Dimethicone for hard tick otoacariasis: a rapid, safe alternative to conventional agents

Introduction

The external auditory canal (EAC) in most animals, including humans, is susceptible to infiltration by arachnids—particularly hard ticks. In endemic regions around the world, such as in Sri Lanka, intra-aural tick infestation (otoacariasis) is a common ear nose and throat (ENT) outpatient presentation; while documented presentations here in Australia are less frequent, clinician awareness remains essential (1). Typical symptoms include otalgia, ear itching, tinnitus, and/or otorrhoea. Otoacariasis can cause significant patient distress and carries a risk of secondary complications, including rickettsial infections. Rare but serious sequelae include otitis externa, tympanic membrane perforation, and facial nerve paralysis associated with tick-borne disease (2,3). Although traditional chemical agents such as lidocaine and various oils are widely used, they often fail to achieve rapid or reliable tick inactivation (4). Furthermore, while direct manual removal may be feasible in other anatomical locations, the EAC and tympanic membrane represent confined and delicate structures, making safe tick removal technically challenging and increasing the risk of iatrogenic injury.

There are approximately 71 species of ticks, both hard and soft bodied, that have been identified in Australia (5). Hard bodied ticks (Ixodidae species) are of greater clinical significance due to their virulence and ability to cause local and systemic disease—they can be identified by their hard shell (scutulum) and small size of around 1 mm (1). Fortunately, the majority of Australian ticks do not typically feed on humans however notable varieties include paralysis ticks, such as Ixodes holocyclus and Ixodes cornuatus, the ‘brown dog tick’, Rhipicephalus sanguineus and the ‘ornate kangaroo tick’, Amblyomma triguttatum triguttatum (5). Comparatively, in endemic regions such as Sri Lanka, common ticks include Amblyomma integrum (nymphal stage), Rhipicephalus haemaphysaloides, Rhipicephalus sanguineus, Hyalomma brevipunctata, and Hyalomma marginatum (2). Hard ticks undergo a life cycle comprising egg, larval, nymphal, and adult stages, with each active stage requiring a blood meal. Attachment occurs via barbed mouthparts (the hypostome), often reinforced by a cement-like salivary secretion. During prolonged feeding, ticks secrete saliva containing anticoagulant and immunomodulatory factors that facilitate sustained attachment and reduce host inflammatory response—a mechanism particularly relevant to concealed otologic infestations (6).

Ticks are exceptionally resilient creatures and are well adapted to difficult environments with the ability to survive low oxygen conditions, go without food (host blood) for up to 18 weeks and withstand temperatures up to −18 ℃ (7,8).

Ticks exhibit a similar respiratory system to other insects, consisting of spiracles, closeable valves which serve as the opening for oxygen to enter the respiratory tube system (9). These spiracles are located inferolaterally on either side of the tick’s body and through their lid-like structure, prevent fluid entry and promote virulence. The aperture of the spiracle can be modulated by the tick which therefore makes it difficult to inactivate ticks using conventional liquids (10). Galbreath studied the spiracle structure in Costelytra zealandica larvae and found that the protective lid-like spiracle architecture effectively prevents airway flooding, which may explain the inefficacy of some fluids in killing ticks (10).

Otoacariasis is relatively rare and the clinical presentation varies. A review of Indian subjects found that patients with otoacariasis universally complained of pain, with only 12.7% experiencing ear bleeding. In this cohort, ticks were found attached to the EAC in 86.5% of cases while the remainder were found on the tympanic membrane (11). A retrospective study at Teaching Hospital Ratnapura, Dilrukshi et al. identified Rhipicephalus haemaphysaloides and Amblyomma integrum as the most common species associated with otoacariasis, accounting for 70.8% of cases (2).

Ticks have been known to cause both local and systemic effects on the host. Local effects include local allergic reaction, urticaria or blistering and temporary alopecia. Furthermore, foreign body reaction or subsequent bacterial infection may occur if there is incomplete removal of the tick’s mouthparts—of particular importance when considering the EAC and means of killing/removal (1). Systemic effects include hypersensitivity reactions such as anaphylaxis, symmetrical flaccid paralysis and possible transmission of tick-borne diseases (1). Kularatne et al. documented 29 cases of facial nerve palsy associated with intra-aural tick bites in Kandy, Sri Lanka. Their findings suggest a rickettsial etiology transmitted by ticks (3).

