LETHAL INFECTION BY A PREVIOUSLY UNRECOGNIZED 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, suggest ive of a neoplasm, that subsequently invaded his liver and caused deat h. 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, im munohistochemistry, electron microscopy, and broad-range ribosomal DNA -amplification and sequence analysis. Findings Tissue lesions were cha racterised by peculiar cytoplasmic sacs containing minute cells with v ery prominent nucleoli. The pathological process was recognised as a p arasitic 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 th at the causative agent was previously-uncharacterised cestode. Interpr etation Fatal disease produced by this newly recognised cestode may no t be limited to immunodeficient hosts. Awareness of this metazoan infe ction may allow early diagnosis-by morphology and DNA sequence analysi s-and perhaps successful treatment of subsequent cases.