Letter to the Editor: Deworming Dilemma

nigeria deworming
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© 2006 Emmanuel Esaba Akpo, Courtesy of Photoshare

Re: “Deworming Backfires” on a Eurasia Review article in yesterday’s Global Health NOW, I would argue that the findings reported by Anna Jolles and colleagues are predictable based on macroparasitic epidemiology (Anderson RM & May RM. 1992. Infectious Diseases of Humans: Dynamics and Control. Oxford: Oxford University Press. See chapter 15, Biology of host-macroparasitic associations). 
In simplistic terms, macroparasites will form a baseline presence within a population with a steady-state level based on the number of reproducing parasites, total parasite burden within the group, environmental exposure to the parasites, etc. If we disrupt this equilibrium with an intervention that does not alter the other conditions (for example, only mass deworming), we create a situation in which the macroparasite will once again establish a presence (usually at the previous stable level) within what is now a totally susceptible population. In reestablishing the baseline, it is probable that a “mini-epidemic” of the macroparasite will occur during the reacquisition phase, and produce a peak parasite burden for the group that is higher than the baseline parasite burden—until it is brought under control by the other factors producing the steady-state level.

Anecdotally, following visits by short-term medical teams that de-wormed entire communities in Central America, the prevalence of intestinal complaints increased in the following weeks before returning to “normal”. Perhaps it goes without saying that the short-term teams had not done anything to impact water quality, environmental exposures, or other factors. The observations came from both local health professionals as well as lay people in the communities (this was probably 10 years ago that I heard about this). I could not get anyone interested in looking at what I suspected was happening, but it would fit with the macroparasitic epidemiology model.
Food for thought …

—Michael N Dohn, MD MSc, Center for Global Health, Associate Professor, Depts. of Community Health & Internal Medicine, Boonshoft School of Medicine, Wright State University

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