Marek's Disease in Chickens

Marek's Disease is a viral tumor-causing disease of chickens.  Marek's is distributed worldwide and is so common
that if you have birds, they have been exposed to Marek's, regardless of whether they show symptoms or not.  
There are 4 different forms of Marek's:
  • Cutaneous (skin Form)
  • Neural (nerve form)
  • Ocular (eye form)
  • Visceral (internal-organ form)

Cause

Caused by 6 different herpes viruses primarily affecting young birds.  The disease is often characterized by
abnormal cell growth in the peripheral nerves and central nervous system. Hence, the common name for one
form of Marek's: fowl paralysis. In addition to the nerves, however, the disease also may cause lesions on visceral
organs and other tissues, including feather follicles of the skin. The most prominent lesions may be tumors on the
liver, kidneys, testes, ova, spleen and lungs. In such cases, nerve swelling may not be involved.

How Marek's Disease is Spread

Marek's is highly contagious and spreads by bird to bird contact, by contact with infected dust and dander, and
by darkling beetles and mealworms that live int he chicken house, although the virus has no affect on the beetles
or mealworms.  Chickens are most commonly exposed to Marek's by contact with residual dust and dander in
preciously infected houses, by air contamination from a nearby house, or by virus particles carried by personal
equipment.

Other organisms common to chicken houses such as free living mites, mosquitoes and coccidia do not transmit
the disease.  The virus does not survive the egg incubation process and is not spread by hatching eggs.  Marek's
diaease-causing virus particles can survive for months in chicken house dust and litter.

Signs

The signs and symptoms of Marek's disease vary depending on the form of the disease.
    Cutaneous form:  Enlarged reddened feather follicles and white bumps on the skin that form brown crusty
    scabs.

    Neural form: Characterized by one, all or none of the following symptoms;
  • Progressive paralysis, usually of the leg or wing, a typical leg-paralysis victim will have one leg extended
    forward and one leg extended back.  A swelling of the sciatic nerve is the cause.
  • Weight loss
  • Labored breathing
  • Diarrhea
  • Starvation and death due to an inability to reach feed and water and to trampling by pen mates.

    Ocular form:
  • Grey eye color
  • Misshapen iris
  • Weight loss
  • Blindness
  • Death

    Visceral Form: Tumors on internal organs including heart, ovary, liver and ling.



Prevention

  • Breed for resistance
  • Good sanitation and ventilation
  • Brood chicks separately from adults until 5 months of age
  • Keep turkeys with chicks (the vaccine is made from turkey herpes virus  and raising turkey poults with
    chicks has shown to provide additional immunity to chicken mareks - however could lead to black head
    disease in turkeys)

Tumor formation from Marek's disease can be prevented through vaccination.  
Vaccination at one day of age usually protects birds through their lifetime. There is no treatment for Marek's
disease.
Mareks Disease
Marek's vaccine does not prevent Marek's disease, it prevents the malignant tumors caused by
Marek's disease.  It also helps to reduce the spread of the virus should an outbreak occur.
I hold the chick in my left hand (I am right handed)
and grasp the nap of the neck between my thumb
and forefinger resting the chick on the outside of
my hand on my pinky finger.
I inject the vaccine between my thumb & forefinger.  
(Being careful not to stick my own finger)         
I can feel the vaccine make a bubble under the skin in
the nap of the neck.  I avoid hitting an air sac by injecting
into the skin between the thumb and forefinger.
Vaccinating day old chicks
for Marek's Disease
Rare and Heritage poultry