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.
Description:
SUPPLEMENTARY MATERIAL : FIGURE S1. Time-lapse images of adult worm laying egg. FIGURE S2. Maximum likelihood 28S 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 comprises Cervidellus alutus and Acrobeles complexus (green text). TABLE S1. Primer sequences for nested PCR targeting the large nuclear subunit ribosomal RNA gene of cephalob nematodes. VIDEO S1. Otoscopy of the right external auditory canal, showing the exudative inflammatory tissue mass obstructing the canal. VIDEO S2. External auditory canal exudate cultured on blood agar with E. coli lawn, showing an adult gravid female nematode moving on the surface.
DATA AVAILABILITY STATEMENT : The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author.