MVD is considered a zoonotic disease that is thought to persist in a healthy reservoir host in the endemic areas in Africa. Humans and NHPs are spillover hosts and show a high rate of fatal disease outcomes. Several large-scale attempts to identify the natural host of filovirus infection throughout sub-Saharan Africa had been undertaken in the years since filoviruses first emerged with frustratingly little success [28] [29] [30] [31] . Consistent with ecologic niche modeling of outbreaks and epidemiological patterns, isolated cases have suggested that EBOV is endemic in the rain forests of central and western Africa while MARV is more prevalent in open, dry areas of eastern, south-central Africa [32, 33] . Almost all of the primary infections of natural MVD outbreaks so far have been linked to human entry into caves inhabited by bats (e.g., cave visitors, mine workers) (Table 1) . Thus, bats have long been suspected to play an important role in the transmission cycle of the disease [31, 32, 34] . In 2007, evidence was detected for MARV infection of the common Egyptian fruit bat (Rousettus aegyptiacus) [35, 36] (Figure 2 ), and MARV was isolated from healthy infected R. aegyptiacus bats caught in the same year in Uganda [22] . The bats were collected in Kitaka cave around the same time as human infections occurred that had been linked to the cave (Table 1 and see above, 1. Epidemiology). Genomic analysis of the few isolates of MARV acquired from bats showed that the sequences matched closely to the MARV genomes isolated from patient samples (Figure 1b) . This was also the case for partial MARV sequences isolated from bats inhabiting the Goroumbwa mine in the DRC that was suspected to be the major location for several independent spillover events to gold miners between 1998 and 2000. The bat MARV sequences were closely related to the distinct isolates that had been reported during these outbreaks in humans [36] .