Arbovirus Screening in Mosquitoes in Emilia-Romagna (Italy, 2021) and Isolation of Tahyna Virus

Abstract

Several viruses can be transmitted by mosquitoes. We searched some of these viruses in 20,778 mosquitoes, collected in 95 traps on the plains of Emilia-Romagna (North of Italy) in 2021. We detected West Nile virus (WNV) and Usutu virus (USUV) in pools of Culex (Cx.) pipiens. In addition, we detected two insect-specific flaviviruses in three pools of Aedes (Ae.) caspius and in two of Ae. vexans. Tahyna virus (TAHV) was detected in six pools, three of Ae. caspius and three of Cx. pipiens, and one isolated strain was obtained from one of the Ae. caspius pools. Moreover, we detected TAHV in pools of several mosquito species (Ae. caspius, Ae. vexans, Ae. albopictus, Anopheles maculipennis s.l.) collected in the previous year of surveillance. Our data indicate Ae. caspius as the species most infected with TAHV in the surveyed area. Together with the likely plasticity of the cycle, we reported strong genome stability of the TAHV, probably linked to a successful adaptation of the virus to its ecological niche. Interestingly, in six pools of Cx. pipiens we detected two associated viruses among USUV, WNV, TAHV and all the three viruses in two pools. This result allows us to assume the presence of particular conditions that prompt the circulation of arboviruses, creating the conditions for viral hot spots. While no human diseases related to Tahyna virus were reported in Italy, its detection over the years suggests that it is worth investigating this virus as a potential cause of disease in humans in order to assess its health burden. IMPORTANCE We reported in this work the detection of three Arboviruses (Arthropod-borne viruses) in mosquitoes collected in Emilia-Romagna in 2021. In addition to West Nile and Usutu viruses, which were reported from more than 10 years in the study area, we detected and isolated Tahyna virus (TAHV). We also reported detections of TAHV obtained in previous years of surveillance in different species of mosquitoes. TAHV is the potential causative agent of summer influenza-like diseases and also of meningitis. Even if human cases of disease referable to this virus are not reported in Italy, its relevant presence in mosquitoes suggests investigating the possibility they could.

Keywords: Tahyna virus; Usutu virus; West Nile virus; insect specific flavivirus; mosquito.

FIG 1

Map of Emilia-Romagna with reference to the location of the region in Italy and surveyed area (green) showing (a) the number of mosquitoes collected at the different sites in 2021 (diameter proportional to the number of mosquitoes collected); (b) the sampling sites of flavivirus positive pools in 2021; (c) the sampling sites of Tahyna virus positive pools in 2021 and in previous years. The maps were produced with the free software QGIS (available at https://www.qgis.org/en/site/index.html, accessed on August 8, 2022).

FIG 2

Ultramicrographs of virions observed in the supernatant of VERO cells inoculated with pools of mosquitoes. Roundish particles of 90 to 100 nm with envelopes and tightly packed projections on the surface are shown at low (a), medium (b), and high magnification (c). Negative staining of NaPt 2% (pH 6.8) observed with a TEM FEI Tecnai G2 Spirit Bio-twin.

FIG 3

Maximum likelihood trees obtained from the sequences of the three segments of the new isolated Tahyna virus (strain 404118, in red) and homologous sequences retrieved from GenBank. The accession numbers, the country and the year of isolation are reported (CS, former Czechoslovakia; FR, France; CH, China; AT, Austria; IT, Italy). Bootstrap >75 displayed near the respective branch.