The effects were dramatic: throughout Vienna it was impossible not to notice that the blackbirds were disappearing. Their melodious song no longer rang around the courtyards of the inner city nor woke tired partygoers in the outlying districts. The birds were simply no longer there. Thankfully, they gradually reappeared and a few years later their population had returned to its original levels. But the sudden crash in numbers was alarming and scientists rushed to find the cause.
It soon became apparent that the birds had died as a result of a new kind of viral infection. The culprit turned out to be the Usutu virus, which had previously been identified only in Africa and had only seldom been associated with mortality in animals or birds. It was widely assumed that the virus had crossed from Africa to central Europe with the help of migratory birds – the Barn swallow was generally fingered as the most likely transmitter – and that such sudden outbreaks would appear more frequently as the result of climate change. But these conclusions have been called into question by the latest findings from a team at the University of Veterinary Medicine, Vienna (Vetmeduni Vienna).
Although not widely reported at the time, a large number of birds, especially blackbirds, died in Tuscany, Italy in 1996, five years before the outbreak of Usutu virus in Vienna's blackbirds. The causative agent was not identified but Giacomo Rossi of the University of Camerino had stored tissue samples from the dead birds. Herbert Weissenböck, Norbert Nowotny and colleagues in the Institute of Pathology and the Institute of Virology at the Vetmeduni Vienna recently became aware of the samples' existence and were naturally keen to investigate them. Surprisingly, the researchers found that the Italian samples contained exactly the same strain of Usutu virus that was responsible for the Viennese cases. As in Vienna, the birds were almost wiped out by the virus but resistance soon developed and the population returned to normal levels.
As Weissenböck says, "We still do not fully understand how the virus reached Austria but we have at least uncovered one piece in the jigsaw. Rather than coming directly from Africa to Vienna, the Usutu virus seems to have been present in Italy for some time." The powerful techniques of forensic pathology may be helpful in unravelling the origins of other emerging diseases: for example, we still do not know how the bluetongue virus reached northern Germany or the West Nile virus arrived in central Europe.
The paper Usutu virus, Italy, 1996 by Herbert Weissenböck, Tamás Bakonyi, Giacomo Rossi, Paolo Mani and Norbert Nowotny has just been published in the journal Emerging Infectious Diseases (Vol. 19(2), February 2013: 274-277).
About the Vienna University of Veterinary Medicine
The University of Veterinary Medicine, Vienna is the only academic and research institution in Austria that focuses on the veterinary sciences. About 1000 employees and 2300 students work on the campus in the north of Vienna, which also houses the animal hospital and various spin-off-companies. http://www.vetmeduni.ac.at
Contact:
Klaus Wassermann
Public Relations/Science Communications
University of Veterinary Medicine, Vienna
T +43 1 25077-1153
klaus.wassermann@vetmeduni.ac.at
Scientific contact:
Prof. Herbert Weissenböck
Institute of Pathology and Forensic Veterinary Medicine
University of Veterinary Medicine, Vienna
T +43 1 25077-2418
herbert.weissenboeck@vetmeduni.ac.at
Journal
Emerging Infectious Diseases