**5. Conclusions**

In this study, we have shown the circulation of WN-KOUTV in Niger and its detection in sandflies for the first time. These results extended the number of countries in Africa where this virus is reported, but also the spectrum of potential vectors. The very high virulence in mice [17,21,22], the possibility of multiple vectors, the risk of KOUTV to infect humans, and the increasing threats of flavivirus infections in the world, should contribute to better consideration of WNV-KOUTV as an important emerging pathogen. In this regard, vector competence studies, vertebrate hosts including birds, and viral genetic diversity characterizations are ongoing and will provide new insights on WN-KOUTV transmission, virulence and possibility to diffuse beyond Africa. Seroprevalence studies would also be important in Niger, particularly in Tahoua Region where the virus was isolated, and in Senegal where WN-KOUTV was isolated several times, to assess the potential circulation of KOUTV in humans.

**Author Contributions:** Conceptualization, G.F., D.D., M.D. (Mawlouth Diallo), O.F. (Ousmane Faye), and A.A.S.; methodology, E.H.N., D.D., H.S., G.F., B.D.S., and M.W.; formal analysis, M.W., M.D. (Mamadou Diop), M.H.D.N., and G.F.; validation, D.D., G.F., A.L., M.D. (Moussa Dia), M.H.D.N., C.L., and M.W.; investigation, E.H.N., D.D., H.S., A.L., G.F., M.H.D.N., M.D. (Moussa Dia), A.B., and B.D.S.; resources, A.L., F.S., J.T., B.B.N.; M.W., O.F. (Ousmane Faye), M.D. (Mawlouth Diallo), and A.A.S., writing—original draft preparation, G.F., writing—review and editing, H.S., A.L., D.D., G.F., M.D. (Mawlouth Diallo), O.F. (Ousmane Faye), O.F. (Oumar Faye), M.W., B.B.N., J.T., C.L., and F.S.; supervision, F.S., G.F., D.D., B.D.S., and A.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** The field investigations in Niger were funded by WHO AFRO and the laboratory work was funded by Institut Pasteur de Dakar. This research received no external funding.

**Institutional Review Board Statement:** There is no National Ethics Committee for animals in Senegal. These studies were performed in the context of surveillance at the WHO collaborating center for arboviruses and hemorrhagic fever viruses, and all experiments on animals were conducted by respecting the World Organization for Animal Health regulations (https://www.oie.int/fileadmin/ Home/fr/Health\_standards/tahc/current/chapitre\_aw\_research\_education.pdf) (accessed on 10 January 2021).

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data are included in the manuscript. The virus sequence generated during the current study is available at Genbank (accession number: MN057643).

**Acknowledgments:** The authors thank the authorities of the Ministry of Health of Niger and WHO Country office of Niger and Afro region for facilitating the Rift Valley fever outbreak investigation.

**Conflicts of Interest:** The authors declare no conflict of interest.
