A Canine Case of Nocardia africana Infection Detected by Matrix-Assisted Laser Desorption Ionization—Time-of-Flight Mass Spectrometry

Nocardiosis, a rare infectious disease in dogs and cats, is caused by Gram-positive aerobic actinomycetes of the genus Nocardia. A one-year-old castrated male Great Dane was presented with clinical signs of an ulcerated nodule on the right ear, which was observed after two weeks of treatment with cyclosporine and prednisolone due to idiopathic hepatitis. Cytological examination revealed pyogranulomatous inflammatory cells and blanched filamentous rods. To detect infectious agents, serosanguinous discharge of the nodule was subjected to bacterial and fungal cultures. For phenotyping of the infectious agents, colonies on blood agar culture plates were further analyzed by matrix-assisted laser desorption ionization (MALDI)-time-of-flight (TOF) mass spectrometry (VITEK MS). The MALDI-TOF spectra were identified as N. africana. Thus, the present case was diagnosed as cutaneous nocardiosis. The skin lesions of ulcerated nodules with fistulous tracts were gradually resolved by the administration of meropenem (8 mg/kg TID, IV) and doxycycline (5 mg/kg BID, PO). Although complete resolution of the skin lesions was observed on day 91 after the initial presentation, single administration of doxycycline was continued until day 198 after the initial presentation to prevent recurrence. To the best of our knowledge, this is the first report of Nocardia africana infection in a dog. In addition, our results show that MALDI-TOF mass spectrometry analysis could be a useful tool for the detection of Nocardia. spps.