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What is Marek's Disease?

Marek’s disease is a very common disease that may affect your chickens. It spreads quickly through a flock, affecting young birds between the ages of 8 and 20 weeks of age. If you raise chickens, it is vital to understand the signs of this virulent disease so that you can take action against it. There is no cure, with prevention being the most important course of action to take. The disease occurs most commonly as the nervous form, with progressive paralysis in one or both limbs, and sometimes showing in the neck or wings as one of the main symptoms.

Marek’s disease is highly contagious amongst chicken flocks and is caused by the herpesvirus. There is no cure and it brings a high mortality rate.

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Symptoms of Marek's Disease in Birds

  • Vision impairment, with a change in the eye colour showing a grey iris or irregular pupil 
  • Skin change in texture around the feather follicles, often appearing raised and bumpy 
  • Lameness and leg weakness without any visible signs of swelling or heat within the limb 
  • Partial or progressive paralysis of the limbs is a typical symptom of Marek’s disease 
  • The paralysis can also affect your chicken’s neck or wings causing your bird distress  
  • Loss of weight due to the inability to reach the water and their feed  
  • Difficulty in breathing 
  • Diarrhea 


Nervous Form

 The most common type of Marek’s disease begins as a progressive paralysis of the neck or wings, and limbs, affecting the sciatic nerve (main leg nerve). If your bird has this type of MD it may seem uncoordinated on its feet. Paralysis takes over very quickly and blindness can occur.

Visceral Form

This presents as tumors within the internal organs of your bird such as ovaries, spleen, liver and heart. Symptoms include depression, paralysis, loss of weight, anemia (pale combs) and sometimes diarrhea. Your bird may die suddenly without any sign of the disease.

Causes of Marek's Disease in Birds

  • Marek’s disease is caused by the herpesvirus or more specifically, it is a DNA virus 
  • This highly contagious disease (among your chickens) is spread by chicken dander (dust) through inhalation 
  • This condition increases the risk of other diseases as the immune system is compromised 
  • It can also spread rapidly through contact with other contaminated chickens in the flock 
  • Dander from other wild birds, the wind, human shoes can all spread the disease 
  • It can be spread through environmental factors such as an infected enclosure
  • MD can survive in the soil where chickens are kept for at least five months

Diagnosis of Marek's Disease in Birds

If your notice any of the symptoms of Marek’s disease within your bird population you will need veterinary assistance to diagnosis this condition. On examination, the symptoms will be a major factor, and if any of your flock have died, a post mortem will confirm your veterinarian’s analysis. With post mortem findings, the enlargement of the nerves such as the sciatic nerve will be obvious, and changes within the internal organs may be visible. 

There is a vaccination (for commercial poultry but small doses are not yet available to the backyard bird keeper) against MD that is advisable for your birds; it is not a cure, it only helps your bird to build up a resistance to the disease. In other words, just because your bird is vaccinated it is no guarantee that it will not catch this disease. Marek’s disease is a common virus that occurs where there a flock of chickens being raised. It can spread rapidly in unvaccinated birds, so that they become infected. They can carry the virus for life and can shed the virus through the feather follicles which then spreads rapidly in the dust and fluff in the environment. One thing to note, it is not spread from the hen to the chick through the egg, and the meat and eggs from infected birds are perfectly safe to eat.

Treatment of Marek's Disease in Birds

There is no cure or treatment for Marek’s disease. Those birds who are diseased should be removed from the others, and sadly humanely destroyed. Close monitoring of your remaining birds to see if they are infected is important. Although vaccinations are commonly used for those commercial poultry farmers, it is not available in small doses for the hobby poultry keeper. If you are buying new birds choose from a commercial source that has vaccinated its stock. Although it will not prevent your birds from getting this disease, it will make them more resistant to it.

Preventative measures are also important, such as ensuring chicks are separated and reared so that they don’t get the infected fluff and dust of older birds. A regular clean out of the shed or enclosure, and equipment such as feeding bowls is very important. Disinfecting these areas will help prevent MD. Superior quality feed and regular treatment from parasites is also good practice. By practicing good management, it will ensure your birds have the best chance to resist Marek’s disease. Consult your veterinarian regularly as to the annual care for members of your backyard flock.

Recovery of Marek's Disease in Birds

There is no cure for this disease. There is only prevention and management of your birds. Because MD is spread via chicken dander and dust, maintaining good conditions within enclosures is important. Sterilising of the utensils, perches and even relocating the birds to another enclosure while you turn over and treat the soil (if you have a dirt floor) is a good routine to get into. MD is not contagious to humans thankfully. But care with new breeding stock or chicks from reputable breeders who vaccinate their birds is important. Because this disease is so contagious it can travel through your flock of birds leaving them decimated within weeks. Prevention is an essential part of bird rearing management.

Marek's Disease Questions and Advice from Veterinary Professionals

2 Years
Moderate condition
0 found helpful
Moderate condition

Has Symptoms

see above

In a year and a half had 3 hens display similar signs of illness. Wondering if it’s merricks. All lost weight, slowed down, slept or closed eyes , comb went black/ or pale puffed up their feathers , lost use of legs. Other hens seem fine and long periods between each bird getting symptoms ( a year from 1st to 3rd) . Any ideas. Vets here in Wales are very unhelpful when It comes to hens.

Dr. Michele King, DVM
Dr. Michele King, DVM
681 Recommendations
Thank you for your email. It is possible that your chickens are showing signs of Merrick's disease. There is a vaccination for that disease, and you may have more luck consulting with a large animal veterinarian, or a bird specialist who will know more about chicken health concerns and preventive care.

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Silkie hen
4 Months
Moderate condition
1 found helpful
Moderate condition

Has Symptoms


Hi, my hen is alert and has a good appetite, but unable to stand. This began three days ago where she was not able to put weight on one leg, now she can't stand at all. Can you please help? Thanks

Dr. Callum Turner, DVM
Dr. Callum Turner, DVM
2159 Recommendations
Most issues with chickens not putting weight on their feet occur under the age of six weeks and is normally attributable to perosis; some dietary deficiencies may also cause issues but most likely some trauma to the affected leg is the cause. For the time being, if there are no other symptoms ensure that Hop is on a sufficient diet and all rest; if there is no improvement over the next week or so I would drop in to your Veterinarian. Regards Dr Callum Turner DVM

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