Prospective questionnaire and sample collection, and in vitro laboratory assay and analyses.
1) To identify the presence of insecticide resistance in donkey lice, 2) to identify risk factors for pediculosis, 3) to develop a useful tool for diagnosing and estimating louse burden, 4) developing targeted selective treatment, 5) develop novel methods for controlling lice in donkeys.
A strong seasonal pattern of louse infestation was observed, with the highest number of donkeys infested in winter (Oct-Mar); with more than 80% of the animals were infested in the winter months. A significant age variation in lice infestation was also observed; young and old donkeys of age less than 4 years and greater than 30 yrs, respectively, were found infested with more lice than middle aged animals. The axilla and supraorbital fossa were identified as being the sites most commonly populated by live lice in both housed and outdoor donkeys (P<0.05). In addition, the presence of lice eggs in the first 2cm of the coat is a good indicator of an active infestation. Donkeys’ hair length was positively correlated with the presence of lice (P<0.05) but not with the number of lice each donkey carried (P=0.1). Excoriation consistent with hair fibre shortening was indicative of pediculosis and the amount of this type of lesion was positively correlated with louse burdens. However, more severe dermal rub lesions, such as alopecia, showed no association. Clipping in the winter was found to have no significant effect (P=0.15) on louse abundance examined after 2 or more weeks clipping; however, in the summer months clipping had a detrimental effect on louse populations.
The efficacy study revealed a high level of tolerance to permethrin ((SwitchTM, VetPlus Ltd, 4% (w/v) and cypermethrin (DeosectTM, Pfizer Ltd., 0.1% (w/v) consistent with resistance development. In vitro contact assays showed that 4% permethrin and cypermethrin resulted in less than 30% louse mortality after 24 h exposure. On the other hand, tea tree and lavender essential oils were identified as clinically and statistically significant (P<0.05) methods of louse control used at 5% concentration as a topical grooming spray.