Introduction: Mosquito-borne diseases (MBDs) are spreading worldwide due to globalization and climate change, representing a threat for both humans and animals. Of great concern are the infections caused by viruses belonging to the Flavivirus genus as West Nile virus (WNV) and Usutu virus (USUV) transmitted by Culex sp. or Dengue virus and Zika virus (ZIKV), transmitted by Aedes sp. This work describes the surveillance protocol enforced in Piedmont (Northwestern Italy) to control MBDs spread, focusing on the activities performed on mosquitoes during the 2015 vector season.
Materials and methods: From July to October, mosquitoes were fortnightly sampled in 50 selected sites according to risk factors with CDC dry ice-baited traps and BG-Sentinel traps baited with BG-Lure and dry ice. Adults were counted, identified to species level, pooled, and screened for flaviviruses using different reverse transcription-PCR protocols and sequencing. Finally, phylogenetic analysis was performed on a dataset including 2014 and 2015 WNV sequences and reference sequences retrieved from GenBank.
Results and discussion: A total of 17,000 mosquitoes, grouped in 730 pools, were tested. Five pools of Culex pipiens were positive for WNV Lineage 2 in Novara, Alessandria, Vercelli, and Torino Provinces. One pool of C. pipiens and one pool of Anopheles maculipennis s.l. were positive for USUV in Vercelli and Alessandria Provinces. In Vercelli Province one pool of C. pipiens resulted positive both for WNV and USUV. Control measures were quickly implemented. Phylogenetic analyses showed that the WNV Lin 2 sequences from Piedmont region cluster with those circulating in Northeastern Italy in the previous years. Given the positive trend in WNV activity compared to 2014 and the emergence caused by other flavivirus as ZIKV, the level of attention for the 2016 vector season may be increased and this surveillance protocol could represent an important tool for public health authorities.
Keywords: West Nile; flavivirus; mosquito(es); surveillance; vector-borne.