Naturally occurring tetanus in a rabbit (Oryctolagus cuniculus) associated with Psoroptes cuniculi otitis

Background: Natural infection with tetanus in rabbits is not well studied, despite the fact that rabbits have been used for more than 100 years as a laboratory model of tetanus infections. Case Description: An adult male intact domestic rabbit (Oryctolagus cuniculus) was presented for lethargy and bilateral crusting with purulent discharge from the external ear canals. Cytology of the aural crusts confirmed the presence of Psoroptes cuniculi and Gram stain of the purulent material confirmed concurrent mixed bacterial otitis with a large number of nonsporulating Gram positive rods. Eight hours after presentation, the animal progressed to full body rigidity and increased respiratory effort. Tetanus was suspected based on clinical appearance, but presumptive treatment with tetanus antitoxin was declined and the patient was euthanized. Necropsy and histopathology confirmed an intact tympanum bilaterally, and no evidence of otitis media/interna or intracranial disease. Anaerobic culture of the purulent aural debris was positive for Clostridium sp. 16S rRNA gene partial sequencing on the anaerobic bacterial isolate showed 87% homology to Clostridium tetani. PCR analysis confirmed the presence of the neurotoxin gene, TetX, and the bacteria's origin as C. tetani. Western blotting and ELISA analyses did not detect free neurotoxin. Conclusions and Case Relevance: This case is unique to veterinary medicine in its confirmation of association of a C. tetani infection with Psoroptes cuniculi and otitis externa rather than associated with a penetrating injury or otitis media. Furthermore, naturally occurring tetanus in rabbits is underreported.