[Characteristics of the "tache noire" of boutonneuse fever]

Humans show little sensitivity to the bites of healthy Rhipicephalus sanguineus and the skin lesion is extremely slight. The "tache noire" - innoculation eschar - corresponding to the infecting bite of the tick with R. conori is discussed and histopathological findings reported. The patient is frequently unaware of the eschar on his body and elements relating to the duration of the infecting bite are deduced. Apart from its typical features, the tache noire may be very small, with surrounding hyper-ergic reaction, or it may even not be present, depending on different conditions of tissue reactivity. The pathogenesis is mentioned and the need for careful research for diagnostic purposes stressed.