Multiple Lineages of Usutu Virus (Flaviviridae, Flavivirus) in Blackbirds (Turdus merula) and Mosquitoes (Culex pipiens, Cx. modestus) in the Czech Republic (2016–2019)

Abstract

Usutu virus (USUV) is a flavivirus (Flaviviridae: Flavivirus) of an African origin transmitted among its natural hosts (diverse species of birds) by mosquitoes. The virus was introduced multiple times to Europe where it caused mortality of blackbirds (Turdus merula) and certain other susceptible species of birds. In this study, we report detection of USUV RNA in blackbirds, Culex pipiens and Cx. modestus mosquitoes in the Czech Republic, and isolation of 10 new Czech USUV strains from carcasses of blackbirds in cell culture. Multiple lineages (Europe 1, 2 and Africa 3) of USUV were found in blackbirds and mosquitoes in the southeastern part of the country. A single USUV lineage (Europe 3) was found in Prague and was likely associated with increased mortalities in the local blackbird population seen in this area in 2018. USUV genomic RNA (lineage Europe 2) was detected in a pool of Cx. pipiens mosquitoes from South Bohemia (southern part of the country), where no major mortality of birds has been reported so far, and no flavivirus RNA has been found in randomly sampled cadavers of blackbirds. The obtained data contributes to our knowledge about USUV genetic variability, distribution and spread in Central Europe.

Epidemiology of Usutu Virus: The European Scenario

“…One pool of Cx. modestus mosquitoes (South Moravia, 2016) also tested positive for USUV RNA (Europe 2 lineage) [ 18 ]. There are no reports on human USUV infections.…”

“…In addition, the virus was detected in different native (mainly Culex pipiens ) and invasive mosquito species ( Aedes albopictus , Ae. japonicus ) [ 13 , 14 , 15 , 16 , 17 , 18 ]. USUV RNA was also found in bats ( Pipistrellus pipistrellus ) in Germany and Belgium [ 19 , 20 ].…”

“…Few cases of neuroinvasive disease and USUV fever, as well as seroconversion in blood donors were reported in Europe since 2009 [ 11 , 28 , 29 , 30 , 31 , 32 , 33 ]. Phylogenetic analyses showed that the majority of USUV strains detected in humans, birds and mosquitoes belong to European USUV lineages, however several reports indicated the presence of African lineages as well [ 18 , 34 , 35 , 36 ].…”

Parasitofauna survey of song thrushes (Turdus philomelos) from the eastern part of Spain

“…Although corporal condition of evaluated thrushes was not affected, probably due to the low intensity of parasitism derived from an evolutionary adaptation [16], under stressful conditions (migration) the consecutive immunosuppression can compromise the health status of Turdus when pathogens are present, making it difficult for birds to travel long migratory distances [23]. There is scarce information related to thrushes parasitofauna both in Europe and concretely in Spain, since most of studies have been traditionally focused on viral processes [6,7] or only in one parasitic species, mainly M. polonicum [1,4]. Because the parasitic richness of migratory birds could be higher than the one of resident specimens [24], it is important to consider the results in the present study to evaluate their consequences on the thrushes' migration [24][25][26].…”

“…[3][4][5]. These birds have been widely studied as reservoirs of some viral pathogens (e.g., highly pathogenic influenza aviar and usutu virus; [6,7]), but it is still unclear their role as reservoir of parasites for domestic poultry, humans or other game bird species. In this sense, factors like seasonal migration, habitat changes or thrushes' diet (mainly based on insects, earthworms, snails, etc.…”