Lyme borreliosis (LB) is the most prevalent tick-borne disease in Europe. The most common clinical manifestation is an erythema migrans, a red expanding rash at the site of the tick bite. If left untreated, the infection can disseminate, causing more severe disease. In addition, patients may report persisting non-specific symptoms after treatment, a syndrome often referred to as post-treatment Lyme disease syndrome (PTLDS). Although, in Belgium, different surveillance systems have been in place to follow-up LB trends since many years, knowledge gaps have remained. This thesis aims to contribute to the assessment of the burden of LB in Belgium, amongst others, by setting up a prospective cohort study. This work resulted in estimations of the incidence of the clinical manifestations of LB, the proportion of patients developing PTLDS and the costs related to the disease. In addition, the occurrence of other tick-borne infections in patients with a tick bite in Belgium was investigated. ; (SP - Sciences de la santé publique) -- UCL, 2021