Usutu virus (USUV), a flavivirus of the Japanese en
cephalitis virus
complex, was for the first time dete
cted outside Afri
ca in the region around Vienna (Austria) in 2001 by Weissenbö
ck et al. [Weissenbö
ck, H., Kolodziejek, J., Url, A., Lussy, H., Rebel-Bauder, B., Nowotny, N., 2002. Emergen
ce of Usutu virus, an Afri
can mosquito-borne flavivirus of the Japanese en
cephalitis virus group,
central Europe. Emerg. Infe
ct. Dis. 8, 652–656]. USUV is an arthropod-borne virus (arbovirus)
cir
culating between arthropod ve
ctors (mainly mosquitoes of the
Culex pipiens complex) and avian amplifi
cation hosts. Infe
ctions of mammalian hosts or humans, as observed for the related West Nile virus (WNV), are rare. However, USUV infe
ction leads to a high mortality in birds, espe
cially bla
ckbirds (
Turdus merula), and has similar dynami
cs with the WNV in North Ameri
ca, whi
ch, amongst others,
caused mortality in Ameri
can robins (
Turdus migratorius). We hypothesized that the transmission of USUV is determined by an intera
ction of developing proportion of the avian hosts immune and
climati
c fa
ctors affe
cting the mosquito population. This me
chanism is implemented into the present model that simulates the seasonal
cy
cles of mosquito and bird populations as well as USUV
cross-infe
ctions. Observed monthly
climate data are spe
cified for the temperature-dependent development rates of the mosquitoes as well as the temperature-dependent extrinsi
c-in
cubation period. Our model reprodu
ced the observed number of dead birds in Austria between 2001 and 2005, in
cluding 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 predi
ctions indi
cate that >70%of the bird population a
cquired immunity, but also that the per
centage would drop rapidly within only a
couple of years. We estimated annually averaged basi
c reprodu
ction numbers between
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ckbirds killed by USUV were dete
cted by the Austrian USUV monitoring program [Chvala, S., Bakonyi, T.,
Bukovsky, C., Meister, T., Brugger, K., Rubel, F., Nowotny, N., Weissenbö
ck, H., 2007. Monitoring of Usutu virus a
ctivity and spread by using dead bird surveillan
ce in Austria, 2003–2005. Vet. Mi
crobiol. 122, 237–245]. These results suggest that the model presented is able to quantitatively des
cribe the pro
cess of USUV dynami
cs.