Relevance of the synergy of surveillance and populational networks in understanding the Usutu virus outbreak within common blackbirds (Turdus merula) in Metropolitan France, 2018

Abstract

AbstractUsutu virus (USUV) was first isolated in Africa in 1959 and has since spread to and through Europe with a typical enzootic mosquito-bird cycle. In France, it was first detected in birds in 2015, but in 2018 the spread of USUV was particularly significant throughout the country, killing mainly common blackbirds (Turdus merula) and to a lesser extent great grey owls (Strix nebulosa), among other captive and non-captive wild bird species. Data on this 2018 outbreak were collected through both an event-based network (SAGIR) and the health surveillance of the French-speaking Association of Zoo Veterinarians (AFVPZ). In addition, common blackbird populations could be monitored through another network (REZOP). Statistical analysis (spatial, temporal, spatiotemporal and environmental determinants) of the SAGIR and AFVPZ networks helped to highlight the early appearance of separate large clusters of USUV cases in mid-July 2018, the subsequent diffusion into smaller and secondary clusters at the end of August 2018, and a meanwhile enlargement of the first clusters with an increase in the number of cases. The locations of USUV cases were also significantly associated with high human density and wetlands. Using generalised additive mixed models on REZOP data, we also highlighted the decline in common blackbird population trends in areas with high USUV pressure (areas defined based on SAGIR-AFVPZ data) following the 2018 outbreak. Our results highlighted the need to work with synergistic networks to assess infection spread in wild bird species, as well as the negative impact of an emerging arbovirus.