In vitro bioassays for plant extracts with tick-repellent and acaricidal properties: a systematic review and meta-analysis

Ticks are arthropods which transmit pathogens to humans and animals causing great economic losses [1]. Chemical-based anti-tick measures include pyrethroids, organophosphates, amitraz and avermectins with significant costs, resistance development and environmental impacts [2]. Plant-based alternatives may have high efficacy, low toxicity and reduced environmental impacts [3]. We collated peer-reviewed articles on plants with tick-repellent and/or acaricidal properties through literature searches in veterinary databases and conducted meta-analyses on the outcomes.

Bioassays used include: tick climbing repellency, olfactometry, larval-packet and immersion tests [4]. Significant differences exist in the methods and their outcomes. Meta-analysis was conducted using the Fixed-effect model in an Excel programme. Using a total of 1,428; 1,924; 574; 281 and 68 events, the median efficiency value (MEV) for acaricidal, larvicidal, egg hatching inhibition, inhibition of oviposition, repellency, acaricidal effects of the Lamiaceae and Asteraceae families were 80.12% (CI_95%: 79.20 – 81.04), 86.05% (CI_95%: 85.13 – 86.97), 83.39% (CI_95%: 82.47 – 84.31), 53.01% (CI_95%: 52.08 – 53.93), 92.00% (CI_95%: 91.08 – 92.93), 80.79% (CI_95%: 79.87 – 81.71) and 48.34% (CI_95%: 47.42 – 49.26) respectively.

The plants displayed very good to excellent acaricidal, larvicidal, egg hatching inhibition, and repellency inhibition effects but relatively poor inhibition of oviposition. However, there was minimum to wide disparities compared to the MEV for each category. Approximately 63% and 69% of all the plants evaluated for acaricidal and larvicidal assays out-surpass the MEV for all plants assayed respectively. While ethnoveterinary plants hold huge potential as parasiticides, standardization of components, extraction techniques and experimental design is mandatory, as well as mammalian toxicological profiling and excipient development. Similarly, investigation of the residual activities and shelf-life of these plants are required to maximise their potential. Translational research should also be used to convert in vitro studies to in vivo tests and the possibility of drug resistance associated with these promising alternatives should be explored.

Acknowledgements: Financial support from Technology and Innovation Agency (TIA) in collaboration with Council for Scientific and Industrial Research (CSIR, Pretoria), University of Pretoria, L'Oreal-UNESCO Fellowship and the Schlumberger Faculty for the Future Foundation is thankfully acknowledged.

Keywords: acaricidal, larvicidal, egg hatching inhibition, repellency, bioassays, medicinal plants.

References:

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