First global map of loiasis

Help for treatment of river blindness and lymphatic filariasis

TDR news item
28 July 2011

A new global map on where loiasis is endemic in Africa quantifies the total population at risk and shows previously unidentified areas, according to the authors of a PLoS Neglected Tropical Diseases article. While this eye worm disease in itself is not a major public health problem, it does present problems when people are treated with ivermectin for either onchocerciasis (called river blindness) or lymphatic filariasis. When patients also have a high intensity of loiasis infection, the drug can cause severe adverse reactions such as encephalopathy that can be fatal if not adequately managed.

Ivermectin is a drug that is being scaled up for use across Africa to treat river blindness and lymphatic filariasis, so this new map is a critical piece of information that can help health authorities know where the drug can be used safely and where it should be avoided.

The Democratic Republic of Congo and Cameroon together account for 80% of the estimated 14.4 million people living in high risk areas. Equatorial Guinea and Gabon are the most endemic countries in the world. Some areas were newly identified, such as a highly endemic area in south Chad.

The detailed information is particularly important for lymphatic filariasis elimination, where loiasis has been a major barrier in Central Africa. The map shows where loiasis endemicity is low or nil so that treatment can go ahead.

The map is the first to be built from actual survey data. Previous maps were created from environmental risk models, which were not always sufficiently precise. The current map is based on surveys in thousands of randomly selected villages using a rapid assessment method, called RAPLOA, which was developed and tested by TDR in Cameroon and Nigeria in 2001. Following validation of RAPLOA in the Democratic Republic of Congo, the method was endorsed in 2004 by the Mectizan Expert Committee and adopted by the African Programme for Onchocerciasis Control (APOC) for large-scale mapping of loiasis in the 11 countries identified as being potentially endemic.

APOC is providing detailed maps to the endemic countries and their partners, and are publishing them on their website (

For more information, contact
Hans Remme at , or
Honorat Zouré at

Map of the estimated prevalence of eye worm history in Africa