Point prevalence mapping reveals hotspot for onchocerciasis transmission in the Ndikinimeki Health District (Centre Region, Cameroon)

doi:10.21203/rs.3.rs-32110/v2

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Point prevalence mapping reveals hotspot for onchocerciasis transmission in the Ndikinimeki Health District (Centre Region, Cameroon)

https://doi.org/10.21203/rs.3.rs-32110/v2

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published 16 Oct, 2020

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Background

Ivermectin-based preventive chemotherapy (PC) is distributed annually to all at-risk individuals to control and/or eliminate onchocerciasis. Information on the impact of mass ivermectin administration on onchocerciasis transmission are scanty, and it is tricky to appreciate the progress towards elimination and engage corrective measures. To fill that gap in the Centre Region in Cameroon, the current onchocerciasis endemicity level in the Ndikinimeki Health District after about two decades of mass treatments was assessed.

Methods

A cluster-based cross-sectional survey was carried out in the Ndikinimeki Health District and all volunteers aged ≥5 years were (i) interviewed on their compliance to ivermectin over the past five years and (ii) underwent clinical (nodule palpation and visual search for onchocercal lesions) and parasitological examinations (skin snip) for onchocerciasis.

Results

The overall Onchocerca volvulus prevalence was 7.0% (95% CI: 5.2-9.3). The prevalence of the disease was significantly higher in the communities Kiboum 1 and Kiboum 2 compared to the other communities (highest prevalence in Makénéné Town Water: 8.5%; 95% CI: 2.3-20.4) (χ2 = 51.314, df = 11, P = 0.0001). The proportion of systematic non-compliers to ivermectin was 23.3% (95% CI: 19.9-27.1) among individuals interviewed. In the sentinel sites (Kiboum communities), onchocerciasis prevalence decreased from 95.2% (95% CI: 88.3-98.1) to 23.7% (95% CI: 14.7-36.0).

Conclusions

This study has revealed that the Ndikinimeki Health District is hypo-endemic for onchocerciasis after about two decades of preventive chemotherapy. However, transmission is ongoing, with a potential hotspot in the Kiboum 1 and Kiboum 2 communities, which are known as first-line communities (closest to the breeding sites of the vector). Alternative or complementary strategies to annual ivermectin appear compulsory to accelerate the momentum towards onchocerciasis elimination.

Parasitology

Onchocerciasis

CDTI

Hotspot

Ndikinimeki Health District

Cameroon

Onchocerciasis, better known as river blindness because of the high prevalence of blindness in villages located along fast-flowing rivers where the vectors breed [1], is a neglected tropical disease (NTD) affecting over 20.9 million people worldwide, of which 99% reside in Africa [2]. In Cameroon, onchocerciasis is endemic in all the 10 Regions with approximately 6 million people infected and about 60% of the population living in high risk areas for the disease [3]. This disease is caused by the parasitic nematode Onchocerca volvulus and transmitted via the bites of female blackflies of the genus Simulium during blood feeding. People at highest risk of acquiring onchocerciasis are those living or working near fast-flowing and well-oxygenated streams or rivers appropriate to blackfly breeding. This infection rarely causes death but imposes suffering, stigmatization, and hardship to affected individuals and communities. It is the second leading cause of infectious blindness worldwide after trachoma [4]. The pathogenesis of the diseases is essentially due to microfilariae, while adult worms usually induce no pathology or simply stimulate the development of characteristic subcutaneous nodules.