Conventional methods for tick inactivation and removal include manual extraction under local or general anesthesia in conjunction with or without chemical agents which aim to immobilise or kill the tick prior to removal. As mentioned however, ticks demonstrate resistance to most chemical agents due to their hard shell and through adjustment of the spiracle (12). Orobello et al. assessed the efficacy of common reagents in killing ticks within the EAC. Tested substances included acetone, isopropyl alcohol, and 95% ethanol where tick inactivity/death was recorded at 9.3, 18, and 18 minutes respectively (4). Notably, 4% lidocaine was also tested and failed to kill the tick even after 30 minutes of exposure. The study did not include any oil-based agents (4). Previously work by Scherk-Nixon et al. has also demonstrated that otic preparations without miticidal active ingredients were still effective in managing otoacariasis in cats—highlighting the potential of physical agents in treatment (13).

Dimethicone is a widely used organosilicon compound found in shampoos, contact lens fluids, and food additives. It is non-toxic and safe for human use. It offers a novel, potentially effective method of killing ticks due to its low surface tension and ability to penetrate the tick’s spiracle system, obstruct respiration and therefore safely kill the tick (14-16). This study aims to investigate whether dimethicone outperforms commonly used agents such as coconut oil, olive oil, and 2% xylocaine in inactivating hard ticks.

Methods

Reporting checklist

This study is reported according to the ARRIVE reporting guidelines (available at https://www.theajo.com/article/view/10.21037/ajo-25-61/rc).

Study design and tick collection

This laboratory-based experimental study used Rhipicephalus haemaphysaloides ticks collected from canines by a qualified veterinary surgeon. Only intact and active ticks were included.

A small feasibility pilot (3 ticks/group) was conducted to confirm assay performance and provide preliminary indication of between-group separation and variability; given the limited pilot size, the study was conservatively designed with 12 ticks per group to ensure robust estimation of efficacy while allowing for biological variability and potential tick loss.

Ticks were initially examined prior to allocation, and any individuals that were dead or visibly damaged were excluded; no additional exclusions occurred after randomisation.

Experimental procedure

A total of 48 ticks were randomly assigned to four treatment groups: dimethicone (n=12), olive oil (n=12), coconut oil (n=12) and 2% xylocaine (n=12). Olive oil and coconut oil were included as comparator (vehicle control) groups, representing commonly used non-active topical agents, while dimethicone and 2% xylocaine were evaluated as active interventions; a no-treatment control was not included as all groups required submersion to ensure consistent exposure. Randomisation was performed by thoroughly mixing all ticks in a single container and randomly selecting individual ticks for sequential assignment to each treatment group (n=12 per group).

Each tick was submerged in 3 mL of the test agent in a sterile petri dish and gently agitated using a probe. Ticks were observed under magnification. Inactivity and therefore death were defined as complete cessation of leg movement even after stimulation. To minimise potential confounding, all ticks were processed individually under identical testing conditions using the same exposure volume (3 mL), application technique (dropper), and observation criteria. Treatments were applied sequentially with ticks drawn from a mixed pool, and outcome measurement (time to inactivity) was performed immediately following exposure for each individual tick.

No formal blinding or randomisation of treatment order was undertaken. Given the ex vivo nature of the experiment and the short duration of each assay, environmental and order effects were considered minimal.

Data collection

Time to complete inactivity was recorded in seconds using a stopwatch. Observations and timing were performed by a single investigator per treatment group. Each investigator was responsible for observing and recording outcomes for one treatment group only. Investigators were not blinded to the treatment administered, as they were directly involved in applying the test agent. Assignment of investigators to treatment groups was performed by the lead investigator using random allocation. No inter-observer agreement or duplicate measurements were undertaken. Given the objective nature of the outcome (time to complete inactivity), the risk of observer bias was considered low. All data were recorded on excel and subsequently entered into Statistical Package for Social Sciences (SPSS) version 1.0.0.1406 for analysis.

