Validation of the rapid assessment procedure for loiasis (RAPLOA) in the Democratic Republic of Congo

Abstract

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 well-known 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.

Figure 1

Location of the validation villages in the Democratic Republic of Congo.

Figure 2

Relationship between the prevalence of high microfilarial loads (> 8000 Mf/ml) and the prevalence of microfilaraemia at the community level (original and validation data). The black and red lines show the calibration models fitted to the original and validation data, respectively. The left-hand panel shows the data and models on the log-odds scale, the right-hand panel on the prevalence scale. The original data are from [10]).

Figure 3

Relationship between the prevalence of microfilaraemia and the prevalence of the history of eye worm (RAPLOA) (original and validation data). The black and red lines show the calibration models fitted to the original and validation data, respectively. The left-hand panel shows the data and models on the log-odds scale, the right-hand panel on the prevalence scale. The original data are from [10]).

Figure 4

Relationship between the prevalence of high intensity of microfilaraemia (> 8000 Mf/ml) and the prevalence of the history of eye worm (RAPLOA) (original and validation data). The solid line shows the regression model fitted to the validation data. The original data are from [10]).

Figure 5

Relationship between the prevalence of very high intensity of microfilaraemia (> 30,000 Mf/ml) and the prevalence of the history of eye worm (RAPLOA): (original and validation data). The solid line shows the regression model fitted to the validation data. The original data are from [10]).

Figure 6

ROC curves for the sensitivity and specificity of the RAPLOA index as a proxy for parasitological thresholds 20% positive Mf (left-hand panel), 5% Mf > 8 K (centre panel) and 2% Mf > 30 K (right-hand panel). The arrow on each ROC curve identifies the point closest to (0,1).