Expanded Special Project for Elimination Neglected Tropical Diseases
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Accurate survey data describing the pre-control distribution of NTDs are important to ensure that programmes are appropriately geographically targeted. The WHO provides a number of operational guidelines and standardised methodologies for conducting mapping surveys. Here we collate available pre-control mapping data for each of the ESPEN priority diseases.
The need for mass treatment for each of the NTDs is determined by the implementation unit endemicity status. Implementation units are classified as endemic (and therefore warrant preventive chemotherapy) when prevalence of infection exceeds WHO-recommended disease-specific prevalence thresholds, as assessed in communities or schools during mapping or impact assessment surveys.
Preventive chemotherapy (PC) can be defined as treatment of all targeted individuals within an implementation unit, regardless of individual infection status. Attaining universal high treatment coverage is critical for achieving programme goals, and as such the WHO has determined disease-specific treatment coverage thresholds: 65% for lymphatic filariasis and onchocerciasis, 75% for soil-transmitted helminthiasis and schistosomiasis, and 80% for trachoma.
To effectively reduce community infection rates to levels at which transmission cannot be maintained , preventive chemotherapy programs must deliver repeated rounds of treatment. For some diseases, including lymphatic filariasis and onchocerciasis, this is because the currently available treatments cannot clear all stages of the infection in infected individuals. For others, such as soil-transmitted helminthiasis, infectious stages in the environment can quickly lead to reinfection. The number of treatment rounds required is disease specific.
Periodic evaluation of infection indicators through sentinel site or spot check surveys are necessary to monitor the impact of preventive chemotherapy (PC) programs. WHO recommends impact assessment surveys after several treatment rounds have been conducted, to determine whether infections have been reduced below target thresholds and PC can stop, or if there is need to change PC strategy. Once PC has stopped, impact assessments can be used as surveillance tools to monitor whether infection levels are sustained below target thresholds. Here we collate available site-level post-MDA data. The assembled data can be used to determine the current burden of disease, to identify implementation units where preventive chemotherapy (PC) can be stopped, and where there is need to change PC strategy. They also help to highlight where further survey data are required.