Seroepidemiological study of Zika virus in selected West African countries between 2007 and 2012

Zika virus is a flavivirus transmitted by mosquitoes of the Aedes genus, isolated for the first time in Uganda in 1947 and usually associated with a mild disease clinically similar to other arbovirosis, such as Dengue and Chikungunya fevers. Few cases of infection were reported until 2007, when an outbreak occurred in Micronesia, followed by a large epidemic in French Polynesia and the Americas. During its emergence, Zika virus has been associated with more severe clinical manifestations, including neurological sequelae and congenital defects such as microcephaly. Before the recent spread, serological investigations conducted between the 1960s and the 1990s showed the wide presence of Zika virus in Africa. However, limited data are available on the recent prevalence in the African population. According to the World Health Organization, the entire Africa continent is at risk of Zika outbreak due to the presence of the virus, competent vectors and the low capacity of surveillance and containment of an epidemic. In the context of West Africa, three countries with different transmission potential have been identified: Senegal, with present local cases; Mali, with only serological evidences; and The Gambia with local cases of Dengue and Chikungunya. The aim of this study was to evaluate the immunity against Zika virus in samples of a selected cohort for each of these countries, in order to investigate the circulation of the virus in the region during the first years of its emergence in the Pacific. Human serum samples were collected in 2007 and between 2011 and 2012 from a cohort of subjects residing in Mali, Senegal and The Gambia. Samples were tested using an ELISA detection kit and positives were further confirmed by microneutralization test. Results indicate that Zika virus is present and actively circulating in Senegal and The Gambia. Although no significant differences were found in prevalence during the time period considered, seroconversion of some subjects showed the active circulation of Zika virus in the West African area. Analysis by age showed an increase in immunity in relation with increasing age, demonstrating that the population is consistently exposed to the virus throughout life and with a high possibility to be infected during reproductive-age. In conclusion, the results obtained allow a better knowledge of the circulation of Zika virus within three different ecological and demographic contexts, updating the few data currently available.