Circulation of zoonotic Dirofilaria spp. in mosquito vectors in Emilia Romagna and co-infection with West Nile Virus (WNV).

Dirofilaria immitis, the agent of canine and feline heartworm disease and Dirofilaria repens, the agent of subcutaneous dirofilariosis, are widespread mosquito-borne helminths. They are also agents of emerging zoonoses. Furthermore, it has been reported that mosquitos harboring filarial larvae show enhanced transmission of West Nile Virus (WNV) in endemic areas. The present study is aimed at updating current knowledge of the composition of potentially competent vector species in the northern region of Emilia Romagna, a traditionally endemic area for D. immitis and D. repens and at evaluating co-infections with WNV. Mosquitoes were collected in 2022 and 2023. The capture zones included peri-urban and rural areas and mosquitos were captured with CDC-CO2 traps. DNA from approximately 30% of female mosquitoes of each captured species (Culex pipiens, Aedes caspius, Aedes vexans, Aedes albopictus) was extracted and analyzed for the presence of D. immitis and D. repens. From the positive pools, RNA was also extracted and analyzed for the presence of WNV. A total of 140 pools (~ 20 mosquitos/each) in 2022 and 133 in 2023 were analyzed. DNA of D. immitis was identified in 14 pools in 2022 and in 15 pools in 2023. None of the pools was positive for D. repens or for WNV. In 2022, about 85% of the positive pools belonged to Ae. caspius species (11/13) and the other three pools to Ae. vexans. In 2023, 73% of the positive pools belonged to Ae. caspius, followed by Ae. vexans and Ae. albopictus (both 13.3%). A significant overlap emerged from the same traps positioned in Ferrara and Bologna province, which tested positive for D. immitis in both 2022 and 2023. No co-infections with WNV were identified, even though it had been observed in C. pipiens captured in the region in 2019. These data highlight how, despite the abundance of C. pipiens captured, the most receptive species for D. immitis appear to be Ae. caspius and Ae. vexans. Furthermore, the geographical data highlights how the areas of the province of Ferrara and Bologna are the main geographical reservoirs of the parasite.