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Ostertagia ostertagi



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Ostertagia ostertagi
Brown stomach worm

General Description:
Adults are brownish and thread-like, growing to 9 mm in length.

Life Cycle:
Adults in the abomasum lay eggs that pass in feces. Once hatched, larvae undergo two molts to become infective third-stage larvae, which migrate onto herbage and are ingested by grazing cattle. Once ingested, these parasitic larvae grow and molt twice more to become egg-laying adults. Environmental conditions of cold or excessive dryness may trigger a condition known as hypobiosis, in which larval development is arrested so that maturation may take several months. Prepatent period is 17 to 21 days.


Geographical Distribution:
Worldwide in cattle raising areas. Significance: Brown stomach worm is a widespread parasite of cattle. Affected cattle not only lose weight but often die of overwhelming clinical ostertagiasis.

Effect on Host:
Ostertagiasis occurs in two forms, Type I and Type II disease. Type I form occurs in calves during their first grazing season as a result of maturation of ingested larvae in the abomasum. Type II disease occurs in older animals as a result of resumed development of larvae which have undergone arrested development, or hypobiosis. Usually this occurs 2.5 to 4 months after the end of the period of acquisition of inhibition prone larvae. The end of this period happens sometime in November in the north and June in the south. Ingested larvae enter the glands of the abomasum, where they grow and molt to become adults (17 to 21 days), at the same time causing erosion of the cells. (Larvae that undergo hypobiosis stay in the cells for longer periods.) Cells damaged by the larvae are replaced by rapidly dividing cells that lack the function of producing hydrochloric acid and the enzyme pepsinogen. In a normal abomasum, the pH of the contents is maintained at 2 to 2.5. When large numbers of the parietal cells are lost, the pH of the abomasal contents may rise to 7. Consequences of this are (a.) pepsinogen is not activated to its active form, pepsin, (b.) proteins are not denatured and digested, (c.) there is an increase in the number of bacteria in the abomasum, (d.) there is leakage of blood and blood-proteins into gut. Dietary energy and protein which would otherwise be used for growth must be used to replace these proteins. Weight loss is the result. Albumin in the intestine also inhibits fluid absorption by the gut, causing diarrhea. Severe infections may cause death. The loss of albumin also causes body fluids toe or feet in lower parts of the body such as under the jaw (bottle jaw) or in the abdomen (aseites). The disease condition produced by these worms is known as ostertagiasis and is characterized by severe diarrhea, edema, and weight loss leading to emaciation.

Diagnostic Information:
Strongyle-type eggs appear in the feces; third-stage larvae cultured from them may be identified as Ostertagia. Elevated blood pepsinogen levels may be diagnostic of Type II ostertagiasis.

Avoid overstocking, use pasture management to avoid the accumulation of infective larvae on herbage, and treat regularly with an anthelmintic known to be effective against the inhibited fourth larvae stage.


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