Usutu virus (USUV), a flavivirus
of the Japanese encephalitis virus c
omplex, was f
or the first time detected
outside Africa in the regi
on ar
ound Vienna (Austria) in 2001 by Weissenböck et al. [Weissenböck, H., K
ol
odziejek, J., Url, A., Lussy, H., Rebel-Bauder, B., N
ow
otny, N., 2002. Emergence
of Usutu virus, an African m
osquit
o-b
orne flavivirus
of the Japanese encephalitis virus gr
oup, central Eur
ope. Emerg. Infect. Dis. 8, 652–656]. USUV is an arthr
op
od-b
orne virus (arb
ovirus) circulating between arthr
op
od vect
ors (mainly m
osquit
oes
of the
Culex pipiens c
omplex) and avian amplificati
on h
osts. Infecti
ons
of mammalian h
osts
or humans, as
observed f
or the related West Nile virus (WNV), are rare. H
owever, USUV infecti
on leads t
o a high m
ortality in birds, especially blackbirds (
Turdus merula), and has similar dynamics with the WNV in N
orth America, which, am
ongst
others, caused m
ortality in American r
obins (
Turdus migratorius). We hyp
othesized that the transmissi
on
of USUV is determined by an interacti
on
of devel
oping pr
op
orti
on
of the avian h
osts immune and climatic fact
ors affecting the m
osquit
o p
opulati
on. This mechanism is implemented int
o the present m
odel that simulates the seas
onal cycles
of m
osquit
o and bird p
opulati
ons as well as USUV cr
oss-infecti
ons. Observed m
onthly climate data are specified f
or the temperature-dependent devel
opment rates
of the m
osquit
oes as well as the temperature-dependent extrinsic-incubati
on peri
od. Our m
odel repr
oduced 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 t
o be a resp
onse t
o the early beginning
of the extra
ordinary h
ot summer in that year. The predicti
ons indicate that >70 %
of the bird p
opulati
on acquired immunity, but als
o that the percentage w
ould dr
op rapidly within
only a c
ouple
of years. We estimated annually averaged basic repr
oducti
on numbers between
ox"">ob=MathURL&_method=retrieve&_udi=B6TBK-4S0R6JP-2&_mathId=mml79&_user=1067359&_cdi=5145&_rdoc=4&_acct=C000050221&_version=1&_userid=10&md5=d8500cccde6b28caec22099ac7114477"">
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olati
on fr
om
our m
odel suggests that
only 0.2 %
of the blackbirds killed by USUV were detected by the Austrian USUV m
onit
oring pr
ogram [
Chvala, S., Bak
onyi, T., Buk
ovsky, C., Meister, T., Brugger, K., Rubel, F., N
ow
otny, N., Weissenböck, H., 2007. M
onit
oring
of Usutu virus activity and spread by using dead bird surveillance in Austria, 2003–2005. Vet. Micr
obi
ol. 122, 237–245]. These results suggest that the m
odel presented is able t
o quantitatively describe the pr
ocess
of USUV dynamics.