RNA sequences taken from gorillas and chimpanzees that had died of Ebola between 2001 and 2006 showed that the virus belonged to a new genetic lineage of ZEBOV
Scientists studying the Ebola virus have discovered a new lineage of the pathogen, and have found evidence of genetic recombination, a process which is extremely rare in the group of viruses to which Ebola belongs. 
Photo: David Ball
Researchers from France's Institute for Development Research (IRD) and the International Medical Research Centre of Franceville, Gabon, made the discoveries after mapping viral genetic sequences taken from gorillas and chimpanzees. Previously, analyses of this kind had only been conducted on samples taken from humans. The findings should allow reassessment of the models of Ebola epidemics that have occurred in recent years.
The recombination would have taken place between 1996 and 2001, say the researchers, giving rise to the viruses responsible for the epidemics that occurred between 2001 and 2003.
To date, scientists have been unable to determine the evolutionary development of the Ebola virus, in particular the virulent Zaire species (ZEBOV), due to a lack of data. What little data there was suggested that every epidemic stemmed from the first recorded outbreak in 1976. However, the new data based on viral samples from apes challenge this hypothesis.
RNA sequences taken from gorillas and chimpanzees that had died of Ebola between 2001 and 2006 showed that the virus belonged to a new genetic lineage of ZEBOV, lineage B, which diverged from the original lineage A by 2%-3%. A similar study of the viruses responsible for human epidemics documented since 2001 confirmed that, until 2003, the viral strains belonged to lineage A. However, the viruses responsible for the most recent outbreaks in 2003 and 2005 belonged to lineage B.
The findings prompted new investigations, this time focusing on a different sequence of the viral genome. These found that the viral strains responsible for the human epidemics that occurred between 2001 and 2003 all fall into lineage B. The apparently contradictory results provide proof that wild strains of the Ebola virus are capable of exchanging genetic material by recombination, say the researchers. This process is well known in positive RNA viruses, such as HIV, but is rare in negative RNA viruses, which include Ebola.
The fact that the virus can undergo recombination should be taken into account in the development of live attenuated vaccines, the researchers say, as the attenuated virus could mix with a wild strain of Ebola, giving rise to a new pathogenic virus. The IRD now plans to identify the exact location in the genome where the exchange of genetic material takes place, to better understand the processes involved. This will require a complete genetic mapping of the different viral strains.
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