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.

Keywords: Belgium, Lineage, Evolution, Epizootic; Bird; France; Germany; Netherlands; Usutu virus.

Figure 1

Number (panel A) and cumulative percentage (panel B) of outbreak-related USUV-positive live and dead birds, western Europe^a, 2016 (n=164)^b

Figure 2

Mean daily basic reproduction number and distribution of outbreak-related USUV-positive birds, western Europe^a, 2016 (n=164 birds)

Figure 3

Monthly temperature anomalies and distribution of outbreak-related USUV-positive birds, western Europe^a, 2016 (n=164)^b

Figure 4

Phylogenetic tree of USUV variants responsible for outbreaks in captive and wild birds and the possible origin and spread pattern, western Europe^a, 2016