Ivermectin (Mectizan®) is the only known effective and safe drug used for preventive chemotherapy (PC) against onchocerciasis [5]. Since this drug has a limited macrofilaricidal activity [6] and adult O. volvulus is long-lived (lifespan > 14 years [7]), treatments must be repeated yearly for 12 to 15 years to break the transmission cycle [8]. Community-directed treatment with ivermectin (CDTI), formally adopted by the African Programme for Onchocerciasis Control (APOC) in 1997, has so far remained the main control strategy to eliminate this disease in Africa. Indeed, CDTI relies on active community participation, by focusing on empowering communities to take responsibility for ivermectin delivery, deciding how, when and by whom the ivermectin treatment should be administered [2]. This strategy, implemented once-a-year in most African countries, including Cameroon, has significantly improved ivermectin treatment coverage [9-10]. Unlike Latin America where the biannual large-scale treatment with ivermectin has succeeded in eliminating the infection in four of the six endemic countries (Columbia in 2013, Ecuador in 2014, Mexico in 2015 and Guatemala in 2016) [11], transmission of the disease has been interrupted only in limited foci in some endemic countries in Africa (Mali, Senegal and Nigeria) [12-14]. In most foci in Africa, including in Cameroon, the disease is persisting with prevalence up to 50% despite almost three decades of CDTI [15-18]. In order to improve current control approaches and define a more pinpointed strategy, it is worth carrying out regular surveys to assess the impact of control approaches on the disease epidemiology. Therefore, this study assessed onchocerciasis endemicity in the Ndikinimeki Health District after about two decades of CDTI, using a district-wide rather than sentinel site approach.

Study area

The study was carried out in the Ndikinimeki Health District, chosen because onchocerciasis-related monitoring and evaluation information was scanty or only sentinel site-based, although ivermectin mass administration was ongoing since 1998. The Health District consists of six Health Areas namely Makenene, Nitoukou, Nyokon, Ndokowanen, Ndikinimeki and Boutourou. The Ndikinimeki Health District (4.76°N, 10.83°E) is found in the Mbam and Inoubou Division of the Centre Region of Cameroon. The climate is equatorial and divided into four seasons: a long dry season (November-February), a short rainy season (March-June), a short dry season (June-August) and a long rainy season (August-November) [19]. The mean annual temperature is 22.4°C and the average annual rainfall is 1,440 mm. The region is highly irrigated by the Inoubou, Makombé and Makénéné rivers and their various tributaries. The main activities of the inhabitants are agriculture (cocoa farming, fishing) and sand mining. The Health District has a population size of about 44,519 inhabitants based on the 2017 health population denominators [20].

Study design and participants

A cross-sectional survey was carried out in the Ndikinimeki Health District following a cluster sampling approach. Clusters were selected using the Probability Proportionate to Estimate Size (PPES) strategy. In order to ensure that all clusters have the same probability of selection, communities (clusters) were organized into Health Areas prior to the PPES procedure to take into account the difference in the number of communities per Health Area and the difference in community size. A total of 12 clusters were selected by the PPES procedure. Considering the onchocerciasis prevalence (54.7%) in the Ndikinimeki Health District according to the most recent impact assessment survey (2011) by the National Onchocerciasis Control Program (NOCP), a minimal sample size of 381 was needed to estimate the true prevalence of onchocerciasis in 2019 in the Ndikinimeki Health District with 5% precision, and 95% confidence interval. Eligible participants were both males and females, aged five years and above, and who had been living in the selected clusters for at least five years. In each cluster, socio-demographic data, history of, and adherence to ivermectin treatments during the past five years preceding the survey, were collected from eligible participants using a structured questionnaire. Although eligible to ivermectin-based PC, individuals aged <10 years old were excluded from history and adherence to mass drug administration (MDA) since they are less likely to provide accurate enough answers to such questions. All the individuals who accepted to participate underwent clinical and parasitological examinations, respectively. Furthermore, follow-up of the trend in onchocerciasis prevalence over three decades (or 25 years of annual mass ivermectin treatment) was carried out only in the Boutourou Health Area where a sentinel site (Kiboum communities) was identified during mapping exercise, based on the availability of baseline data. Both the baseline (1991) and the follow-up (2011) surveys were carried out by the NOCP, with the support of APOC (NOCP, unpublished reports).

Clinical examination

The clinical examination included nodule palpation, visual inspection for skin disease and anamnesis for pruritus. Nodule palpation was performed on partially disrobed participants in a closed but well-illuminated room. Attention was paid to bony prominences of the torso, iliac crests, and upper trochanter of the femurs as was already described as election sites of onchocercal nodules in Africa [21]. Participants were also asked whether they suffer from pruritus and their skin visually inspected for cutaneous signs of onchocerciasis, especially depigmentation (leopard skin) and skin rashes [21-22].

