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Abstract：
Usutu virus (USUV) is an emerging flavivirus that is maintained in an enzootic cycle with mosquitoes as vectors and birds as amplifying hosts. In Europe, the virus has caused mass mortality of wild birds, mainly among Common Blackbird (Turdus merula) populations. While mosquitoes are the primary vectors for USUV, Common Blackbirds and other avian species are exposed to other arthropod ectoparasites, such as ticks. It is unknown, however, if ticks can maintain and transmit USUV. We addressed this question using in vitro and in vivo experiments and field collected data. USUV replicated in IRE/CTVM19 Ixodes ricinus tick cells and in injected ticks. Moreover, I. ricinus nymphs acquired the virus via artificial membrane blood-feeding and maintained the virus for at least 70 days. Transstadial transmission of USUV from nymphs to adults was confirmed in 4.9% of the ticks. USUV disseminated from the midgut to the haemocoel, and was transmitted via the saliva of the tick during artificial membrane blood-feeding. We further explored the role of ticks by monitoring USUV in questing ticks and in ticks feeding on wild birds in the Netherlands between 2016 and 2019. In total, 622 wild birds and the Ixodes ticks they carried were tested for USUV RNA. Of these birds, 48 (7.7%) carried USUV-positive ticks. The presence of negative-sense USUV RNA in ticks, as confirmed via small RNA-sequencing, showed active virus replication. In contrast, we did not detect USUV in 15,381 questing ticks collected in 2017 and 2019. We conclude that I. ricinus can be infected with USUV and can transstadially and horizontally transmit USUV. However, in comparison to mosquito-borne transmission, the role of I. ricinus ticks in the epidemiology of USUV is expected to be minor.
摘要：
Usutu病毒（USUV）是一种新兴的黄病毒，以蚊子为载体，鸟类为扩增宿主，维持在植物性周期中。在欧洲,这种病毒导致了野生鸟类的大量死亡，主要在普通黑鸟（Turdusmerula）种群中。虽然蚊子是USUV的主要载体，常见的黑鸟和其他鸟类暴露于其他节肢动物外寄生虫，比如蜱。它是未知的，然而,如果蜱能保持和传播USUV。我们使用体外和体内实验以及现场收集的数据解决了这个问题。USUV在IRE/CTVM19蓖麻蜱细胞和注射的蜱中复制。此外，I.蓖麻若虫通过人工膜血液喂养获得病毒，并将病毒维持至少70天。在4.9％的蜱中证实了USUV从若虫到成人的跨天线传播。USUV从中肠扩散到血脑细胞，在人工膜采血过程中通过蜱的唾液传播。我们通过监测USUV在2016年至2019年期间在荷兰寻找蜱和以野生鸟类为食的蜱进一步探索了蜱的作用。总的来说,对622只野生鸟类和它们携带的Ixodes蜱进行了USUVRNA测试。这些鸟,48（7.7％）携带USUV阳性蜱。蜱中存在负义USUVRNA，通过小RNA测序证实，病毒复制活跃。相比之下,我们在2017年和2019年收集的15381个调查蜱中没有检测到USUV。我们得出的结论是，I.ricinus可以感染USUV，并且可以跨性别和水平传播USUV。然而,与蚊媒传播相比，预计I.ricinustick在USUV流行病学中的作用较小。
