"The discovery of viral RNA in 13 specimens of Epomops franqueti, Hypsignathus monstrosus, and Myonycteris torquata collected during the EVD outbreak investigations in Gabon, 2003, entrenched fruit bats as the likely reservoir. However, the virus itself could not be isolated from these samples and despite an intensive search, it has not been possible to generate viral sequences from bats captured since.

Rather, there was a shift in the proportion of PCR- and seropositive individuals over a 5-month period: viral prevalence in Mbomo soon after onset of the outbreak was 22.6%, and no bats exhibited antibodies. Five months later, viral prevalence declined to 2.2%, and antibody prevalence had increased to 7.5%. Thus, fruit bats at the beginning of the outbreak seemed not to have had previous EBOV exposure and appeared being able to clear infections (Leroy et al. 2005)."

No fruit bat hunter has been reported as index-case, despite widespread hunting across Africa (Mickleburgh et al. 2009; Kamins et al. 2011)

The only proposed epidemiological link between fruit bats and an outbreak relies on limited evidence from the Luebo-2007 outbreak (Leroy et al. 2009); it was suggested that the first person to succumb to EVD (a 4-year-old child) was infected via sweat by her father, who had bought fruit bat meat from the local market and was presumed to be the index-case. The father did not fall ill or show typical signs of EVD, nor were any of the hunters or villagers involved in the annual 3-week mass-hunting and butchering of migrating fruit bats among the first to succumb to the virus. While evidence of asymptomatic infections is mounting, individuals are currently only presumed infectious when symptomatic (Leroy et al. 2000; Becquart et al. 2010; Schoepp et al. 2014). Whether zoonotic transmission resulted from fruit bat bushmeat purchased by the father or via the exposure of the 4-year-old child to an alternative zoonotic source remains unclear. It was not possible to isolate EBOV from any wildlife in the region, although a second human outbreak occurred 1 year later, and high genetic similarity between EBOV strains from these human outbreaks suggests the virus had persisted undetected in local wildlife between outbreaks rather than in migrating fruit bats (Grard et al. 2011).

The only proposed epidemiological link between fruit bats and an outbreak relies on limited evidence from the Luebo-2007 outbreak (Leroy et al. 2009); it was suggested that the first person to succumb to EVD (a 4-year-old child) was infected via sweat by her father, who had bought fruit bat meat from the local market and was presumed to be the index-case. The father did not fall ill or show typical signs of EVD, nor were any of the hunters or villagers involved in the annual 3-week mass-hunting and butchering of migrating fruit bats among the first to succumb to the virus. While evidence of asymptomatic infections is mounting, individuals are currently only presumed infectious when symptomatic (Leroy et al. 2000; Becquart et al. 2010; Schoepp et al. 2014). Whether zoonotic transmission resulted from fruit bat bushmeat purchased by the father or via the exposure of the 4-year-old child to an alternative zoonotic source remains unclear. It was not possible to isolate EBOV from any wildlife in the region, although a second human outbreak occurred 1 year later, and high genetic similarity between EBOV strains from these human outbreaks suggests the virus had persisted undetected in local wildlife between outbreaks rather than in migrating fruit bats (Grard et al. 2011).

Evidence for a filovirus–fruit bat link is stronger for Marburg virus (MARV), although knowledge gaps regarding the full host range and circulation also remain for this fi- lovirus (Swanepoel et al. 2007; Towner et al. 2009; Amman et al. 2012; Paweska et al. 2015; reviewed in Olival and Hayman 2014). Virological studies focused on R. aegyptiacus inhabiting East African caves where MARV outbreaks occurred, found live, healthy specimens of R. aegyptiacus to be MARV PCR and seropositive. Population PCR prevalence up to 13.3% was recorded and in contrast to EBOV, live MARV was isolated from wild bat spleens and livers (Towner et al. 2009; Amman et al. 2014). However, virus was not detected in feces or urine collected from infected specimens or the cave floor (Amman et al. 2012). Laboratory experimental subcutaneous infection of R. aegyptiacus identified a number of PCR-positive tissues including salivary glands in asymptomatic bats and viral loads detected in oral and rectal swabs are consistent with biting as a mode of bat–bat transmission (Amman et al. 2015; Paweska et al. 2015). However, the period during which the virus could be isolated was limited to a few days, and no transmission from the infected specimens to naıve, incontact conspecifics could be induced.

Collectively, these results indicate that insectivorous bats are involved in EBOV ecology and possibly an EBOV source for humans. Aspects of insectivorous bat ecology may be informative for predicting future EVD outbreaks.

Interestingly, such a complex viral ecology would not be without precedent. Other zoonotic viruses indeed exist, which are able to infect multiple, phylogenetically distant hosts (e.g., lymphocytic choriomeningitis virus in domestic mice and hamsters; Albarin˜o et al. 2010), including some primary reservoirs of which are bats (e.g., SARS and MERS coronaviruses in bats and small carnivores and bats and camels, respectively; Chan et al. 2015). Despite valiant efforts and large-scale sampling of an impressive number of taxa, followed by a decade of more targeted sampling of fruit bats following the discovery of viral RNA in a number of species (Leroy et al. 2005), the evidence for a fruit bat reservoir is still far from decisive. Bats are evidently involved in EBOV ecology and may represent the best place to begin studying EBOV circulation. However, it remains possible that bats are intermediate hosts occasionally exposed via another intermediate host or unknown reservoir. Viral emergence might be more related to environmental factors and other hosts than bats themselves. The combination of ecological factors determining the occurrence of outbreaks has not been identified (Pigott et al. 2014), and there is little agreement on if and how movement of EBOV occurs between the large distances observed between outbreaks (Leroy et al. 2004; Walsh et al. 2005; Biek et al. 2006; Wittmann et al. 2007).