Rapid epidemiological mapping of onchocerciasis (REMO)
To treat a disease using mass administration of a drug you must first know where the disease is and which populations are at greatest risk. When ivermectin became available for the treatment of onchocerciasis in 1987, a new tool was urgently needed to determine the geographical distribution of the disease and to identify which communities to treat.
A tool to rapidly assess the onchocerciasis situation was developed by the UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR). Called ‘REMO’ – or rapid epidemiological mapping of onchocerciasis – communities at high risk from onchocerciasis could quickly and cheaply be identified and mapped.
How REMO works
REMO uses geographical information – particularly the presence of river basins – to identify communities likely to be at high risk of infection. A sample, representing 2–4% of villages in the area, is then quickly assessed for the presence of onchocerciasis by feeling for the sub-cutaneous worm nodules in 50 adults per village. The adults are aged at least 20 years old and have been resident in the community for at least 10 years. If ≥20% of adults have nodules, mass treatment is required and this is extrapolated to the local area. In communities where the nodule rate is less than 20% clinic-based treatment is applied.
Once the data have been collected country-wide, they are then integrated in a geographical information system (GIS). The onchocerciasis map is overlapped with a population map, allowing control programmes to plan which communities to treat. It also provides better estimates of the number of people to be treated, and a better estimate of the burden of disease.
A three colour scheme is used on REMO maps to indicate different treatment strategies. In the red zones, onchocerciasis is highly endemic and constitutes a significant public health problem. These zones are treatment priority areas.
Green zones indicate where mass treatment is not needed. In these zones, the prevalence of skin nodules is ≤20%.
Yellow zones are where results are not clear and additional rapid epidemiological assessment surveys are needed.
Some REMO maps show pie charts which describe the percentage level of skin nodules.