West Nile Virus and Usutu Virus Neutralizing Antibodies Found in Dutch Rodent Species

Background: In the Netherlands, Usutu virus (USUV) is endemic in birds, and recently West Nile virus (WNV) was also detected in birds, mosquitoes and humans. Here we investigated the possible role of rodents in the viruses' transmission ecology. Materials and Methods: We sampled rodents at six locations including sites where WNV had been previously detected. Brains (n = 668), oral swabs (n = 282), and ticks (n = 91) collected from rodents were tested for arboviruses via Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). Also, sera from 118 rodents were tested for WNV- and USUV-antibodies. Results and Conclusion: Brain samples, swabs, and ticks tested negative for viral RNA. However, 2.5% (3/118; two wood mice, one field vole) of rodents had WNV-neutralizing antibodies (WNV-NAbs). USUV-NAbs were detected in a wood mouse. Two bank voles had NAbs against both viruses. The WNV and USUV antibody-positive rodents were found at locations with previous WNV and USUV circulations, suggesting that rodents may be involved in the ecology of WNV and USUV.