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PARASITIC GASTRO-ENTERITIS
Parasitic gastro-enteritis (PGE) in Britain is a disease primarily of lambs, characterised by weight loss and diarrhoea..
AETIOLOGY
The principal nematodes present in outbreaks are Ostertagia and Trichostrongylus occasionally Haemonchus, Strongyloides, Cooperia, Nematodirus spp. Bunostomum and Chabertia are involved. In most cases infection is by ingestion of the larvae.
PATHOLOGY
The main function of the gastro-intestinal tract is to digest and absorb nutrients. In addition, it plays a major role in fluid and electrolyte balance and protein metabolism. The presence of large numbers of parasites in the gastro-intestinal tract will interfere with these functions with obvious and serious consequences.
INTESTINAL PARASITES
Intestinal function is to complete digestion and to absorb nutrients; the intestine also plays a major role in fluid and electrolyte balance and protein metabolism. To do this it has an enormous surface area for absorption of nutrients.
The effect of the presence of parasites such as Trichostrongylus colubriformis and Nematodirus battus is to reduce surface area and therefore reduce ability to absorb. The brush border enzymes may also be lost and hence there is reduced ability to digest. If there is a severe exudate present this will act as a barrier and interfere with digestion and absorption.
The clinical consequences of these changes are:
1. Diarrhoea. This is the cardinal clinical sign of enteritis. It can be defined as a consequence of malabsorption of water and electrolytes.
2. Malnutrition. Due to malabsorption and leading to weight loss, poor quality wool and impaired milk production.
3. Excessive loss of protein through the intestine.
CLINICAL SIGNS
Outbreaks of clinical disease are predominantly seen in lambs during the months of July, August and September. They are of sudden onset and several animals are usually affected, the main clinical sign being a profuse, watery diarrhoea which results in soiling of the fleece around the tail and perineum with faecal material. Affected animals become dull and the wool loses its bloom. Initially weight gain is arrested but as the diarrhoea persists there is a loss of weight and eventually animals may become markedly dehydrated followed by recumbency and death.
Young sheep may develop a severe diarrhoea during the late winter months. The first clinical sign is a gradual loss of condition which may be difficult to appreciate and this is followed by the appearance, in a number of animals, of a severe diarrhoea which is of a very dark colour. After the onset of the diarrhoea, deterioration is rapid.
Adult sheep frequently carry a worm burden which does not appear to affect their general health provided the animals receive an adequate diet. When food is scarce any parasitic burden may exaggerate the effects of malnutrition. Under these circumstances affected animals show a progressive weight loss without diarrhoea.
