Epidemiological and environmental risk factors of tick-borne diseases : combining hazard and exposure

Tick-borne diseases are infectious diseases transmitted by the bite of infected ticks. Usually circulating in animal populations but occasionally transmitted to humans, they are a complex system involving a pathogen, a vector, natural or accidental hosts and the environment. In order to understand disease dynamics and mitigate the risk, there is a crucial need for a better understanding the factors determining their spatial distribution. Focusing on Belgium, the main objectives of this thesis were: 1) to assess the risk of tick-borne diseases, and 2) to identify the epidemiological and environmental risk factors affecting the risk of tick-borne diseases. Assessing the risk of tick-borne diseases can be done by focusing on the vector, animal hosts or humans. Focusing of humans allows us to also highlight variables associated to the exposure part of the risk. Indeed, risk assessment is a combination of hazard (related to vector and host ecology) and exposure (possibility of contact between humans and infected vectors). This dissertation allows expanding the knowledge of Lyme disease in Belgium. For the first time, a comparison of the risk of infection with tick-borne diseases between populations with different risk profiles is achieved. A robust methodology is developed to identify environmental and individual risk factors by integrating both aspect linked to the hazard and the exposure part of the risk. This innovative methodology is applied to study the risk of tick bites in a population of Scouts and the seroprevalence of Borrelia burdgdorferi in two groups professionally exposed: Belgian veterinarians and farmers and forest rangers. This dissertation demonstrates that the exposure of people has a great impact on the risk. Therefore, prevention of tick bites both for population at risk through their professional or recreational activities is very important to reduce tick-borne diseases in Belgium.