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, how-
ever, 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 trans-
mission of USUV from nymphs to adults was confirmed in 4.9% of the ticks. USUV dissemi-
nated 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 replica-
tion. 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 hori-
zontally 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.
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, how-
ever, 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 trans-
mission of USUV from nymphs to adults was confirmed in 4.9% of the ticks. USUV dissemi-
nated 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 replica-
tion. 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 hori-
zontally 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.
| Original language | English |
|---|---|
| Article number | e0012172 |
| Journal | PLoS Neglected Tropical Diseases |
| DOIs | |
| Publication status | Published - 10 Jul 2024 |