Ferreira et al.
Identification of a non-host semiochemical from tick-resistant donkeys (Equus asinus) against Amblyomma sculptum ticks.
Ticks Tick Borne Dis. 2019, in press, doi:.org/10.1016/j.ttbdis.2019.02.006
The tick Amblyomma sculptum belongs to the A. cajennense complex and is widely distributed in the New World with a wide host range. This tick is the most important vector of Rickettsia rickettsii, the causative agent of Brazilian spotted fever in humans. Parasitism by A. sculptum causes skin damage on horses, reducing their market value. Donkeys (Equus asinus) seem to be resistant to A. sculptum and the authors advance the view that donkeys produce a natural repellent (a volatile semiochemical -naturally-occurring behavior modifying chemical) against this tick species. The authors have extracted chemical compounds from the sebum of donkeys and horses, and gas chromatography analyses revealed four compounds that were only present in the sebum from donkeys. One compound, (E)-2-octenal (also called trans-2-octenal, an aldehyde), showed repellent activity in a Y-tube olfactometer assay on A. sculptum nymphs, even in concentrations as low as 0.125 M in a behavioral assay with ticks. The (E)-2-octenal interfered with the attractiveness of ammonia, a known volatile host compound. (E)-2-octenal may have the potential to be used as a repellent for reducing A. sculptum populations on animals and humans.