For the first time, Ebola virus sequences have been detected in terrestrial small mammals. This work, achieved in the Central African Republic, through a collaboration between teams headed by Jacques MORVAN ( Institut Pasteur of Bangui ), Marc COLYN ( CNRS - Rennes-I University), Vincent DEUBEL and Pierre GOUNON ( Institut Pasteur in Paris) is an important step in the search for the natural reservoir of the Ebola virus. These results are in press in " Microbes and Infections* ". They will be exposed during the Institut Pasteur symposium : "Microbiological surveillance and emergences" ( october 14, 15, 1999 - Paris, France).
The life cycle of the Ebola virus, which causes an haemorrhagic fever in humans with a mortality rate up to nearly 90%, remains unknown. Since the first epidemic in ex-Zaïre (DRC) and Sudan (1976), thousands of vertebrates (bats, birds, rodents...) and invertebrates captured around the epidemic foci have been tested. These tests have all given negative results : no trace of Ebola virus has been found in healthy non primate animals. From these results, it was concluded that Ebola virus should be present in the heart of the rainforest environment, probably in arboreal animals such as bats and in animals living in the canopy.
The present study, conducted in Central African Republic, has been founded on a quite different hypothesis.
Studies of Marc COLYN, Laboratory of Ethology-Evolution-Ecology (CNRS-
Rennes-I Univ) had suggested to search for the Ebola virus elsewhere than
in the heart of the rainforest. Historical biogeographic analysis, based
on the locations of the sites of known epidemics, had led to suggest that
the Ebola virus might circulate in animals living in an environment other
than mature forest, called "mosaic" area, which was savannah more
than thousand years ago and since then, partially recolonized by forest.
In addition, between 1994-1997, studies of the Institut Pasteur of Bangui had shown evidence of the circulation of the virus in the Central African Republic : antibodies against the Ebola virus were found in forest-dwelling populations
( pygmees and bantus).
Under Jacques MORVAN's ( director of the Institut Pasteur of Bangui) impulse, as part of an approach of microbiological surveillance developed by the International Network of Instituts Pasteur, and Marc COLYN's ones, it was decided to search for the presence of the Ebola virus in animals of the Central African Republic.
Some of the animals captured for ecological studies in 3 different "mosaic" areas, in forest , on the side of savannah and in gallery forest, from North to South, have been tested. Both teams of Institut Pasteur in Bangui and in Paris have searched for the presence of the virus in different organs of 242 animals ( rodents, shrews and bats). Live virus has not been detected. But using sophisticated molecular biology tools ( RT-PCR and molecular hybridization), viral sequences have been detected in 7 animals captured at ground level which didn't show any signs of disease when they were caught : one shrew ( Sylvisorex ollula ) and 6 rodents from 3 different species (Mus setulosus, Praomys sp.1 and sp.2), caught in the different sites. These sequences are identical to those of the Ebola virus strains isolated in ex-Zaïre and Gabon.
Moreover, tubular structures very similar to the Ebola virus ones have been observed, by the Central Station of Electron Microscopy of Institut Pasteur in Paris, in the spleen cells from one of the rodents.
This work provides evidence that different rodent species and one shrew species have been in contact with the Ebola virus : terrestrial species are concerned, contrary to current hypothesis.
In addition, these results fit well with the history of fauna in tropical Africa. They show that there is a common Ebola virus subtype for Central African Republic, Democratic Republic of Congo and Gabon. This subtype differs from that of Ivory Coast. Recent biogeographic studies have concluded that fauna from the Congo basin clearly differs from the one of West African regions. The evolution of virus seems to follow that of the mammalian fauna, suggesting a common history.
This multidisciplinary study should help research toward the natural reservoir of the Ebola virus : it brings a way for a better targeting of the sites to capture animals and it underlines new strategies for the detection of the virus, based on molecular and ultramicroscopic methods. An ecological and epidemiological surveillance of small mammals populating and a molecular virology research on the presence of the Ebola virus are in progress since october 1998.
