The anthelmintic efficacy of thiabendazole and levamisole against inhibited Haemonchus contortus larvae in sheep

Authors: McKenna PB
Publication: New Zealand Veterinary Journal, Volume 22, Issue 9, pp 163-166, Sep 1974
Publisher: Taylor and Francis

Animal type: Livestock, Production animal, Ruminant, Sheep
Subject Terms: Alimentary system/gastroenterology, Animal remedies/veterinary medicines, Anthelmintics, Parasite control, Parasites - internal, Treatment/therapy, Nematode
Article class: Scientific Article

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Abstract: Inhibition in the parasitic develolpment of trichostrongylid nematodes is a commonly reported phenomenon (Michel, 1968) and its occurrence in Ostertagia ostertagi infections in cattle particularly well documented (Martin et al 1957; Michel, 1963; Anderson et al 1965; Armour et al 1969a, b;. Brunsdon, 1973). In this parasite inhibition occurs at the early fourth larval stage and of primary veterinary importance in the fact that, in contrast to normally developing larvae, such inhibited forms are insusceptible to all known amthelmintics (Armour, 1970). Inhibition at an early fourth stage is also a common feature of Haemonchus contortus infections in sheep (Muller, 1968; Connan, 1968, 1971; Blitz and Gibbs, 1972a, b) and it is generally assumed, by analogy with O. ostertagi, that such larvae are similarly refractory to anthelmintic treatment. There is, however, little direct evidence to support or refute this assumption. In New Zealand appreciable infections of inhibited H. contortus larvae have been recorded in sheep (McKenna 1973a, and unpublished observations) . Such larvae are considered by Blitz and Gibbs (1972a) to provide the primary source of overwintering infection in most temperate regions. Thus any anthelmintic capable of eliminating these inhibited forms may have important implications in the control of this parasite. Accordingly the following trial was undertaken to ascertain the efficacy of two anthelmintics, thiabendazole and levamisole, against inhibited H. contortus larvae in sheep.

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