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

Abstract

Background: 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.

Case report: 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. A 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 died shortly after admission to the intensive care unit. The immediate cause of death was bronchopneumonia. During the autopsy, an extensive involvement of the right middle cranial fossa was found, with destruction of the squamous and petrous parts of the temporal bone.

Results: We identified adult, larval, and egg stages of a free-living nematode in the antemortem external auditory canal tissue mass and 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.

Conclusions: 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 nematode's size and anatomical features, and the clinical presentation and duration of illness, prompted the consideration of an alternative species. We speculate that an initial bacterial otitis externa provided the opportunity for colonization by the nematode from an environmental source and subsequent invasion.

Keywords: Cephalobus cubaensis; central nervous system; free-living nematode; meningoencephalitis.

Figure 1

Antemortem computed tomography (CT) brain scans. Arrows indicate respective lesions. (A) Non-enhanced CT showing bony destruction and erosion of the right-side mastoid bone and facial nerve canal, the petrous and squamous temporal bones, and zygomatic process. (B) Non-enhanced CT at orbital cavity level showing extracranial soft tissue swelling and temporal bone erosion. (C) Contrast-enhanced CT demonstrating the hyperdense left parietal parenchymal brain lesion with surrounding edema that extends inferiorly, shown in (D).

Figure 2

Pathological features at autopsy. (A) Extradural necrotic material in the right side of the middle cranial fossa base and external auditory meatus. (B,C) Histopathological images of brain tissue, showing nematode adults (A), larvae (L), and eggs (E) in various section planes (arrows) and a mixed inflammatory infiltrate (H&E stain; bars = 100 µm).

Figure 3

Free-living Cephalobus cubaensis nematodes in ear canal exudate sample. (A) Low-power view, showing adults, larvae, and eggs, standard illumination. (B) Adult female and larval stages, interference contrast illumination. Note the rhabitiform single-bulb esophagus (arrow). (C) Adult female stage, with egg in uterus; free eggs in the exudate. (D) Embryonated egg. All bars = 100 µm.

Figure 4

Maximum likelihood 18S rRNA phylogenetic tree showing Cephalobus cubaensis’ relationship to related species with bootstrap support above 70% (GenBank accession numbers in parentheses). The isolate sample in this study is in black text. The scale bar represents the inferred substitutions per nucleotide position. Outgroup is Drilocephalobus species (green text).