* "Identification of Ebola virus sequences present as RNA or DNA in organs of terrestrial small mammals of the Central African Republic", Microbes and Infections, November 1999.
Jacques M. MORVAN1, Vincent DEUBEL2, Pierre GOUNON3, Emmanuel
NAKOUNE1, Patrick BARRIERE4, Séverine MURRI2, Olivier PERPETE4, Benjamin
SELEKON1, Daniel COUDRIER2, Annie GAUTIER-HION4, Marc COLYN4
1 Laboratoire des Arbovirus et Virus des Fièvres Hémorragiques, Institut Pasteur de Bangui, République Centrafricaine; 2 Centre National de Référence pour les Arbovirus et Fièvres Hémorragiques Virales, Unité des Arbovirus et Virus des Fièvres Hémorragiques, Institut Pasteur, Paris; 3Station Centrale de Microscopie Electronique, Institut Pasteur, Paris, France ; 4Laboratoire d'Ethologie-Evolution-Ecologie, UMR 6552, CNRS, Université de Rennes 1, France.
Jacques MORVAN : WHO Collaborating Center for Arboviruses and
Viral haemorrhagic Fevers - Laboratory of Arboviruses and Viral Haemorrhagic
Fevers Bangui, Central African Republic.
tel : 236 61 28 37
Vincent DEUBEL : National Reference Center for Arboviruses and
Viral Haemorrhagic fevers Head of the Unit of Arboviruses and Haemorrhagic
fevers -, Institut Pasteur, Paris, France.
tel : 33 01 45 68 87 23
Marc COLYN : Laboratory of Ethologie-Evolution-Ecology, UMR 6552,
CNRS, RennesI University, Biological station, Paimpont, France.
tel : 33 02 99 61 81 62
Institut Pasteur Press Office :
tel : 33.01.45.68.81.46 / e-mail : email@example.com
CNRS - Life sciences / Communication
Thierry PILORGE, tel : 33 01 44 96 40 26
The Ebola virus is one of the most virulent in humans : it causes a severe haemorrhagic fever causing death in 50-90% of all clinically-ill cases. After 2 to 21 days of incubation, the disease is characterised by a sudden onset of fever, weakness, muscle pain, headhache and sore throat. Then, the sick person is affected with vomiting, diarrhoea, limited kidney functions and both internal and external bleeding. The Ebola virus is transmitted by direct contact with the blood and the secretions of infected patients .
All the human cases have been recorded in Africa except one non fatal case which has occurred in a laboratory in United Kingdom. First epidemics emerged in 1976 in Sudan ( 284 cases, 150 deaths ) and in ex-Zaïre ( 318 cases, 280 deaths). An isolated fatal case occurred in ex-Zaïre in 1977 and a second epidemic affected Sudan in 1979 ( 34 cases, 22 deaths ). In 1994, a scientist was infected by autopsying ill or dead chimpanzees* in Ivory Coast and recevered spontaneously. In the 1995 outbreak in Kikwit, Zaïre, there were 315 cases and 244 deaths. In 1996, epidemics occurred in Gabon, in February and in July, in the same region ( 37 cases and 21 deaths in Makokou, related to cooking a chimpanzee and 61 cases and 45 deaths in Booué).
* In addition to humans, Ebola haemorrhagic fever affects also monkeys.
In Ivory Coast, 40 chimpanzees have shown signs of disease and 12 died.
In the United States, the disease occurred in macaques imported from the
Philippines, in 1989-90 and in 1996 : the same viral strain, called Reston,
was isolated in these animals. This strain was different from that isolated
in humans in Zaïre, in Gabon and in Ivory Coast. People in charge of
the macaques developed antibodies against virus, but none was ill, suggesting
that the Ebola-Reston strain is not pathogenic in humans.
If these primates are able to transport the disease , they are not the reservoir of the virus because they are affected by the disease.