Parasitological examination

Two skin snips were taken with a sterile 2 mm corneoscleral punch (type Holth) from the two posterior iliac crests of each participant. The skin snips were placed in two separate wells of a microtitration plate containing ~200 µL of normal saline (0.9 %) and incubated for 24 hours at room temperature. The fluid of each well of the microtitration plate was examined for Onchocerca microfilariae using bright-field microscopy under low magnification (40×) [23]. The number of microfilariae in the fluid was counted (when positive) and the individual microfilarial densities were computed as the arithmetic mean number of microfilariae in the two skin snips (mf/ss).

Statistical analyses and onchocerciasis distribution map

All data collected as part of this study (clinical signs, nodules, mf count and compliance with ivermectin PC) were recorded into a purpose-built Microsoft Access database and subsequently exported into a Predictive Analytics Software (PASW) Statistics version 18 (SPSS Inc., Chicago, IL, USA) for statistical analyses. Prevalence of skin microfilariae, skin disease and onchocercal nodules (whatever the number of nodules per participant) were expressed as the percentage of infected or affected individuals among the total number of individuals examined. Compliance with ivermectin PC was defined as the proportion of individuals eligible to ivermectin who actually ingested the drug. The 95% confidence interval (CI) for proportion/prevalence was calculated using the Wilson method not corrected for continuity [24]. The intensity of infection was evaluated using two metrics, the skin microfilarial density and the community microfilarial load (CMFL). The skin microfilarial density was defined as the arithmetic mean of individual microfilarial densities with standard deviation (SD) to account for sampling fluctuations. The CMFL was computed as the geometric mean number of microfilariae per skin snip (mf/ss) among adults aged 20 years or more, using the log (x + 1) transformation to take into account zero counts [25], especially after multiple rounds of ivermectin treatments. Chi-square, Mann-Whitney and Kruskal-Wallis tests were used to compare onchocerciasis prevalence and mean microfilarial density between clusters, genders and age groups, respectively.

The geographical coordinates of each community visited were recorded using a high sensitivity global positioning system [GPS eTrex; Garmin (Europe) Ltd, Southampton, U.K.]. A thematic analysis was performed using a geographical information system (GIS) software (ArcGIS, version 10.2, ESRI Inc.) to map the distribution, at cluster (community) level, of onchocerciasis point prevalence in the Ndikinimeki Health District; three main layers (roads, vegetation cover and rivers/streams, the latest representing potential blackfly breeding sites) were used to create/illustrate the map.

A total of 603 participants aged 5 to 88 (median: 32; interquartile range (IQR): 42) years were examined in 12 clusters (communities) of the six Health Areas of the Ndikinimeki Health District. The sex ratio (M/F) was 1.04 (proportion of males: 50.9%).

Prevalence and intensity of O. volvulus infection

Of the 603 participants examined, 42 (7.0%; 95% CI: 5.2-9.3) were found to be infected with O. volvulus. The prevalence of onchocerciasis was significantly higher in the Boutourou Health Area (21.6% (95% CI: 14.5-30.1) (χ² = 48.708, df = 5 P = 0.0001), among males (11.1%; 95% CI: 7.7-15.1) (χ²= 16.301, df = 1, P = 0.0001) and among younger adults (20-34 years) (18.3%; 95% CI: 11.0-27.6) (χ²= 25.727, df = 3, P = 0.0001) (Table 1). At the community or cluster level, onchocerciasis prevalence ranged between 0.00% (95% CI: 0.0-8.8) and 23.7% (95% CI: 13.6-36.6). A significantly higher burden of the disease was observed in the communities Kiboum 1 (19.3%; 95% CI: 10.0-31.9) and Kiboum 2 (23.7%; 95% CI: 13.6-36.6) compared to the other communities (highest prevalence in Makénéné Town Water: 8.5%; 95% CI: 2.3-20.4) (p = 0.0001) (Figure 1) (Table 2) (Additional file 1: Table S1). Furthermore, a significantly higher prevalence of the disease was observed among farmers (p = 0.0001).

