African Programme for Onchocerciasis Control (APOC)

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

A skin nodule
A skin nodule on the arm of a man

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.

REMO maps

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.

REMO map of Liberia, showing nodule prevalence (pie charts) and treatment priority areas (red zones)