Reports this week have touted headlines such as “Ebola is not mutating as fast as scientists feared” and “Ebola virus in latest outbreak does not show unusual mutations.” These headlines are based on a report published in the journal Science last week that is at odds with a previous article published in the same journal. However, these headlines are missing the mark based on a lack of understanding of viral mutations.
Viruses carry proteins known as polymerases that are built to copy the viral genome. In the case of Ebola virus, the polymerase is prone to making mistakes. This means that some times instead of making an exact copy, it makes a copy of the genome that contains an error – a mutation.
The rate of mutation (error) does not change significantly for polymerases of the same virus. This is a function that is inherently programmed into the polymerase. Thus, it is a complete misnomer to say that a virus is mutating faster or slower. The mutation rate does not change. This confusion comes from looking at what is called the substitution rate (how many mutations are observed over a period of time). The substitution rate is influenced by evolutionary factors that may allow for some mutations to persist while others cannot.
The two Science papers conflict in their measuring of the substitution rate, which could in part be due to different analysis methods, but no mater which way the results are interpreted, the virus was never mutating at a different rate nor was that claim made by scientists.
Managing Correspondent: Joseph Timpona
Acknowledgements: Many thanks to Aaron Lin, a graduate student in the Virology program at Harvard University for commentary on the topic.