The overall microfilarial density was 0.557 (SD: 3.7843) mf/ss, significantly higher in the Boutourou Health Area (χ² = 47.576, df = 5, P = 0.0001), among males (Mann Whitney U-test: U = 41645.5, Z = -4.016, P = 0.0001) and young adults aged 20-34 years (χ² = 25.703, df = 3, P = 0.0001) (Table 2). The intensity of infection was also significantly higher in Kiboum 1 (1.395; SD: 8.4143) and Kiboum 2 (1.814; SD: 5.1986) communities compared to other communities (highest microfilarial density in Makénéné Town Water: 0.979; SD: 4.2643) (χ² = 50.490, df = 11, P = 0.0001). The overall CMFL in the study area was 0.168 mf/ss, significantly higher in the Kiboum 1 (0.383 mf/ss) and Kiboum 2 (0.538mf/ss) communities (Additional file 1: Table S1).

Morbidity associated with onchocerciasis

The overall prevalence of palpable nodules was 0.3% (95% CI: 0.1-1.2), ranging between 0.0% and 0.6% but the difference was not significant between Health Areas (χ² = 1.416, df = 5, P = 0.923), communities (χ² = 8.768, df = 11, P = 0.643), age groups (χ² = 2.892, df = 3, P = 0.409) and genders (χ² = 0.001, df = 1, P = 1).

The overall prevalence of skin depigmentation and rashes was 3.0% and 0.3%, respectively, and no significant difference (p>0.330) was found between Health Areas (χ² = 5.762, df = 5, P = 0.330). The difference was also not significant between genders (χ² = 0.154, df = 1, P = 0.694), age groups (χ² = 1.037, df = 3, P = 0.792) and clusters (χ² = 9.015, df = 11, P = 0.620).

Regarding pruritus, the proportion of individuals affected was significantly higher in the Nyokon Health Area (26.9%; 95% CI: 16.8-40.3) compared to the other Health Areas (χ² = 21.925, df = 5, P = 0.001), the difference was also significant when considering clusters (χ² = 92.731, df = 11, P < 0.0001) and age groups (χ² = 18.498, df = 3, P < 0.0001), but the difference was not significant when considering genders (χ² = 1.436, df = 1, P = 0.231).

History and adherence to ivermectin treatment

Overall, 74.8% (95% CI: 71.2-78.1) of participants reported that they have swallowed ivermectin at least once during the past five years. The proportion of individuals who reported that they have ingested ivermectin every year during the past five years was 34.5% (95% CI: 30.8-38.4), comparable between males (36.2%; 95% CI: 31.0-41.7) and females (32.8%; 95% CI: 27.7-38.3) (χ² = 0.76, df = 1, P = 0.3833). A significant increase in the trend of compliance with ivermectin treatment was observed between the age groups (χ² = 64.08, df = 3, P < 0.0001), 22.6% (95% CI: 16.3-30.4) of participants aged 10-19 years (individuals <10 excluded), 20.4% (95% CI: 13.5-29.7) of participants aged 20-34 years, 44.0% (95% CI: 35.1-53.4) of participants aged 35-49 years, and 60.3% (95% CI: 53.1-67.1) of participants aged ≥50 years declared having taken ivermectin tablets during the past five years.

The proportion of systematic non-compliers, that is those individuals who never ingested ivermectin tablets during the past five years, was 23.3% (95% CI: 19.9-27.1), slightly higher in females (26.3%; 95% CI: 21.3-31.9) than in males (20.4%; 95% CI: 15.9-25.7) although statistically non-significant (χ² = 2.5, df = 1, P = 0.1138). However, a significantly higher proportion of non-compliance with ivermectin treatment was observed between the age groups (χ² = 24.59, df = 3, P < 0.0001). Participants aged <34 years exhibited higher proportion of non-compliance with ivermectin treatment compared to their older counterparts (χ² = 64.08, df = 3, P < 0.0001). Overall, 31.6% (95% CI: 24.3-39.9) of participants aged 10-19 years (participants <10 excluded), 36.6% (95% CI: 27.5-46.7) of participants aged 20-34 years, 15.6% (95% CI: 10.0-23.6) of participants aged 35-49 years, and 15.2% (95% CI: 10.7-21.1) of participants aged ≥50 years declared that they have never swallowed ivermectin tablets during the past five years.

