Case Study: Marek’s Disease

Over a period of several months, starting in the fall of 2019, I dealt with the first cases of suspected and confirmed cases of Marek’s Disease in my flock.

What Is Marek’s Disease?

Marek’s is a Herpes virus spread by infected feather-follicle dander. The route of transmission is usually respiratory and the disease is highly contagious because it can survive at room temperature in feather dust for at least a year.

Once in the body the virus initially circulates in the blood stream and within a week it infects white blood cells and kills B Lymphocytes, which produce antibodies that are essential for a healthy immune system.

Antibodies attach to pathogens and stimulate other immune cells to recognize it as a foreign invader and spark a complicated process of destroying it. As the B Lymphocytes are destroyed by the Marek’s virus the bird’s immune system becomes compromised making it more vulnerable to other diseases such as respiratory diseases and coccidiosis.

Marek’s also infects the T cells, which are involved in controlling the bird’s response to infection and its effects on the immune system. T cells are not killed by Marek’s, but are changed in a way which will eventually kill the bird. The infected T cells stay dormant for about 10 weeks, then start to multiply forming tumours in various organs including the liver, kidney and spleen. Birds slowly lose weight but outwardly appear normal, until at some stage they become incapacitated.

The disease manifests in various ways:

• Young birds (10-12 weeks old) often present with neurological issues: nerve cells are affected resulting in nerve failure and paralysis of the leg, wing and neck. It typically affects the sciatic nerve causing the classic one legged paralysis, which makes the bird appear to be doing the splits.
• The second phase, seen as birds mature, is the development of tumours in the heart, ovaries, testes, muscles and lungs.
• Birds can have ocular abnormalities: greying of the iris; misshapen iris; blindness; eye lesions; and tumours in the feather follicles.

My Case Studies

Case 1  (Appenzeller Spitzhauben x Easter Egger pullet  June 11, 2019- Sept. 8, 2019)

Day 1: In the flock’s scramble running for some treats I noticed that she was a bit unsteady on her feet. I attributed it to her being knocked off balance by some larger birds, but her wobbling continued so I crated her for further observation.

She seemed a bit underweight, but was eating, drinking and passed normal poop. Within a day her appetite seemed to decline and her poop was looser. I scrambled some eggs, which she was happy to eat. I noticed that something was amiss with her eyes – she seemed to blink a lot, but not when I shone a light in her eyes. I was concerned that her vision was impaired, but she was able to follow the food bowl if I moved it and to pick up individual pieces with no problem. She was standing but not moving much.

Day 3: She developed paralysis of her legs and loss of control of her neck. If I propped her upright she could sit, but once I put her down she flattened out and could not raise her head on her own. I posted her symptoms on a Facebook group with moderators knowledgeable in avian medicine and asked if it was Marek’s Disease. For whatever reason they thought not and suggested she might have ingested mold or a toxin and had aspergillosis. They advised flushing her system by giving her Epsom salts in water via syringe. I did that for a day with no success.

Day 4: It was apparent she now had an impacted crop and was not pooping. Still assuming it was an issue related to a toxin I withheld food and gave her molasses diluted in water via syringe to try to flush her system, but, again, was unsuccessful.

Day 5: Third day with paralysis:  she had no control of her legs; when they moved they hit her wings and she couldn’t hold her head up on her own. She had made no improvement and her crop was still impacted. I made the sad decision to euthanize her and didn’t send her body for a necropsy so I was left guessing as to what she was suffering from. In retrospect, her leg paralysis was a classic sign of Marek’s.

Case 2 (Appenzeller Spitzhauben x Easter Egger cockerel, June 10, 2019 – Oct. 31, 2019)

Day 1: Noticed him roosting on the floor for the first time

Day 3: Unsteady gait

Day 4: Started to drag his wing

Day 6: His wing appeared normal, but his gait was still off

Day 11: No improvement; euthanized, sent for necropsy:

Diagnosis: Marek’s Disease, Congenital Kidney Atrophy

• Complete atrophy of right kidney
• Mild evidence of M.D. in brain and sciatic nerve

Case 3 (Buff Orpington x cockerel Aug. 26, 2019- Oct. 31, 2019)

For the first six weeks of his life he appeared healthy, then seemed to not grow as quickly as his hatch mates, who all were unaffected.

Day 1: Bluish-purplish face. He was eating and drinking normally, but was less active.

Over the next two weeks he isolated himself, appeared hunched and cold and peeped a lot. At 9 weeks of age he was still roosting under his mother at night. On his final night he roosted on the coop floor.

Euthanized and sent for necropsy.

Diagnosis: Marek’s Disease, Crop Mycosis (Candida)

• Mild evidence of M.D. in brain and sciatic nerve

Case 4 (sibling of case 2, Appenzeller Spitzhauben x Easter Egger pullet, June 10, 2019 – Feb. 1, 2020)

Day 1: Starting limping, isolated her in a crate for observation.

Day 2: She was able to stand upright, but one foot was tightly curled and she didn’t seem to be able to open it. She did not have ‘splits’ like Case 1. She ate, drank and pooped normally. I, again, posted in an online chicken support group and was advised to treat as an injury.

Day 10: Deteriorated and was not standing. Euthanized, but did not send for necropsy.

Case 5 (Runty: sibling of cases 2 & 4, Appenzeller Spitzhauben x Easter Egger pullet June 10, 2019 – April 2, 2020)

This bird appeared normal for the first six weeks of her life and then virtually stopped growing. She spent most of her time with her siblings and ate, drank and pooped as normal. Her feathers always appeared lank and after the death of her hatch mates she often stood off by herself.

At 10 months she was still stunted and seemed to be loosing weight. Some diarrhea. Odd bumps around the feather follicles reminiscent of Marek’s Disease. Euthanized, but didn’t send for necropsy.

Case 6 (Pixie: Mille Fleur D’Uccle x Easter Egger July 23, 2018 – April 23, 2020)

I got Pixie as a four-month-old pullet. She hatched and raised cases 2, 4 and 5.

She appeared healthy until the day before she died when I noticed her stumble. I observed her drinking, but not eating. Upon picking her up I noted she was underweight. Crated her for the night and she had died by the following morning. This photo was taken five days before her death.

Necropsy Diagnosis: Marek’s Disease

• Marked swelling of the liver and spleen
• Liver is pale, meaty and friable
• Diffuse tan tumour infiltrates involving the lung, kidneys and intestinal mesentery
• No lesions present in brain, sciatic nerve or trachea
• “It is unusual to see Marek’s Disease in a bird of this age. Pixie is now the oldest bird I have diagnosed with Marek’s Disease.” – Dr Vicki Bowes, Animal Health Centre

As you can see from my six cases (three suspected and three confirmed) that they have expressed various manifestations of Marek’s in birds ranging from 9 weeks to 21 months old: paralysis of nerves affecting legs, wing and neck; eye issues; and tumours (lungs, kidneys, and intestinal mesentery).

In hindsight, I wish I had gotten necropsies done on all of them, but it’s not always practical or affordable. At least now I am aware of the potential signs of Marek’s and ways to mitigate my remaining birds from becoming sick in the future.

Read more about Marek’s Disease here. To join the Facebook group Marek’s Disease Information and Support click here.