Still mesoendemic onchocerciasis in two Cameroonian community-directed treatment with ivermectin projects despite more than 15 years of mass treatment

Guy-Roger Kamga, Fanny N Dissak-Delon, Hugues C Nana-Djeunga, Benjamin D Biholong, Stephen Mbigha-Ghogomu, Jacob Souopgui, Honorat G M Zoure, Michel Boussinesq, Joseph Kamgno, Annie Robert, Guy-Roger Kamga, Fanny N Dissak-Delon, Hugues C Nana-Djeunga, Benjamin D Biholong, Stephen Mbigha-Ghogomu, Jacob Souopgui, Honorat G M Zoure, Michel Boussinesq, Joseph Kamgno, Annie Robert

Abstract

Background: After more than a decade of community-directed treatment with ivermectin (CDTI) in Centre and Littoral Regions of Cameroon, onchocerciasis endemicity was still high in some communities according to the 2011 epidemiological evaluations. Some corrective measures were undertaken to improve the CDTI process and therefore reduce the burden of the disease. The objective of the present study was to assess the progress made towards the elimination of onchocerciasis in the Centre 1 and Littoral 2 CDTI projects where the worst performances were found in 2011. To this end, a cross-sectional survey was conducted in April 2015 in eight communities in two health districts (HD), Bafia in Centre 1 and Yabassi in Littoral 2, chosen because assessed at baseline and in 2011. All volunteers living for at least five years in the community, aged five years or more, underwent clinical and parasitological examinations. Individual compliance to ivermectin treatment was also assessed. Analyses of data were weighted proportionally to age and gender distribution in the population.

Results: In the Bafia and Yabassi HD, 514 and 242 individuals were examined with a mean age of 35.1 (standard deviation, SD: 20.7) and 44.6 (SD: 16.3) years, respectively. In the Bafia HD, the weighted prevalences varied from 24.4 to 57.0 % for microfilaridermia and from 3.6 to 37.4 % for nodule presence across the surveyed communities. The community microfilarial load (CMFL), expressed in microfilariae/skin snip (mf/ss), significantly dropped from 20.84-114.50 mf/ss in 1991 to 0.31-1.62 mf/ss in 2015 in all the surveyed communities. In the Yabassi HD, the weighted prevalences varied from 12.3 to 59.3 % for microfilaridermia and from 1.5 to 3.7 % for nodule presence across the surveyed communities, while a significant drop was observed in CMFL, from 20.40-28.50 mf/ss in 1999 to 0.48-1.74 mf/ss in 2015. The 2014 weighted therapeutic coverage of participants varied from 65.8 % (95 % CI: 58.4-73.2) in Yabassi HD, to 68.0 % (95 % CI: 63.3-72.7) in Bafia HD, with important variations among communities.

Conclusions: After more than 15 years of CDTI, onchocerciasis is still mesoendemic in the surveyed communities. Further studies targeting therapeutic coverage, socio-anthropological considerations of CDTI implementation and entomological studies would bring more insights to the persistence of the disease as observed in the present study.

Keywords: Bafia; Cameroon; Elimination; Ivermectin; Onchocerciasis; Persistence; Yabassi.

Figures

Fig. 1
Fig. 1
Map of Cameroon showing the study areas and communities surveyed
Fig. 2
Fig. 2
Therapeutic coverage in Centre 1 and Littoral 2 CDTI projects
Fig. 3
Fig. 3
Comparison of weighted microfilaridermia prevalences at baseline, 1991, with follow-up surveys in 2011 and 2015, in the communities surveyed in the Bafia health district
Fig. 4
Fig. 4
Comparison of community microfilarial load at baseline, 1991, with follow-up surveys in 2011 and 2015, in the communities surveyed in the Bafia health district. Abbreviations: mf, microfilaria; ss, skin snip
Fig. 5
Fig. 5
Comparison of weighted microfilaridermia prevalences at baseline, 1999, with follow-up surveys in 2015, in the communities surveyed in the Yabassi health district
Fig. 6
Fig. 6
Comparison of community microfilarial load at baseline, 1999, with follow-up surveys in 2015, in the communities surveyed in the Yabassi health district. Abbreviations: mf, microfilaria; ss, skin snip
Fig. 7
Fig. 7
Distribution of nodules according to the anatomical localization in carriers
Fig. 8
Fig. 8
Proportion of participants according to ivermectin treatment in the Bafia health district
Fig. 9
Fig. 9
Proportion of participants according to ivermectin treatment in the Yabassi health district
Fig. 10
Fig. 10
Arithmetic mean of microfilaria per skin snip according to the number of ivermectin treatment taken during the last five years among carriers in Bafia and Yabassi health districts

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