Establishment of a Pure Infection of the Nematode Ostertagia circumcincta in the Sheep

Abstract

THE four smaller nematode parasites of the abomasum of the sheep, Ostertagia circumcincta, O. trifurcata, Teladorsagia davtiani and O. mentulata, commonly occur as mixed infections. A search of the literature revealed only three instances^1–3 in which it was claimed that pure infections of O. circumcincta had been used. In all three, the evidence on which the claim was based was not provided. However, Horak (personal communication) states of his pure strain that he has “examined thousands of male worms and all have been O. circumcincta”. In Australia and elsewhere, mixed infections have been reported to be the common finding by Gordon (personal communication); Sommerville⁴; Armstrong⁵ in New Zealand; Todd⁶ in the United States; Parnell⁷ in Great Britain, the proportions of the different species being between 80 and 90 per cent O. circumcincta^4,6, and the remainder one or a mixture of the others, the predominant species being O. trifurcata.