Massive subcutaneous filariosis by Filaria martis in beech marten (Martes foina) in Italy

The beech marten (<i>Martes foina</i>) is a small-size mustelid endangered according to the IUCN Red List. Despite the plethora of parasites potentially affecting its population decline, subcutaneous filarioids are occasionally reported in martens and their competent arthropod vectors are to date unknown. Therefore, from January 2023 to August 2024, this study investigated the presence of subcutaneous filarioids and ectoparasites of road-killed beech martens (<i>n</i> = 7) from southwestern Italy. One marten (14.3 %, 95 % CI: 2.6-51.3) was massively infected with subcutaneous filarioids, i.e., 18 specimens (11 males and 7 females) in the dorso-posterior region, where mild redness and sloughing of skin were found. All the filarioids were identified as <i>Filaria martis</i> via morphology and Sanger sequencing of the <i>cytochrome c oxidase</i> subunit I (<i>cox</i>1) gene that revealed a single sequence type (GenBank accession number PQ034642) having 100 % nucleotide identity with those available in the literature. The phylogenetic analysis displayed a bootstrap value of 100 % between the <i>cox</i>1 sequences of <i>F. martis</i> of this study and those of beech martens from Italy and European minks from Spain. Haemolymph, gut, and salivary glands of the <i>Ixodes ricinus</i> ticks collected from the infected marten scored negative for <i>F. martis</i> larvae and DNA by dissection and PCR, respectively. This study reported for the first time <i>F. martis</i> subcutaneous filariosis in southwestern Italy, previously outlined only in northern and southeastern areas, indicating the circulation of this poorly investigated filarioid. Knowledge of the competent vectors involved in the biological cycle of <i>F. martis</i> requires further experimental studies.