Modified BG sentinel trap as an alternative to CDC for Flavivirus surveillance in Italy

INTRODUCTION. Early detection of pathogens in arthropod vectors is highly important in prevention of vectorborne diseases and has the potential of providing the timely indicator of pathogens circulation before reaching humans. Here we propose a BG Sentinel trapping method based on the maintenance of mosquitoes alive through a sugar delivery system that avoids the need of cool chain for their preservation. This approach might be particularly useful in arbovirus surveillance and can be a possible alternative to CDC traps used for WNV surveillance in Italy. MATERIALS AND METHODS. BG-sentinel trap baited with BG-lure and CO2, modified to collect mosquitoes in a chamber containing a honey-based solution as a feeding source (Timmins et al., 2018 J Med Entomol. 55: 1638- 41), was compared to CDC-CO2 trap in 10 sites of Veneto region characterized by both high vector densities and viral circulation of WNV and USUV. Overall, 4 captures per site have been carried out on alternate weeks from July to August 2019. BG traps worked for two consecutive days while CDC were active for one day. Mosquitoes were identified and RNA was extracted from pools and screened for the presence of Flavivirus using a one-step SYBR Green-Based rRT-PCR and sequencing (Scaramozzino et al., 2001 J Clin Microb. 39: 1922–27). Data were statistically analysed through GLM models. RESULTS AND CONCLUSIONS. In total, 39,313 mosquitoes were collected. The BG caught higher species diversity (Shannon H, BG:0.98 CDC:0.40) with better identification rates (BG:0.02%, CDC:3.2%) but with lower 1-day median trapped mosquitoes (BG:169, CDC:267), comparable only at low density. Median abundances of Culex pipiens were higher for CDC (BG:96, CDC:189) but no differences were observed at 2-days sampling. Equal or greater abundance of secondary vectors was observed in BGat1-day sampling (Ochlerotatus caspius BG:8.5, CDC:10.5; Aedes albopictus BG:7.5, CDC:1). Flavivirus prevalences were equivalent at 2-days sampling (WNV, BG: 0.027% CDC: 0.03%; USUV, BG: 0.054%, CDC: 0.06%). In conclusion, this modified BG shows useful performance in arbovirus surveillance: i) working for consecutive days without the need of cool chain; ii) collecting a higher number of species -and potentially viruses- than CDC ensuring an increase in species identification.