Susceptibility of wild and domestic songbirds to Usutu virus

Usutu virus (USUV) is an emerging mosquito-borne orthoflavivirus that can cause neuroinvasive disease in humans and wild birds. USUV clusters phylogenetically within the Japanese encephalitis virus serocomplex, sharing antigenic and ecological similarity with West Nile virus (WNV). USUV is maintained in an enzootic cycle primarily involving passerine birds and Culex spp. mosquitoes. USUV was first isolated in South Africa in 1959 and has since spread throughout Africa and Europe, causing mortality and disease in several wild bird populations, specifically the Eurasian blackbird (Turdus merula). To understand transmission and pathogenesis of USUV in birds, we sought to develop passerine bird models of infection using wild-caught house finches (Haemorhous mexicanus), wild-caught American robins (Turdus migratorius), domestic canaries (Serinus canaria domestica), and captive-bred zebra finches (Taeniopygia guttata). Birds were inoculated with one or two isolates of USUV and viremia was measured. House finches, American robins, and canaries were susceptible to USUV, with 100% of inoculated birds developing viremia. These avian species reach viremias that have the potential to infect Cx. quinquefasciatus mosquitoes. Clinical disease and histopathological evidence of disease were severe in American robins and moderate to severe in canaries, with limited disease in house finches. However, zebra finches inoculated with one isolate of USUV did not develop detectable viremia. These findings provide additional tools for studying USUV enzootic transmission and pathogenesis in passerine birds.