[Functioning of virus-vector systems]

The transmission of viruses by arthropod vectors is a very complex biological phenomenon, and a very efficient one epidemiologically speaking; it takes place in three successive stages: arthropod infection, virus replication and dissemination within the arthropod, transmission to the vertebrate with, possibly, trans-stadial, vertical and/or venereal transmission. Many factors influence this transmission: endogenous factors, specific of the two components of the system (physiology, biology, genetics of the virus as well as the arthropod) determining vectorial competence, and exogenous environmental factors, which, along with previous ones, condition vectorial capacity. These facts have important consequences on arbovirus evolution, through different mechanisms for segmented or non-segmented genome viruses. They also have practical implications on epidemiology of arbovirus infections, through selective pressures exerted on each development stage of these viruses. These considerations lead us to state some directions for future researches: exact mechanisms of the different virus development stages within their vectors and type of their genetical control, defense reactions of arthropods and pathogenic effects of the viral infection, possible interference with other micro-organisms or with homologous or heterologous antibodies,.. Researchers working in that field should approach the problem not only with "arboviruses" and their vectors, but with consideration for all virus-arthropod relationships, and should take in account the necessity of not too much wandering from conditions of the nature in their experiments.