Entomological Surveillance For West Nile And Usutu Viruses In Sardinia (Italy) During 2015

Purpose: West Nile Virus and USUV are a re-emerged health problem in Europe. In Sardinia outbreaks of West Nile Disease have been reported since 2011 while in 2013, USUV was detected for the first time in mosquitoes. The aim of this study was to identify the mosquitoes involved in viral transmission and their seasonal abundance in the framework of the entomological activities defined in the Italian surveillance plan for West Nile Disease (WND) in 2015. Methods & Materials: Entomological surveillance was conducted using CDC Light Traps operating for 24 hours in 35 geo-referenced sites every two weeks, from April until October 2015. Sampled mosquitoes were identified at the species level and then pooled according to species, sex, presence or absence of blood in the abdomen, station and date of sampling, with a maximum of 50 individuals per pool. Mosquito pools were assayed by two real-time RT PCR for the detection of WNV lineage 1-2 and USUV RNA. Results: During 2015 a total of 5,345 adult mosquitoes representing 17 different species were collected. The most abundant species were O. caspius with 1,454 specimens (27.2%), C. pipiens 994 (18.6%), C. theileri 764 (14.3%) and O. detritus 732 (13.7%). The seasonal abundance peak of O. caspius and O. detritus were recorded in October with a maximum of 859 and 324 individuals, respectively. C. pipiens and C. theileri showed a peak in July with 208 and 577 adults, respectively. Overall 1,004 pools were sorted and tested for WNV and USUV. WNV lineage 1 was detected in a single pool of 3 not-engorged females of C. pipiens collected in September in Bari Sardo municipality. USUV was detected in 4 pools consisting of not-engorged females of C. pipiens captured from August to October in Siniscola (6), Oschiri (8), Alghero (3) and Olbia (7) municipalities. Conclusion: The entomological surveillance was able to detect circulation of WNV lineage 1 and USUV confirming the vector role of C. pipiens in Sardinia.