title: Evaluation of onchocerciasis seroprevalence in Bioko Island (Equatorial Guinea) after years of disease control programmes.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  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.
authors.affiliation: Helminth Unit, Parasitology Department, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Crtra. Majadahonda-Pozuelo, km 2.2, 28220, Majadahonda, Madrid, Spain.|Network Biomedical Research on Tropical Diseases (RICET), Madrid, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Hernández-González
authors.affiliation: National Centre for Tropical Medicine, Instituto de Salud Carlos III, C/ Sinesio Delgado, 4, 28029, Madrid, Spain.|Jimenez Diaz Foundation University Hospital, Avda. Reyes Católicos, 2, 28040, Madrid, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Moya
authors.affiliation: Helminth Unit, Parasitology Department, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Crtra. Majadahonda-Pozuelo, km 2.2, 28220, Majadahonda, Madrid, Spain.|Network Biomedical Research on Tropical Diseases (RICET), Madrid, Spain.
authors.forename: María J
authors.initials: MJ
authors.lastname: Perteguer
authors.affiliation: National Centre for Tropical Medicine, Instituto de Salud Carlos III, C/ Sinesio Delgado, 4, 28029, Madrid, Spain.|Network Biomedical Research on Tropical Diseases (RICET), Madrid, Spain.
authors.forename: Zaida
authors.initials: Z
authors.lastname: Herrador
authors.affiliation: Network Biomedical Research on Tropical Diseases (RICET), Madrid, Spain.|National Program for Control of Onchocerciasis and other Filariasis, Ministry of Health, Malabo, Equatorial Guinea.
authors.forename: Rufino
authors.initials: R
authors.lastname: Nguema
authors.affiliation: Network Biomedical Research on Tropical Diseases (RICET), Madrid, Spain.|National Program for Control of Onchocerciasis and other Filariasis, Ministry of Health, Malabo, Equatorial Guinea.
authors.forename: Justino
authors.initials: J
authors.lastname: Nguema
authors.affiliation: National Centre for Tropical Medicine, Instituto de Salud Carlos III, C/ Sinesio Delgado, 4, 28029, Madrid, Spain.|Network Biomedical Research on Tropical Diseases (RICET), Madrid, Spain.
authors.forename: Pilar
authors.initials: P
authors.lastname: Aparicio
authors.affiliation: National Centre for Tropical Medicine, Instituto de Salud Carlos III, C/ Sinesio Delgado, 4, 28029, Madrid, Spain.|Network Biomedical Research on Tropical Diseases (RICET), Madrid, Spain.
authors.forename: Agustín
authors.initials: A
authors.lastname: Benito
authors.affiliation: Helminth Unit, Parasitology Department, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Crtra. Majadahonda-Pozuelo, km 2.2, 28220, Majadahonda, Madrid, Spain. tgarate@isciii.es.|Network Biomedical Research on Tropical Diseases (RICET), Madrid, Spain. tgarate@isciii.es.
authors.forename: Teresa
authors.initials: T
authors.lastname: Gárate
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000909:Antibodies, Helminth / Q000097:blood*; D000947:Antigens, Helminth / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D004797:Enzyme-Linked Immunosorbent Assay; D016703:Equatorial Guinea / Q000453:epidemiology; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D007303:Insect Vectors / Q000469:parasitology; D007559:Ivermectin / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D017181:Onchocerca volvulus / Q000276:immunology* / Q000302:isolation & purification; D009855:Onchocerciasis / Q000188:drug therapy / Q000453:epidemiology* / Q000276:immunology; D015827:Onchocerciasis, Ocular / Q000188:drug therapy / Q000453:epidemiology* / Q000276:immunology / Q000469:parasitology; D015995:Prevalence; D016036:Seroepidemiologic Studies; D012843:Simuliidae / Q000469:parasitology; D055815:Young Adult
chemical_list: D000909:Antibodies, Helminth; D000947:Antigens, Helminth; D007074:Immunoglobulin G; D007559:Ivermectin
keywords: Bioko Island; Equatorial Guinea; Onchocerca volvulus; Onchocerciasis; Ov-16/IgG4 ELISA; Seroprevalence