Repellent activity of natural products to the Lone Star tick, Amblyomma americanum

Authors: LE MAUFF, ANAIS - University Of Florida; Norris, Edmund; Li, Andrew; SWALE, DANIEL - University Of Florida

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2024
Publication Date: 5/6/2024
Citation: Le Mauff, A., Norris, E.J., Li, A.Y., Swale, D.R. 2024. Repellent activity of natural products to the Lone Star tick, Amblyomma americanum. ACS Infectious Diseases. 17:202. https://doi.org/10.1186/s13071-024-06246-0.
DOI: https://doi.org/10.1186/s13071-024-06246-0

Interpretive Summary: The Lone Star tick, Amblyomma americanum is of relevance to human health due to a variety of pathogenic organisms transmitted to humans during feeding events, which underscores the need to identify novel approaches to prevent tick bites. Thus, the goal of this study was to test natural and synthetic molecules for repellent activity against ticks in spatial, contact, and human fingertip bioassays. To test the ability to translate these non-host assays to efficacy when used on the human host, we quantified repellency using a finger-climbing assay that quantified distance traveled on human skin. TCA, nootkatone, and DEET were equally effective in the fingertip assay and patchouli oil was the only natural oil that significantly repelled ticks. Interestingly, repellent potencies from the fingertip assay was negatively correlated to activity observed in the spatial or contact bioassays. These results indicate that select natural products are promising repellents against ticks and potentially other public health arthropods.

Technical Abstract: The Lone Star tick, Amblyomma americanum is of relevance to human health due to a variety of pathogenic organisms transmitted to humans during feeding events, which underscores the need to identify novel approaches to prevent tick bites. Thus, the goal of this study was to test natural and synthetic molecules for repellent activity against ticks in spatial, contact, and human fingertip bioassays. Concentration response curves after contact exposure to TCA led to a concentration required to repel 50% of ticks (EC50) of 5.6 µg/cm2, which was found to be 5- and 7-fold more active than DEET and nootkatone, respectively. For contact repellency, the rank order of repellency at 50 µg/cm² for natural oils was clove > geranium > oregano > cedarwood > thyme > amyris > patchouli > citronella > juniper berry > peppermint > cassia. For spatial bioassays, TCA was approximately 2-fold more active than DEET and nootkatone at 50 'g/cm2, but were not significantly different at 10 'g/cm2. In spatial assays, thyme and cassia were the most active compounds tested with 100% and 80% ticks repelled within 15 minutes of exposure respectively and was approximately 2-fold more effective than DEET at the same concentration. To test the ability to translate these non-host assays to efficacy when used on the human host, we quantified repellency using a finger-climbing assay that quantified distance traveled on human skin. TCA, nootkatone, and DEET were equally effective in the fingertip assay and patchouli oil was the only natural oil that significantly repelled ticks. Interestingly, repellent potencies from the fingertip assay was negatively correlated to activity observed in the spatial or contact bioassays. Together, these suggest TCA, which is naturally derived, is a promising candidate for a tick repellent that is comparable to commercialized tick repellents and further, that assay design is critical for tick repellent development to ensure translation from lab to field.