Abstract
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 Onchocerca volvulus (O. volvulus) 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.
Highlights
Onchocerciasis or "river blindness" is a chronic parasitic neglected tropical disease caused by the filarial nematode Onchocerca volvulus (O. volvulus)
Our study provides evidence towards the fact that onchocerciasis transmission might have been achieved in Bioko Island after more than sixteen years of onchocerciasis control activities
Our results show that, even though some onchocerciasis clinical features can still be found in the population, there is a marked reduction in both the prevalence and the intensity of infection compared to the initiation of onchocerciasis control activities in the study area
Summary
Onchocerciasis or "river blindness" is a chronic parasitic neglected tropical disease caused by the filarial nematode Onchocerca volvulus (O. volvulus). The presence of one or another clinical manifestation varies depending on the most prevalent parasite strain circulating in the area: blindness tends to occur more frequently in the West African areas of savannah while onchocerciasis cutaneous disease (OCD) prevails in African forest areas [1]. Murdoch et al (1993) described a grading system for OCD and defined five main categories, which can coexist together: acute papular onchodermatitis, chronic papular onchodermatitis, lichenified onchodermatitis, atrophic onchodermatitis and depigmented onchodermatitis [3]. This classification and grading system allowed to highlight the linkages between the different OCD forms with onchocerciasis epidemiology in different endemic areas [4]
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