A 12-year-old boy from Buenos Aires who had a January 2018 diagnosis of intermediate-risk pre-B acute lymphoblastic leukemia received an unrelated allogeneic HSCT in February 2022. A month after HSCT, the child was treated with antiviral therapy for reactivation of cytomegalovirus, adenovirus, and Epstein-Barr virus infections. Three months post-HSCT, under immunosuppressive therapy with tacrolimus (0.1 mg/kg/d), he received antimicrobial treatment with meropenem (60 mg/kg/d), linezolid (30 mg/kg/d), and liposomal amphotericin B (3 mg/kg/d) to combat prolonged fever and abdominal symptoms. Videoendoscopy of the upper digestive tract confirmed gastrointestinal graft-versus-host disease, and ultrasound showed splenomegaly with multiple rounded hypodense images in the spleen and liver. We also noted distension of the ileal and colonic loops, predominantly in the right colon, and ascites.

We treated the child with liposomal amphotericin B (3 mg/kg/d) to address persistent febrile symptoms and visceral lesions compatible with chronic disseminated candidiasis. Four months after HSCT, the child sought treatment for chronic diarrhea (>1 month) and abdominal pain. Prior to microbiological documentation, we prescribed empirical treatment of metronidazole (30 mg/kg/d), which produced no improvement of symptoms.

Figure

Figure. Enterocytozoon bieneusidetection in fecal sample and liver aspiration biopsy sample from a child with hematopoietic stem cell transplant, Argentina. A) Light microscopy of fecal samples after Weber’s modified trichome...

Coproanalysis revealed typical polymicrobial bacterial flora, with no detection of bacterial toxins, adenovirus, rotavirus, or parasites. Calcofluor White and Weber’s modified trichrome staining revealed structures compatible with microsporidian spores in single and serial fecal specimens (Figure, panels A, B). Analysis of liver aspiration biopsy samples rendered no conclusive results. On the basis of microscopic results, we immediately initiated albendazole treatment (400 mg/d) for microsporidiosis (7).

We conducted molecular biology studies based on fecal samples and liver aspiration biopsy samples. We determined E. bieneusi and genotype identification by using a nested PCR protocol that targeted the entire internal transcribed spacer and also amplified portions of the flanking large and small subunits of the ribosomal RNA (≈400 bp) gene (8,9) (Figure, panels C, D). We confirmed the presence of E. bieneusi genotype D based on Sanger sequencing using the inner-nested PCR primers (2). We named the nucleotide sequence generated BsAs1 and deposited it into GenBank (accession no. OP650902). Despite a decrease in diarrhea symptoms, the child died 18 days after initiation of albendazole treatment due to fulminant hyperacute lymphoproliferative syndrome, before identification of E. bieneusi was determined.

E. bieneusi has been reported commonly in cancer patients undergoing chemotherapy (1,3,4,10). We report a case of E. bieneusi genotype D microsporidiosis, with intestinal and hepatic localization, in a child with leukemia and immunosuppression after a bone marrow transplant in Argentina. Our findings highlight the need to incorporate microsporidiosis in the differential diagnosis of immunosuppressed children after transplant surgery, as well as for other patient populations at high risk for opportunistic infections. Our report also emphasizes the critical importance of microsporidia identification because albendazole is effective against some Encephalitozoon species but not against E. bieneusi (1,7). Genotyping isolates of clinical E. bieneusi may help to identify potential environmental sources. Although nitazoxanide could be used as an alternative treatment, fumagillin has a wider range of activity effectively targeting E. bieneusi (7). The unavailability of fumagillin for treating human infections in several countries, including Argentina, underscores the need for enhanced accessibility to microsporidia treatment options, especially for vulnerable populations.