Marek's Disease In Poultry: Signs, Causes, Control & Treatment

Marek’s Disease In Poultry: Signs, Causes, Control  & Treatment; Marek’s Diseases (MD); Marek’s Disease is somewhat rare, which is considered as good news. It does not occur too often in small flocks.  You may never even hear of any case of this disease in a lifetime even if you are involved in animal husbandry or veterinary medicine; yes, it is that rare.  Additionally, the problem can be prevented almost completely. 

On the other hand, the viral cause of this condition is common or ubiquitous.  It is also seen as a globally endemic virus in poultry. If your chicken ever contacts it, the chicken will most likely die since there is rarely any treatment for the viral infection.

Marek’s Diseases nature

•    The disease is characterized by internal organ and nerve enlargements; it is also highly contagious 
•    The economic significance is great


Causes Of Marek’s Disease In Poultry

•    The Marek’s Diseases is caused by herpes virus
•    The virus can remain alive for up to 24 hours at 37oC in a poultry house. Dander, feather follicles, dust, litter, and droppings. It can remain active for several weeks or even months.
•    You can apply common chemical disinfectants to inactivate the virus. The disinfectant can be applied within just 10 minutes of applying treatment. The virus can equally be inactivated using high humidity.
•    The virus undergoes maturity into a fully enveloped and infective form in the feather follicles’ epithelium. It is then released to the environment from here.
•    Also, it can remain active in dust and litter of the poultry house. Infection can be aided by dander and dust from infected chicken.
•    The transmission can take place both directly and indirectly by inhalation of infective materials like dust that contains the epithelial cells of the infected feather follicles. It can also be transmitted via dander.  An aerosol is yet another common route of contracting it.
•    The infection can spread fast among brides population once it is introduced into one of them; the spreading cannot be hampered by the vaccination status of the birds.
•      Any bird infected can continue to bear the infection for a very long time, and such a bird can infect other birds.  Vaccinating the birds before the infection can only reduce the quality of virus released, but cannot prevent infection of the bird.
•    Beetles, personnel, and fomites can be involved in transmitting the infection
•    The virus cannot be transmitted via eggs  
•    The rate at which the virus infect commercial flocks varies and depend on the dose and strain of the virus involved in the infection. Other determining factors are stress, other concurrent diseases, genetics, host gender, maternal antibody, age at exposure and several environmental factors.

Clinical Symptoms of Marek’s Disease in Poultry

Marek's Disease In Poultry: Signs, Causes, Control & Treatment
Lymphoid tumours in internal organs


Marek's Disease In Poultry: Signs, Causes, Control & Treatment
Enlarged feather folliclees


Marek's Disease In Poultry: Signs, Causes, Control & Treatment
Leg paralysis
•    The diseases can come up in two different forms, which are the classical and acute forms      
•    The disease can manifest in the form of paralysis and lameness some 12 weeks of age.
•    Sudden death can occur in acute infection; this is due to the development of lymphomas in internal organs.
•    Some other symptoms shown by infected birds are diarrhea, weight loss, emaciation, anorexia, anemia, depression and so on. 
•    The acute form affects birds between the ages of six and ten weeks and can also start from four weeks old birds. Generally, the birds suffer mortality rate as high as 60%.
•    Lesion occurs in the nerves of those birds affected by the classical form of the infection, especially those birds that are older than 12 weeks. The mortality rate of this form of the infection is about 30%. The infection can occur in the bird for a very long period.
•    In most cases, the bird loses coordination, becomes lame, and experiences complete or partial legs and wings paralysis, rendering it unable to stand.
•    Marek’s Diseases is equally associated with a transient paralysis syndrome which is a unilateral leg paresis. This condition can lead to a characteristic posture of one of the legs being stretched forward, while the other one is stretched backwards; this occurs with the progression of the lesions.
•    The bird will have a characteristic split leg appearance due to the stretching of the wings and legs as described above.
•    The bird can also experience neck twisting, called torticollis, which is due to the speared of the infection of the cervical nerves. The vagus nerve can be involved and lead to crop dilation and paralysis.          
•    The bird can experience bilateral or unilateral blindness due to the involvement of the eyes.


Gross lesions

•    The bid can experience nodular or diffuse lymphoid tumors, which can appear in several organs, like proventriculus, muscle, kidney, lung, heart, gonads, spleen and liver.
•    The nerves can become enlarged; this is among the most consistent of all the gross lesions that come up in the infected birds
•    The feather follicles can also occur in infected birds; this is usually called skin leukosis.  


Control and prevention

•    One of the most economical and exploited means of treating Marek’s Diseases is vaccination. The bird will develop very good immunity after seven days of giving the vaccination,
•    Many developed countries now use automated technology to carry out vaccination, which involves vaccination of 18-day-old embryo.
•    Stocks should be bought from sources that are resistant to Marek’s Diseases, and regular testing for Marek’s Diseases should be carried out on the stock
•    The infection cycle can be broken via disinfection. The chances of propagation of the infection can be minimised by adopting an all-in-all-out policy for rearing the stocks.
•    It is important to carry our adequate sanitation and hygiene, as well as very strict biosecurity, in addition to vaccination. This way, the disease can be adequately prevented.
•    5% formalin should be used in disinfecting the premise after an outbreak. This solution should also remain with the stock for up to one month afterwards.
The recommended vaccination schedule for layers is given in the table below:
Age in days
Name of vaccine
MD (Bivalent)
MD (Bivalent)

Treatment of Marek’s Disease in Poultry

Marek’s Diseases cannot be cured yet. The best thing to do is to remove any bird that contacts the infection from the other birds to prevent spread. The separated bird should also be humanely destroyed. The remaining birds should also be closely monitored to finds out if they are not showing any sign of infection.


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