Although transmitted by hematophagous insects which present a seasonal population dynamics and are almost inactive during the unfavourable period, vector-borne diseases may persist over several years in temperate climates with disastrous consequences for human and animal health (chikungunya, dengue fever, African horse sickness, etc ...). A better understanding of this persistence beyond the unfavorable season for vectors is a major scientific challenge to limit the emergence or reemergence of vector-borne diseases. In temperate climates and in the Sahel region, seasons regulate the life cycle of hematophagous insects. Hence, summer and the wet season are favorable to insects (and therefore to transmission), whereas winter and the dry season are unfavorable to insects that overwinter and therefore do no transmit pathogens anymore. Three independent mechanisms enable a pathogen to persist beyond the unfavourable season for its vector: i) a low continuous transmission associated to the survival and a residual biting activity of the adult vector, ii) persistence in the host, and iii) persistence in the resistance stages of the vector. First, a continuous transmission could occur in regions where vectors bite hosts all year round, the low winter temperatures increasing the interval between two meals and the duration of the extrinsic incubation period. This mechanism could be involved in the virus persistence in the Culex/West Nile virus system in southern California. Moreover, pathogens may develop adaptive strategies against vector mechanisms to overpass unfavorable conditions. They may persist in the host or in vector resistance forms. Pathogen persistence in hosts can be related to a long viremia, to vertical transmission, or to a chronic infection phenomenon with resurgent viremia. For example, in the system Culicoides/bluetongue virus, cattle present a long viremia and the vertical transmission of the virus in the host is possible. In the system Culex/Western equin