final program.qxd - Parallels Plesk Panel

FP 1.11
Bats as potential reservoirs for Ebola virus
Pourrut Xavier, Leroy Eric
IRD(UR178)/CIRMF Franceville, GABON
Ebola virus (EBOV), together with Marburg virus, belongs to the Filoviridae family, a group
of enveloped, non-segmented, negative-strand RNA viruses. EBOV includes three
subtypes in Africa (Sudan ebolavirus, Zaïre ebolavirus, Ivory Coast ebolavirus) and one in
Asia (Reston ebolavirus). Ebola causes severe hemorrhagic fever in humans and great
apes. The human case-fatality rate is about 80% for the Ebola Zaire subtype (EBOV-Z),
which is the most pathogenic one. Accidental transmission of the disease to humans
occurs by direct contact with infected dead animals, mainly chimpanzees and gorillas.
Great apes are very vulnerable to infection by EBOV-Z. It has been estimated that 50 to
80 % of chimpanzee and gorilla populations disappeared during previous outbreaks in
affected regions of Republic of Congo (RC) and Gabon. The lack of identity in the
glycoprotein (GP) sequences detected from different animal carcasses suggests that
infection of great apes resulted from simultaneous but independent transmission events
from the reservoir species. Over the past 30 years, the natural reservoir for Ebola
remained a mystery, despite intensive efforts to identify it. Recently however, we showed
for the first time that some fruit bat specimens were asymptomatically infected with
EBOV-Z. During the outbreaks in Gabon in 2001 and RC in 2003, 1030 animals were
captured and tested for the virus, including 679 bats, 222 birds and 129 small terrestrial
vertebrates. Evidence for EBOV was found only in bats. Specific antibodies (IgG) for
Ebola virus were detected in serum from three different frugivorous bat species,
Hypsignathus monstrosus (4/17), Epomops franqueti (8/117), Myonycteris torquata (4/58).
Viral nucleotide sequences were detected by PCR in organs of the same species (4/21 in
H.m., 5/117 in E.f., and 4/141 in M.t.). These results strongly suggested that these bat
species are a natural EBOV reservoir, although other animal species may also be
involved. The next step will be to understand how bats can transmit EBOV to great apes.
EBOV outbreaks mainly occur during the end of the dry season, which is birthing season
for bats. At this time of year, fruit is scarce in the forest and this may lead bats and gorillas
to forage in the same trees for food. EBOV transmission to great apes may occur directly
through infected fluids such as saliva, blood or foetal envelopes. In Asia, bats are the
reservoir for two viruses, Nipah and Hendra, both of which belong to Paramyxoviridae, a
virus family that shares strong genetic similarities with the Filoviridae. Viral transmission
from bats to vulnerable species (pigs and horses) can occur either by saliva (Nipah) or by
placenta (Hendra).A better understanding of viral transmission from bats may help to
develop strategies to prevent Ebola outbreaks in great apes and humans.
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