Subcutaneous nodules and dermatitis associated with non- immitis non -repens dirofilariosis morphologically consistent with Dirofilaria striata in a 2-year-old male domestic cat in Florida, USA.

A 2-year-old male neutered domestic shorthair cat from Florida, USA, presented with a one-month history of multiple subcutaneous nodules affecting the entire body. Dermatohistopathology revealed nodular to diffuse, eosinophilic, histiocytic, and mastocytic dermatitis and panniculitis with collagen flame figures, and many nematode larvae and adults within nodules and migration tracts. The worms were morphologically consistent with Dirofilaria striata. The serum antibody test was positive for D. immitis with a negative antigen assay result (both with and without heat treatment), and microfilariae were not recovered by a modified Knott's test. PCR and sequencing of 18S rRNA and mitochondrial 12S rRNA and cytochrome oxidase subunit I genes confirmed the presence of a Dirofilaria spp. Unfortunately, there is no available reference sequence or material for D. striata for comparison. The cat was treated with monthly topical 10% imidacloprid/1% moxidectin. Lesions clinically resolved within one month, but new lesions appeared on different locations despite the monthly treatment. Resolution occurred without changing the treatment regimen, as no additional nodules were noted after 1 year. This Dirofilaria sp. may cause subcutaneous nodules in the domestic cat and should be included in the differential diagnosis for felines with nodular dermatitis, and is present in Florida.