Ostertagia ostertagi, commonly known as the medium stomach worm or brown stomach worm, is a parasitic nematode (round worm) of cattle. O. ostertagi can also be found to a lesser extent in sheep, goats, wild ruminants, and horses. It causes ostertagiosis, which is potentially fatal in cattle. It is found worldwide and is economically important to cattle industries, particularly those found in temperate climates.
The abomasal nematode O. ostertagi is a clade V nematode of the order Strongylida, the family Trichostrongylidae and genus Ostertagia.Blaxter, M. L., De Ley, P., Garey, J. R., Liu, L. X., Scheldeman P., Vierstraete, A., Vanfleteren, J. R., Mackey, L. Y., Dorris, M., Frisse, L. M., Vida, J. T., and Thomas W. K. 1998. A molecular evolutionary framework for the phylum Nematoda. Nature 392: 71–75. Ransom first described the genus Ostertagia in 1907, which currently contains approximately 15 species. All species of the genus Ostertagia infect domestic or wild ruminants. These species form a large and complex group, the taxonomy of which has not been fully elucidated.
Life cycle O. ostertagi has a life cycle which consists of two stages: the free-living, pre-parasitic stage and the parasitic stage in the host (e.g. cattle). Eggs from mature females in the abomasum are passed in the faeces. These eggs hatch in the faeces to first-stage larvae (L1). The L1 larvae grow and moult to second-stage larvae (L2), which then moult to become the infective third-stage larvae (L3). The L3s retain the cuticle from the second stage (L2) as a protective sheath, and can survive for long periods within the faeces. The time taken to develop into infective larvae is dependent on favourable stimuli such as temperature (approximately ) and humidity. Typically, development takes 10 days to 2 weeks.Fox, M. T. 2014. Gastrointestinal Parasites of Cattle: Gastrointestinal Parasites of Ruminants: Merck Veterinary Manual. Merck Veterinary Manual. Retrieved from http://www.merckvetmanual.com/mvm/digestive_system/gastrointestinal_parasites_of_ruminants/gastrointestinal_parasites_of_cattle.html
The parasitic stage of the life cycle begins when warm moist conditions cause the L3 larvae to migrate onto herbage surrounding the fecal pat, which are ingested during grazing. In the host's rumen, the L3 larvae shed their protective sheath and pass into the abomasum, where they penetrate the gastric glands. After exsheathment and penetration into the gastric glands the L3 moult into L4 and subsequently to L5 larvae. The young adult worms then emerge from the gastric glands and continue their maturation on the mucosal surface of the abomasum.Fox, M. T. 1993. Pathophysiology of infection with Ostertagia ostertagi in cattle. Vet Parasitol 46: 143–158. Once fully mature, sexual reproduction begins and eggs are produced, thus completing the life cycle.
The normal prepatent period for O. ostertagi is 21 days. However, under certain circumstances, ingested L3 larvae can suspend their maturation and become dormant as inhibited L4 larvae inside the gastric glands. This arrested development is called hypobiosis, and can last for up to six or seven months. Studies suggest that the inhibition process in O. ostertagi depends on the weather conditions to which the infective L3 larvae are exposed on pasture, and the length of time that L3 larvae spend on pasture. In temperate regions of the northern hemisphere, hypobiosis occurs in autumn and early winter, but in the southern hemisphere there is evidence that this phenomenon occurs in spring and early summer.Couvillion, C. E., Siefker, C., and Evans, R. R. 1996. Epidemiological study of nematode infections in a grazing beef cow-calf herd in Mississippi. Vet Parasitol 64: 207–218. Fernández, A. S., Fiel, C. A., and Steffan, P. E. 1999. Study on the inductive factors of hypobiosis of Ostertagia ostertagi in cattle. Vet Parasitol 81: 295–307.
Morphology O. ostertagi adults are slender reddish-brown worms. Adult males are long, adult females long, and the eggs long. Identification of adult medium stomach worms is based on the structure of the bursa, genital cone, and spicules in males and on the dimensions of the oesophageal valve and the configuration of the synlophe in males and females.Lichtenfels JR, H. E. 1993. The systematics of nematodes that cause ostertagiasis in domestic and wild ruminants in North America: an update and a key to species. Vet Parasitol 46: 33–53. The cuticle in the anterior region is striated transversely whereas the rest of the body is unstriated and bears around 36 longitudinal ridges.Taylor, M. A., Coop, R. L., and Wall, R. L. 2015. Veterinary Parasitology 4th Edition. Wiley-Blackwell . The Ostertaginae are characterized by a reduced buccal capsule and square head, and well-developed copulatory bursa in the male. The genital cone ventrally bears two small slender papillae and dorsally bears two long slender papillae surrounded by an accessory bursal membrane. The lateral rays of the copulatory bursa are in a pattern of 2-1-2 or 2-2-1 pattern. The key to morphologically identifying O. ostertagi males is a prominent proconus and the remainder of the genital cone is not prominent. The spicules are of equal length and shape, tapering towards the distal end.Taylor, M. A., Coop, R. L., and Wall, R. L. 2015. Veterinary Parasitology 4th Edition. Wiley-Blackwell . The key to morphologically identifying O. ostertagi females is the lateral synlophe with one pair of ridges ending next to the lateral ridge between cervical papilla and the posterior end of the oesophagus. The cervical papillae are prominent and thornlike. A large number of surface cuticular ridges (synlophe) are perpendicular to the surface.Lichtenfels JR, H. E. 1993. The systematics of nematodes that cause ostertagiasis in domestic and wild ruminants in North America: an update and a key to species. Vet Parasitol 46: 33–53.Lichtenfels, J. R., Hoberg, E. P., and Zarlenga, D. S. 1997. Systematics of gastrointestinal nematodes of domestic ruminants: advances between 1992 and 1995 and proposals for future research. Vet Parasitol 72: 225–245. .
