Chiropteran and Filoviruses in Africa: Unveiling an ancient history

Ebolavirus and Marburgvirus belong to the Filovirus family and are responsible for hemorrhagic fevers in Africa. The first documented Filovirus outbreak in Africa occurred in Central Africa and was attributed to Ebolavirus species. In the last four decades, Filoviral hemorrhagic fevers (FHFs) outbreaks caused by Ebola and Marburg viruses have been on the increase in Africa. The 2013-2015 outbreak has been the largest outbreak in human and has had the most devastating human and economic impact. Epidemics usually originate from a primary single introduction of the virus into simian or human population followed by an interspecies spill over. Multiple, short and isolated transmissions to humans have been also observed. Since the 1976 Yambuko (Democratic Republic of Congo) and Nzara (Sudan) epidemics, several investigations of different animal species have been undertaken but failed to identify the natural reservoirs of Ebolavirus. Further studies identified bats as probable reservoirs of Ebolavirus in Gabon, and major natural reservoirs of Marburgvirus in Uganda, supposed central forested areas of Africa as the epicenter where these viruses originated from, before dissemination. Chimpanzees, gorillas and duikers have been identified as highly sensitive hosts of Ebolavirus within wildlife. However, the relative importance of potential vertebrate hosts in the FHFs emergence into human population remains unclear. Different transmission routes involving bats have been proposed. Filoviruses have a zoonotic origin; amplified and maintained in nature between potential reservoirs in a jungle cycle. Ebolavirus mostly escapes these natural foci, when other sensitive secondary simian are infected and transmit the virus to human population via hunting, bat’s saliva infected wild fruit collection or land monitoring, while Marburgvirus emergence was linked to monkey’s tissues handling or human entry into bat sheltering habitats. This review discusses the dissemination of filoviruses circulating within their possible chiropteran reservoir species. Vertebrate hosts suspected in the maintenance/transmission cycles are reviewed and their bioecological features discussed. Despite the importance of the findings about reservoirs’ discovery, several other questions such as plurispecific associations, migration routes, breeding cycles need to be addressed and are pointed out in this review, in order to generate risk maps for filoviruses’ (re)emergence in West Africa.