Intraocular protothecosis: a case report and literature review

Protothecosis is an extremely rare infectious disease in humans caused by achlorophyllous algae within the genus Prototheca, which is present in many natural environments. To date, very few cases of ocular involvement have been reported.

We present the case of an immunocompetent patient with progressive loss of visual acuity in the right eye and with a history of cataract surgery in the same eye 5 years before. Ocular examination revealed numerous whitish retrolental deposits in the anterior chamber. A vitrectomy was performed and samples of vitreous humour, vitreous snowbank, and anterior chamber fibrin were cultured. After 48 h, yeast-like colonies were obtained and identified by proteomic techniques (MALDI-TOF) as Prototheca wickerhamii, an identification that was confirmed at a reference centre. In the in vitro susceptibility testing, low minimal inhibitory concentrations (MICs) were obtained for amphotericin B, posaconazole, isavuconazole, itraconazole, and voriconazole. The highest MIC values were obtained for fluconazole, 5-fluorocytosine, and echinocandins (caspofungin, micafungin, and anidulafungin). Following vitrectomy and combined treatment with corticosteroids, posaconazole, and topical anti-inflammatories, the patient's condition improved, although with reduced visual acuity.

To date, there have been very few reported cases of protothecosis affecting the eye. The most common sample is usually a corneal scraping, and the microbiological diagnosis is based on the macro- and microscopic morphological features of the alga, confirmed using proteomic or molecular techniques. Treatment combines surgical techniques, antifungals, and steroids, with good outcomes in most cases.