ebola reservoir

ebola reservoir - Vol 438|1 December 2005 BRIEF...

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Vol 438 | 1 December 2005 575 Fruit bats as reservoirs of Ebola virus Bat species eaten by people in central Africa show evidence of symptomless Ebola infection. The first recorded human outbreak of Ebola virus was in 1976, but the wild reservoir of this virus is still unknown 1 . Here we test for Ebola in more than a thousand small vertebrates that were collected during Ebola outbreaks in humans and great apes between 2001 and 2003 in Gabon and the Republic of the Congo. We find evidence of asymptomatic infection by Ebola virus in three species of fruit bat, indi- cating that these animals may be acting as a reservoir for this deadly virus. Human Ebola outbreaks that occurred between 2001 and 2005 in Gabon and the Republic of the Congo were linked to concur- rent outbreaks that devastated local gorilla and chimpanzee populations 2,3 . To identify the viral reservoir, we undertook three trapping expeditions in areas close to infected gorilla and chimpanzee carcasses, just after their dis- covery (Fig. 1a). In total, 1,030 animals were captured, including 679 bats, 222 birds and 129 small terrestrial vertebrates, and were tested for evidence of infection by Ebola virus (for details, see supplementary information). Of the infected animals identified during these field collections, immunoglobulin G (IgG) specific for Ebola virus was detected in serum from three different bat species (4 of 17 Hypsignathus monstrosus , 8 of 117 Epomops franqueti and 4 of 58 Myonycteris torquata ). Two of the principal organs targeted by Ebola virus are the liver and spleen 4 . Viral nucleotide sequences were detected in these organs in other bats from the same populations (4 of 21, 5 of 117 and 4 of 141, respectively). No viral RNA was detected in kidney, heart or lung in these animals after amplification by polymerase chain reaction (PCR) and no viral nucleotide sequences were revealed in any of the other animal species tested. Nucleotide-sequence analysis of purified PCR products identified seven different frag- ments amplified from the 13 PCR-positive animals, all clustering phylogenetically within the Zaire clade (Fig. 1b). The fragments dif- fered not only from one collection to another, but also within a given collection, among the three bat species, and within a given species. The need to use nested PCR indicated that the viral RNA load in tissues was extremely low, which probably explains why we failed to iso- late the virus itself. Surprisingly, none of the IgG-positive ani- mals was PCR-positive, and none of the PCR- positive animals was IgG-positive. This may be because PCR-positive bats were recently infected and were tested before they developed a detectable immune response. Alternatively, it could be that differences in the virulence of Ebola virus strains led to different immuno- logical responsiveness and viral replication patterns. Of the bat species collected at Mbomo in February 2003, 7 of 31 (22.6%) and 0 of 10 (0%) were PCR-positive and IgG-posi- tive, respectively, but five months later the cor-
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ebola reservoir - Vol 438|1 December 2005 BRIEF...

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