First dengue virus seroprevalence study on Madeira Island after the 2012 outbreak indicates unreported dengue circulation

Heidi Auerswald,Ana De Jesus,Sokthearom Mao,Saraden In,Philippe Dussart,Carla Alexandra Sousa,Ana Clara Silva,Teresa Nazareth,Richard Paul,Veasna Duong,Gonçalo Seixas

doi:10.1186/s13071-019-3357-3

Abstract

BackgroundIn 2012, the first dengue virus outbreak was reported on the Portuguese island of Madeira with 1080 confirmed cases. Dengue virus of serotype 1 (DENV-1), probably imported from Venezuela, caused this outbreak with autochthonous transmission by invasive Aedes aegypti mosquitoes.ResultsWe investigated the seroprevalence among the population on Madeira Island four years after the outbreak. Study participants (n = 358), representative of the island population regarding their age and gender, were enrolled in 2012 in a cross-sectional study. Dengue antibodies were detected with an in-house enzyme-linked immunosorbent assay (ELISA) using the dimer of domain III (ED3) of the DENV-1 envelope protein as well as commercial Panbio indirect and capture IgG ELISAs. Positive ELISA results were validated with a neutralization test. The overall seroprevalence was found to be 7.8% (28/358) with the in-house ELISA, whereas the commercial DENV indirect ELISA detected IgG antibodies in 8.9% of the individuals (32/358). The results of the foci reduction neutralization test confirmed DENV-1 imported from South America as the causative agent of the 2012 epidemic. Additionally, we found a higher seroprevalence in study participants with an age above 60 years old and probable secondary DENV infected individuals indicating unreported dengue circulation before or after 2012 on Madeira Island.ConclusionsThis study revealed that the number of infections might have been much higher than estimated from only confirmed cases in 2012/2013. These mainly DENV-1 immune individuals are not protected from a secondary DENV infection and the majority of the population of Madeira Island is still naïve for DENV. Surveillance of mosquitoes and arboviruses should be continued on Madeira Island as well as in other European areas where invasive vector mosquitoes are present.

Highlights

In 2012, the first dengue virus outbreak was reported on the Portuguese island of Madeira with 1080 confirmed cases
Seroprevalence The dengue seroprevalence of the study participants was tested by in-house dengue virus (DENV) immunoglobulin G (IgG) indirect enzyme-linked immunosorbent assay (ELISA) using dimer of Domain III (ED3) of the Dengue virus of serotype 1 (DENV-1) envelope protein and the DENV IgG indirect ELISA from Panbio
The in-house ELISA detected 7.8% (28/358) of the study participants as positive, whereas the commercial DENV indirect ELISA detected IgG antibodies in 8.9% of the individuals (32/358; Table 2)

Summary

Introduction

In 2012, the first dengue virus outbreak was reported on the Portuguese island of Madeira with 1080 confirmed cases. Dengue virus of serotype 1 (DENV-1), probably imported from Venezuela, caused this outbreak with autochthonous transmission by invasive Aedes aegypti mosquitoes. Dengue fever is the most widespread mosquito-borne viral disease causing an annual estimated 390 million infections [1] and 25,000 deaths [2]. Infection by any one of four antigenically distinct serotypes of dengue virus (DENV) can lead to symptoms including high fever or more severe disease with haemorrhage and plasma leakage. Due to the increasing number of imported DENV infections [6, 7], there is a growing likelihood of autochthonous infections where competent vectors are present.

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