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

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.

Onchodermatitis: Where Are We Now?

“…Prior to control measures on the island of Bioko, Equatorial Guinea, a survey in the mid 1980s reported that 28.8% of the study population suffered from dermatitis, pigmentation changes and cutaneous atrophy. After vector elimination in 2005 and more than 16 years of CDTi on Bioko Island, a community-based cross-sectional survey was performed in 2014, including a full cutaneous examination [ 67 ]. Although these workers found that 50.4% individuals reported never having taken ivermectin and only 28% had taken it more than twice within the past five years, there was a reduction in pruritus and skin lesions (14.9% complained of pruritus, 3% had nodules, 1.3% had ‘onchodermatitis’ and a further 1.8% had leopard skin.…”

Factors affecting onchocerciasis transmission: lessons for infection control

“…This was achieved by a combination of applications by helicopter and ground-based spraying of the organophosphate insecticide temephos that was managed by the WHO African Programme for Onchocerciasis Control (APOC). A follow-up study in early 2014 has shown that no children less than 10 years old have been infected showing that disease elimination is in progress [26].…”

Onchocerca volvulus infection in Tihama region - west of Yemen: Continuing transmission in ivermectin-targeted endemic foci and unveiled endemicity in districts with previously unknown status

“…volvulus transmission following regular ivermectin distribution to infected individuals and CDTI campaigns in such districts. This is in contrast to the success of ivermectin MDA campaigns to interrupt onchocerciasis transmission and its elimination from a number of countries and certain endemic foci in some countries of Africa and Latin America [ 10 , 21 , 22 , 34 – 40 ]. However, it could be unrealistic to compare between the successful high-coverage efforts devoted by onchocerciasis elimination programs over a long time in such countries and the low-coverage campaigns implemented by an NGO in the governorates of Tihama.…”