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Animal Disease: Usutu virus kills birds


Usutu outbreak leads to mass extinction of native bird species
The so-called Usutu virus has triggered extensive bird extinction in parts of Germany this year. The Naturschutzbund Deutschland (NABU) reports numerous reports of dead birds. The results of virus researchers have confirmed an expansion of the outbreak area.

The tropical virus was first detected in mosquitoes in Germany in 2010. In 2011 and 2012 there was a mass extinction among domestic birds, especially blackbirds, reports the NABU. The situation then calmed down and there were no further major outbreaks. This year, however, the recorded reports indicate a significant increase in infections.

Usutu harmless to humans
The virus is harmless to humans and, according to NABU, so far only five people across Europe have been proven to be infected with the Usutu virus - mostly people with a damaged immune system. But the population of the bird population is often threatened by the virus. The blackbird population in particular has been almost completely eliminated in the course of the previous outbreaks in some regions. "After a few years without major outbreaks, the virus appears again in 2016," reports the NABU. Since the end of July, reports of sick blackbirds that died a short time later had been received by NABU.

611 suspected cases reported
As of September 23, NABU had called for online reporting of suspicious bird diseases and a total of 611 reports were received in just eleven days. This is a remarkably large number of suspected Usutu cases compared to around 400 reports in autumn 2011 and 1,040 reports in the entire outbreak year 2012, reports the NABU. This time, the largest number of reports of sick and dead blackbirds came from North Rhine-Westphalia, in particular from the Lower Rhine and from the Aachen area.

North Rhine-Westphalia most affected
In addition, many suspected cases were reported to the NABU from the areas along the Rhine from Freiburg to Cologne, where a known outbreak area was found in 2011 and 2012. Furthermore, reports from the Leipzig and Berlin area, as well as from the north of Lower Saxony and Schleswig-Holstein, were received. As soon as the received reports have been evaluated and other illnesses have been excluded, the actual spread of the Usutu virus can be determined, reports the NABU.

Examination of dead birds at the BNI
In addition to online reporting, there is also the option of sending dead birds suspected of Usutu to the Bernhard Nocht Institute for Tropical Medicine (BNI) in Hamburg. 20 blackbirds and several other birds have already been examined here and "overall, the BNI and other laboratories were able to confirm suspicion of Usutu infestation in at least 21 cases," the NABU said. 15 blackbirds and six bearded owls kept in captivity were affected. This also confirmed the observation from the 2011/12 outbreak that besides blackbirds, owls are particularly affected by Usutu diseases.

Infections depend on the mosquito season
Bird deaths from the Usutu virus occur during the mosquito season from May to November. The increased incidence of Usutu infections this year was certainly favored by the weather, reports the NABU. A mild winter was followed by a damp early summer and a dry and warm late summer. These are ideal conditions for mosquitoes. The current outbreak areas largely correspond to the areas with the highest late summer daytime temperatures in Germany, according to NABU.

Infected birds usually die within a few days
Birds infected with the Usutu virus appear to be ill, become apathetic and no longer flee, reports the NABU. Usually the animals would die within a few days. Given the high proportion of blackbirds affected, the Usutu epidemic has also become known as "blackbird death". But other bird species would also be infected by the virus and can die from it. Contrary to the 2011/12 epidemic, only a few reports of almost complete collapse of local blackbird populations were reported this year. These come from areas where the virus did not yet appear in 2011/12. With the onset of autumn weather and a decline in mosquito activity, the outbreak is expected to slowly fade away.

Monitoring the spread of the Usutu virus
In subsequent years, the experts estimate that the infections will reappear from April / May, with a periodic recurrence of major Usutu outbreaks in the established distribution area of ​​the virus is likely. At this point in time, one can only speculate about the effects of renewed blackbird extinction on the stock of this species. Overall, the outbreak of Usutu infections in Germany represents a unique opportunity to track and analyze the spread and consequences of a new bird disease. "NABU is therefore working with scientists at the BNI to document and understand the spread of the virus and its effects on our bird life in order to be able to assess this new cause of danger for bird species in comparison with other causes of danger," said the Nature Conservation Association. (fp)

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