Hunting down Ebola
French scientists have, for the first time, found Ebola virus sequences in small terrestrial mammals, a critical step in the search for the natural reservoir of the Ebola virus.
The research, to be published in the upcoming issue of Microbes and Infections, was carried out in the Central African Republic by a collaboration of teams headed by Jacques Morvan, Institut Pasteur. Until now, the ebola virus was known to infect only humans and apes. The new research adds to the understanding of the evolution of the virus and may eventually point to its natural reservoir.
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 epidemics among humans in the 1970s in Democratic Republic of Congo (Za´re) and Sudan, thousands of vertebrates - such as bats, birds and rodents - and invertebrates, captured around the epidemic foci, have been tested. But no trace of Ebola virus could be found in healthy non-primate animals.
It was concluded that Ebola virus should be present in the heart of the rainforest environment, probably in arboreal animals such as bats and other animals living in the canopy. The present study, however, took a different approach.
Bio-geographic analysis, based on the locations of the sites of known epidemics, had suggested that Ebola might circulate in animals living in "mosaic" area - land that was once savannah, more than thousand years ago, and has since been partially recolonised by forest.
Teams from the Institut Pasteur in Bangui and in Paris searched for the presence of the virus in different organs of 242 animals ( rodents, shrews and bats). Live virus was not 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 and 6 rodents from 3 different species.
The results 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. The evolution of virus seems to follow that of the mammalian fauna, suggesting a common history.
The Ebola virus is one of the most virulent in humans. It causes a severe haemorrhagic fever causing death in 50-90% of all cases. The disease is characterised by a sudden onset of fever, weakness, muscle pain, headhache and sore throat, then 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.