Thirty-year trend of onchocerciasis in the Boutourou Health Area

A significant decrease in the prevalence of onchocerciasis was observed, between current findings (2019) and both baseline data (1991) (χ² = 41.59, df = 1, P < 0.0001), and the first decade trend (2011) (χ² = 15.25, df = 1, P < 0.0001) (Figure 2).

Based on the prevalence of microfilaridermia, onchocerciasis endemic levels have been classified as hypo-endemic (prevalence ˂ 35 %), meso-endemic (35 % ≤ prevalence ˂ 60 %) or hyper-endemic (prevalence ≥ 60 %) [26]. After two decades of CDTI, the Ndikinimeki Health District moved from hyper-endemic (prevalence = 95.2%) to hypo-endemic for onchocerciasis (prevalence = 7.0%). The intensity of infection, expressed either by the microfilarial densities (at individual level) or by the CMFL (at the community level), was below 2mf/ss. Finally, onchocercal clinical signs were almost inexistent in communities visited. These observations suggest that the CDTI that has been going on in the Ndikinimeki Health District for almost two decades has drastically reduced the burden of the disease, as observed in previous studies in Cameroon [27].

The higher proportion of infection among farmers and males could be explained by the occupational exposure and susceptibility of individuals. Farmers and males are more involved in outdoor activities, exposing themselves to infective blackfly bites. This agrees with the findings by Kamga et al. [16], who reported a higher prevalence of onchocerciasis in males than in females in the Yabassi Health District (Littoral Region, Cameroon). Furthermore, the high prevalence of the disease observed among participants aged 20-34 years may be due to the fact that individuals within this age group are usually the most active members in the communities and may have higher risk of getting infected because of their involvement in outdoor activities such as farming, sand mining and fishing. Indeed, a significantly higher prevalence of the disease was observed among farmers, compared to students, traders, housekeepers, and civil servants (nurses, teachers). In addition, because of their outdoor activities, these individuals are usually absent during household-based direct observance mass administration of ivermectin and this might therefore explain why these groups exhibit a low adherence to ivermectin treatment. Our observations disagree with the findings by Ikpo et al. [28] who reported a peak prevalence of onchocerciasis among individuals aged 41-50 years old in the Oji River Local Government Area (Enugu State, Nigeria). In fact, onchocerciasis is known to be naturally cumulative, but treatments administered for 18-21 years might have disrupted this relationship, thus favoring the shift in prevalence peak among individuals highly exposed and poorly compliant with ivermectin MDA.

Despite the fact that preventive chemotherapies contributed to reducing onchocerciasis to hypo-endemic levels (microfilaridermia prevalence ˂ 35%) in all the surveyed Health Areas and communities, values were still above the expected level (≤ 20% for a pretreatment endemicity ≥ 80 % assuming a therapeutic coverage of 65% [29-30] in the Kiboum 1 and Kiboum 2 communities (Boutourou Health Area). This hotspot of onchocerciasis transmission may be due to the close proximity of these clusters to fast flowing rivers where blackflies breed. This is supportive of a change in the current strategies if one expects transmission interruption of onchocerciasis. Indeed, alternative treatment strategies (biannual CDTI, vector control using ground larviciding, vector control using vegetation slashing and clearing of blackfly breeding sites, test and treatment with the long-regimen macrofilaricidal drug doxycycline …) have been developed by the African Programme for Onchocerciasis Control (APOC), and recently reshaped for adapted implementation purpose [31]. In the current situation with the persistence of onchocerciasis in a restricted hotspot area, implementation of multiple annual rounds of CDTI complemented with localized vector control by using for example ground larviciding might help boost the momentum towards the elimination of onchocerciasis in the Ndikinimeki Health District, and serve as a proof of concept for strategy improvement for countrywide elimination of onchocerciasis.

