Intra-aural tick bite causing unilateral facial nerve palsy in 29 cases over 16 years in Kandy, Sri Lanka: is rickettsial aetiology possible?

Background: Over the last two decades intra-aural tick infestation (otoacariasis) has been a common occurrence in the hilly central region in Sri Lanka. Very occasional detection of isolated unilateral facial nerve palsy associated with otoacariasis attributed to toxin damage of the nerve prompted us to study the clinico-epidemiology and aetio-pathology of the problem. Methods: All cases having isolated unilateral facial nerve palsy associated with otoacariasis presented to, Ear Nose and Throat clinic at General Hospital Kandy, Sri Lanka from 2001 to 2016 were included in the study. The facial palsies were assessed with nerve conduction studies and, harvested ticks were identified. Results: There were 29 patients with mean age of 46 years (range 22-76 years) with male to female ratio of 1:1.9. First 12 patients without specific treatment took 1-55 months for recovery and 4 had axonal degeneration. Last 5 patients were treated with doxycycline and recovered in 4 weeks. They had strong sero-conversion of immunofluorescence antibodies against spotted fever rickettsioses and the tick harvested from the last patient was PCR positive for rickettsial DNA. Identified ticks belonged to Dermacentor, Amblyomma, Rhipicephalus and Hyalomma species. Conclusions: On contrary to popular toxin theory, we were able to demonstrate treatable rickettsial aetio-pathology as the cause of otoacariasis associated lower motor facial palsy in Sri Lanka.