Skip to main content

Marek's Disease

Index of Bird Diseases ... Symptoms and Potential Causes ... Bird Species and Diseases They are Most Susceptible to


Cause / Transmission: A herpes-virus. Highly contagious. Spreads by bird-to-bird contact, by contact with infected dust and dander, and by darkling beetles and mealworms that live in the chicken house.Morbidity is 10-50% and mortality up to 100%. Mortality in an affected flock typically continues at a moderate or high rate for quite a few weeks.

Occurs mainly in chickens under 16 weeks of age. In late Marek's the mortality can extend to 40 weeks of age. Affected birds are more susceptible to other diseases, both parasitic and bacterial. The virus doesn’t survive the incubation process well and is not spread by hatching eggs. Immune transfer from the hen to the chick provides some protection to the chick for the first few days of life.

Different forms of Marek’s Disease:

Cutaneous form (skin form): Enlarged reddened feather follicles and white bumps on the skin that form brown crusty scabs.

Neural (nerve form): Progressive leg or wing paralysis - 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.. Other possible symptoms: Twisted neck, weight loss, labored breathing, eye lesions, vision impairment, diarrhea, starvation and death due to an inability to reach feed and water and to trampling by other chickens.

Visceral (internal-organ form), i.e. tumors on visceral organs,- such as heart, ovary, tests, muscles, lungs

Treatment: None. High mortality.

Control: Vaccination of chicks at one day of age. Hygiene is of utmost importance. Please note that Marek’s disease-causing virus particles can survive for months in chicken-house dust and litter.

Similar Diseases / Conditions:

Find Your Local Avian Veterinarian

Information contained on this website is provided as general reference only. For application to specific circumstances, professional advice should be sought.


The Avianweb strives to maintain accurate and up-to-date information; however, mistakes do happen. If you would like to correct or update any of the information, please send us an e-mail. THANK YOU!


Add new comment

Plain text

  • No HTML tags allowed.
  • Lines and paragraphs break automatically.
  • Web page addresses and email addresses turn into links automatically.