Diagnostic odyssey of a German shepherd dog with disseminated Penicillium labradoris infection: a case report

Below, the first confirmed canine infection caused by <i>Penicillium labradorum</i> (syn. <i>P. labradoris</i>) in Italy is reported, diagnosed using a multidisciplinary approach. In November 2021, a 10-year-old spayed female German Shepherd dog with urinary incontinence was presented. Physical examination of the right forelimb revealed a non-painful soft tissue enlargement with firm consistency, while peripheral lymph nodes were unremarkable. Hematological, serum biochemical, and urinalysis tests showed no significant abnormalities. Radiographic examination revealed a proliferative lesion of the right radial bone, whereas abdominal ultrasonography did not identify anatomical alterations. Computed tomography (CT) revealed aggressive proliferative and lytic lesions of the radius associated with soft tissue oedema. Cytological examination of fine-needle aspirates showed marked neutrophilic and moderate macrophagic inflammation with evidence of fungal hyphae. Histological examination of a bone biopsy revealed severe fibroplasia and fibrosis associated with mixed inflammatory infiltrates, and Grocott-Gomori's methenamine silver (GMS), and Periodic acid-Schiff (PAS) staining confirmed the presence of fungal hyphae. Bone biopsy and urine cultures yielded fungal growth, which was morphologically identified as <i>Penicillium</i> spp. Molecular identification, based on amplification and sequencing of the nuclear ITS region, β-tubulin, and calmodulin genes from urine and biopsy samples, confirmed the isolate as <i>Penicillium labradorum</i>. The dog was treated with itraconazole (11 mg/kg). Approximately 190 days after the initial diagnosis, the dog died; necropsy was not performed because owner consent was not granted. Disseminated fungal infections are often associated with a poor prognosis due to delayed diagnosis. This case highlights that fungal infections should always be considered in the differential diagnosis of bone lesions in dogs.