Usutu virus promotes West Nile virus replication in Culex pipiens biotype molestus during simultaneous and sequential co-infections
- 1Friedrich-Loeffler-Institut – Federal Research Institute for Animal Health (FLI), Institute of Infectology, Greifswald - Insel Riems, Germany
Abstract
The epidemiological co-circulation of the two flaviviruses West Nile virus (WNV) and Usutu virus (USUV) in several European countries poses the risk of co-infections in vertebrate hosts and mosquito vectors. WNV is an important human pathogen, whereas USUV is primarily relevant in veterinary and wildlife health. Co-infections have been detected in birds and, occasionally, in humans. To determine the potential consequences of co-exposure and co-infections in mosquitoes on viral transmission, lab-reared Culex pipiens biotype molestus were orally infected with both viruses either simultaneously or sequentially at 7-day intervals with German isolates of WNV lineage 2 and USUV lineage Europe 3. Simultaneous exposure resulted in a significantly increased WNV infection rate, while infection and transmission of USUV were inhibited at the same time. During sequential exposure, prior WNV exposure also had a negative effect on susceptibility to USUV, whereas conversely, WNV infection rates were not altered by prior USUV exposure. Furthermore, mosquitoes with established co-infections after simultaneous co-exposure exhibited higher WNV viral loads than those infected exclusively with WNV. The study reveals complex interactions between WNV, USUV, and the mosquito vector, which could influence vector competence and vector capacity of Culex pipiens biotype molestus in areas with co-circulation of WNV and USUV. Author summary: West Nile virus and Usutu virus are two closely related flaviviruses transmitted by mosquitoes. Both viruses share a very similar transmission cycle and often occur in the same regions. Consequently, co-infections with both viruses are possible in vertebrates as well as in mosquitoes. To investigate potential consequences of these co-infections in mosquitoes on transmission of both viruses, we infected mosquitoes of the species Culex pipiens biotype molestus with both viruses simultaneously or at a 7-day interval via virus-containing blood feeding. We were able to demonstrate that West Nile virus benefits from simultaneous exposure to Usutu virus, especially in the case of established co-infections. At the same time, a simultaneous or prior exposure to West Nile virus inhibits replication of Usutu virus. These interactions between both viruses and the mosquito can have a crucial impact on viral transmission.
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BibTeX
@article{korsten2026usutu,
title = {{Usutu virus promotes West Nile virus replication in Culex pipiens biotype molestus during simultaneous and sequential co-infections}},
author = {Christin Körsten and Cornelia Silaghi and Mandy Schäfer},
journal = {PLOS Pathogens},
year = {2026},
month = sep,
doi = {10.1371/journal.ppat.1014601},
url = {https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014601},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Usutu virus promotes West Nile virus replication in Culex pipiens biotype molestus during simultaneous and sequential co-infections
AU - Christin Körsten
AU - Cornelia Silaghi
AU - Mandy Schäfer
PY - 2026
DA - 2026/09/11
JO - PLOS Pathogens
DO - 10.1371/journal.ppat.1014601
UR - https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014601
AB - The epidemiological co-circulation of the two flaviviruses West Nile virus (WNV) and Usutu virus (USUV) in several European countries poses the risk of co-infections in vertebrate hosts and mosquito vectors. WNV is an important human pathogen, whereas USUV is primarily relevant in veterinary and wildlife health. Co-infections have been detected in birds and, occasionally, in humans. To determine the potential consequences of co-exposure and co-infections in mosquitoes on viral transmission, lab-reared Culex pipiens biotype molestus were orally infected with both viruses either simultaneously or sequentially at 7-day intervals with German isolates of WNV lineage 2 and USUV lineage Europe 3. Simultaneous exposure resulted in a significantly increased WNV infection rate, while infection and transmission of USUV were inhibited at the same time. During sequential exposure, prior WNV exposure also had a negative effect on susceptibility to USUV, whereas conversely, WNV infection rates were not altered by prior USUV exposure. Furthermore, mosquitoes with established co-infections after simultaneous co-exposure exhibited higher WNV viral loads than those infected exclusively with WNV. The study reveals complex interactions between WNV, USUV, and the mosquito vector, which could influence vector competence and vector capacity of Culex pipiens biotype molestus in areas with co-circulation of WNV and USUV. Author summary: West Nile virus and Usutu virus are two closely related flaviviruses transmitted by mosquitoes. Both viruses share a very similar transmission cycle and often occur in the same regions. Consequently, co-infections with both viruses are possible in vertebrates as well as in mosquitoes. To investigate potential consequences of these co-infections in mosquitoes on transmission of both viruses, we infected mosquitoes of the species Culex pipiens biotype molestus with both viruses simultaneously or at a 7-day interval via virus-containing blood feeding. We were able to demonstrate that West Nile virus benefits from simultaneous exposure to Usutu virus, especially in the case of established co-infections. At the same time, a simultaneous or prior exposure to West Nile virus inhibits replication of Usutu virus. These interactions between both viruses and the mosquito can have a crucial impact on viral transmission.
SN - 1553-7374
ER -