[Virus carriers: analysis of states of equilibrium between the virus and its host].
The various mechanisms of virus persistence are described. Four kinds of virus persistence are presented, depending on their epidemiological significance, persistence associated with continuous multiplication and transmission (feline calicivirus, calf rotavirus); persistence associated with continuous multiplication but discontinuous transmission (equine infectious anemia retrovirus); persistence with continuous multiplication associated with immunotolerance (feline leukaemia retrovirus; mucosal disease pestivirus); latent carrier state with discontinuous transmission (feline and pigeon herpesvirus; infectious bovine rhinotracheitis herpesvirus). The classification of these kinds of virus persistence is based upon their epidemiological significance, even if the mechanisms allowing the persistence are completely different.