The Birth of Ebola

May 1, 2015

By Medical Discovery News

Colorized micrograph of Ebola by Dr. F.A. Murphy

For most Americans, the Ebola scare seems to have come and gone, but that doesn’t mean the outbreak is over in Africa or that we’ve seen the last of the virus, especially considering its history. Scientists believed that Ebola is relatively new as far as viruses go – only 10,000 years old. However, ancient animal bones show that Ebola appeared between 16 and 23 million years ago, perhaps even earlier.

The Ebola virus was discovered in 1976 during two outbreaks in what was then called Northern Zaire (now the Democratic Republic of the Congo) and Southern Sudan. The outbreaks were actually caused by two different strains of the Ebola virus named Zaire and Sudan, with 90 and 50 percent mortality rates respectively. Since then, three other strains have been identified: Tai Forest, Bundibugyo, and Reston, which is the only one that doesn’t affect people. Overall, there have been 27 outbreaks, but the current outbreak that started in March 2014 is by far the worst, infecting almost 25,000 people and killing over 10,000, thereby making it the world’s first Ebola epidemic.

Ebola is a member of the filovirus family, which also includes the Marburg virus discovered in 1967. Filoviruses are zoonotic, meaning they replicate in other animals, their natural reservoirs, before transmitting to humans. The Ebola virus’s natural reservoir is African fruit bats, so it can transfer to humans who come into contact with an infected bat or another species that has been infected, such as chimpanzees, antelope, and porcupine. Then the virus can spread from person to person.

New research into the origins of filoviruses shows that they have evolutionary ties that go back millions of years. Scientists tracked the viruses’ origins by looking for pieces of their genetic information in fossilized animal bones. While using the bones to study the genomes of ancient voles and hamsters, they found the same pieces of the viruses’ genetic material in the same locations in both rodent species. This suggests that the viruses have existed at least as long as the two species have.

Given the billions of bases each animal has in its genome, it is highly unlikely that these fragments of viral genetic information would have been inserted in exactly the same locations during different infections. Scientists therefore concluded that the virus had infected a common ancestor of these two rodents sometime before the Miocene Epoch, 5-23 million years ago, around the time the great apes arose. Furthermore, the viral genetic elements more closely resemble Ebola than Marburg, meaning the two viruses had already diverged from each other. Sometime before then, the two viruses shared a common ancestor that has not yet been identified.

This means that these viruses have been coevolving with mammals for millions and millions of years, much longer than previously believed. An understanding of the origins and evolution of filoviruses could help us better prevent outbreaks of them and hopefully even create a vaccine that would be effective against all of them.

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