Understanding Marek's Disease: Symptoms, Spread, and Prevention
Marek's Disease (MD) is a highly infectious poultry disease characterized by paralysis, lymphoid tumors, and various forms affecting chickens. Learn about its etiology, methods of spread, symptoms, and vaccination strategies to protect your poultry flock.
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poultry diseases fourth stage Marek s Disease (MD)+ Lymphoid leukosis (LL) Dr.HarithAbdulla Department of Pathology and Poultry Disease College of veterinary medicine university of Basrah University of Basrah- College of veterinary medicine- Department of Pathology and Poultry Disease
MD is a highly infectious disease of chickens characterized by paralysis of wings and legs and presence of lymphoid tumors in various organs,due to mononuclear cell infiltration in the peripheral nerves and various other organs and tissues including iris and skin. Etiology Etiology :Group :Group of B Herpes virus . Incubation period Incubation period : 4 12 weeks . Course of disease Course of disease :- 10 12 weeks .
Method of spread 1. Feather follicles , dander , secretion and excretion . 2. Air currents . 3. Carriers . 4. Beetls , Alphitobius diaperinus . Mortality Layers 10 50 %. Breeder hens 5 25 % . Forms of the disease 1. Nervous form : Classical form . 2. Visceral form . 3. Eye form .(Ocular form) 4. Skin form .(Cutaneous form) Method of spread :- Mortality :- Broilers 1 5 % . Forms of the disease
1.Asymmetric progressive paresis, later complete paralysis of one or more extremities. 2.Involvement of vagus nerve can result in paralysis and dilation of crop and /or gasping. 3.Incoordination or stilted gait may be the first sign. 4.Characteristic sign is one leg stretched forward and the other back due to unilateral paresis or paralysis of the leg(Fan shape posture). 5.Pupil becomes irregular in size . 6.Iris becomes gray in color . 7.Pale shriveled combs .
1. Vaccines Used: Herpesvirus SB Rispens 2. Vaccine Types: Live attenuated vaccines Often used in combination (e.g., 3. Administration: In Subcutaneous 4. Goals: Does not prevent infection or shedding Prevents tumor formation and paralysis Reduces economic losses 5. Immunity Onset: Partial immunity begins about 5 5- -7 days post Full protection may take up to 2 weeks 1. Vaccines Used: Herpesvirus of Turkey (HVT) SB- -1 1 (serotype 2) Rispens (CVI988) 2. Vaccine Types: Live attenuated vaccines of Turkey (HVT) (CVI988) most protective combination (e.g., Rispens Rispens + HVT) + HVT) for enhanced protection. 3. Administration: In ovo Subcutaneous at hatch (day-old chicks) 4. Goals: not prevent infection or shedding tumor formation and paralysis (clinical disease) economic losses 5. Immunity Onset: ovo at 18 days of embryonation 7 days post- -vaccination 2 weeks vaccination
1.Feather follicles are enlarged . 2.Tumors in any tissue or organs .The lesions appear as diffuse enlargement in most organs, focal or nodular may be also observed. 3.Enlarged, edematous and loss of cross- striation of peripheral nerves.(Sciatic and brachial nerves). 4.Many birds may die without lesions due to viremia .
Differential 1. Lymphoid leukosis . 2. Riboflavin deficiency . 3. Histomoniasis( Black Head Disease). 4. Any disease causing nervous signs . Diagnosis 1. Signs . 2. Lesions. 3. Histopathology . 4. Viral isolation . Prevention Differential Diagnosis : Diagnosis : Diagnosis : : Prevention : :- - Vaccination.
Lymphoid neoplastic disease of adult chickens ( over 14 16 produces lymphoid tumors, liver and spleen, other visceral organs such as ovary and lungs may also affected . Etiology: Small RNA leukosis / sarcoma virus . Incubation period Method 1. Transovarian . 2. Lateral transmission . 3. Blood sucking parasites . leukosis of is a LL bursal characteristically particularly in dependent weeks age). Etiology: Incubation period : : 14 30 weeks . Method of spread of spread :-
Clinical signs: 1 1.The disease is chronic in nature ,but affected birds may die without signs. 2.Pale shriveled combs . 3. Progressive emaciation and diarrhea. 4.Total loss may approach 20% . 5.Losses most severe after onset of egg production 6.Abdominal enlargement. 7.Blood blisters may occur in the skin ,their rupture causing hemorrhage. Clinical signs: .The disease is chronic in nature ,but affected birds may die without signs.
Post 1. Hepatomegaly : The liver is filling the entire abdominal cavity ,(Big Liver Disease). It is firm, fibrous, and gritty. 2.Enlarged bursa of Fabricius . 3.Tumors on the mesentery and other abdominal viscera. 4.Tumors are soft, smooth, and glistening. 5.Tumors may be nodular ,miliary ,diffuse or combination of these forms. 6.Sometime tumors in the bones . Post mortem lesions : mortem lesions :
Differential 1. Marek s disease(Visceral form) . 2. Avian tuberculosis . 3. Coligranuloma. 4. Histomoniasis {Black Head Disease} . Diagnosis 1. Signs . 2. Post mortem lesions:- A. Bursa of Fabricius enlargement . B. Lack of nerve involvement . 3. Histopathology . 4. ELISA. Differential Diagnosis: Diagnosis: Diagnosis : :
1. Elimination of the virus from breeder hens . A. Test and slaughter . B. Virus is spread to the progeny . 2 . Genetic resistant birds.
Mareks disease 1. Age : Young and adult . 2. Nerves: Are affected . 3. Skin : Is affected . 4. Bursa of Fabricius is mainly not involved. Lymphoid leukosis (LL 1.Age:Over 14 16 weeks. 2.Nerves: Not involved . 3.Skin: Is not affected . 4.Bursa of Fabricius:Is the target organ.
