This de-wormed world?

Abstract

Just as Dr. Armand Kuris’s presidential address (Kuris, 2012) one year ago began with homage to Dr. Norman Stoll’s epic 1947 JP paper, “This Wormy World”, so too does this address. Whereas Dr. Kuris used his talk to provide an authoritative overview of the biology of human parasites, including their origins, infectious strategies and biogeography, my purpose is somewhat different. I intend to highlight that the coming decades are likely to see large reductions in the abundance of many human helminths from the conspicuous levels of per capita infection noted by Stoll in 1947. I am deliberately emphasizing an optimistic point of view throughout this talk, but one that is leavened with plenty of realistic caveats that will surely impede our progress in this endeavor to one extent or another. I am hopeful though that when future historians of science consider the times we live in, among the achievements noted will be, along with documentation of the reality of the Higgs boson, the $1000 genome and the eradication of polio, the elimination of helminth infections as significant human public health concerns. Regardless of the eventual level of success or the rapidity with which it is achieved, this effort will dramatically change our discipline, including how we portray it to the world in both publications and in teaching. Part of my goal is also to point out that the members of ASP have had, and will continue to have, important roles in play in the grand endeavor of bringing human helminthiasis under control. In 1946, Stoll estimated for 25 different helminth species that there were 2.3 billion helminth infections distributed among 2.2 billion people alive at the time, or 1.04 infections per person. One notable feature of that time was that a significant proportion of the infections still occurred in individuals living within more developed countries (184 million helminth infections in North America and Europe for example). Crompton (1999) provided an update, estimating 5.8 billion people carried in aggregate 4.5 billion helminth infections (0.775 infections per person). Noteworthy here is that even though billions of helminth infections were still present, the overall average rate of infection per person was declining. A 2012 estimate from Lustigman et al. (2012) estimated 4.2 billion helminth infections among a human population of about 7 billion, for 0.606 infections per person (Table 1). The authors note that there is nothing even-handed about the distribution of these infections: they are concentrated among the marginalized, disadvantaged under-resourced poor people who often bear more than one species of helminth per person. It’s clear the world’s “bottom billion” suffer disproportionately from helminths, and in particular, sub-Saharan Africa and tropical Asia are the great remaining redoubts for human helminths. Although we must bear in mind that all these figures are estimates, even though the number of people in the world has increased dramatically, the overall number of helminth infections has declined, and the proportion of helminth-free people has increased. However, let’s be clear that there are still over 4 billion helminth infections currently afflicting humans. Given this, how can it really be argued that human helminths will anytime soon be relegated to insignificance from a public health point of view?