Validation of the rapid assessment procedure for loiasis (RAPLOA) in the democratic republic of Congo

Samuel Wanji 0 2 Dowo O Akotshi 1 Maurice N Mutro 6 Floribert Tepage 5 Tony O Ukety 4 Peter J Diggle 3 Jan H Remme 7 0 University of Buea, Faculty of Science, Department Microbiology and Parasitology , P.O. Box 63, Buea , Cameroon 1 Programme National de Lutte contre l'Onchocercose, Ministere de la Sante Publique , Kinshasa, Republique democratique du Congo 2 Research Foundation for Tropical Diseases and the Environment (REFOTDE) , P.O. Box 474, Buea , Cameroon 3 Faculty of Health and Medicine, Lancaster University , Lancaster LA1 4YB , UK 4 World Health Organization, Prevention of Blindness and Deafness , Avenue Appia 20, 1211 Geneva 27 , Switzerland 5 Programme National de Lutte contre l'Onchocercose, Ministere de la Sante Publique , Buta, Republique democratique du Congo 6 Centre de Recherche en Maladies Tropicales de l'Ituri, Hopital General de Reference de Rethy , Republique democratique du Congo 7 120 Rue des Campanules , 01210 Ornex , France Background: A simple method called RAPLOA, to rapidly assess what proportion of people in a community are infected with L. loa and hence which communities are at high risk of severe adverse reactions following ivermectin treatment, was developed in Cameroon and Nigeria. The method needed further validation in other geographical and cultural contexts before its application in all endemic countries. The present study was designed to validate RAPLOA in two regions in the North East and South West of the Democratic Republic of Congo. Methods: In each study region, villages were selected from different bio-ecological zones in order to cover a wide range of loiasis endemicity. In each selected community, 80 people above the age of 15 years were interviewed for a history of eye worm (migration of adult L. loa under the conjunctiva of the eye) and parasitologically examined for the presence and intensity of L. loa infection. In total, 8100 individuals from 99 villages were enrolled into the study. Results: The results confirmed the findings of the original RAPLOA study: i) the eye worm phenomenon was wellknown in all endemic areas, ii) there was a clear relationship between the prevalence of eye worm history and the prevalence and intensity of L. loa microfilaraemia, and iii) using a threshold of 40%, the prevalence of eye worm history was a sensitive and specific indicator of high-risk communities. Conclusion: Following this successful validation, RAPLOA was recommended for the assessment of loiasis endemicity in areas targeted for ivermectin treatment by lymphatic filariasis and onchocerciasis control programmes. - Background The control of onchocerciasis in Africa is based on mass treatment with ivermectin. Community-directed distribution of annual doses of ivermectin, introduced by the African Programme for Onchocerciasis Control (APOC), is an important component of the control strategy. Each community itself is in charge of designing and implementing the ivermectin treatment [1]. This strategy has been very successful and more than 65 million people in onchocerciasis endemic areas are treated annually with ivermectin [2,3]. However, several reports from Cameroon indicated that high microfilaraemia of Loa loa may be associated with severe and sometimes fatal encephalopathic reactions in patients who had taken ivermectin against onchocerciasis [4-6]. The risk of severe adverse reactions has been a major preoccupation for ivermectin treatment programmes throughout the central African subregion where L. loa coexists with Onchocerca volvulus [7]. Several treatment programmes have been interrupted in Cameroon and the Democratic Republic of Congo (DRC). The risk of severe adverse reactions to ivermectin treatment in L. loa infected individuals is related to the intensity of loiasis infection: the risk of developing marked or serious reactions is significantly higher when the L. loa exceeds 8,000 microfilariae/ml. The severity of adverse reaction becomes obvious in patients with more than 30,000 microfilariae/ml and the risk is very high for loads above 50,000 microfilariae/ml [5]. The prevalence of high microfilarial loads is closely related to the overall prevalence of microfilaraemia, and it has been proposed that a microfilarial prevalence of 20% be regarded as the threshold, above which there is an unacceptable risk of severe adverse reactions [8]. It is critical, therefore, that onchocerciasis control programmes identify such high-risk communities and withhold ivermectin treatment or make special provisions to ensure that severe adverse reactions are quickly detected and properly managed. In the search for simple, non-invasive methods that can facilitate the large scale identification of high risk communities, a study carried out in Cameroon and Nigeria in 2001, supported by the UNDP/World bank/ WHO Special Programme for Research and Training in Tropical Diseases (TDR) and APOC, led to the development of a Rapid Assessment Procedure for loiasis (RAPLOA) [9,10]. This method is based on a striking clinical manifestation of loiasis, the migration of the adult L loa worm under the conjunctiva of the eye. The major findings from the RAPLOA development study were the following: (i) the eye worm phenomenon is well known in L. loa endemic areas and people always have local names for it; (ii) there was a clear relationship between the percentage of community members that reported a history of eye worm and the community prevalence of loiasis infection; (iii) using a threshold of 40%, the prevalence of eye worm history was a good indicator of high-risk communities, i.e. communities where the prevalence of L. loa microfilaraemia was greater than 20%, the prevalence of high microfilarial loads (> 8,000 mf/ml) was greater than 5%, or the prevalence of very high microfilarial loads (> 30,000 mf/ml) was greater than 2%; (iv) the Rapid Assessment procedure of loaisis (RAPLOA) based on the prevalence of the history of eye worm had a high sensitivity and specificity for detecting high risk communities. Based on these results, the independent expert committee of the African Programme for Onchocerciasis Control (APOC) endorsed the operational use of RAPLOA in Cameroon and Nigeria, but recommended further validation in other geographical areas to find out if those major findings are reproducible before the method could be recommended for all loiasis endemic countries. A validation study was therefore undertaken in two sites located at some 2000 km from each other in the South West and North East of the Democratic Republic of Congo. Following the completion of the validation study in 2004, the results were reported to the expert committees of APOC and the Mectizan Donation Programme which jointly recommended the use of RAPLOA to estimate the prevalence of L. loa in all areas in Africa suspected to be endemic for this parasite [11]. APOC subsequently started a large-scale application of RAPLOA for mapping the distribution of loiasis endemicit (...truncated)