Evaluation of onchocerciasis seroprevalence in Bioko Island (Equatorial Guinea) after years of disease control programmes

BACKGROUND: Onchocerciasis or "river blindness" is a chronic parasitic disease caused by the filarial worm Onchocerca volvulus, transmitted through infected blackflies (Simulium spp.). Bioko Island (Equatorial Guinea) used to show a high endemicity for onchocerciasis. During the last years, the disease control programmes using different larvicides and ivermectin administration have considerably reduced the prevalence and intensity of infection. Based on this new epidemiological scenario, in the present work we aimed to assess the impact of the strategies applied against onchocerciasis in Bioko Island by an evaluation of IgG4 antibodies specific for recombinant Ov-16 in ELISA. METHODS: A cross-sectional study was conducted in Bioko Island from mid-January to mid-February, 2014. Twenty communities were randomly selected from rural and urban settings. A total of 140 households were chosen. In every selected household, all individuals aged 5 years and above were recruited; 544 study participants agreed to be part of this work. No previous data on onchocerciasis seroprevalence in the selected communities were available. Blood samples were collected and used in an "ELISA in-house" prepared with recombinant Ov-16, expressed and further purified. IgG4 antibodies specific for recombinant Ov-16 were evaluated by ELISA in all of the participants. RESULTS: Based on the Ov-16 ELISA, the onchocerciasis seroprevalence was 7.9 %, mainly concentrated in rural settings; samples from community Catedral Ela Nguema (# 16) were missed during the field work. Among the rural setups, communities Inasa Maule (# 7), Ruiché (# 20) and Barrios Adyacentes Riaba (# 14), had the highest seropositivity percentages (29.2, 26.9 and 23.8 %, respectively). With respect to the urban settings, we did not find any positive case in communities Manzana Casa Bola (# 3), Colas Sesgas (# 6), Getesa (# 8), Moka Bioko (# 9), Impecsa (# 10), Baney Zona Baja (# 12) and Santo Tomás de Aquino (# 1). No onchocerciasis seropositive samples were found in 10-year-old individuals or younger. The IgG4 positive titles increased in older participants. CONCLUSIONS: A significant decline in onchocerciasis prevalence was observed in Bioko Island after years of disease-vector control and CDTI strategy. The seroprevalence increased with age, mainly in rural settings that could be due to previous exposure of population to the filarial parasite, eliminated by the control programmes introduced against onchocerciasis. A new Ov-16 serological evaluation with a larger sample size of children below 10 years of age is required to demonstrate the interruption of transmission of O. volvulus in the human population of Bioko Island (Equatorial Guinea) according to the WHO criteria.We would like to thank the National Program for Control of Onchocerciasis and other Filariasis in Equatorial Guinea for supporting us to obtain the information on which this study is based. We are grateful to the study participants for volunteering to participate in the study and the data collectors for performing field work. Our gratitude to the Unit of Serological Diagnosis, Department of Parasitology, Centro Nacional de Microbiología, and the Spanish Red Cross for providing some control samples. Thanks are also due to Diana Gomez-Barroso, from the National Centre of Epidemiology (ISCIII) for her help with the mapping.S

Spatial clustering of onchocerciasis in Bioko Island, Equatorial Guinea

INTRODUCTION: Onchocerciasis is a chronic neglected tropical disease caused by the filarial nematode Onchocerca volvulus, which is endemic in Equatorial Guinea. The aim was to estimate the current spatial distribution of onchocerciasis, and its related factors, in Bioko Island after several years of mass drug administration and vector control activities, by using GIS technics. METHODOLOGY: The survey was carried out within the framework of a wider research project entitled "Strengthening the National Programme for Control of Onchocerciasis and other Filariasis in Equatorial Guinea". A structured questionnaire was designed to cover basic socio-demographic information and risk factors for onchocerciasis and the coordinates of household. the hydrographic network data to calculate the positive onchocerciasis rate was used. Poisson generalized linear model was used to explore the association between onchocerciasis and the following covariates: distance to the river, preventive practices, water source and household´s main source of income. Two different cluster analysis methods were used: Getis-Ord Gi statistic and SaTScan™ purely spatial statistic estimator. RESULTS: The risk of onchocerciasis was higher for those who drank water from external sources (RR 25.3) than for those who drank home tap water (RR 8.0). The clusters with z-score higher were located at the east of the island. For 5 km and 1 km distances, one significant cluster in the east was detected (RR 5.91 and RR 7.15). CONCLUSION: No environmental factors related with onchocerciasis were found, including proximity to rivers. This could be partially explained by the fact that the vector was eliminated in 2005.S

Evidence for Suppression of Onchocerciasis Transmission in Bioko Island, Equatorial Guinea

<div><p>Onchocerciasis or "river blindness" is a chronic parasitic neglected tropical disease which is endemic both in mainland and insular Equatorial Guinea. We aim to estimate the current epidemiological situation of onchocerciasis in Bioko Island after vector elimination in 2005 and more than sixteen years of Community Directed Treatment with Ivermectin (CDTI) by using molecular and serological approaches for onchocerciasis diagnosis. A community-based cross-sectional study was carried out in Bioko Island from mid-January to mid-February 2014. A total of 544 study participants were recruited. A complete dermatological examination was performed and three skin snips were performed in every participant for parasitological and molecular assessments. Blood spots were also taken for determination of Ov16 IgG4 antibodies trough an “in-house” ELISA assay. Overall, we found 15 out of 522 individuals suffering any onchocerciasis specific cutaneous lesions and 16 out of 528 (3.0%) with onchocercal nodules in the skin. Nodules were significantly associated with age, being more common in subjects older than 10 years than in younger people (3.9% vs. 0%, p = 0.029). Regarding the onchocerciasis laboratory assessment, no positive parasitological test for microfilaria detection was found in the skin snips. The calculated seroprevalence through IgG4 serology was 7.9%. No children less than 10 years old were found to be positive for this test. Only one case was positive for <i>Onchocerca volvulus</i> (<i>O</i>. <i>volvulus</i>) after skin PCR. The present study points out that the on-going mass ivermectin treatment has been effective in reducing the prevalence of onchocerciasis and corroborates the interruption of transmission in Bioko Island. To our knowledge, this is the first time that accurate information through molecular and serological techniques is generated to estimate the onchocerciasis prevalence in this zone. Sustained support from the national program and appropriate communication and health education strategies to reinforce participation in CDTI activities are essential to ensure progress towards onchocerciasis elimination in the country.</p></div

House-holds distribution in the study area, Bioko Island, Equatorial Guinea.

<p>House-holds distribution in the study area, Bioko Island, Equatorial Guinea.</p

Laboratory assessments, Bioko Island, January 2014.

<p>Laboratory assessments, Bioko Island, January 2014.</p

Clinical characteristics of onchocerciasis of the study population, by age Bioko Island, Equatorial Guinea, January 2014.

<p>Clinical characteristics of onchocerciasis of the study population, by age Bioko Island, Equatorial Guinea, January 2014.</p

Preventive treatment by age Bioko Island, Equatorial Guinea, January 2014.

<p>Preventive treatment by age Bioko Island, Equatorial Guinea, January 2014.</p