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. 2019 Mar 13;12(1):103.
doi: 10.1186/s13071-019-3357-3.

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

Heidi Auerswald  1 , Ana de Jesus  2   3 , Gonçalo Seixas  2   3 , Teresa Nazareth  2   3 , Saraden In  1 , Sokthearom Mao  1 , Veasna Duong  1 , Ana Clara Silva  4   5 , Richard Paul  6   7 , Philippe Dussart  8 , Carla Alexandra Sousa  2   3
Affiliations

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

Heidi Auerswald et al. Parasit Vectors. .

Abstract

Background: 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.

Results: We 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.

Conclusions: This 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.

Keywords: Dengue virus; Madeira Island; Seroprevalence; Serotype.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Geographical distribution of the seroprevalence across Madeira Island. Districts with dengue seropositive study participants are shown in blue and the respective residences are marked with red dots. The map was created using QGIS 2.14.3 and the base layer data were obtained from DIVA GIS (http://www.diva-gis.org/gdata)
Fig. 2
Fig. 2
Individual FRNT90 titers of all FRNT positive study participants (n = 29). Mean FRNT90 titers with standard error for FRNT positive samples. Overall, 28 samples were positive in the FRNT using the reference strains of DENV-1 (red), DENV-2 (blue), DENV-3 (green) and DENV-4 (yellow). An additional FRNT with DENV-1 genotype V (pink) added one more seropositive study participant. The dashed line indicates threshold of 20. Asterisks indicate the statistically significant different mean FRNT90 titers between the DENV-1 reference strain and the DENV-1 genotype V strain with the other DENV serotypes (Mann-Whitney test, P < 0.0001)
See this image and copyright information in PMC

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