The usutu virus, an avian virus originating from South Africa, is circulating again among Flemish songbirds. This became apparent after WHG detected the virus in a dead blackbird (Turdus merula) and Eurasian blue tit (Cyanistes caeruleus) brought in by the rescue center for Birds & Wild Animals (VOC) in Merelbeke.
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The usutu virus is not unknown to Flanders. Already in 2016, 2017 and 2018 it caused massive mortality among blackbirds. It is not yet known why blackbirds are so susceptible to this virus. Other songbirds and certain owl species also appear to be sensitive, but mortality remains sporadic.
The virus probably reached Europe via infected migratory birds. A first outbreak was identified in Italy in 1996, then Austria in 2001. Since then, the virus has spread to Spain, Croatia, Hungary, Switzerland, the Czech Republic, Germany, the Netherlands and Belgium. Mosquitoes play an important role in the transmission of the virus. That is why mortality is often observed in summer and autumn.
Depending on the bird species infected and the organ where the virus occurs, different symptoms are known. However, in blackbirds it causes so-called nerve symptoms. The bird is drowsy and may show signs of convulsion and incoordination. Ultimately, most blackbirds die from the viral infection.
It remains unclear how many blackbirds survive the infection, and whether they build up immunity. The Flemish blackbird population already suffered greatly due to the virus. Natuurpunt reported a loss of 15% in 2016. The Flemish breeding population further decreased in the following years. Other factors are likely to play a role in this crash as well.
The virus poses no danger to pets or humans. In immunocompromised people, it can cause mild symptoms. It is therefore always advisable to handle dead birds with gloves.
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