January 23, 2021

I, Science

The science magazine of Imperial College

Isobel Sims asks how has Ebola spread to humans in the first place?

ebolaThe world has watched in horror over the last six months as the Ebola epidemic has unfolded. With the World Health Organisation (WHO) reporting in the last week that the death toll has surpassed 5000 and that transmission is still occurring (albeit at a slightly slower rate than previously), Ebola virus disease is understandably a major worldwide concern at present. Previous outbreaks however have affected mostly central and sub-Saharan Africa, so the big question is how did Ebola virus reach West Africa for the most recent outbreak?

It’s possible that Ebola virus has always been present in West Africa but until now has gone unnoticed due to the virus being present at low level in animal populations. Furthermore, the three most severely affected countries, Sierra Leone, Guinea and Liberia, are three of the most underdeveloped countries in the world, ranking 183rd, 179th and 175th respectively out of the 187 countries listed on the United Nations Human Development Index. Inadequate healthcare and diagnostics in these countries may have prevented Ebola virus from being detected in the past, particularly as its presentation is similar to that of other viral haemorrhagic diseases endemic to the area.

Another explanation for the appearance of Ebola virus is that it was bought to West Africa through another vector. It’s was unlikely to be a human since there is little trade between Central Africa and the countries of the West coast and due to the incubation time of Ebola virus, the traveller would have had to make a very speedy journey. The most probable carrier of the virus? Bats.

Evidence from blood serum samples from Gabon and the Republic of the Congo, including 679 bats, showed that there was evidence of asymptomatic Ebola virus infection in three species of fruit bats. The three infected species have large ranges across sub-Saharan Africa and have been observed to migrate long distances, meaning that one of them could have carried Ebola virus to West Africa.

The question of how Ebola virus made the species jump from bats to humans is most likely answered by looking at the socioeconomic and political conditions of the countries in question. Guinea, Sierra Leone and Liberia have all experienced a great deal of political upheaval in recent years. This, coupled with a lack of public infrastructure and increasing levels of poverty, often causes people to go further into nature in order to survive. Going deeper into forests to find food and firewood and eating infected bush meat, including bats, puts people at risk of being exposed to Ebola virus.

Doctors and aid workers continue to flood to Ebola stricken areas of West Africa to help those in need – and rightly so – but it seems that the spread of this devastating disease has a much deeper cause, rooted in politics and the economy, that must be addressed if we are to prevent outbreaks like this one in the future.

Image reproduced with permission from Dr. Frederick Murphy, Centers for Disease Control and Prevention’s Public Health Image Library