In October 2015, members of the NTD Modelling Consortium published a collection of papers in Parasites and Vectors. This collection contains novel analyses on the dynamics of nine NTDs, ranging from model comparisons to new estimates of key parameters.
Preventive chemotherapy diseases
Preventive chemotherapy and transmission control (PCT) is the main strategy for control of onchocerciasis, lymphatic filariasis, schistosomiasis, soil-transmitted helminthiasis and trachoma. The strategy involves regular provision of preventive treatment (in the form of mass drug administration (MDA) campaigns) to entire populations or targeted risk groups (e.g. schoolchildren). This strategy reduces disease progression in treated individuals and prevents transmission of infection to others. Mass drug administration (MDA) programmes are rapidly expanding, although important questions remain. For example, will the planned MDA programmes be sufficient to achieve elimination in all epidemiological settings? To what extent is successful elimination jeopardized by low coverage and systematic non-adherence? When, and on the basis of what criteria can MDA be safely interrupted? Each of the modelling analyses highlight the importance of groups who systematically, or semi-systematically do not access MDA programs in sustaining transmission. This potential for undermining program success is particularly acute if groups of the population who are most at risk through their behaviours (e.g. those who most frequently go to the river) are also those who are most difficult to access through an MDA campaign. The results support previous analyses that increased coverage, across different age groups, or through general coverage, may be more important than frequency of treatment.
Intensified disease management diseases
A number of neglected tropical diseases are controlled by increased diagnosis and management of cases (intensified disease management, IDM). The four IDM diseases in this study are Chagas disease, the Gambian form of human African trypanosomiasis, leprosy globally and visceral leishmaniasis on the Indian sub-continent. Whilst these diseases cause significant morbidity and mortality, the disease courses are quite long, the epidemic growth rate is slow and the transmission is usually highly focal. They are often associated with disadvantaged populations and hard-to-reach groups. Given this concentration of disease in populations with poor access to care, and the potentially long time periods over which their disease course and dynamics occur, these diseases have been difficult to study and so quantitative estimates of key parameters are scarce. In the model analyses of these diseases the authors have aimed to provide novel estimates of key parameters and provide both qualitative and quantitative insights on the dynamics of these infections and their consequences for control.