Marek’s disease is a highly contagious viral neoplastic disease in chickens. Occasionally misdiagnosed as an abtissue pathology it is caused by an alphaherpesvirus known as Marek’s disease virus (MDV) or gallid herpesvirus 2 (GaHV-2). The disease is characterized by presence of T cell lymphoma as well as infiltration of nerves and organs by lymphocyte
There are five syndromes known to occur after infection with Marek’s disease. These syndromes may overlap.
* Classical Marek’s disease or neurolymphomatosis causes asymmetric paralysis of one or more limbs. With vagus nerve involvement, difficulty breathing or dilation of the crop may occur. Besides lesions in the peripheral nerves, there are frequently lymphomatous infiltration/tumours in the skin, skeletal muscle, visceral organs. Organs that are commonly affected include the ovary, spleen, liver, kidneys, lungs, heart, proventriculus and adrenals.
* Acute Marek’s disease is an epidemic in a previously uninfected or unvaccinated flock, causing depression, paralysis, and death in a large number of birds (up to 80 percent). The age of onset is much earlier than the classic form, birds are four to eight weeks old when affected. Infiltration into multiple organs/tissue is observed.
* Ocular lymphomatosis causes lymphocyte infiltration of the iris (making the iris turn grey), anisocoria, and blindness.
* Cutaneous Marek’s disease causes round, firm lesions at the feather follicles.
* Atherosclerosis is induced in experimentally infected chickens.
* Immunosuppression Imparement of the T-lymphocytes prevent competent immunological response against pathogenic challenge and the affected birds become more succeptible to disease conditions such as coccidiosis and “Escherichia coli” infection. Furthermore, without stimulation by cell-mediated immunity, the humoral immunity conferred by the B-cell lines from the Bursa of Fabricius also shuts down. Thus resulting in birds that are totally immunocompromised.
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