New pathogens, and diseases old and new. I) Afipia felis and Rochalimaea. II) Parvovirus B 19. III) herpesvirus 6.

The paper describes events that in the last fifteen years, have led to the identification of the aetiological agents of three widely known diseases: cat scratch disease, erythema infectiosum and exanthem subitum. The particular features of Afipia felis and Rochalimaea, Parvovirus B 19 and Herpesvirus 6 are presented. The paternity of new diseases (i.e. bacillary angiomatosis, bacillary peliosis hepatitis, LES-like syndrome, chronic fatigue syndrome, petechial glove and sock syndrome, etc.) has also been attributed to some of these pathogens as has the paternity of some older ones (i.e. aplastic crisis, erythroblastosis fetalis, trench fever, hepatitis, opportunistic infection, etc.). It has been argued that the same pathogen can cause different diseases depending on the immunogenic state of the subject. To date, persisting difficulties in isolating the pathogen or differentiating between latent or active infection, still in some cases raises doubts concerning the attribution of the disease to a specific agent. New immunological or molecular techniques, allowing the direct detection of in vivo replication, are still needed in order to establish a sure connection between some of these agents and some of these diseases. Progress here will both give more accurate data about the epidemiology of some diseases and allow us to apply more appropriate treatment and prevention techniques.