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Type of publication: Journal Article
Type of document: Full Paper

Year: 2008

Authors: Rubel, F; Brugger, K; Hantel, M; Chvala-Mannsberger, S; Bakonyi, T; Weissenböck, H; Nowotny, N

Title: Explaining Usutu virus dynamics in Austria: model development and calibration.

Source: Prev Vet Med. 2008; 85(3-4):166-186

Authors Vetmeduni Vienna:

Bakonyi Tamas
Brugger Katharina
Chvala-Mannsberger Sonja
Nowotny Norbert
Rubel Franz
Weissenböck Herbert

Vetmed Research Units
Institute of Pathology
Institute of Virology
Institute of Physiology, Pathohysiology and Biophysics, Unit of Physiology and Biophysics

Project(s): Application of an mathematical model to explain the Usutu virus dynamics in the region of Vienna

Usutu virus (USUV), a flavivirus of the Japanese encephalitis virus complex, was for the first time detected outside Africa in the region around Vienna (Austria) in 2001 by Weissenböck et al. [Weissenböck, H., Kolodziejek, J., Url, A., Lussy, H., Rebel-Bauder, B., Nowotny, N., 2002. Emergence of Usutu virus, an African mosquito-borne flavivirus of the Japanese encephalitis virus group, central Europe. Emerg. Infect. Dis. 8, 652-656]. USUV is an arthropod-borne virus (arbovirus) circulating between arthropod vectors (mainly mosquitoes of the Culex pipiens complex) and avian amplification hosts. Infections of mammalian hosts or humans, as observed for the related West Nile virus (WNV), are rare. However, USUV infection leads to a high mortality in birds, especially blackbirds (Turdus merula), and has similar dynamics with the WNV in North America, which, amongst others, caused mortality in American robins (Turdus migratorius). We hypothesized that the transmission of USUV is determined by an interaction of developing proportion of the avian hosts immune and climatic factors affecting the mosquito population. This mechanism is implemented into the present model that simulates the seasonal cycles of mosquito and bird populations as well as USUV cross-infections. Observed monthly climate data are specified for the temperature-dependent development rates of the mosquitoes as well as the temperature-dependent extrinsic-incubation period. Our model reproduced the observed number of dead birds in Austria between 2001 and 2005, including the peaks in the relevant years. The high number of USUV cases in 2003 seems to be a response to the early beginning of the extraordinary hot summer in that year. The predictions indicate that >70% of the bird population acquired immunity, but also that the percentage would drop rapidly within only a couple of years. We estimated annually averaged basic reproduction numbers between R (0)=0.54 (2004) and 1.35 (2003). Finally, extrapolation from our model suggests that only 0.2% of the blackbirds killed by USUV were detected by the Austrian USUV monitoring program [Chvala, S., Bakonyi, T., Bukovsky, C., Meister, T., Brugger, K., Rubel, F., Nowotny, N., Weissenböck, H., 2007. Monitoring of Usutu virus activity and spread by using dead bird surveillance in Austria, 2003-2005. Vet. Microbiol. 122, 237-245]. These results suggest that the model presented is able to quantitatively describe the process of USUV dynamics.

Keywords Pubmed: Animals
Basic Reproduction Number
Bird Diseases/epidemiology
Bird Diseases/immunology
Bird Diseases/transmission
Bird Diseases/virology*
Computer Simulation
Disease Outbreaks/veterinary
Encephalitis Viruses, Japanese/growth & development
Encephalitis Viruses, Japanese/immunology
Encephalitis Viruses, Japanese/physiology*
Flaviviridae Infections/epidemiology
Flaviviridae Infections/transmission
Flaviviridae Infections/veterinary*
Flaviviridae Infections/virology
Models, Biological*

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