Sunday, September 14, 2014

Ebola: Mutation, selection, and all that

File:Charles Darwin by Julia Margaret Cameron 2.jpgThe New York Times recently published an op-ed on the Ebola situation in western Africa. One of the things discussed by Michael Osterholmn in that essay is the possibility that "an Ebola virus could mutate to become transmissible through the air." I think this is an interesting idea; if the currently circulating virus were to become dramatically more transmissible, it would make an already desperate situation dire.

The issue of mutation and selection is complex, as described in an excellent post by Jamie Jones. What selective pressures are acting upon Ebola viruses circulating in western Africa currently, and how those might alter the clinical epidemiology of the disease, are interesting and relevant questions.

Many have reacted to the question of how real the risk described by Osterholm is. I think positing such possibilities, and the ensuing discussion, is helpful. Even if the possibility is a false alarm, having people think through the issue, likelihood, and potential impact has value. It should not, however, distract us from important and desperately needed public health operations on the ground, or advocacy efforts to increase the resources for those operations.

(image source: Wikipedia)


  1. I'm glad you covered this - I read that Osterholm peice and wondered about the likelyhood. Is the ebola virus lightweight enough to become aerosolized easily? My understanding, and please correct me if I'm wrong, is that airborne transmission has a lot to do with the physical size of the damn thing - rhinovirus colds are light, and get around in the air pretty well, while some of the other "bad guys" are relatively heavy and don't float as long. How dramatically would airborne ebola change the modeling simulations?

    1. It's complex, but here's the simplistic way I think of it. Pathogens that are dominantly spread via aerosols tend to infect the epithelium of the oropharynx and respiratory tract, causing a high concentrations of virus in those tissues. Infectious aerosols are generated in the course of coughing, sneezing, or talking. Whether this strain of Ebola is likely to evolve in that direction is unknown, but many think it's unlikely. Such a development could change the results of the models, depending upon the model and its assumptions.