Diversity of West Nile and Usutu virus strains in mosquitoes at an international airport in Austria

Abstract

Increased globalization and international transportation have resulted in the inadvertent introduction of exotic mosquitoes and new mosquito-borne diseases. International airports are among the possible points of entry for mosquitoes and their pathogens. We established a mosquito and mosquito-borne diseases monitoring programme at the largest international airport in Austria and report the results for the first two years, 2018 and 2019. This included weekly monitoring and sampling of adult mosquitoes, and screening them for the presence of viral nucleic acids by standard molecular diagnostic techniques. Additionally, we surveyed the avian community at the airport, as birds are potentially amplifying hosts. In 2018, West Nile virus (WNV) was detected in 14 pools and Usutu virus (USUV) was detected in another 14 pools of mosquitoes (minimum infection rate [MIR] of 6.8 for each virus). Of these 28 pools, 26 consisted of female Culex pipiens/torrentium, and two contained male Culex sp. mosquitoes. Cx. pipiens/torrentium mosquitoes were the most frequently captured mosquito species at the airport. The detected WNV strains belonged to five sub-clusters within the sub-lineage 2d-1, and all detected USUV strains were grouped to at least seven sub-clusters among the cluster Europe 2; all strains were previously shown to be endemic in Austria. In 2019, all mosquito pools were negative for any viral nucleic acids tested. Our study suggests that airports may serve as foci of arbovirus activity, particularly during epidemic years, and should be considered when designing mosquito control and arbovirus monitoring programmes.

Keywords: Austria; Culex pipiens; Usutu virus; West Nile virus; airport; mosquito-borne diseases; virus monitoring.

FIGURE 1

Number of collected mosquitoes of the genus Culex in 2018 and the corresponding number of positive virus pools

FIGURE 2

Phylogenetic tree demonstrating the genetic relationships among 60 WNV lineage 2 sequences. The 10 sequences generated in this study are indicated by red diamonds. Asterisks indicate sequences exhibiting deletions within the 3′UTR. Phylogenetic analysis was performed on 690‐bp long sequences within the NS5/3′UTR genomic region (positions 10147–10976 according to the WNV complete genome sequence, GenBank acc. no. DQ116961). For each sequence, the corresponding GenBank accession number, host species, country of origin, and collection year are indicated. Horizontal lines represent the genetic distances. Genetic sub‐lineages are indicated by vertical bars on the right. Bootstrap values above 60 are displayed at the nodes.

FIGURE 3

Phylogenetic tree demonstrating the genetic relationships among 62 USUV sequences. The 12 sequences generated in this study are indicated by blue diamonds. Asterisks indicate sequences exhibiting deletions within the 3′UTR. Phylogenetic analysis was performed on 695‐bp long sequences within the NS5/3′UTR genomic region (positions 10106–10800 according to the USUV complete genome sequence, GenBank acc. no. AY453411). For each sequence, the corresponding GenBank accession number, host species, country of origin, and collection year are indicated. Horizontal lines represent the genetic distances. Genetic lineages are indicated by vertical bars on the right. Bootstrap values above 60 are displayed at the nodes.

FIGURE 4

Observed birds at the airport (averaged from 2018 and 2019) during the mosquito‐monitoring period from May to October