Contrasting Epidemiology of Cholera in Bangladesh and Africa.

Studies of the epidemiology of cholera in the Ganges Delta led to understanding cholera's transmission patterns, risk groups, seasonality, and the relationship of cholera with the environment. In Bangladesh and West Bengal cholera is seasonal, transmission occurs consistently every year with only brief periods without cases. By contrast, in most African countries, cholera transmission inconsistent seasonal patterns, and long periods without obvious transmission. Additional differences are observed when molecular methods are used to identify genetic lineages. Transmission patterns of cholera in Africa appear result from intermittent outbreaks followed by elimination of that genetic lineage. Later another outbreak may occur because of reintroduction of new or evolved lineages from adjacent areas, often by human travelers. These then subsequently undergo subsequent elimination. The concept of frequent elimination and reintroduction has several implications when planning for cholera's elimination. These include a) reconsidering concepts regarding the definition of elimination, b) need to enhance methods for rapid detection and response to an outbreak, c) strategies for more effective use of oral cholera vaccine and water-sanitation-hygiene interventions, d) a need to readjust estimates of the disease burden for Africa upon which cost benefit estimates are based, e) re-examination of the role of water as a reservoir for maintaining endemicity of cholera in Africa. This paper will review some of the major features of cholera's epidemiology in most endemic African countries which appear to differ from patterns in the Ganges Delta.