This study reveals that the Ndikinimeki Health District is hypo-endemic for onchocerciasis after about two decades of CDTI. Despite the low prevalence and intensity of the disease in the study area, a hotspot for onchocerciasis transmission was found in the Boutourou Health Area (around Kiboum 1 and Kiboum 2 communities) where alternative treatment strategies might be useful to prompt the elimination of onchocerciasis.

CDTI: community-directed treatment with ivermectin

CI: confidence interval

CMFL: community microfilarial load

MDA: mass drug administration

mf/ss: microfilariae per skin snip

OR: odds ratio

PC: preventive chemotherapy

SD: standard deviation

Acknowledgements

The authors are thankful to the local authorities for their assistance during the implementation of this study, and to the population who willingly accept to participate in this study.

Declarations

Ethics approval and consent to participate

Ethical clearance was granted by the Centre Regional Ethics Committee for Human Health Research (N°667/CRERSH/2019) and Administrative authorization was granted by the Regional Delegation of Public Health and the Ndikinimeki Health District. After approval of the local administrative and traditional authorities, the objectives and schedules of the study were first explained to community leaders and to all eligible individuals. Before any procedure, informed consents were obtained from participants or their parents or guardians (for minors) who agreed to participate, under the discretion of community leaders. An individual barcode was attributed to each participant for anonymous data analysis.

Consent for publication

Not applicable

Availability of data and materials

All data generated or analyzed during this study are included in this published article (and its supplementary information files).

Competing interest

The authors declare that they have no competing interests.

Funding

This work was supported by authors’ personal funds; fees related for field work were covered by Mr René Afor Aza’ah and Drs Laurentine Sumo and Hugues C Nana Djeunga.

Authors’ contributions

RAA conceived the study and designed the experiments, collected field data, analyzed the data and drafted the manuscript. LS conceived the study and designed the experiments, supervised and coordinated the study and helped to draft the manuscript. NHN conceived the study and designed the experiments and helped to draft the manuscript. JB collected field data and contributed to the preparation of the manuscript. RHB collected field data and contributed to the preparation of the manuscript. HCND conceived the study and designed the experiments, supervised and coordinated the study, analyzed the data and drafted the manuscript. All authors read and approved the final manuscript. HCND and LS are guarantors of the paper.