The infective L3 larvae of O. ostertagi can also be identified morphologically. The L3 will have an external sheath. The larva head is rounded and can be distinguished from Cooperia spp. as it lacks the two refractive bodies in the head that is seen in this species. The tail of the larvae within the sheath is rounded and the body contains 16 intestinal cells. The external sheath of the O. ostertagi larvae also has a much blunter tip then that of Copperia spp. or Haemonchus placei. O. ostertagi can also be distinguished from the L3 larvae of Trichostrongylus spp. as it has a much longer sheath tail extension.van Wyk, J. ., Cabaret, J., and Michael, L. . 2004. Morphological identification of nematode larvae of small ruminants and cattle simplified. Vet Parasitol 119: 277–306.
Molecular biology The genome size estimate for O. ostertagi is ~58 MB, based on T. circumcincta (Ostertagia circumcincta), whose genome is 58.6 MB and on H. contortus at 52 MB, based on flow cytometry.Casser, R. B., Ranganathan, S., Baillie, D., Sternberg, P., Mitreva, M., Mardis, E., and Wilson, R. K. 2007. Whole genome sequences of nematodes of the order strongylida. Proposal. http://eprints.ugd.edu.mk/2898/. Accessed online March 22, 2016. There are 7,006 identified expressed sequenced tags (ESTs), representing 2,564 genes.Casser, R. B., Ranganathan, S., Baillie, D., Sternberg, P., Mitreva, M., Mardis, E., and Wilson, R. K. 2007. Whole genome sequences of nematodes of the order strongylida. Proposal. http://eprints.ugd.edu.mk/2898/. Accessed online March 22, 2016.
Disease Clinical ostertagiosis normally occurs in first grazing season calves but can affect mature animals.Merial. 2001. Ostertagia ostertagi. Online Producer Publication: http://us.merial.com/producers/pdfs/Ostertagia_ostertagi.pdf . Accessed March 23, 2016. Subclinical infection results in reduced weight gain and growth rate, reduced reproductive efficiency and reduced milk production.Gibbs, H. C. 1988. The epidemiology of bovine ostertagiasis in the north temperate regions of North America. Vet Parasitol 27: 39–47. The primary clinical symptom of fulminant bovine ostertagiosis is watery diarrhoea and is usually accompanied by reduced appetite.Gibbs, H. C. 1988. The epidemiology of bovine ostertagiasis in the north temperate regions of North America. Vet Parasitol 27: 39–47. Infected animals are characterised by dull, rough coats and hindquarters soiled with faeces as a result of the profuse diarrhoea. Cattle are frequently co-infected with many gastrointestinal nematodes including species of the following genera: Ostertagia, Haemonchus, Bunostomum, Oesophagostomum, Trichuris, Trichostrongylus, Cooperia, and Nematodirus. The clinical signs between these species of nematodes are difficult to distinguish from each other, and are often referred to as a syndrome called parasitic gastroenteritis.Boden, E., and Andrews, A. 2015. Black's Veterinary Dictionary Vol. 17. Bloomsbury. Clinical ostertagiosis can be observed under two sets of circumstances referred to as type I and type II disease.
Type I disease Type I disease occurs in young cattle grazing on pastures for their first time during the period of high pasture contamination.Merial. 2016. Endoparasites – Ostertagia. Online Publication: http://www.merial.co.nz/Cattle/beef/disease_information/Pages/oster.aspx. Accessed March 23, 2016.Beck, M. A., Colwell, D. D., Goater, C. P., Kienzle, S. W. 2015. Where's the risk? Landscape epidemiology of gastrointestinal parasitism in Alberta beef cattle. Parasit Vectors 8: 434. This syndrome usually occurs in the summer and fall months in the Northern hemisphere and during the winter and spring months in the Southern hemisphere.Stromberg, B. E. 1997. Environmental factors influencing transmission. Vet Parasitiol 72: 247–264. Infective larvae are ingested daily by the young stock on pasture. The pathological and clinical signs are due to the direct development of large numbers of L3 larvae to adult worms over a relatively short period of time (approximately 3 weeks) in young animals with an immune system naïve to Ostertagia infections.Merial. 2016. Endoparasites – Ostertagia. Online Publication: http://www.merial.co.nz/Cattle/beef/disease_information/Pages/oster.aspx. Accessed March 23, 2016. The young adult worms then break out of the gastric glands, causing substantial damage to the abomasal wall. Mild cases result in reduced growth or production and severe cases can result in fulminating disease characterized by profuse watery diarrhoea, rapid weight loss, submandibular oedema ("bottle jaw"), anemia and death.Merial. 2016. Endoparasites – Ostertagia. Online Publication: http://www.merial.co.nz/Cattle/beef/disease_information/Pages/oster.aspx. Accessed March 23, 2016.Myers, G. H., and Taylor, R. F. 1989. Ostertagiasis in cattle. J Vet Diagn Invest 1: 195–200.
Type II disease