Rapid assessment procedures for loiasis: report of a multi-centre study

Overview

Several cases of severe adverse reactions to ivermectin treatment have been reported from Cameroon in individuals with a high intensity of Loa loa infection. Concerns about possible severe adverse reactions have paralysed ivermectin treatment programmes for onchocerciasis in areas that are possibly co-endemic for Loa loa.

There is an urgent need, therefore, for a simple rapid assessment tool of loiasis endemicity that can help identify communities where there is a high risk of severe adverse reactions.

A multi-centre study supported by the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR) and the African Programme for Onchocerciasis Control (APOC) was carried out in Cameroon and Nigeria to evaluate the use of specific clinical symptoms in rapid assessment of the endemicity of loiasis.

Study communities were selected in areas presumed to be hypo-, meso- and hyperendemic for Loa loa from the Cross River State, south eastern Nigeria (28 communities), the South West and North West Provinces of Cameroon (42 communities) and the Eastern Province of Cameroon (32 communities).

Standardised questionnaires were developed based on key clinical manifestations of loiasis (Eye Worm and Calabar Swelling) and administered by trained interviewers. Eligible individuals had been resident in the community for at least 5 years, were above 15 years of age and had not taken any anti-filarial drug recently. Blood samples were also collected from each individual interviewed and the microfilaraemia determined using the thick blood film method.

The study showed that the clinical manifestations of loiasis were well known in highly endemic communities where local names were associated with them. However, in hypoendemic communities, these local names were not known.