Endoparasiticides - Donkey

Interval dosing with potent, broad-spectrum anthelmintics used for horses is also suitable for donkeys (Trawford, 2004). The epidemiology, pathophysiology, clinical findings and treatment of parasitic infections in donkeys are described in detail the parasite section. Further information on antiparasitic treatment of working donkeys outside the UK is given in Exotic Infections - Donkey section.

Three principal chemical classes of anthelmintics (macrocyclic lactones, benzimidazoles and tetrahydropyrimidines) are used most commonly.

Macrocyclic Lactones

Macrocyclic lactones (e.g. ivermectin, moxidectin) are highly lipophilic and are distributed widely and eliminated slowly, thus producing persistent anthelmintic activity. Ivermectin and moxidectin have a broad spectrum of activity and high efficacy against the adult stages of the major parasites of the horse with the exception of tapeworms. Moxidectin suppresses faecal worm egg output for longer than ivermectin, due to in part to physicochemical differences between the two compounds. Ivermectin has only limited activity against fourth-stage cyathostome larvae and variable activity against fourth-stage ascarids. Moxidectin is fairly ineffective against bots (Gasterophilus spp. larvae).

Dictyocaulus arnfieldi alone rarely causes clinical problems in donkeys, although it may exacerbate respiratory infections due to other causes. Due to the reported incidence of this parasite in donkeys, particularly when they are co-grazed with horses, where lungworm can cause significant clinical problems, a general control strategy (e.g. with ivermectin) is recommended.

Although macrocyclic lactones are marketed as endectocides for ruminants and dogs, the formulations approved for use in the donkey or the horse have no label claim for efficacy against lice, mites or ticks. The macrocyclic lactones are extremely safe in mammals. However, moxidectin can produce side effects (neurological signs) in animals with insufficient adipose tissue, e.g. in young foals or emaciated animals.

Benzimidazoles

The benzimidazoles (e.g. fenbendazole, oxfendazole, mebendazole) bind nematode tubulin and have a slow onset of the anthelmintic effect relative to anthelmintics that disrupt parasite neurotransmission (e.g. the macrocyclic lactones).

Fenbendazole and mebendazole have a broad spectrum of activity against adult strongyles (in the absence of resistant cyathostome populations), ascarids and lungworm but NOT tapeworm or bots.

The benzimidazole triclabendazole is effective against liver fluke.

Tetrahydropyrimidines

Tetrahydropyrimidines (e.g. pyrantel embonate) are active against adult and luminal stages of strongyles and ascarids but have only LIMITED efficacy against migrating larval parasites and NO activity against bots. Double dose rates can be used to treat tapeworms.

References

• Horspool, L. (2008) Clinical pharmacology In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) The Professional Handbook of the Donkey, 4th edition, Whittet Books, Chapter 12
• Trawford, A.F. (2004). ‘Prescribing for donkeys’. The Veterinary Formulary. 6th edition. Y. Bishop (ed). The Pharmaceutical Press, London.

PHARMACOLOGY - DONKEY