An unusual case of granulomatous lymphadenitis due to Prototheca zopfii var. portoricensis in an immunocompetent man in China

SummaryBackgroundProtothecosis is an uncommon human infection caused by Prototheca. Prototheca spp can be considered as saprophytes, and in spite of their frequency in the environment, they are of low virulence and may cause chronic infection with low-grade inflammation in humans. At present, only three species are recognized: Prototheca wickerhamii, Prototheca zopfii and Prototheca stagnora. Of these, the former two have been associated with human disease. This study was an investigation of the clinical and microbiological features of a case of granulomatous lymphadenitis due to P. zopfii var. portoricensis in an immunocompetent man in China.MethodsWe report the case of a 39-year-old male, who presented with swollen lymph nodes, from which the organism was isolated and identified by the RapidID Yeast Plus test (Remel, Santa Fe, NM, USA) and PCR molecular analysis. The pathogenicity of the isolate was confirmed in a mouse model and antifungal drug susceptibility testing was carried out.ResultsThe pathogen was identified as Prototheca zopfii. The DNA sequence of the 18S SSU rDNA regions of the isolate strain were 100% (1205/1205) identical with Prototheca zopfii var. portoricensis. Antifungal susceptibility tests revealed that it was sensitive to amphotericin B, but resistant to 5-flucytosine, fluconazole, ketoconazole, and itraconazole. The patient responded to treatment with intravenous itraconazole and amphotericin B.ConclusionsBased on the patient's symptoms and microscopic evaluation, cultures, and molecular analyses of the isolate, granulomatous lymphadenitis due to P. zopfii var. portoricensis was diagnosed. P. zopfii var. portoricensis as a causative agent of human lymphadenitis in an immunocompetent case has not been reported, though a few cases of protothecosis have been reported in China. The real number of protothecosis cases may be greater than that reported in the literature. Thus, clinicians should be vigilant for any unknown cause of granulomatous lymphadenitis and should undertake an intensive histopathology, mycology examination, and even molecular analysis to rule out or confirm a potential Prototheca infection