Marek’s Disease – Highly Contagious and Easily Transmitted

What Is It?

Curious Chicken

Marek’s disease is a tumor-causing herpesvirus that affects chickens worldwide.  It can also infect Quail and Turkeys but is much less common.  It is so widespread that if you have chickens you can assume that they have been exposed – whether or not they show signs of illness or disease.

What Does It Do?

Marek’s disease has 4 basic forms.

  • Cutaneous (skin) Form – enlarged feather follicles and white bumps that form crusty scabs
  • Neural Form – Paralysis (usually 1 leg forward, 1 leg back), weight loss, diarrhea, labored breathing, starvation and death
  • Ocular (eye) Form – grey eye color, misshapen iris, weight loss, blindness, death
  • Visceral Form – tumors on internal organs

Splay Leg Chicken

Affected birds may have multiple symptoms, only one of the above signs or only depression prior to death.

How Does It Spread?

This virus is highly contagious.  It can be spread by bird-to-bird contact, contact with infected dander and dust in the chicken coop, by beetles and mealworms that live in the coop, on the air from a nearby chicken house or carried in by people or objects.  Once it gets into your flock, the virus can spread rapidly between birds – even if they have been vaccinated!


It is not spread from an infected hen into the egg.  Neither mosquitoes nor mites carry the disease.

How Do I Know My Chicken Has Marek’s Disease

Diagnosis can only be confirmed after your chicken has died.  However, history and symptoms can suggest that it is present.  The death rate from Marek’s in an unvaccinated flock can be up to 60%.  If your flock is vaccinated – mortality is usually less than 5%.  You can see how vaccination makes a huge difference.

So, What Do I Do?

There is no treatment for Marek’s Disease – none.

The most common recommendation is to cull or provide a humane euthanasia for affected birds.

Can’t Treat, Can’t Diagnose…What Do I Do?

Vaccination is the key to controlling Marek’s Disease.  Chicks should be vaccinated at 1 day of age or in ovo (egg).  It takes about a week for immunity to develop so it is a good idea to keep chicks separated from adults.


Buy vaccinated chicks or eggs – it usually only costs a little more.


Vaccinate your own chicks or eggs – contact your local feed store about purchasing the vaccine.  There is one made by Fort Dodge that is not very expensive.  But it is only good for about 1 hour once liquified.  You can’t keep it to use later – make sure to throw it out when you are done.

The Merck Veterinary Manual
The University of New Hampshire
UC Davis Animal Science
The Poultry Site

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s