The Crosskey-Davies Experiment and Onchocerciasis Control in West Africa

Professionals and practitioners in global health often confront problems of planetary dimensions with comparatively meager resources. This imbalance is rarely more daunting than for those concerned with neglected tropical diseases (NTDs). By definition, NTDs do not receive the political and financial resources dedicated to the highest priorities in global health. Yet the death and disability attributed to them is no less meaningful for their victims, and the imperative to act is no less urgent for those willing to pick up the gauntlet. Although it never attracted the resources or attention of malaria or HIV, onchocerciasis in Africa is rare among NTDs because it has been the target of two World Health Organization (WHO) programs and is now controlled in many countries, despite numerous obstacles such as a parasite that lives for 10–14 years and a vector capable of migrating hundreds of kilometers. Both control programs were underpinned by knowledge gained by many individuals working in relative isolation at different times and places around the sub-Sahara, typically with a primary focus on some other problem. This paper examines one such example, a rural Nigerian project from the 1950s, to demonstrate the public health progress that can be made even when personnel are limited and resources virtually nonexistent. In a story of happenstance, innovation, dedication, and careful analysis, it shows the difference the right investigator can make. It shows how three people discovered features of the epidemiology, transmission, and control of onchocerciasis in Africa that were among the many essential intellectual and practical contributions to the design of the Onchocerciasis Control Programme (OCP), which ran from 1974–2002 and largely defeated the disease in West Africa. By the end of the 1940s, onchocerciasis was known to colonial investigators as a locally significant cause of blindness in some rural areas of Africa, but its study remained a matter of individual initiative. A quarter century later, it had become an internationally recognized problem targeted across most of West Africa by the foremost global authority in public health. Perhaps more than any other single effort, the Crosskey-Davies Experiment of 1954–1960 contributed to the scientific and technical basis of this transformation by developing disease transmission monitoring techniques that would serve as standards for the next half century and by demonstrating that local control based on larviciding was unlikely to succeed because as the density of flies fell, the infectivity of those surviving rose.