Abstract
Arthropod-borne viruses (arboviruses) are viruses that can be transmitted to vertebrates, including humans, by arthropod vectors such as mosquitoes and ticks. According the International Committee on Taxonomy of viruses (ICTV), a total of 492 viruses are known, probable or possible arboviruses. They belong to nine viral families and 25 genera (Vasilakis et Gubler 2016). With the implementation of new molecular technologies like next generation and high-throughput metagenomic sequencing, the number of arboviruses is subject to regular updates and increases. To date, 135 arboviruses are known to infect humans, causing a significant burden in terms of morbidity and mortality worldwide. Arboviruses that represent an important threat for public health belong to three families: Flaviviridae, Peribunyaviridae and Togaviridae (Gubler 2002).Many of arboviral infections are asymptomatic and/or benign, but in some cases, they can be severe and deadly, causing hemorrhages (e.g. Dengue virus and Rift Valley Fever virus) or invasive neurological diseases (e.g. Japanese encephalitis virus, West Nile virus and Zika virus). To date only three approved human vaccines are available, targeting yellow fever virus, Japanese encephalitis virus and tick-borne encephalitis virus. The worldwide increasing incidence of arboviroses is stimulating the development of vaccines against other arboviruses of public health importance (e.g. Dengue virus, Zika virus, West Nile virus, Chikungunya virus, Rift Valley Fever virus…).To be maintained in the nature, most arboviruses display an enzootic cycle involving at least a vertebrate host and an arthropod vector. Spillover to humans or domestic animals occurs when these enter the natural zoonotic cycle. For some arboviruses like Dengue virus or Chikungunya virus, vectors have adapted to human environment, and transmission cycles only involve human and mosquitoes as reservoir-hosts. Since arboviruses are strongly linked to their vectors, their global distribution somehow mirrors the distribution of their vectors.The environmental disturbance of anthropogenic origin (urbanization, travel, deforestation, agricultural practices, global warming) will likely widen the distribution of vectors and arboviruses in the coming years, leading to the emergence and re-emergence of arboviral diseases at a global level. Madagascar is an interesting setting to investigate the epidemiology and evolutionary histories of arboviral transmission cycles. Indeed, Madagascar is home to a unique diversity of mosquito vectors, which may allow the establishment of original transmission chains involving endemic mosquito species as primary or bridge vectors. Moreover, the insularity of the country facilitates the investigation of introduction and spread mechanisms as best exemplified by studies disentangling the epidemiology of Rift Valley Fever outbreaks that occurred in the last 40 years.