Abstract This paper is concerned with Bartoszyński's process for rabies viruses introduced by Bartoszyński [R. Bartoszyński, A model for risk rabies, ISI invited paper No. 9, ISI 1–9, IX Warsaw, 1975, pp. 545–552; Math. Biosci. 24 (1975) 355; W. Klonecki (Ed.) Proceedings of the IASPS Symposium to honour Jerzy Neyman, Warsaw, 1976, pp. 19–28]. Our main interests are in developing mechanisms of a symptom – how the probability of the occurrence of the symptom is related to the process. Four mechanisms are suggested based on various biological backgrounds. The main variable of interests is the survival time – the time elapsing between initial infection and the occurrence of the symptom. Analytical results about the survival functions induced from the four suggested mechanisms are studied.