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Ostertagia spp.
Kingdom Animalia
Phylum Nematoda
Super-family Trichostrongyloidea
Genus Ostertagia
Species O. osteragi


Ostertagia spp. are small bursate nematodes that parasitise the gastrointestinal tract of mammals and birds. These species are responsible for mortality and morbidity in a number of ruminants especially O. ostertagi which is widely considered the most important parasite of cattle.

Ostertagia ostertagi

Also known as: O. ostertagi

O. lyrata
Skrjabinagia lyrata

These worms are found throughout the world, and are considered the most important parasite of cattle, especially in temperate regions. The primary host is cattle but they can also be found in deer and goats occasionally.


The adult O. ostertagi worms are thread like, reddish worms with short buccal cavities. The males can measure 6-8mm, the females 8-9mm. There are several cuticle morphologies used to identify these worms at a microscopic level. The head of both sexes is square and the adults have 16 gut cells. The anterior cuticle has transverse striations, where as the rest of the body has longitudinal ridges. Male spicules are brown and curved, they split at the posterior to form 3 hooks. In the females the tail tapers to a fine end with a rounded tip and the vulva is covered by a cuticular flap.


O. ostertagi have a direct, non-migratory life-cycle. Calves are infected following ingestion of L3 that under moist conditions migrate from the faeces to pasture. The larvae are swallowed, pass through the forestomachs and develop in the abomasal gastric glands to the L4 stage, emerging as adult (L5) worms after nearly 3 weeks. Adult female worms then produce strongyle eggs which are passed out with the faeces. The prepatent period is 16 - 23 days (5-6 months if arrested at early (E)L4 stage).

Epidemiology and Pathogenesis

The epidemiology of O.ostertagi is complex due to the hardyness of the eggs in the environment and the ability of larvae to hyperbiose. Clinical infections of this worm are termed Ostertagiosis, the clinical page explains the pathophysiology and the epidemiology of the disease.

Teladorsagia (Ostertagia) circumcincta

Also known as: Sheep brown stomach worm

This is a major abomasal worm of sheep and goats, that is found worldwide. This worm is of great economical importance in both causing mortality and decreased weight gain in production animals. Resistance to all types of anthelmintics is common amongst the wild species making control and treatment difficult.


Adult worms have a common ostertagia appearance, slender, reddish in colour with a short buccal capsule. The worms are very short, males 6-8mm, female 8-10mm. Microscopically male T. circumcincta worms have well developed lateral lobes of the bursa and long thin spicules. In females a vulval flap is present, the tail is transversely striated and tapers to a fine rounded tip.

There are two morph species of T. circumcincta; T. davtiani and Ostertagia trifurcata, both of which have slightly different microscopic appearances to the T. circumcincta. In males the bursa is longer in both species and the spicules, shorter and broader.

Life Cycle

The life cycle is the same as that of O. ostertagi described above.

Epidemiology and Pathogenesis

T. circumcincta and O. trifurcata are responsible for clinical disease predominantly in lambs. The Pathophysiology of the disease is analogous to ostertagiasis in cattle, though the type II form of disease is not seen as often in sheep and goats. The main feature in the epidemiology is the occurrence of a peri-parturient rise (PPR) in the number of larvae present as is seen in the disease in cattle.