November 3, 2016

expert reaction to two different studies reporting on the adaptation of the Ebola virus throughout the West African outbreak

Two papers published in the journal Cell have examined how the Ebola virus adapted during the outbreak in West Africa.

All our previous output on this subject can be seen here. The SMC also produced a Factsheet on Ebola virus.

Dr Mike Skinner, Reader in Virology, Imperial College London, said:

“These two papers appear to confirm what many virologists might have anticipated (based on studies of many other viruses), that during a prolonged outbreak of Ebola in humans (such as we saw in West Africa), evolutionary selection for genetic types of the virus that are “fitter” for transmission between humans would emerge. The newer form would not necessarily be more dangerous to the infected individual, though the Diehl paper^ǂ reveals otherwise unsubstantiated indications of increased virulence which merit further study.

“The good news from both papers is that the newer form only seems to transmit better between cells from primates (including humans), not from other mammals. Indeed the Urbanowicz paper* indicates it transmits less well between cells of rodents and bats. This means that the human adaptation is unlikely to persist in the natural reservoir. In terms of adaptation of the virus to humans, the race has effectively been set back to the start – with any new outbreak the “fitter” form will have to evolve and emerge again.”

Dr Ed Wright, Senior Lecturer and Virologist, University of Westminster, said:

“The reports published today provide further insight into possible reasons the outbreak of Ebola virus in West Africa may have been so much larger than previous outbreaks. The studies identify specific changes to the virus’ genes that emerged as the outbreak unfolded. It appears the virus was adapting so it could infect human cells more efficiently.

“One of these changes occurred around the time when the number of cases started to dramatically increase. This gives rise to the possibility that this change could have been pivotal in the virus’ ability to infect humans and ultimately the scale of the outbreak. However, these studies do not definitively answer the latter question. Further studies will be needed to gauge the clinical impact of the changes to the virus. They will however, be useful in informing on the use of control measures in future outbreaks.

“As well as analysis of clinical data from the outbreak, it would be interesting to know if the emergence of the same changes were observed in any of the previous outbreaks of Ebola. And while the changes appear to alter the ability of the virus to infect human cells it still remains unclear whether they modify its ability to transmit from person to person.

“The adaptation of viruses to improve their ability to infect humans is not unique to Ebola.  Such viruses that are primarily found in animals, which also includes influenza viruses, try to rapidly evolve once inside humans so they can more easily replicate and be transmitted from person to person.”

‘Human Adaptation of Ebola Virus during the West African Outbreak’  by Urbanowicz et al. & ^ǂ‘Ebola Virus Glycoprotein with Increased Infectivity Dominated the 2013–2016 Epidemic’ by Diehl et al. published in Cell on Thursday 3rd November. 

Declared interests

Dr Mike Skinner: No conflicts of interest.

Dr Ed Wright: “I have received grant funding to work on the development of Ebola virus vaccines and drugs.”