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Book Contents

Diseases of Poultry
By Ivan Dinev, DVM, PhD


VIRUS-INDUCED NEOPLASTIC DISEASES MAREK'S DISEASE

279 280 281

279.280.281.Acute (visceral) form.It is characterized by diffuse or nodular lymphomatous lesions in various viscera (liver, spleen, heart, kidneys, lungs, gonads, proventriculus, pancreas etc.), the skeletal muscles and the skin. MD affects mainly hens, and is rarely observed in turkeys. It is most commonly encoun¬tered in birds at the age of 89 weeks and in layer hens. The cases at the age of 16-20 and 24-30 weeks are pre¬dominant. MD is prevalent all around the world and in fact, all flocks are exposed to the effect of the aetiological factor.

 
282

282.Diffuse lymphomatous growths in the heart, resulting in its transformation into an amorphous tumourous mass.

 
283

283.Bilateral enlargement of kidneys because of a diffuse lymphoid cell proliferation.

 
284

284.Neoplastically modified right lung in MD.

 
285

285.Typical cauliflower-like appearance of the ovary, distinctive for MD.

 
286.

286.Marked asymmetry of testes on a cock following unilateral lymphoid cell proliferation.

 
287

287.Diffuse neoplastic growths affecting the pancreas.

 
288 289

288.289.The manifold enlarged proventriculus with the shape of a round bottom flask (288) result of diffuse neoplastic growth and the severely narrowed lumen (289) are a typical finding in MD. The causative agent of MD is a type B cell associated herpesvirus (MDV). There are three MDV serotypes. The isolates of serotype 1 are widely distributed among hens and vary from highly virulent (w+) oncogenic to almost avirulent strains. The serotype 2 is common for hens and is not oncogenic. The isolates of serotype 3, known also as turkey herpesviruses (HVT) are naturally occurring in turkeys and are non-oncogenic. The three serotypes possess a significant cross reactivity.

 
290

290.Multicentric MD tumours (arrows) prominating or seen through the superficial and deep pectoral muscles.

 
291 292

291.292.Chronic (classical) form. It is ecountered as neural type (fowl paralysis) or ocular type (ocular lymphomatosis). Clinically, the neural for is manifested with paralysis of limbs.

 
293 294

293.294.Pathoanatomically, unilateral or bilateral thickening of affected nerves, mainly diffuse and at a various extent, is observed.

 
295

295.The ocular form is characterized with iris depigmentation, deformation of the pupil, sometimes opacity of the cornea and blindness.

 
296

296.Histologically, pleiomorphic lymphoid cell proliferations in affected viscera, nerves or eyes are observed. The Marek's disease is probable provided that at least one of the next conditions is present: peripheral nerves augmentation, depigmentation of the iris or irregularly-shaped pupil; lymphoid tumours in various organs in birds younger than 16 weeks; presence of visceral tumours in birds at the age of 16 weeks and older; simultaneous lack of alterations in the bursa of Fabricius.

 
297

297.Microscopical view of lesions in a peripheral nerve consequent to MD.

 
298

298.Lymphoid cell proliferations in the iris and the ciliary muscles in the ocular form of MD. Three classes of viruses are able to protect fowl from MD: attenuated serotype 1 of MDV-cell associated vaccines; HVT could be used for preparation of cell-free lyophilized vaccines; naturally apatho-genic isolates of serotype 2 cell associated vaccines. The vaccines against MD provide over 90% protection. HVT gives excellent results but in case of failure, a bivalent vaccine could be used.

 
299

299.Transient paralysis. They are observed in chickens and hens, especially non-vaccinated against MD. Most cases present the classical form manifested by flaccid paralysis of the neck and legs for 143 days followed by complete recovery. The syndrome has to be differentiated from the neural form of MD on the basis of its transient nature and the flaccid, but not spastic paralysis.

 
This book is protected by the copyright law. The reproduction, imitation or distribution of the book in whole or in part, in any format (electronic, photocopies etc.) without the prior consent, in writing, of copyright holders is strictly prohibited.

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