Basáñez MG, Pion SD, Churcher TS, Breitling LP, Little MP, Boussinesq M. River blindness: a success story under threat?. PLoS Med. 2006;3(9):e371. doi:10.1371/journal.pmed.0030371.
World Health Organization. Onchocerciasis: key facts. World Health Organ 2019.
Noma M, Zouré HG, Tekle AH, Enyong PA, Nwoke BE, Remme JH. The geographic distribution of onchocerciasis in the 20 participating countries of the African Programme for Onchocerciasis Control: (1) priority areas for ivermectin treatment. Parasit Vectors. 2014;7:325. Published 2014 Jul 22. doi:10.1186/1756-3305-7-325.
World Health Organization. Blindness and vision impairment-fact sheets. World Health Organ 2019.
Centers for Disease Control and Prevention (CDC). Parasites- onchocerciasis (also known as river blindness). Review
Walker M, Pion SD, Fang H, Gardon J, Kamgno J, Basáñez MG, et al. The macrofilaricidal efficacy of repeated doses of ivermectin for the treatment of river blindness. Clin Infect Dis 2017; 65(12): 2026–34.
Plaisier AP, Oortmarssen GJV, Remme J, Habbema JDF. The reproductive lifespan of Onchocerca volvulus in west African savanna. Acta Trop 1991; 48: 271-84.
World Health Organization. Guidelines for stopping mass drug administration and verifying elimination of human onchocerciasis: criteria and procedures. World Health Organ 2016. WHO/HTM/NTD/PCT/2016.1
World Health Organization. The involvement of community-directed distributors of ivermectin in other health and development activities: report of a multi-country study. Geneva, Switzerland, World Health Organ 2003; 55p.
World Health Organization. Community directed interventions for major health problems in Africa: a multi-country study. Geneva, Switzerland, World Health Organ 2003; 132p.
World Health Organization. Progress report on the elimination of human onchocerciasis 2015 -2016. Geneva, Switzerland, World Health Organ
Diawara L, Traore MO, Badji A, Bissan Y, Doumbia K, Goita SF, et al. Feasibility of onchocerciasis elimination with ivermectin treatment in endemic foci in Africa: first evidence from studies in Mali and Senegal. PLoS Negl Trop Dis 2009; 3(7): e497.
Tekle A, Elhassan E, Isiyaku S, Amazigo UV, Bush S, Noma M, et al. Impact of long-term treatment of onchocerciasis with ivermectin in Kaduna State, Nigeria: first evidence of the potential for elimination in the operational area of the African Programme for Onchocerciasis Control. Parasit Vectors 2012; 5: 28.
Traore MO, Sarr MD, Badji A, Bissan Y, Diawara L, Doumbia K, et al. Proof-of-principle of onchocerciasis elimination with ivermectin treatment in endemic foci in Africa: final results of a study in Mali and Senegal. PLoS Negl Trop Dis 2012; 6(9): e1825.
Kamga HL, Shey DN, Assob JC, Njunda AL, Nde Fon P, Njem PK. Prevalence of onchocerciasis in the fundong health district, cameroon after 6 years of continuous community-directed treatment with ivermectin. Pan Afr Med J 2011; 10: 34.
Kamga GR, Dissak-Delon FN, Nana-Djeunga HC, et al. Still mesoendemic onchocerciasis in two Cameroonian community-directed treatment with ivermectin projects despite more than 15 years of mass treatment. Parasit Vectors. 2016;9(1):581. Published 2016 Nov 14. doi:10.1186/s13071-016-1868-8.
Eisenbarth A, Achukwi MD, Renz A. Ongoing transmission of Onchocerca volvulus after 25 years of annual ivermectin mass treatments in the Vina du Nord river valley, in North Cameroon. PLoS Negl Trop Dis. 2016;10(2):e0004392. Published 2016 Feb 29. doi:10.1371/journal.pntd.0004392.
Bakajika D, Senyonjo L, Enyong P, et al. On-going transmission of human onchocerciasis in the Massangam health district in the West Region of Cameroon: Better understanding transmission dynamics to inform changes in programmatic interventions. PLoS Negl Trop Dis. 2018;12(11):e0006904. Published 2018 Nov 14. doi:10.1371/journal.pntd.0006904.
Suchel JB. The climates of Cameroon. Doctoral thesis, University of Bordeaux III, France. ISBN 2950256902. 1987; 1188p.
World Health Organization. Health population denominators 2017 – Cameroon. Yaounde, Cameroon, World Health Organ 2017;
Albiez EJ, Buttner DW, Duke BO. Diagnosis and extirpation of nodules in human onchocerciasis. Trop Med Parasitol. 1988; 39 (Suppl 4): 331–46.
Ngoumou P, Walsh JF, Mace JM. A rapid mapping technique for the prevalence and distribution of onchocerciasis: a Cameroon case study. Ann Trop Med Parasitol. 1994; 88: 463–74.
Moreau J, Prost A, Prod’hon J. An attempt to normalize the methodology of clinico-parasitologic surveys of onchocerciasis in West Africa (author’s transl). Med Trop (March) 1978; 38: 43–51.
Wilson E. Probable inference, the law of succession, and statistical inference. J Am Stat Assoc 1927; 22: 209-12.
Remme J, Ba O, Dadzie KY, Karam M. A force-of-infection model for onchocerciasis and its applications in the epidemiological evaluation of the Onchocerciasis Control Programme in theVolta River basin area. Bull World Health Organ 1986; 64: 667-81.
Prost A, Hervouet JP, Thylefors B. Epidemiologic status of onchocerciasis. Bull World Health Organ. 1979; 57:655–62.
Kamga GR, Dissak-Delon FN, Nana-Djeunga HC, Biholong BD, Ghogomu SM, Souopgui J, Kamgno J, et al. Important progress towards elimination of onchocerciasis in the West Region of Cameroon. Parasit Vectors 2017; 10: 373.
Ikpo AU, Mbanugo JI, Anukwuorji CA, Ugwuanyi IK. Study on the prevalence of Onchocerca volvulus infection among the inhabitants of Awgu and Oji River Local Government Areas of Enugu State, Nigeria. Int J Trop Dis Health 2016; 18(1): 1-9.
African Program for Onchocerciasis Control (WHO/APOC). Conceptual and operational framework of onchocerciasis elimination with ivermectin treatment. World Health Organ 2010; WHO/APOC/MG/10.1. 24p.
Stolk WA, Walker M, Coffeng LE, Basáñez MG, de Vlas SJ. Required duration of mass ivermectin treatment for onchocerciasis elimination in Africa: a comparative modelling analysis. Parasit Vectors 2015. 8(552): 1159-9.
Boussinesq M, Fobi G, Kuesel AC. Alternative treatment strategies to accelerate the elimination of onchocerciasis. Int health 2018; 10(Suppl 1): i40-i8.

