Shared viral burdens: Molecular evidence of Usutu virus infection and multi-arbovirus exposure in migrant and resident birds at wintering locations in Nigeria.

backgroundWest Nile (WNV), Usutu (USUV), and Sindbis (SINV) virus were initially detected in the African region, and subsequently across temperate regions where they were previously absent. Wild birds are primary reservoirs for these arboviruses and are considered major contributors to their global spread through seasonal migration. To understand the transmission dynamics of arboviruses in African wild birds and the potential of migratory birds to spread the viruses at an intercontinental scale, we investigated arboviral infections and exposures in resident and Palearctic migratory birds at wintering locations in Nigeria. METHODOLOGY/PRINCIPAL

findingsOropharyngeal- and cloacal swabs, feathers and blood were collected from resident and migratory birds at two wintering locations (Amurum and Ngel-Nyaki Forest Reserves). Swabs and feathers were tested using RT-PCR for WNV, USUV and SINV, and blood with ELISA and FRNT90 or PRNT80 for antibodies. 573 birds were sampled between 2021-2024 across months coinciding with arrival and departure of migratory birds. USUV RNA was detected in 2.6% of feathers including a positive Icterine warbler and a garden warbler sampled prior to spring migration. None of the swabs were positive for viral RNA but neutralizing antibodies to WNV and USUV were detected in 4.5% of birds. SINV antibodies were also found in 34.1% of birds sampled across the wintering locations. CONCLUSIONS/SIGNIFICANCE: Our findings provide molecular evidence of USUV RNA detection and serological evidence to USUV, WNV and SINV in migratory and resident birds sampled at overwintering locations in Nigeria. These findings are consistent with the possibility that migratory birds may acquire arboviral infections during their overwintering periods in Africa. In addition, detections of viral RNA through RT-PCR in feathers, but not swabs, suggest feathers may be a suitable alternative sample type for surveillance in the absence of a reliable cold chain. The overall detections in wild birds at these locations highlight the need for further surveillance to define the epidemiology and public health risks of these arboviruses in the region.