Central Nervous System Infection by Free-Living Nematode Cephalobus cubaensis in a Human Host in Africa

Human central nervous system infections due to free-living nematodes, although extremely rare, are usually fatal. Immunodeficiency has not been a feature of most of these cases, unlike the situation pertaining to disseminated Strongyloides stercoralis infection. An elderly immunocompetent man presented with a history of tinnitus and otalgia, progressing to central nervous system involvement with confusion, weakness and other neurological signs. Examination revealed a unilateral external auditory canal soft tissue mass, and radiological evidence of ipsilateral temporal bone destruction and brain parenchymal disease. Biopsy of the ear canal mass revealed the presence of an unidentified nematode species, and treatment with anthelminthics was started. The patient’s clinical condition deteriorated and he demised shortly after admission to the intensive care unit. The immediate cause of death was bronchopneumonia. At autopsy extensive involvement of the right middle cranial fossa was found, with destruction of the squamous and petrous parts of the temporal bone. We identified adult, larval and egg stages of a free-living nematode in the ante-mortem external auditory canal tissue mass and in the post-mortem brain samples. Polymerase chain reaction assays, with Sanger and whole genome sequencing, identified Cephalobus cubaensis. This is a free-living species not previously known to be pathogenic to humans, although nematodes of the same genus have caused mastitis in horses. Microscopic appearance and the invasive behaviour of the pathogen evoked a putative diagnosis of Halicephalobus gingivalis, the most frequently reported free-living nematode infecting humans. However, this the nematode’s size and anatomical features, and the clinical presentation and duration of illness, prompted consideration of an alternative species. We speculate that an initial bacterial otitis externa provided the opportunity for colonisation by the nematode from an environmental source, and subsequent invasion.