Widespread activity of multiple lineages of Usutu virus, western Europe, 2016

Abstract

In the summer of 2016, Belgium, France, Germany and the Netherlands reported widespread Usutu virus (USUV) activity based on live and dead bird surveillance. The causative USUV strains represented four lineages, of which two putative novel lineages were most likely recently introduced into Germany and spread to other western European countries. The spatial extent of the outbreak area corresponded with R0 values > 1. The occurrence of the outbreak, the largest USUV epizootic registered so far in Europe, allowed us to gain insight in how a recently introduced arbovirus with potential public health implications can spread and become a resident pathogen in a naïve environment. Understanding the ecological and epidemiological factors that drive the emergence or re-emergence of USUV is critical to develop and implement timely surveillance strategies for adequate preventive and control measures. Public health authorities, blood transfusion services and clinicians in countries where USUV was detected should be aware of the risk of possible USUV infection in humans, including in patients with unexplained encephalitis or other neurological impairments, especially during late summer when mosquito densities peak.

Blood donor screening for West Nile virus (WNV) revealed acute Usutu virus (USUV) infection, Germany, September 2016

“…Since the first emergence in the mid-1990s in Europe, USUV has been responsible for smaller periodic epizootics in several European countries, the largest one being registered in 2016 [1,4-6]. USUV can cause Usutu fever in humans with mild to severe symptoms characterised by fever, rash, jaundice, headache, nuchal rigidity, hand tremor, and hyperreflexia [7-10].…”

Usutu virus: current knowledge and future perspectives

“…89 In addition, widespread USUV activity was also described in 2016 in Belgium, France, and Germany, with 17 live and 147 dead USUV-positive birds in these countries. 13 Phylogenetic analysis indicates that the virus was most probably introduced from Germany by infected semi-resident birds, although the role of migrating birds or mosquitoes cannot be excluded. All these data clearly demonstrated a spread of USUV activity throughout the continent ( Figure 5).…”

“…5 Two other lineages, Europe 3 and Africa 2, were most likely introduced into Germany and recently spread to other western European countries, since the viruses detected in Belgium, France, and the Netherlands clustered with those previously circulating in mosquito vectors, wild birds, and/ or bats in Germany between 2011 and 2014. 13 According to a recent report, 11 the estimated time of the most recent common ancestor of the European strains dates back to 20.9 or 22.8 years, depending on whether the analysis is based on the NS5 or the E genomic sequences, thus suggesting that the probable time of arrival of USUV in Europe was in the middle of 1990s. This estimation is consistent with the retrospective identification of USUV in Italian dead bird samples from 1996.…”

The role of Culex pipiens mosquitoes in transmission of West Nile virus in Europe

“…However, considering the presence of intrinsically competent mosquito vectors (Balenghien et al 2008, Balenghien et al 2007, Blagrove et al 2016, Fortuna et al 2015a, Fortuna et al 2015b, Fros et al 2015a, Fros et al 2015b, and susceptible bird hosts (Lim et al 2015, Lim et al 2014, together with predictions of more frequent and prolonged temperature anomalies, we see no limiting factors that can rule out future WNV circulation in northern Europe. In fact, the recent circulation of Usutu virus in northern Europe during the autumn of 2016 (Cadar et al 2017), exemplifies that there are no evident restrictions for Culex-borne flaviviruses to become endemic in northern Europe. Because of the similar transmission cycle and comparable transmission rates of both Usutu and West Nile virus with their main vector Cx.…”

“…Global warming will likely favour the northward movement of WNV and other related arboviruses in Europe. During the relatively warm autumn of 2016, Usutu virus, a flavivirus closely related to WNV, was detected for the first time in The Netherlands (Cadar et al 2017, Rijks et al 2016. Due to the similar ecology of WNV and Usutu virus, I consider the circulation of Usutu virus in The Netherlands as a prelude for WNV transmission (Fros et al 2015b).…”