Different dynamics of Usutu virus infections in Austria and Hungary, 2017–2018

Abstract

Usutu virus (USUV), a mosquito‐borne flavivirus closely related to West Nile virus, emerged in Austria in 2001, when it caused a considerable mass‐mortality of Eurasian blackbirds. Cases in birds increased until 2003 and quickly declined thereafter, presumably due to developing herd immunity. Since 2006, no further cases were recorded, until two blackbirds were tested positive in 2016. In Hungary, USUV first appeared in 2005 and has caused only sporadic infections since then. Initially, the only genetic USUV lineage found across both countries was Europe 1. This changed in 2015/2016, when Europe 2 emerged, which has since then become the prevalent lineage. Due to dispersal of these strains and introduction of new genetic lineages, USUV infections are now widespread across Europe. In 2009, the first cases of USUV‐related encephalitis were described in humans, and the virus has been frequently detected in blood donations since 2016. To monitor USUV infections among the Austrian wild bird population in 2017/2018, 86 samples were investigated by RT‐PCR. In 67 of them, USUV nucleic acid was detected (17 in 2017, 50 in 2018). The majority of succumbed birds were blackbirds, found in Vienna and Lower Austria. However, the virus also spread westwards to Upper Austria and southwards to Styria and Carinthia. In Hungary, 253 wild birds were examined, but only six of them were infected with USUV (five in 2017, one in 2018). Thus, in contrast to the considerable increase in USUV‐associated bird mortality in Austria, the number of infections in Hungary declined after a peak in 2016. Except for one case of USUV lineage Africa 3 in Austria in 2017, Europe 2 remains the most prevalent genetic lineage in both countries. Since USUV transmission largely depends on temperature, which affects vector populations, climate change may cause more frequent USUV outbreaks in the future.

Haemosporidioses in wild Eurasian blackbirds (Turdus merula) and song thrushes (T. philomelos): an in situ hybridization study with emphasis on exo-erythrocytic parasite burden

“…It is important to note, that the infected birds in this study all died naturally, and it remains open, to what extent they suffered from concomitant diseases or other pathogens that might have favoured the severity of malaria infections. Birds of the family Turdidae, in particular Eurasian blackbirds, are highly susceptible to Usutu virus (USUV) infection, and epizootic USUV-associated bird mortalities have been reported from several European countries, including Austria [31,[44][45][46][47][48][49][50][51][52]. More recent studies reported high USUV and Plasmodium coinfection rates in Eurasian blackbirds, suggesting that coinfection increases the likeliness of mortalities in infected birds [24,44].…”

Multi-Approach Investigation Regarding the West Nile Virus Situation in Hungary, 2018

“…A passive surveillance regarding wild bird mortality cases was performed at the Veterinary Diagnostic Directorate of the National Food Chain Safety Office. Bird carcasses examined in the avian influenza monitoring scheme were also tested for Flavivirus infection as previously described [18]. Pathology, histology, and polymerase chain reaction (PCR) were performed, and partial WNV sequences were obtained from positive cases.…”

In Vitro and In Vivo Models to Study the Zoonotic Mosquito-Borne Usutu Virus

“…However, it seems to be most often associated with Culex pipiens [ 22 , 29 , 38 , 39 , 40 ]. The main natural reservoir hosts of USUV are birds; the virus presence was demonstrated to date in 101 bird species belonging to 18 orders and 38 families [ 7 , 8 , 22 , 41 ]. However, the natural virulence spectrum of USUV seems rather limited, with a marked virulence in the European blackbird ( Turdus merula ) [ 42 ], house sparrow ( Passer domesticus ) [ 43 ], grey owl ( Strix nebulosa ) [ 44 ], and common scoter ( Melanitta nigra ) [ 7 ].…”