Acaricidal activity of Melaleuca alternifolia (tea tree) oil: in vitro sensitivity of sarcoptes scabiei var hominis to terpinen-4-ol.
OBJECTIVE
To compare the acaricidal activity of Melaleuca alternifolia (tea tree) oil (TTO) and some of its individual active components on the itch mite Sarcoptes scabiei var hominis.


METHODS
In vitro acaricide sensitivity assessment.


METHODS
The Menzies School of Health Research laboratory, located near the Infectious Diseases Ward of the Royal Darwin Hospital, Australia, where patients are admitted and treated for crusted scabies.


METHODS
Scabies mites (S scabiei var hominis) were collected from a 20-year-old Aboriginal woman admitted to the Royal Darwin Hospital with crusted scabies. Interventions Within 3 hours of collection, scabies mites were placed in continuous direct contact with the TTO products and control acaricides and were observed at regular intervals.


METHODS
Percentage of mites dead at regular observation intervals between 5 minutes and 24 hours during continuous exposure to the TTO products and acaricides.


RESULTS
The 5% TTO and active component terpinen-4-ol were highly effective in reducing mite survival times. Statistically significant differences in mite survival curves were observed for 5% TTO, 2.1% terpinen-4-ol, 5% permethrin, and ivermectin (100 microg/g of Emulsifying Ointment British Pharmacopoeia 88). In vivo effectiveness was also observed.


CONCLUSIONS
Documentation of resistance against antiectoparasitic compounds is increasing. Reported S scabiei treatment failures with lindane, crotamiton, and benzyl benzoate, as well as likely emerging resistance to 5% permethrin and oral ivermectin, are of concern and advocate for the identification and development of novel acaricidal drugs. Tea tree oil is a membrane-active biocide extracted from the tree M alternifolia. It is a principal antimicrobial in a wide range of pharmaceuticals sold in Australia, with the main active component being oxygenated terpenoids. The results suggest that TTO has a potential role as a new topical acaricide and confirm terpinen-4-ol as the primary active component.
Walton
Shelley F
SF
Menzies School of Health Research, and Northern Territory Clinical School, Flinders University, Darwin, Australia. shelley.walton@menzies.edu.au
McKinnon
Melita
M
Pizzutto
Susan
S
Dougall
Annette
A
Williams
Edwina
E
Currie
Bart J
BJ
D000328:Adult; D000818:Animals; D005260:Female; D006801:Humans; D020128:Inhibitory Concentration 50; D007306:Insecticides / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D031650:Melaleuca; D008517:Phytotherapy; D012520:Sarcoptes scabiei / Q000187:drug effects*; D012532:Scabies / Q000188:drug therapy*; D020947:Tea Tree Oil / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use
D007306:Insecticides; D020947:Tea Tree Oil