Molecular Epidemiology of Travel-Associated and Locally Acquired Dengue Virus Infections in Catalonia, Spain, 2019

Abstract

Dengue virus (DENV) is the most important arbovirus worldwide. In 2019, a significant increase in dengue cases was reported worldwide, resulting in a peak of imported cases in some European countries such as Spain. We aimed to describe travel-associated and locally acquired DENV strains detected in 2019 in the Catalonia region (northeastern Spain), a hotspot for dengue introduction in Europe. Through sequencing and phylogenetic analysis of the envelope gene, 75 imported viremic cases and two local strains were described. Autochthonous transmission events included an infection of a local mosquito with an imported dengue strain and a locally acquired human dengue infection from a locally infected mosquito. Overall, all four DENV serotypes and up to 10 different genotypes were detected. Phylogenetic analysis revealed transcontinental circulations associated with DENV-1 and DENV-2 and the presence of DENV-4 genotype I in Indonesia, where few cases had been previously described. A molecular study of the autochthonous events determined that local Ae. albopictus mosquitoes were infected by an African DENV-1 genotype V strain, while the locally acquired human case was caused by a DENV-3 genotype I of Asian origin. These findings underline the wide variability of imported strains and the high risk of DENV introduction into this territory, emphasizing the importance and usefulness of molecular characterization and phylogenetics for both local and global surveillance of the disease.

Keywords: Aedes albopictus; autochthonous transmission; dengue; molecular epidemiology; phylogenetic analysis; surveillance.

Figure 1

Distribution of RT-PCR-positive dengue serotyped cases detected in Catalonia by month (A) and by country’s source of importation (B). In this work, no dengue cases were imported from either the Eastern Mediterranean or European regions.

Figure 2

Phylogenetic tree of DENV-1 imported strains based on the E gene. The analysis was performed using a Maximum Likelihood method (TN93 + G) with a bootstrap of 1000 replicates. Sequences obtained in this work are marked with green dots. Reference sequences are described with GenBank accession number, place and year of isolation and the scale bar indicates substitutions per site.

Figure 3

Phylogenetic tree of DENV-2 imported strains based on the E gene. The analysis was performed using a Maximum Likelihood method (TN93 + G + I) with a bootstrap of 1000 replicates. Sequences obtained in this work are marked with green dots. Reference sequences are described with GenBank accession number, place and year of isolation and the scale bar indicates substitutions per site.

Figure 4

Phylogenetic tree of imported strains based on the E gene. (A) Phylogenetic tree of DENV-3 imported strains obtained through the TN93 + G model. (B) Phylogenetic tree of DENV-4 imported strains obtained through the TN93 + G + I model. Green dots correspond to samples detected in our center. Reference sequences are described with GenBank accession number, place and year of isolation and the scale bar indicates substitutions per site. The analysis was performed using a bootstrap of 1000 replicates.

Figure 5

DENV phylogenetic trees based on the E-NS1 junction. (A) DENV-1 phylogenetic tree obtained through the K2 + I model. (B) DENV-4 phylogenetic tree obtained through the K2 + G model. Green dots correspond to samples detected in our center. Reference sequences only include the E-NS1 junction region targeted by our amplification protocol for low viral load samples. Those without the E-NS1 junction region were excluded in order to optimize the analysis. The analysis was performed using a bootstrap of 1000 replicates.

Figure 6

Phylogenetic tree of the DENV-1 autochthonous transmission event based on the E gene. Phylogenetic tree of autochthonous DENV-1 strain obtained from a local mosquito pool (Mosquito Spain sample) and the imported strain from Gabon (HCBD1398 sample). Green dots correspond to samples detected in our center. Reference sequences are noted with the GenBank accession number, place and year of isolation and the scale bar indicates substitutions per site. The analysis was performed using a Maximum Likelihood method (TN93 + G) with a bootstrap of 1000 replicates. The sequence obtained from the DENV mosquito strain can be found in the GenBank database with the accession number PP897402.

Figure 7

Phylogenetic tree of the locally acquired DENV-3 strain based on the complete E gene. Reference sequences are noted with the GenBank accession number, place and year of isolation and the scale bar indicates substitutions per site. The green dot corresponds to the autochthonous strain detected in our center, and the analysis was performed using a Maximum Likelihood method (TN93 + G) with a bootstrap of 1000 replicates. The sequence obtained from the DENV mosquito strain can be found in the GenBank database with the accession number PP897403.