Background: Otoacariasis, the infestation of the external auditory canal (EAC) by ticks, is a common presentation in endemic regions and an emerging clinical consideration in Australia. Conventional agents, including local anaesthetics and oils, often fail to rapidly inactivate hard ticks, potentially prolonging patient discomfort and increasing the risk of infectious complications. Dimethicone, a low-toxicity, low-viscosity organosilicon compound, has demonstrated efficacy against arthropods but has not been formally evaluated for hard tick otoacariasis. This study aims to investigate whether dimethicone outperforms conventional agents in inactivating hard ticks.
Methods: In a laboratory-based experiment, 48 Rhipicephalus haemaphysaloides ticks were randomly allocated into four treatment groups (n=12 per group): dimethicone, olive oil, coconut oil, and 2% xylocaine. Ticks were submerged in the test agent and observed under magnification, with time to complete inactivity recorded. Inactivity was defined as cessation of all leg movement despite stimulation. Data were analysed using Statistical Package for Social Sciences (SPSS), with between-group comparisons performed to assess differences in time to inactivity.
Results: Time to inactivity was significantly shorter in the dimethicone group (75.0±10.4 s) compared with olive oil (753.3±78.3 s), coconut oil (1,056.6±122.8 s), and 2% xylocaine, in which no inactivity was observed within the 1,800-second observation period (all comparisons P<0.001).
Conclusions: Dimethicone rapidly and reliably inactivated hard ticks in vitro, outperforming commonly used agents. This effect is likely mediated by its ability to penetrate the tick spiracular system and impair respiration. Given its favourable safety profile and rapid action, dimethicone may represent a practical option for managing otoacariasis in outpatient and emergency settings. Further in vivo studies are warranted to confirm clinical applicability in the Australian context.