Comparative study on the effectiveness of different mosquito traps in arbovirus surveillance with a focus on WNV detection

• Based on physiological age, Gravid Traps showed the highest collection capacity of potentially infected females, but its performance can be influenced by environmental conditions.
• CAA2004 CO2-baited traps attracted the highest number of species in different environments. On average, its attractiveness towards potentially infectious females is not different from GT.
• CAA2004 CO2-baited trap is appropriate for WNV integrated surveillance system because its collection capacity of a range of mosquito species allows to screen for possible other pathogens. GT can be an effective additional tool to increase the fraction of potentially infectious females.
• Resting box and the BG-Sentinel trap were not effective in sampling Culex pipiens population.

The selection of the ideal trap for arbovirus surveillance is an issue of primary importance to increase the sensitivity of virus detection and the cost-effectiveness of the entomological surveillance. During the summer 2011, the effectiveness of five types of mosquito traps (CDC gravid trap, CO2-baited trap, BG-Sentinel™ and two experimental prototypes) to attract females potentially infected with West Nile virus were assessed. The study was carried out in three natural wetland sites located in the Emilia-Romagna Region (Northern Italy), using a Latin square scheme. Single night collections of adult females were performed and determination of species and physiological state (gravid, nulliparous or parous) was made upon return to the laboratory. The species most frequently collected in the gravid trap was Culex pipiens sl. L., being gravid females the large majority of the individuals. Species diversity was much higher in CO2-baited traps, which may therefore enable a more comprehensive description of the vector species composition and their role in arboviruses circulation. Our findings indicate that gravid traps can be a valid tool and should be integrated in the West Nile virus surveillance system in the Emilia-Romagna region, mainly based on collections made with CO2-baited traps.

CAA2004 CO2-baited trap is the more appropriate trap for a reliable West Nile virus integrated surveillance system, thanks to its high Culex spp. collection efficiency, easy management and better standardization. In spite of the difficulty to standardize the performance of the Gravid traps, we believe they should be considered an effective additional tool to increase the fraction of individuals suitable for being analyzed for of WNV and other arboviruses, in consideration of their specific attractiveness to potentially infectious females.In the Emilia-Romagna region, since 2009, a system integrating environmental (mosquitoes and birds) and human surveillance has been implemented and progressively improved. The monitoring plan relies mainly on CO2-baited traps with the introduction in 2013 and 2014, of 16 Gravid traps. The system enabled early detection of WNV circulation 3–4 weeks before human cases of WN Neuroinvasive Disease, detected virus circulation at the enzootic level, and the information was area-specific.Figure optionsDownload as PowerPoint slide