Preliminary data on the vector competence of Aedes caspius for Dirofililaria immitis in a traditionally endemic area of northern Italy

Background: Dirofilaria immitis, the agent of canine and feline heartworm disease, and Dirofilaria repens, the agent of subcutaneous dirofilariosis, are widespread mosquito-borne helminths. The present study is aimed at updating current knowledge of the composition of potential vector species in the northern region of Emilia-Romagna, a traditionally endemic area for D. immitis and D. repens. Methods: Mosquitoes were collected in 2022 and 2023 as part of the regional surveillance plan for West Nile Virus (WNV). The capture zones included peri-urban and rural areas and mosquitoes 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. Results: A total of 140 pools (~ 20 mosquitoes each) in 2022 and 133 in 2023 have been 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. 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 provinces, which tested positive for D. immitis in both 2022 and 2023. Conclusions: These data highlight how, despite the abundance of Cx. 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.