[What should you request to the laboratory for a patient bitten by a tick ?].

Ticks are a growing concern for the public, owing to their abundance and a longer activity season. In Switzerland, more than 99% of ticks removed from humans are of the species Ixodes ricinus. This article reviews the tick-borne diseases documented in the country : Lyme borreliosis, tick-borne encephalitis, tularaemia, neoehrlichiosis, anaplasmosis, babesiosis, Borrelia miyamotoi relapsing fever, and rickettsiosis. Carriage of a microorganism by a tick does not imply infection, just as isolated seropositivity does not imply disease. Testing should be guided by pretest probability and disease stage, using validated assays only. Here, the laboratory is a key partner : it guides test selection and the interpretation of results, helping to avoid both under and overdiagnosis.