Friday, March 01, 2013

Good and bad news for donkey lice

Lice can be a problem for donkeys, especially in older or debilitated animals.

Lice are obligate parasites, passing their whole life cycle on the host. This makes them easier to control, but only if they are susceptible to the anti-parasitic products used to control them. Unfortunately, recent work suggests that donkey lice may be developing resistance to commonly used treatments.

Lauren Ellse, Faith Burden and Richard Wall studied the value of pyrethroid-based insecticides on a population of donkey lice. They found a high level of pyrethroid tolerance in the lice tested, and suggested that this was likely to reflect the development of resistance.

In laboratory tests, they assessed the effect of cypermethrin and permethrin on chewing lice (Bovicola (Werneckiella) ocellatus ) collected from donkeys.

They compared the efficacy with that of diazinon, an organophosphate compound to which the lice were unlikely to have been exposed previously.

Neither permethrin, nor cypermethrin, (at concentrations recommended for use on animals) had any significant effect on mortality of B. ocellatus. Combining cypermethrin and permethrin with piperonyl butoxide (which may enhance their activity) did not make them any more

In contrast, 0.04% diazinon caused 70% mortality within 4 hours and 100% mortality after 24 hours exposure.

Another study raised the possibility of using essential and non-essential oils in the control of biting lice.

Rose Talbert and Richard Wall examined the toxicity of six essential plant oils to the chewing louse, B ocellatus collected from donkeys,

They found that tea-tree, lavender, peppermint, eucalyptus and clove bud showed high levels of toxicity to lice.

They suggest that these botanical products may offer environmentally and toxicologically safe, alternative veterinary treatments for the control of ectoparasitic lice. 

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