title: Laboratory evaluation of aromatic essential oils from thirteen plant species as candidate repellents against Leptotrombidium chiggers (Acari: Trombiculidae), the vector of scrub typhus.
abstract: Scrub typhus, a rickettsial disease transmitted by several species of Leptotrombidium chiggers (larvae), is endemic in many areas of Asia. The disease is best prevented by the use of personal protective measures, including repellents. In this study commercially produced aromatic, essential oils of 13 plant species and ethanol (control) were tested in the laboratory for repellency against host-seeking chiggers of Leptotrombidium imphalum Vercammen-Grandjean and Langston (Acari: Trombiculidae). A rapid, simple and economic in vitro test method was used by exposing the chigger for up to 5 min. Repellency was based on relative percentages of chiggers attracted to test and control substances. Four of the 13 essential oils showed promise as effective repellent against L. imphalum chiggers. Syzygium aromaticum (clove) oil exhibited 100% repellency at 5% concentration (dilution with absolute ethanol), whereas Melaleuca alternifolia (tea tree) oil exhibited 100% repellency at 40% concentration. Undiluted oils of Zingiber cassamunar (plai) and Eucalyptus globules (blue gum) exhibited 100% repellency. Of the remaining nine essential oils, only 100% Pelargonium graveolens (geranium) exhibited >50% repellency (viz. 57%). Styrax torkinensis (benzoin) oil did not exhibit any repellency. These findings show that several aromatic, essential oils of plants may be useful as chigger repellent for the prevention of scrub typhus. Syzygium aromaticum oil may be safer and more economical to prevent chigger attacks than commercially available synthetic chemicals, such as DEET that may have harmful side effects.
authors.affiliation: Department of Parasitology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand. sipes@mahidol.ac.th
authors.forename: Praphathip
authors.initials: P
authors.lastname: Eamsobhana
authors.forename: Adisak
authors.initials: A
authors.lastname: Yoolek
authors.forename: Wittaya
authors.initials: W
authors.lastname: Kongkaew
authors.forename: Kriangkrai
authors.initials: K
authors.lastname: Lerdthusnee
authors.forename: Nittaya
authors.initials: N
authors.lastname: Khlaimanee
authors.forename: Anchana
authors.initials: A
authors.lastname: Parsartvit
authors.forename: Nat
authors.initials: N
authors.lastname: Malainual
authors.forename: Hoi-Sen
authors.initials: HS
authors.lastname: Yong
mesh_terms: D000818:Animals; D001096:Arachnid Vectors / Q000187:drug effects*; D007302:Insect Repellents / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects; D008924:Mite Infestations / Q000517:prevention & control; D009822:Oils, Volatile / Q000494:pharmacology*; D010938:Plant Oils / Q000494:pharmacology*; D012612:Scrub Typhus / Q000517:prevention & control; D014324:Trombiculidae / Q000187:drug effects*
chemical_list: D007302:Insect Repellents; D009822:Oils, Volatile; D010938:Plant Oils