Table 1 Prevalence of onchocerciasis in the Ndikinimeki Health District according to Health Areas, genders and age groups

Variables	No. individuals examined	No. individuals infected	% prevalence (95% CI)
Health Area
Boutourou	116	25	21.6 (14.5–30.1)
Makénéné	160	8	5.0 (2.1 – 9.6)
Ndikinimeki	198	7	3.5 (1.4 – 7.1)
Ndokowonen	37	1	2.7 (0.0 – 14.2)
Nitoukou	40	0	0.0 (0.0 – 8.8)
Nyokon	52	1	1.9 (0.0 – 10.3)
Gender
Males	307	34	11.1 (7.7 – 15.1)
Females	296	8	2.7 (1.2 – 5.3)
Age group
5-19	217	5	2.3 (0.7 – 5.3)
20-34	93	17	18.3 (11.0 – 27.6)
35-49	109	8	7.3 (3.2 – 14.0)
50-over	184	12	6.5 (3.4 – 11.1)
Overall	603	42	7.0 (5.2 – 9.3)

No.: number of; CI: confidence interval

Table 2 Intensity of Onchocerca volvulus infection in the Ndikinimeki Health District according to Health Areas, genders and age groups

Variables	No. individuals examined	Mean microfilarial Density (mf/ss)	Standard Deviation	Min – Max	CMFL (mf/ss)
Health Area
Boutourou	116	1.608	6.9391	0.0 - 63.5	0.465
Makénéné	160	0.641	4.0020	0.0 - 37.5	0.165
Ndikinimeki	198	0.189	1.1893	0.0 - 12.0	0.103
Ndokowonen	37	0.230	1.3974	0.0 - 8.5	0.084
Nitoukou	40	0.000	0.0000	0.0 - 0.0	0.000
Nyokon	52	0.019	0.1387	0.0 - 1.0	0.021
Gender
Males	307	0.746	3.5845	0.0 - 37.5	0.266
Females	296	0.361	3.9776	0.0 - 63.5	0.079
Age group
5-19	217	0.168	1.8036	0.0 - 25.5	-
20-34	93	1.785	7.9075	0.0 - 63.5	0.357
35-49	109	0.321	1.9239	0.0 - 18.0	0.096
50-over	184	0.535	2.9449	0.0 - 27.5	0.125
Overall	603	0.557	3.7843	0.0 - 63.5	0.168

No.: number of; mf/ss: microfilariae/skin snip; Min: minimum; Max: maximum; CMFL: community microfilarial load

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published 16 Oct, 2020

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Point prevalence mapping reveals hotspot for onchocerciasis transmission in the Ndikinimeki Health District (Centre Region, Cameroon)

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