Viruses dating back millions of years identified

By Dr. Ananya Mandal, MDApr 5 2018

Scientists have now discovered over 200 viruses that were till date unknown to humans. These belong to same strains that cause diseases such as hemorrhagic fevers (Dengue or Ebola) and influenza. Their origins have been traced back to millions of years when the animals first roamed earth. The study appeared in the latest issue of the journal Nature and was released online yesterday 4th April 2018.

Mya Breitbart, an environmental virologist and author of the study from the University of South Florida in St Petersburg says that this study sheds light on the RNA viruses and how they have evolved over the years. This can also predict how these viruses may infect humans in the future. Until now researchers have been looking at viruses that infect humans, mammals and birds. This is the first time that they also looked at other vertebrates such as amphibians, reptiles and fishes to understand how these viruses have evolved over the centuries.

Simple viruses diagram describing RNA and DNA virus, including bacteriophage. RNA is orange orange while DNA viruses have blue. The long virus purposed for ebolavirus and its families. Image Credit: VectoRaith / Shutterstock

Edward Holmes, an evolutionary virologist at the Marie Bashir Institute for Infectious Diseases & Biosecurity at the University of Sydney and lead author of the study, explained that this study reveals that these RNA viruses have been existing way before we suspected and also are more widespread that believed till now. These could cause diseases and infections that humans are unaware of he said.

According to Holmes, the team looked at over 190 animals such as reptiles, turtles, newts, salamanders, jawless fish such as lampreys etc. Lampreys have changed very little since evolution so they could provide clues, he explained. They extracted RNA from the guts, livers, gills and lungs of these animals and found 214 unique unknown RNA viruses. These viruses are commonly of the same families that infect birds and mammals. For example they noted viruses similar to Ebola in fish. Holmes hastens to add that these viruses are incapable of infecting humans from fishes because the viruses that infect fish are incapable of infecting humans as humans and fishes are so different from each other.

The researchers then mapped out an evolutionary tree of the RNA viruses and the evolving vertebrates and noted that as the vertebrate animals moved from water or seas to land and evolved with time, so did the RNA viruses that were carried within these animals. These RNA viruses are probably the ancestors of the RNA viruses that affect humans and animals today, they explain.

The team noted that these viruses exist within single cell organisms such as amoeba as well as in invertebrates such as worms and insects as well. This was suspected for a long time by scientists but has now been proven said Eric Delwart, a virologist at the Blood Systems Research Institute in San Francisco, California. Study author Yong-Zhen Zhang, a virologist at the Chinese Center for Disease Control and Prevention in Beijing said that while this study conclusively shows the evolution of these viruses, it also is just the beginning. Much more needs to be understood and more viruses need to be discovered in other vertebrates and invertebrates. He explained that his team only analysed the RNA viruses from samples that had a genetic makeup similar to the now known viruses. The assessments thus were blind to other RNA viruses that bear no resemblance genetically with the currently found RNA viruses.

Immunologists Mark Zeller and Kristian Anderson from the Scrips Research Institute in California, have written an accompanying editorial with this article. They have lauded Holmes and the team of researchers for finding the “astonishing biodiversity” of the vertebrate RNA viruses. Only around 0.5 percent of the whole sample has been assessed they add. More information on ancient RNA viruses remains to be uncovered they write.