Co-endemicity of Loiasis and Onchocerciasis in Rain Forest Communities in Southwestern Nigeria

<div><p>Background</p><p>Loiasis is currently receiving attention as a disease of public health importance because of the possibility of increased risk of developing neurologic serious adverse event following mass ivermectin treatment against onchocerciasis in individual co-infected with <i>Onchocerca volvulus</i> and <i>Loa loa</i>.</p><p>Methodology/Principal Findings</p><p>Rapid assessment procedure for loiasis (RAPLOA) was conducted in 12 communities covering the 3 senatorial districts of Osun State, Nigeria. A total of 960 people were interviewed for history of eye worm using the WHO guidelines for rapid assessment. The survey confirmed the presence of loiasis in all the 12 communities with 4 in Osun East/Ife south senatorial district being at high risk with a prevalence of over 40%. Based on the RAPLOA results, communities within Osun East/Ife south senatorial district were selected for microfilaraemic assessment of <i>L</i>. <i>loa</i> and <i>O</i>. <i>volvulus</i>. A total of 1115 and 1091 individuals were screened for <i>L</i>. <i>loa</i> and <i>O</i>. <i>volvulus</i> microfilaria worms respectively. 160 (14.3%) had <i>L</i>. <i>loa</i> microfilaria detected in their blood with 8 (5.0%) individuals having <i>L</i>. <i>loa</i> loads above 8000 mf/ml. 166 (15.2%) subjects had <i>O</i>. <i>volvulus</i> microfilaria (range 4-504 mf/ml) detected in their skin snip. 30 (2.69%) subjects were co-infected with both <i>L</i>. <i>loa</i> and <i>O</i>. <i>volvulus</i>. There was a significant variation in the prevalence (2.1% to 33.3%) of onchocerciasis in the communities studied (p = 0.001). Five (41.7%) of the studied communities had a prevalence that is equal to or greater than 20%.</p><p>Conclusions/Significance</p><p>Low prevalence of onchocerciasis and loiasis co-infection in this study suggests that loiasis may not pose a serious epidemiological threat to the continuous distribution and sustainability of ivermectin for the treatment of onchocerciasis. Evaluation of the interruption of onchocerciasis transmissions in this region using all the indicators set forth by WHO is therefore suggested.</p></div

Map of Osun State showing the three senatorial districts and the communities within the districts that were selected for the study.

<p>Map of Osun State showing the three senatorial districts and the communities within the districts that were selected for the study.</p

Distribution of <i>Loa loa</i> microfilaraemia and <i>O</i>.<i>volvulus</i> by age and sex.

<p>Distribution of <i>Loa loa</i> microfilaraemia and <i>O</i>.<i>volvulus</i> by age and sex.</p

Clinical spectrum observed from filarial infected members of the surveyed population.

<p>Clinical spectrum observed from filarial infected members of the surveyed population.</p

The prevalence of loiasis and onchocerciasis in the selected rural communities in Osun State.

<p>The prevalence of loiasis and onchocerciasis in the selected rural communities in Osun State.</p

Number of villages surveyed and number of people interviewed in 12 villages of Osun State for RAPLOA.

<p>Number of villages surveyed and number of people interviewed in 12 villages of Osun State for RAPLOA.</p