Successful treatment of the first reported case of Prototheca wickerhamii infection in a dog living in Tasmania, Australia.

Canine protothecosis is an uncommon opportunistic infection, most frequently reported in warm, humid climates. In dogs, it typically presents as disseminated disease following primary colonic involvement and carries a poor prognosis for clinical cure. No standardised treatment protocol exists in veterinary medicine. Regimens that maintain an acceptable quality of life often incorporate posaconazole, while amphotericin B may be used with curative intent in selected cases. We report the first documented case of localised cutaneous protothecosis due to Prototheca wickerhamii in a dog from Tasmania, Australia, together with its successful management. A 2-year-old neutered male Chihuahua cross presented with painful swelling and ulceration of the metacarpal and metatarsal pads, resulting in marked lameness. Diagnosis was established by cytology, histopathology, culture and MALDI-ToF mass spectrometry on samples from affected pads. Three sequential treatment protocols were trialled: (i) modified pulsed itraconazole therapy, (ii) oral posaconazole and (iii) intralesional amphotericin B deoxycholate. Itraconazole was ineffective. Posaconazole led to the resolution of clinical signs, although ongoing therapy was required, and relapse occurred after cessation of therapy. Subsequent treatment with intralesional amphotericin B achieved sustained clinical remission, consistent with sustained clinical remission and possible cure. This case expands the recognised geographic and clinical spectrum of canine protothecosis, documenting infection in a temperate region and in a localised cutaneous form. It highlights the importance of considering protothecosis in atypical dermatological presentations and supports the use of posaconazole for disease control and amphotericin B, specifically intralesional administration, for definitive therapy in clinical veterinary practice settings.