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Parasitic Gastroenteritis (view source)
Revision as of 18:33, 26 December 2008
, 18:33, 26 December 2008→Host Immunity
e.g. hypersensitivity reaction to ''Haemonchus'' in some ewes.
e.g. hypersensitivity reaction to ''Haemonchus'' in some ewes.
== Pathogenesis ==
=== Introduction ===
The pathogenic effects of a worm burden on the host depend on:
*'''Species''' of worm and '''stage''' of life-cycle present (affects feeding, site and host reaction).
*'''Numbers''' of worms present (or invading).
*'''Host immunity''' (affects worm population and pathogenicity).
*'''Nutrition''' (may affect both host '''resilience''', ability of an animal to withstand the effects of infection, and host '''resistance''', ability of an animal to prevent establishment and/or development of infection).
=== Mechanisms ===
The nematodes responsible for PGE impair productivity by adversely affecting:
a) ''Appetite'':
Very important; the reduction in appetite is the main cause of impaired liveweight gain.
b) ''Digestion'':
*'''Digestibility''': decrease in abosomal infections - compensatory increase in intestinal digestion.
*'''Gut microflora''': change in flora and increase in numbers in abosomal infections.
*'''Gut hormones''': increase in gastrin secretion (abosomal infections due to an increase in gastric pH) - cause of decrease in appetite?
*'''Malabsorption of nutrients''': in intestinal infections due to villous atrophy - affects amino acids, fats and minerals.
c) ''Protein metabolism'':
Normally there is a dynamic equilibrium between dietary protein in the gut, amino acids absorbed into the circulation, protein synthesis in the liver, protein storage in the muscle and protein catabolism (i.e. protein breakdown). In PGE, this equilibrium is upset:
*dietary protein intake decreases
*dietary protein breakdown decreases
*amino acid absorption decreases
*change in distribution of protein synthesis (reduced muscle; increased haemoglobin, albumin, immunoglobulins)
*protein leak due to an increase in mucosal permeability
d) ''Mineral metabolism'':
Decreased calcium and phosphorus absorption (villous atrophy) leads to a decrease in bone mineralisation (osteoporosis).
e) ''Energy metabolism'':
Decrease in appetite leads to mobilisation of adipose tissue.