Distribution of Usutu Virus in Germany and Its Effect on Breeding Bird Populations

Abstract

Usutu virus (USUV) is an emerging mosquitoborne flavivirus with an increasing number of reports from several countries in Europe, where USUV infection has caused high avian mortality rates. However, 20 years after the first observed outbreak of USUV in Europe, there is still no reliable assessment of the large-scale impact of USUV outbreaks on bird populations. In this study, we identified the areas suitable for USUV circulation in Germany and analyzed the effects of USUV on breeding bird populations. We calculated the USUV-associated additional decline of common blackbird (Turdus merula) populations as 15.7% inside USUV-suitable areas but found no significant effect for the other 14 common bird species investigated. Our results show that the emergence of USUV is a further threat for birds in Europe and that the large-scale impact on population levels, at least for common blackbirds, must be considered.

Keywords: Germany; Usutu virus; bird population decline; breeding birds; common blackbird; flavivirus; vector-borne infections.

Figure 1

Probability of Usutu virus (USUV) occurrence in Germany derived from 300 boosted regression tree models. Black dots denote sites with dead birds that tested positive for USUV. The color intensity indicates the probability of occurrence of USUV.

Figure 2

Areas suitable (green) and unsuitable (white) for Usutu virus (USUV) in Germany derived from 300 boosted regression tree models. Black dots denote sites with dead birds detected positive for USUV.

Figure 3

Index curves of the generalized additive model (GAM) approach with 300 bootstraps for breeding bird survey data of 4 bird species for Usutu virus (USUV)–suitable and USUV-unsuitable areas in Germany, 2016. A) Common blackbird; B) Eurasian tree sparrow; C) house sparrow; D) great tit. Solid lines indicate the mean indices from a GAM with 3 df; dashed/dotted lines represent nonoverlapping 95% bootstrap CIs. The horizontal line indicates the baseline year 2011 (index = 100), which is the last time point when bird abundance data were collected before the first known epizootic outbreak of USUV in Germany. Double arrows indicate the difference between the mean index curves for 2016.