Marek's Disease in Chickens Symptoms & Treatments

Signs, symptoms, causes, and prevention for Marek's Disease in Chickens. Watch our featured video: Marek's Disease Symptoms in Chickens. There is no treatment available for affected birds. However, Marek's disease is preventable with a vaccine. People cannot catch Marek's Disease from chickens.

How Chickens Get Marek's Disease

Image of early stages of Marek's Disease. CHOE

Marek's Disease is a virus that causes tumors in chickens. This disease is worldwide and most if not all chickens have been exposed to it even if they do not show symptoms of the virus. It is caused by 6 different herpes viruses which affect very young birds. It usually is in the base of the feather follicles and then is shed in the birds dander. This virus is spread by bird to bird contact and contact with infected dirty litter and dander. It can survive for many months in chicken coop litter and dust. Contrary to popular beliefs, Marek's is not spread by mosquitoes, mites, coccidia (a parasite that reproduces inside an animals cell) or by hatching eggs. Exposure to the disease usually comes from contaminated bedding, dust, dander, can travel through the air from nearby infected poultry houses, and can be transferred by contaminated personnel and equipment. Scroll down to see signs/symptoms/treatments and more.

Marek's Disease: An Evolving Problem (Biology of Animal Infections)

Signs & Symptoms Depend on Which Form of Marek's The Bird Has-There are Four Forms of Marek's Disease

Signs of Marek's depends on which form of the disease is present.
There are four forms of Mareks.

Cutaneous (skin form)-"Cutaneous form: Enlarged reddened feather follicles and white bumps on the skin that form brown crusty scabs".
Neural (nerve form)-Characterized by one, all, or none of the following symptoms -Progressive paralysis which usually happens in the leg or wing, 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. Weight loss, labored breathing, diarrhea, starvation and death due to an inability to reach feed and water and can be easily trampled by pen mates.
Ocular (eye form)- Gray eye color, misshaped iris, weight loss, blindness, and death.
Visceral (internal-organ form) - Tumors on internal organs (heart, ovary, liver, and lungs).

Baby Chicks Have Protection From Marek's Disease for the First Few Days of Life

Newly hatched baby chicks have maternal protection from Marek's for the first few days of life. Immunization can be done in ovo (inside the egg -this is usually done by machine) or one day after hatching. Immunization can help prevent the chicks from contracting Marek's during their lifetime.

Marek's Disease Morbidity and Mortality Facts

Marek's disease morbidity and mortality rates are high in unvaccinated flocks. Morbidity (number affected) in unvaccinated flocks can reach 60 percent. Vaccinated flocks fare much better with less than 5 percent affected. Mortality in affected birds can travel quickly through the flock and reach nearly 100 percent over a 10-week period. Pullets are more likely to be affected than cockerels. Diagnosis is derived from the flock history, symptoms and necropsy (autopsy) findings.

How to Prevent Marek's Disease

Breed for resistance
Buy chicks that are vaccinated or vaccinate newly hatched chicks at one day old.
Good sanitation and ventilation.
Brood chicks separately from adults until 5 months of age.
Keep turkeys with chickens (this may help the chickens with Marek’s, but can lead to black head disease in the turkeys).
Vaccinate all chicks at 1 day old; keep chicks from exposure until immunity has developed, about 7 days.
Treatment for infected birds-No known treatment exists at this time.
"Cull affected birds. Some birds develop temporary paralysis that disappears after 1-2 days. They appear to return to normal, but frequently die from internal tumors a short time later" (University of New Hampshire Coop Extension, 2017).
https://extension.unh.edu/Agriculture/Dairy-Livestock-Poultry

MD-Vac CFL is the Recommended Vaccination for One Day Old Chicks

"MD-Vac CFL is recommended for the vaccination of healthy one-day-old chicks only, to aid in the prevention of the signs and lesions of Marek’s disease .For vaccination, an automatic syringe with 22- to 20-gauge needles, 3/8-inch to 1/2-inch in length, is recommended. Make certain that all equipment is sterilized and change needles frequently. Inject each chick subcutaneously with 0.2 ml prepared vaccine. Live virus; requires mixing" (Valley Vet Supply, 2017).
https://www.valleyvet.com/ct_detail.html?pgguid=0a374926-e913-44e0-9eb3-4de559b5efaa

Studies Show Revaccination With Marek's Vaccine is more effective Than a Single Dose

After extensive testing in field trials of chickens from different poultry houses infected with Marek's Disease researchers have proven that chickens are better protected by 11.7 to 18.5% against MD if they are vaccinated more than one time, when vaccination with cell-associated Fc126 was applied. "Chickens from four flocks with 2,064 chickens each were immunized with the Fc126 or CVI988 MD vaccine at 1 day of age or were boosted at 7 days of age. Thirty-six unvaccinated chickens were housed with each vaccinated flock to indicate the degree of contamination and the virulence of the field MDV strains on the farm. The rates of mortality for each unvaccinated group ranged from 33.3 to 36.1% in the different experimental houses, indicating that the rate of contamination with pathogenic MDV was heavy during the trials. The results of the trials showed that revaccination with Fc126 significantly reduced the rate of mortality from MD from 9.7% to 3.4% (P < 0.005), and revaccination with CVI988 gave the best protection (P < 0.005), with rates of mortality from MD of 1.9% among chickens revaccinated with CVI988 and 6.1% among the chickens in the flock that received a single vaccination".
Citation: AMAWu C, Gan J, Jin Q, et al. Revaccination with Marek’s Disease Vaccines Induces Productive Infection and Superior Immunity . Clinical and Vaccine Immunology : CVI. 2009;16(2):184-193. doi:10.1128/CVI.00201-08.
MLAWu, Changxin et al. “Revaccination with Marek’s Disease Vaccines Induces Productive Infection and Superior Immunity .” Clinical and Vaccine Immunology : CVI 16.2 (2009): 184–193. PMC. Web. 18 Sept. 2017.
APAWu, C., Gan, J., Jin, Q., Chen, C., Liang, P., Wu, Y., … Davison, F. (2009). Revaccination with Marek’s Disease Vaccines Induces Productive Infection and Superior Immunity . Clinical and Vaccine Immunology : CVI, 16(2), 184–193. http://doi.org/10.1128/CVI.00201-08