Data analysis

Statistical analysis was performed using independent samples Welch’s t-tests to compare mean time to inactivity between dimethicone and comparator groups. Results are expressed as mean ± standard deviation. A P value <0.05 was considered statistically significant.

Ethical considerations

The collection and experimental testing of ticks were conducted in Sri Lanka. Ticks are invertebrates and do not fall under the definition of animals requiring ethical approval under the Australian Code for the Care and Use of Animals for Scientific Purposes, which mandates ethics review primarily for vertebrates and higher-order invertebrates (e.g., cephalopods) (17). Similarly, under Directive 2010/63/EU of the European Parliament and of the Council and the U.S. Animal Welfare Act, experimental use of invertebrates such as ticks does not require formal ethical clearance (18,19). Accordingly, no institutional animal ethics approval was required for this study.

Results

Mean time to inactivity varied across test groups with dimethicone outperforming all other agents (Figure 1). 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 (1,800±0 s)—with all comparisons reaching statistical significance (P<0.001).

Figure 1 Average time to tick inactivity following application of different substances.

Discussion

Dimethicone, due to its low surface tension and non-toxic nature, demonstrated significantly faster tick inactivation. It effectively penetrates the spiracular openings and blocks the respiratory system (9,15,16). This mechanism explains its superiority over more viscous oils like olive and coconut oil.

Our findings support previous conclusions by Orobello et al., who found that lidocaine was ineffective in tick eradication even after prolonged exposure (4). While oil-based agents have some efficacy, their action is delayed. Dimethicone bridges this gap by combining rapid action with a favourable safety profile in non-otic applications.

From a clinical perspective, dimethicone could reduce the need for general anesthesia in outpatient settings and pediatric patients. Additionally, its rapid action may reduce the risk of tick body compression and pathogen release during removal—a key concern in tick-borne disease transmission (3,14).

Dimethicone is a widely used organosilicon compound present in shampoos, contact lens fluids, food additives, and topical antiparasitic formulations, where it has demonstrated a favourable safety profile with minimal systemic absorption (15,20). While it shows promise for potential utility in otolaryngologic practice, otic safety has not been directly evaluated. In particular, the possibility of middle-ear exposure in the presence of a tympanic membrane perforation or ventilation tube warrants caution, as topical agents introduced into the middle ear may carry a theoretical risk of ototoxicity (21,22). Although dimethicone-based products are readily available for human use, such as 4% dimethicone formulations for head lice treatment, these products are not designed or approved for otic administration and their excipients may not be suitable for use within the external or middle ear (23). Accordingly, while dimethicone appears promising compared with commonly used agents such as coconut oil, olive oil, and 2% xylocaine, further in vivo otologic safety and ototoxicity studies are required before routine clinical application can be recommended.

This study has several limitations. Firstly, it was conducted in a controlled laboratory setting and not in a clinical setting, as such it is not fully representative of the clinical environments of otoacariasis. Secondly, this research focused solely on a single tick species, Rhipicephalus haemaphysaloides, limiting the generalizability of the results to other tick species commonly involved in otoacariasis. Thirdly, no specific controls for treatment order or measurement order were implemented during data collection. Finally, the study did not directly assess the safety or efficacy of dimethicone within the ear. Therefore, further research should include a wider range of tick species and evaluate the applicability and safety of dimethicone in vivo, including assessment of potential adverse events, local tissue effects, and ototoxicity within the human ear, before progression to human clinical trials.

Conclusions

Dimethicone demonstrates rapid and consistent acaricidal activity, outperforming coconut oil, olive oil, and 2% xylocaine in tick inactivation. Given its efficacy and non-toxic safety profile, dimethicone has strong potential as a first-line agent in otoacariasis management, particularly in emergency and primary care settings.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the ARRIVE reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-25-61/rc

Data Sharing Statement: Available at https://www.theajo.com/article/view/10.21037/ajo-25-61/dss

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-25-61/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-25-61/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. No institutional animal ethics approval was required for this study because ticks are invertebrates and are exempt from mandatory ethics review under the Australian Code for the Care and Use of Animals for Scientific Purposes, Directive 2010/63/EU of the European Parliament, and the U.S. Animal Welfare Act.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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