The Etiology of Fear

A blog entry for PLoS ONE @ Two - in celebration of the 2nd Anniversary of PLoS ONE

While browsing for mince-pies last week, I heard a pubic health broadcast that admonished parents to supply their kids with hankies and encourage them to wash their hands after sneezing.

The ad incorporated language from the folk rhyme, "Ring a-ring o' roses". The version of the nursery rhyme that I'm familiar with runs:

Ring a-ring o' roses,
A pocketful of posies,
a-tishoo!, a-tishoo!
We all fall down.

This kind of chant makes a great backdrop to a psychological horror film. In fact, there have been horror films inspired by the ditty for almost 100 years, from 1897 to 2006. But that's the point, we're supposed to be scared. This tactic has been exploited far more blatantly in the past - remember the AIDS ads of the 80's? These may be a little over-the-top, with a comically grotesque spinning baby as the grim reaper picks up a spare.

The Department of Health clearly believes that giving us a little fright can alter our behavior, but what kind of effect should fear have on the spread of disease? This was the question posed by Joshua Epstein and colleagues in their December 2008 paper published in PLoS ONE. The team used agent-based models to investigate the impact of the reaction of individuals to fear of a malady on the spread and extent of disease epidemics. The work expands upon previous models by allowing individuals to communicate with one another allowing the spread of fear independently of the actual status of the epidemic.

The group consider the effects of both hiding from disease and flight from the disease.Hiding from disease generally suppresses an epidemic. The poem above was employed in the play "The Roses of Eyam", a dramatisation of the events in the plague village of Eyam, where villagers quarantined themselves in a remarkable demonstration of community, preventing the spread of the bubonic plague in 17th century Northern England. On the other hand, even a very small amount of flight behavior can greatly exacerbate an epidemic. The authors note cholera epidemics of the 19th century where the disease erupted along communication lines as large populations fled from outbreaks.

Is the study useful for public health planning? Perhaps, but as always the difficulty comes from comparison of the model to reality. The group note the negative effects of flight behavior and posit a plausible explanation for the occurrence of waves of infection during the 1918 Spanish flu epidemic. However, both of these examples can be grasped intuitively without the need for extensive modeling efforts. Perhaps the study will be most useful as motivation to better understand the psychology behind flight behaviors, and approaches to prevent these kinds of responses. It is also very interesting to consider the possibility that disease agents may have evolved their "scariness" to be just scary enough to make people run but not so scary that everyone hides? Or, perhaps to flare up on appropriate timescales such that people don't run far enough or hide long enough to prevent the re-ignition of the embers of an epidemic (as in the authors' model for Spanish flu).

Of course, there are ethical gray areas for direct experimentation, but perhaps there are opportunities in the public health sector. What will work best to ameliorate the next great pestilence, the horrific images of the 80's or the gentle reminders that ring across the supermarkets today? I don't think we really know & so some empirical approach may be ethically acceptable. Either way, this is a fun cross-disciplinary problem to think about.





Joshua M. Epstein, Jon Parker, Derek Cummings, Ross A. Hammond (2008). Coupled Contagion Dynamics of Fear and Disease: Mathematical and Computational Explorations PLoS ONE, 3 (12) DOI: 10.1371/journal.pone.0003955