The significance of inhibition in the parasitic development of abomasal nematodes in New Zealand sheep

Authors: McKenna PB
Publication: New Zealand Veterinary Journal, Volume 21, Issue 5, pp 98-102, May 1973
Publisher: Taylor and Francis

Animal type: Livestock, Production animal, Ruminant, Sheep
Subject Terms: Alimentary system/gastroenterology, Nematode, Parasites - internal
Article class: Scientific Article

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Abstract: Infective larvae of Haemonchus contortus when ingested by sheep normally undergo development through a series of moults to become sexually mature adults, a process that takes 14 to 15 days (Veglia, 1915). In some circumstances, however, such larvae may become arrested in their development at an early fourth larval stage 3 to 4 days following ingestion (Blitz and Gibbs, 1971). A similar phenomenon of arrested or inhibited development has also been recorded in Ostertagia circumcincta and Trichostrongylus axei infections in sheep; in the former again occurring at an early fourth stage, (Sommerville, 1953, 1954) and in the latter at a loosely defined “fourth larval stage” (Reid and Armour, 1972). The precise aetiology of inhibited development is, as yet, uncertain but a seasonal pattern of occurrence has been demonstrated indicating that inhibited larvae are most common in sheep during the winter months (Muller, 1968; Connan, 1968, 1971; Blitz and Gibbs, 1972b; James and Johnstone, 1967a, 1967b; Reid and Armour, 1972). It has also been shown that, though these inhibited forms may remain dormant for several months in the abomasa of sheep, they are capable of resuming their development to adulthood at some later date (Blitz and Gibbs, 1972b; Dunsmore, 1960, 1963) and the epidemiological significance of this is now generally accepted. Blitz and Gibbs (1972a) consider that for H. contortus inhibited development probably represents the primary means of overwintering in most temperate regions…

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