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The brown stomach worm is one of the most important roundworm species that infect cattle (Ostertagia ostertagi) and sheep (Ostertagia circumcincta), and is most prevalent in temperate regions around the world. This roundworm has a reddish-brown colour and can be found in the abomasum (fourth stomach) of ruminants. It is also the main cause of parasitic gastritis (ostertagiosis) worldwide.
Life cycle of Ostertagia spp
Ostertagia spp has a direct life cycle, similar to Haemonchus contortus. Female roundworms lay eggs in the intestine, with the eggs then excreted through the faeces of the host. Cattle are infected with brown stomach worms while grazing when conditions are favourable. However, even when conditions are unfavourable for the parasite, they can still survive for at least six months in livestock manure.
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The indigested larvae can be found on leaves of herbage and exsheath in the rumen of the host. This process is stimulated by lowered pH, temperature as well as bicarbonate concentration. The exsheathed third-stage larvae migrate to the abomasum and penetrate the gastric glands where further development takes place. The fourth-stage larvae emerge from the gastric glands, and move to the abomasal lumen and moult into egg producing adult worms.
Ostertagiosis
Clinical signs and symptoms of ostertagiosis include anorexia, diarrhoea and weight loss. The adult worm population causes substantial damage to the abomasal mucosa and is referred to as type I ostertagiosis. Ostertagiosis I is typically present in first grazing season calves that have not been exposed to control programmes.
Type II ostertagiosis is when a host is infected with a large number of brown stomach worm larvae that underwent hypobiosis, emerging from the glands months later. Hypobiosis is the process where infective larvae are ingested but development of the larvae is temporarily delayed. Hypobiosis takes place in the abomasum of cattle and leads to serious economic losses for dairy and beef producers.
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Ostertagiosis is a serious problem because it causes gastric acid secretion to decrease, whereas serum pepsinogen and gastrin levels increase. Brown stomach worm invasions cause collateral damage to the gastric mucosa, and several functional disorders can be observed.
The parasite invades the intestinal cells, leading to the cells being destroyed, thus causing repeated damage to the intestines. The damage done to the intestines causes internal bleeding, leading to loss of blood, water and proteins. Due to this damage, livestock cannot absorb nutrients as efficiently.
Ostertagiosis is dangerous because it can cause mortality rates to increase, milk and meat production to decrease, weight loss, anaemia and lowered fertility.
Diagnosis
Diagnosis of Ostertagia spp is done by way of faecal examination using microscopy-based faecal diagnostic tests. These tests identify specific parasitic species based on distinctive morphological characteristics, such as the shape of the eggs, oocysts or larvae. This method of diagnosis is done as it indicates the seriousness of the roundworm infection.
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Methods of control
The infection rate of the brown stomach worm in livestock depends on a variety of conditions such as the host, breed, sex, age, immunity of the host, genotype of the parasite, ambient temperature, rainfall, humidity and vegetation. Excessive amounts of larvae-containing manure also contaminate the pastures on which the cattle graze. Producers should therefore use a variety of chemical and non-chemical control strategies.
Non-chemical control strategies consist of improving the diet of cattle. Cattle that graze on pastures tend to be protein deficient, resulting in weaker immunity due to the lower protein levels in the blood and tissue. Moreover, pastures that are too overcrowded lead to overgrazing, causing poor nutrition and sanitation.
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Where chemical control strategies are concerned, anthelmintics are the best course of action. Anthelmintics should be used systematically as injudicious use can cause anthelmintic resistance, leading to unnecessary production losses and livestock mortalities. Calculated deworming programmes will assist in the control of parasites in livestock and on grazing pastures. – Cleary Martin, Agri FARMACY SA
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