrium dendrobatidis (Bd), causes chytridiomycosis, an infectious disease in amphibian hosts. Chytridiomycosis has been associated with mass mortality and local extinction events of amphibian populations around the world. Bd is a water-borne pathogen that is directly transmitted between tadpoles and adult frogs when the latter return to their breeding ponds. The purpose of my Master thesis project was to test whether anti-fungal treatment of a temperate zone amphibian, the common midwife toad (Alytes obstetricans) can interrupt the epidemiology of chytridiomycosis. I worked in collaboration with Dr. Benedikt Schmidt, head of the ‘Conservation Biology of Amphibians’ research group at the University of Zurich and his PhD student, Corina Geiger. Corina surveyed six populations of the common midwife toad for Bd on a monthly basis over a period of one year. The toads in three of the six populations were treated with an anti-fungal treatment during the summer months. Corina and I used qPCR to determine the prevalence of Bd infection and the Bd zoospore load over time in each of these six populations. I used generalized linear mixed effects models to analyze whether the epidemiology of Bd in the toad populations differs between the treated and control ponds.