Resource-Effective Serosurveillance for the Detection of West Nile Virus in Switzerland Using Abattoir Samples of Free-Range Laying Hens

West Nile virus (WNV) is an important zoonotic pathogen maintained in a natural transmission cycle between mosquitoes and birds as reservoir hosts. In dead-end hosts, such as humans, infection may result in fatal neurologic disease translating into disease and death-related suffering and increased health care costs. In humans, WNV may also be transmitted through blood transfusions and organ transplants. WNV is not present in Switzerland yet, but competent vector species (especially Culex pipiens and Aedes japonicus) are prevalent and an introduction of the virus, likely through wild birds, is expected at any time. Therefore, it is important for Switzerland to be prepared and establish a surveillance system for WNV to initiate increased prevention activities, such as the screening of blood and organ donations and public education activities in case virus circulation is detected. The long-term goal of these surveillance measures would be a reduced infection rate in humans resulting in less suffering and reduced health care costs. To provide the basis for a pragmatic and resource-effective WNV surveillance program, this study used aliquots of serum samples of free-range laying hens taken at the abattoir and collected in the frame of the ongoing Swiss Avian Influenza and Newcastle Disease monitoring program for a 2-year period. All 961 aliquots were analyzed using a commercial competitive WNV enzyme-linked immunosorbent assay (ELISA). The study allowed to set up sampling and laboratory routines as a basis for future WNV surveillance activities. At this stage there is no evidence for circulation of WNV in Switzerland.