Successful treatment of multifocal pedal Prototheca wickerhamii infection in a feline immunodeficiency virus-positive cat with multiple Bowenoid in situ carcinomas containing papillomaviral DNA sequences

Abstract

Case summary: A 16-year-old, castrated male, feline immunodeficiency virus (FIV)-positive, domestic shorthair cat developed multiple skin lesions. Most of these were Bowenoid carcinoma in situ and contained DNA sequences consistent with Felis catus papillomavirus type 2. Two additional lesions that developed in the skin and subcutaneous tissues between the digital and carpal pads on the left forelimb and right hindlimb were shown by cytology, histology and culture to be caused by Prototheca wickerhamii. These lesions failed to improve in response to systemic therapy treatment with itraconazole, but excision by sharp en bloc resection with follow-up oral itraconazole therapy proved curative for one lesion, although the other lesion recurred, necessitating a second surgery.

Relevance and novel information: This is only the second reported case of feline protothecosis from Australia and the first case that has been cultured and identified to the species level. Also of great interest was the presence of multiple papillomavirus-associated neoplastic lesions, which may have afforded a portal of entry for the algal pathogen and the cat's positive FIV status; the latter might have impacted on both viral and algal pathogenesis by effects on immunocompetence.

Figure 1

Protothecal lesion left fore: progressive increase in size over 5 months, from (a) when first noticed, through to (b) and then (c), the day of surgery. (d) At 3 months after surgery, the main pad remains, and there is a space where the lesion and the two toes were removed

Figure 2

Squamous cell carcinoma that likely arose within a Bowenoid in situ carcinoma: multiple densely packed trabecular of dysplastic epidermal/basaloid like cells infiltrate from an ulcerated surface into the dermis

Figure 3

Left fore biopsy: the epidermis is indicated by an asterisk. Multiple-to-coalescing infiltrates of macrophages and neutrophils within the dermis

Figure 4

High power view of lesion shown in Figure 3. The arrows indicate some of the spherical bodies within macrophages, and the inset shows staining of these bodies with Grocott’s methenamine silver stain

Figure 5

(a) Fine-needle aspirate preparation stained with Diff-Quik of left fore lesion showing macrophages, some multinucleate (arrow) containing large numbers of spherical algal bodies. (b) Unstained suspension of a cultured colony of Prototheca wickerhamii organisms. Note spherical spores containing variable numbers of sporangia