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===Pathology===
 
===Pathology===
'''Worms produce''':
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[[Image:dirofilariasis.jpg|right|thumb|125px|<small><center>'''Dirofilariasis'''. Courtesy of T. Scase</center></small>]]
*substances that are:
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[[Image:dirofilariasis 2.jpg|right|thumb|125px|<small><center>'''Dirofilariasis'''. Courtesy of T. Scase</center></small>]]
**antigenic
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**immunomodulatory
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**pharmacologically active.
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'''Lesions are''':
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On post-mortem examination, the right side of the heart is found to be enlarged. There is proliferation of the pulmonary arterial myointima, as well as pulmonary thromboembolism and haemorrhage. If right-sided congestive heart failure was present in life, the hepatomegaly and hepatic congestion will be seen.
*'''not''' confined to the location of the worms
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*also caused by shear stress of high blood flow.
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'''Severity''':
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*not associated with the number of worms
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*exacerbated by exercise (i.e. by high blood flow rate)
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*sedentary dogs often asymptomatic - symptoms most commonly associated with racing greyhounds.
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'''Acute prepatent disease''':
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*immature adult worms in caudal distal pulmonary arteries
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*leads to intense diffuse eosinophilic reaction, which in turn leads to coughing.
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'''Chronic disease''':
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*mature worms in right heart and pulmonary arteries
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*endothelial swelling and sloughing
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*increased permeability → inflammation → periarteritis
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*platelets/white blood cells activated → thrombosis
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*proliferation of smooth muscle, thickening of media:
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→ impairment of blood flow
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pulmonary hypertension
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→ right ventricular strain
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→ right ventricular hypertrophy and right-sided heart failure
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*insufficient blood pumped through pulmonary capillary bed → insufficient preload for left ventricle.
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'''Post Caval Syndrome (Dirofilarial haemoglobinuria)''':
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*can be acute or chronic
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*heavy heartworm infestation:
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**entangled clumps of worms → impaired closure of tricuspid valve → post-caval stagnation → hepatic congestion and hepatic failure
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*this is accompanied by increased red blood cell fragility, haemolytic anaemia and haemolobinuria.
      
==Treatment==
 
==Treatment==
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