Defining neglected tropical diseases
The scope of ‘neglected tropical diseases’ has developed over time, and its definition varies. The term did not exist within the published literature indexed on MEDLINE prior to 2005; citations rose rapidly to 86 in 2011. Initially it referred to diseases where there was little private investment in the development of new drugs and thus required public investment; the term quickly encompassed diseases that occurred in the tropics in poor people. Some of these diseases were amenable to control by mass drug treatments. The World Health Organization (WHO) created the Department of Control of Neglected Tropical Diseases in 2005, and since then has been using a broadly consistent definition, which states that NTDs are "a diverse group of communicable diseases that prevail in tropical and subtropical conditions in 149 countries and affect more than one billion people, costing developing economies billions of dollars every year". The WHO refers specifically to a list of 17 diseases.
However, as the WHO acknowledges, "there are still many tropical, poverty-related diseases that affect the same populations and share many features with the neglected tropical diseases". The criteria used to determine which diseases are included or excluded from this list are difficult to tease out.
A recent article by Horstick et al in PLOS Neglected Tropical Diseases provides a set of disease characteristics that are common to all currently used definitions. This includes occurrence of diseases in the tropics or subtropics; neglected public health attention; neglected research and development in spending and in effective interventions; and affecting exclusively poor populations.
PLOS Neglected Tropical Diseases has promoted a more inclusive list, including over 30 conditions, and also allows for consideration of other infectious diseases on a ‘case-by-case’ basis. This Special Collection and the Cochrane Library browse follow this approach.
The role of Cochrane
There is a lack of reliable evidence for interventions for the prevention and treatment of NTDs. This evidence can potentially result in large health gains for the world’s poorer populations. Particular attention needs to be paid to drugs with severe or common adverse effects. Evidence may come from analyses of comparative effects of drugs balancing benefits against harms, or evaluation of the effectiveness of programmes that deliver them.
Cochrane Reviews are an important independent analysis of research relevant to disease control in NTDs. This Special Collection brings together reviews from Cochrane Review Groups including Cochrane Infectious Diseases, Cochrane Eyes and Vision, and Cochrane Skin; and focuses on the effects of a variety of interventions to prevent and treat the top five groups of NTDs, according to the Global Burden of Disease study 2013 (causing the highest number of years lived with disability). These include diarrhoeal disease, soil-transmitted helminthiases, food-borne trematodiases, schistosomiasis, and lymphatic filariasis. Currently, there are no Cochrane Reviews relating to food-borne trematodiases, highlighting the need for further research in this area.