VPA 211: General Veterinary Parasitology and Helminthology (3+1)

MECHANICAL INTERFERENCE

Occlusion

• Death due to intestinal obstruction by parasites is common, eg. ascarids and tapeworms.
• Occlusions of bile ducts by liver flukes obstruct the flow of bile resulting in icteri.

• Adult filarids lodged in lymphatic ducts cause aggregation of connective tissue that results in blockage of lymph flow and oedema in hosts.
• Gapeworms block the air passages causing dyspnoea and asphyxia in fowls.
• Lungworms such as Dicytocaulus viviparous cause blockage of bronchi leading to atelectasis and emphysema in lungs of cattle. 

Lungworms blocking the bronchi in sheep

• Occlusion of blood vessels with thrombus as in the case of Strongylus vulgaris in horse may prove fatal if the coronary artery or brachiocephalic trunk is involved.
• In haemoprotozoan diseases, such as babesiosis and malaria, protozoa infected erythrocytes get trapped in the microcirculation of organs, impeding blood flow resulting in hypoxia and necrosis of tissues. 

Pressure atropy

• Pressure upon organs by larval stages of parasites, especially those of tapeworms result in atropy or distortion of the organ involved.
• Coenurus cerebralis, the larval stage of the tapeworm Taenia multiceps exert pressure on the brain of sheep causing the condition known as Gid or Staggers.  

Coenurus cerebralis, the larval tapeworm of Taenia multiceps causes pressure atrophy in brain

• Similarly, the larval stages of Echinococcus granulosus, form hydatid cysts in various organs, especially in liver and lungs of animals and man that causes severe problems in intermediate hosts, especially humans.