Virus Highlight - Usutu Virus

Usutu Virus (USUV) is an emerging mosquito-borne flavivirus belonging to the Japanese encephalitis virus serocomplex, with a similar transmission cycle as West Nile virus.2,3 USUV is maintained in the environment through an enzootic cycle between several bird and mosquito species, with humans and mammals as the incidental dead-end hosts.2,3

First isolated in 1959 from Culex neavei mosquitos in South Africa, and named after the nearby Usutu River, USUV has spread from southern Africa to Europe by way of migratory birds, thought to be the major amplifying host, where it has caused significant avian outbreaks and infections in humans and horses.1-3 Infections in humans, while low, range from mild and asymptomatic to serious neuroinvasive diseases like encephalitis and meningoencephalitis. Co-circulation with West Nile virus, confirmed in numerous European countries in mosquito, bird and horse species, and positive serology for both viruses reported in both birds and humans, raises epidemiological issues, furthering the need for research and diagnostic tools to address USUV as a potential human pathogen in the future.2-4

BEI Resources supports this continuing research by offering two Usutu virus isolates available in the BEI Resources catalog: ENT MP 1626 (NR-51185), isolated in 1962 from Mansonia aurites mosquitoes in Zika Forest, Uganda, and the prototype African strain SAAR 1776 (NR-51184), the first isolation of the virus in 1959 from Culex neavei mosquitos in South Africa.


  1. McIntosh, B. M. “Usutu (SAAr 1776); Nouvel Arbovirus du Groupe B.” Int. Cat. Arboviruses 3 (1985): 367- 374.
  2. ClĂ©, M., et al. “Usutu Virus: A New Threat?” Epidemiol. Infect. 147 (2019): e232. PubMed: 31364580.
  3. Roesch, F., et al. “Usutu Virus: An Arbovirus on the Rise.” Viruses 11 (2019): E640. PubMed: 31336826.
  4. Nikolay, B. “A Review of West Nile and Usutu Virus Co-Circulation in Europe: How Much Do Transmission Cycles Overlap?” Trans. R. Soc. Trop. Med. Hyg. 109 (2015): 609-618. PubMed: 26286946.

Image:  Larvae of Culex Mosquitoes (CDC/James Gathany)

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