Molecular and Serological Screening of West Nile and Usutu Virus in Birds and Humans: A Sentinel Study in Finland
Ruut Joensuu, Maija T. Suvanto, Sanna Sainmaa, Viktor Olander, Roope Nykänen, Essi M. Korhonen, Anne J. JääskeläinenABSTRACT
Background
The northward expansion of mosquito‐borne viruses such as West Nile virus (WNV) and Usutu virus (USUV) in Europe, driven partly by climate‐related changes affecting vectors and hosts, poses an increasing threat to human and animal health. Reliable diagnostic tools are therefore essential for early detection and effective surveillance.
Objectives
This study aimed to develop and evaluate sensitive molecular assays for WNV and USUV, apply them to screen wild birds and human patients in Finland, assess bird exposure through serology, and evaluate national preparedness for emerging arboviral threats.
Methods
Real‐time PCR assays for WNV and USUV nucleic acids were developed, optimized and evaluated for the detection of WNV and USUV nucleic acids using bird and human samples. Bird samples were also tested for anti‐WNV antibodies using an in‐house immunofluorescence assay (IFA).
Results and Conclusions
The real‐time PCR assays showed high sensitivity, with limits of detection of 13.0 copies per reaction for WNV and 14.6 copies per reaction for USUV. A total of 163 deceased birds and 337 human serum samples collected during the summer months from patients with suspected acute infections were screened. No WNV or USUV nucleic acids were detected, and bird samples tested negative for WNV antibodies. However, given the active migratory bird flyways from Africa and Southern/Central Europe, and recent detections in neighbouring countries, the introduction of WNV into Finland appears likely. Continued surveillance and the availability of efficient diagnostic tools remain critical for preparedness and early response.