Lethal infection by a previously unrecognised metazoan parasite

Background New microbial pathogens or variant clinical manifestations of known organisms may be first found in immunodeficient patients. An HIV-infected man developed a rapidly-enlarging abdominal mass, suggestive of a neoplasm, that subsequently invaded his liver and caused death. Initial studies showed unusual tissue morphology that could not be matched with any known disease process. Methods Tissues obtained from biopsy at laparotomy and necropsy were studied by light microscopy, immunohistochemistry, electron microscopy, and broad-range ribosomal DNA-amplification and sequence analysis. Findings Tissue lesions were characterised by peculiar cytoplasmic sacs containing minute cells with very prominent nucleoli. The pathological process was recognised as a parasitic infection, although its features were different from those of any known eukaryotic pathogen. Phylogenetic analysis of a 357 bp 18S rDNA sequence amplified directly from the involved tissue indicated that the causative agent was a previously-uncharacterised cestode. Interpretation Fatal disease produced by this newly recognised cestode may not be limited to immunodeficient hosts. Awareness of this metazoan infection may allow early diagnosis—by morphology and DNA sequence analysis—and perhaps successful treatment of subsequent cases.