Abstract
The mosquito-borne flaviviruses USUV and WNV are known to co-circulate in large parts of Europe. Both are a public health concern, and USUV has been the cause of epizootics in both wild and domestic birds, and neurological cases in humans in Europe. Here, we explore the susceptibility of magpies to experimental USUV infection, and how previous exposure to USUV would affect infection with WNV. None of the magpies exposed to USUV showed clinical signs, viremia, or detectable neutralizing antibodies. After challenge with a neurovirulent WNV strain, neither viremia, viral titer of WNV in vascular feathers, nor neutralizing antibody titers of previously USUV-exposed magpies differed significantly with respect to magpies that had not previously been exposed to USUV. However, 75% (6/8) of the USUV-exposed birds survived, while only 22.2% (2/9) of those not previously exposed to USUV survived. WNV antigen labeling by immunohistochemistry in tissues was less evident and more restricted in magpies exposed to USUV prior to challenge with WNV. Our data indicate that previous exposure to USUV partially protects magpies against a lethal challenge with WNV, while it does not prevent viremia and direct transmission, although the mechanism is unclear. These results are relevant for flavivirus ecology and contention.
Highlights
Usutu virus (USUV) is a mosquito-transmitted flavivirus that belongs to the Japanese encephalitis virus serocomplex [1]
In 2016, several countries in Western Europe reported the largest epizootic of the USUV registered so far in Europe, which caused a massive mortality of birds [5]
A final group of 24 juvenile magpies negative for USUV and WNV Nabs and RNA was transported to our biosafety level 3 (BSL-3) facilities, where they were housed in 2 separate boxes (Figure 1) in flight cages (12 birds/cage), equipped as described [19]
Summary
Usutu virus (USUV) is a mosquito-transmitted flavivirus that belongs to the Japanese encephalitis virus serocomplex [1]. After its first identification in South Africa in 1959 [2], the virus was detected in Europe in 2001 in an outbreak in birds in Austria [3], retrospective identification in tissues from blackbird mortalities in Italy suggests it has been circulating in Europe since at least 1996 [4]. Europe, causing high bird mortality [5] and some human cases [6,7,8,9,10]. USUV seropositivity has been reported in more than 58 bird species belonging to 26 families and 13 orders, Passeriformes being the most affected [5,11]. In 2016, several countries in Western Europe reported the largest epizootic of the USUV registered so far in Europe, which caused a massive mortality of birds [5]. Scarce experimental data on USUV infection in avian species are available [12,13,14]
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