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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.

Background: Onchocerciasis and lymphatic filariasis (LF) are endemic in Equatorial Guinea with notable variations in disease incidence between island and mainland regions. Historically, efforts to control and map these diseases were concentrated in Bioko Island, where loiasis is absent, allowing for targeted onchocerciasis interruption strategies. With the cessation of onchocerciasis transmission on Bioko and no reported cases on Annobon island, assessing the transmission status in the previously unaddressed mainland region has become imperative. Mapping efforts in mainland Equatorial Guinea have proven low to moderate level of transmission for LF and onchocerciasis, although the results so far have not been very conclusive. The current study aims to update the prevalence estimates for onchocerciasis and LF in mainland Equatorial Guinea using various diagnostic techniques. Methods: This is the first cross-sectional study carried out to estimate the prevalence of onchocerciasis and LF in the mainland area of Equatorial Guinea, from September to December 2019, based on the combination of skin snip biopsies, thick blood smears, laboratory serological tests (ELISA tests for the detection of IgG4 antibodies against Onchocerca volvulus recombinant antigen Ov16 and Wuchereria bancrofti recombinant antigen Wb123) and molecular laboratory tests. Frequencies and prevalence rates, along with 95% confidence intervals for interval estimation of a binomial proportion, were computed. Results: The overall onchocerciasis seroprevalence calculated for the study was 0.3% (95% CI: 0.1 to 0.5%). Microscopic examination of skin biopsies from the eight individuals seropositive for Ov16, out of the 3951 individuals initially tested, revealed no O. volvulus microfilariae. However, DNA extracted from one skin snip was successfully amplified, with subsequent sequencing confirming the presence of O. volvulus. Among the 3951 individuals, 182 were found to have anti-Wb123 antibodies, suggesting exposure to W. bancrofti, with an estimated seroprevalence of 4.6% (95% CI: 4.0 to 5.3%). Microscopy and Filaria-real time-PCR (F-RT-PCR) analysis for W. bancrofti were negative across all samples. Conclusions: The findings indicate that onchocerciasis may no longer constitutes a public health problem in Equatorial Guinea, positioning the country on the verge of achieving elimination. Additionally, the mapped prevalence of LF will facilitate the formulation of national strategies aimed at eradicating filariases countrywide. [ABSTRACT FROM AUTHOR]