Molecular screening of mosquitoes for filarioid helminths in Slovenia

Dirofilaria repens infections have already been reported in both dogs and humans in Slovenia. Xenomonitoring of mosquitoes for filarioid helminths has been used in many studies across Europe to analyze the autochthonous occurrence of filarioids. The aim of this study was to identify potential mosquito vectors of D. repens and other filarioid helminths in Slovenia, to shed light on the significance and extent of possible autochthonous transmission of filarioids in the country.

This study was a part of the Slovenian nationwide screening program of mosquitoes for filarioid helminths and viruses. Adult mosquitoes were collected from numerous sites throughout Slovenia in 2021 and 2022, and were screened for filarioid helminths using real-time polymerase chain reaction (PCR) targeting a 94-base pair (bp) fragment of the 12S rRNA gene from the mitochondrial genome. Positive samples, which were confirmed by conventional PCR targeting 667 bp of the COI gene, were sequenced and compared with GenBank sequences for species identification.

Almost 56,000 adult mosquitoes were screened for filarioid helminths, which were grouped into 5446 pools. The number of mosquitoes in each pool ranged from 1 to 60. Of all the screened pools, 29 were positive for filarioid helminths, giving a total minimum infection rate (MIR) of 0.52 per 1000 mosquitoes. Alongside D. repens, which was detected in six pools, the following were also identified: Setaria tundra in 15 pools; S. labiatopapillosa in two pools; and an unknown filarioid species in six mosquito pools. In the study, we found eight mosquito species in Slovenia that may transmit filarioid worms, including Aedes vexans, Ae. albopictus, Ae. cinereus, Ae. sticticus, Anopheles maculipennis s.l., An. claviger, Coquillettidia richiardii, and Culex pipiens s.l., indicating that multiple species could contribute to the local transmission of these parasites.

The detection of filarioid helminths in Slovenian mosquitoes is consistent with the previous findings of potential mosquito species that can carry D. repens, S. tundra, and S. labiatopapillosa in Europe, indicating the potential for local transmission. Consequently, dirofilarioid infections in dogs and humans, and setarial infections in roe deer, should be considered. Further research is required to better understand the epidemiology of these infections in Europe.