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

Emma The Survivor

Previously on Feathers, Fur and Scales…

I talked about the dangers of predator attacks in prey species such as birds.  I thought I’d present a success story.

Emma the Amazon

Emma was brought into our clinic after the owners found her injured in her cage.  She had been attacked by a very large predator (a cat, we discovered at a later date).  She had numerous wounds on her head and cheeks.  Her wing drooped.  There were puncture wounds and swelling on her body.  Worst of all, she wasn’t able to use her right leg.  It had been torn up pretty badly.  On the bright side, we weren’t able to feel any broken bones.


She was strong and responding to the initial treatment given by the ER so we anesthetized her for further examination, testing and wound repair.  The wound on her right thigh was extensive.  It required a great deal of work to identify damaged vs healthy tissue and close the skin where possible.  But she did extremely well!


The xray showed a broken wing bone.  Just like us, birds have 2 bones in the forearm.  The second bone (the ulna) is still whole and was acting like a splint.  Swelling around the fracture site made it impossible to feel the break.

Here it is on the first day – the red arrow points to the broken radius.  You can also see a catheter placed into the bone on the other arm for anesthesia support (green arrow).  The second xray was taken about 4 weeks later.  You can see the healing callus around the fracture.

broken wing            healing wing

Initially Emma wasn’t eating well so she had to stay in the hospital for fluid support and tube feedings.  She was on very strong antibiotics due to the severity of the wounds and the concern that a raccoon or large cat was involved.  After about 6 days she was released into her owner’s care.  They were able to continue the antibiotics and pain medications at home.

The wounds on Emma’s leg were very severe and while parts started to heal nicely, other parts did not.  The damage was much worse than originally thought.  Some of the muscle tissue that appeared healthy when she first came in wasn’t – it started to die and had to be removed.  The damage was so extensive that it was hard to close the skin over the wounds.  As Emma started to move around and be more active, she caused the sutures to tear out.  All and all, there were 3 surgeries on that leg before it healed!

Here are a few images of the leg during the healing process:

healing leg

sutured leg

healed leg

A few things strike me about Emma’s case:

The first is the length of time it took to fully heal – it took about 5 weeks for the tendon and ligament wounds to the wing to heal.  She had a very long lasting droop. But it eventually returned to normal.  It took another 3 weeks before she started talking again.  The prolonged healing just goes to show how much damage poor Emma had taken from that cat.  Emma was also on a seed-based or nutritionally deficient diet when it happened.  Luckily we were able to convert her to pellets after about 2 weeks!

The other issue is the lasting effects on Emma.  The bones in her head were damaged in the attack.  As a result, 4 months after we first met Emma, her beak started to show signs of abnormalities.  It is permanently askew and will require periodic beak trims for the rest of her life.

Here is Emma Today

Emma today