Marek’s Disease
Marek’s Disease is a viral tumor-causing disease of chickens. Marek’s is distributed worldwide and is so common that if you have birds, they have been exposed to Marek’s, regardless of whether they show symptoms or not. There are 4 different forms of Marek’s:
Marek’s Disease is caused by 6 different herpes viruses that primarily affect young birds. The virus concentrates in feather follicles and is shed in dander. Marek’s disease-causing virus particles can survive for months in chicken-house dust and litter.
Transmission
Marek’s is highly contagious and 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, although the virus has no affect on the beetles or mealworms.
Other organisms common to chicken houses such as free-living mites, mosquitoes and coccidia do not transmit the disease. Chickens are most commonly exposed to Marek’s by contact with residual dust and dander in previously infected houses, by aerosol (air) contamination from a nearby house, or by virus particles carried by personnel and equipment. 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.
Signs
The signs and symptoms of Marek’s Disease vary depending on the form of disease present.
Cutaneous form: Enlarged reddened feather follicles and white bumps on the skin that form
brown crusty scabs.
Neural form: Characterized by one, all, or none of the following symptoms -
• Progressive paralysis, usually of 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 to trampling by penmates.
• Cutaneous (skin form)
• Neural (nerve form)
• Ocular (eye form)
• Visceral (internal-organ form)
Ocular form:
• Gray eye color
• Misshapen iris
• Weight loss
• Blindness
• Death
Visceral Form: Tumors on internal organs including heart, ovary, liver and lung.
Morbidity and mortality
Morbidity (number affected) in unvaccinated flocks can reach 60 percent. Vaccinated flocks fare better with less than 5 percent affected. Mortality is high in affected birds reaching nearly 100 percent over a 10-week period. Pullets are more likely to be affected than cockerels.
Diagnosis
Diagnosis is derived from the flock history, symptoms and necropsy findings.
Prevention
• Breed for resistance.
• 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
None. 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.
For more fact sheets in the small flock poultry management series return to:
http://extension.unh.edu/Agric/AGDLEP.htm
For more information in
New Hampshire:
Family, Home & Garden Education Center
Toll free Info Line in New Hampshire
1-877-398-4769
M-F • 9 AM - 2 PM
W • 5 - 7:30 PM
or visit:
http://extension.unh.edu/FHGEC/FHGEC.htm
For more information in
Connecticut:
Home & Garden Education Center
Toll free Info Line in Connecticut
1-877-486-6271
M-F • 8 AM - 5 PM
or visit:
http://www.ladybug.uconn.edu/index.html
Fact sheet by Tina Savage, UNH Cooperative Extension Agricultural Resources Educator in collaboration with
Dr. Michael J. Darre, Professor of Animal Science and Extension Poultry Specialist, University of Connecticut, 8/08
Visit our website: extension.unh.edu
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MAREK'S
There are five syndromes known to occur after infection with Marek's disease. These syndromes may overlap.
Classical Marek's disease or neurolymphomatosis causes asymmetric paralysis of one or more limbs. With vagus nerve involvement, difficulty breathing or dilation of the crop may occur. Besides lesions in the peripheral nerves, there are frequently lymphomatous infiltration/tumours in the skin, skeletal muscle, visceral organs. Organs that are commonly affected include the ovary, spleen, liver, kidneys, lungs, heart, proventriculus and adrenals.
Acute Marek's disease is an epidemic in a previously uninfected or unvaccinated flock, causing depression, paralysis, and death in a large number of birds (up to 80 percent). The age of onset is much earlier than the classic form, birds are four to eight weeks old when affected. Infiltration into multiple organs/tissue is observed.
Ocular lymphomatosis causes lymphocyte infiltration of the iris (making the iris turn grey), anisocoria, and blindness.
Cutaneous Marek's disease causes round, firm lesions at the feather follicles.[2]
Atherosclerosis is induced in experimentally infected chickens.[3]
Immunosuppression – Impairment of the T-lymphocytes prevent competent immunological response against pathogenic challenge and the affected birds become more susceptible to disease conditions such as coccidiosis and "Escherichia coli" infection .[4] Furthermore, without stimulation by cell-mediated immunity, the humoral immunity conferred by the B-cell lines from the Bursa of Fabricius also shuts down, thus resulting in birds that are totally immunocompromised.
Marek's Disease
Also known as:
MD; Neuritis; Neurolymphomatosis; Range Paralysis (eye form; gray eye, iritis, ocular lymphomatosis, uveitis)
Symptoms:
The first indication of infection is a variation in the growth rate and degree of feathering.
In chicks over 3 weeks old:
Most commonly 12 to 30 weeks old
Growing thin while eating well (most common form)
Deaths starting at 8 to 10 weeks and persisting until 20 to 25 weeks
In mature birds (6 to 9 months old):
Enlarged reddish feather folicles or white bumps (tumors) on skin that scab over with a brown crust (skin form)
Stilted gait or lack of coordination
Swelling of the peripheral nerves, particularly of the nerves of the leg and wing, is often noticeable
Pale skin
Wing or leg paralysis (involves nerves)
When both legs are paralyzed, one points forward and the other points back under the body
Sometimes rapid weight loss
Gaping or gasping
Transient paralysis lasting 1 to 2 days (pseudo-botulism form)
Dehydration
Emaciation
Coma
Death, due to inability to get to food and water or trampling by other chickens
The visceral organs may contain tumors ranging from microscopic size to fairly large.
Such tumor lesions may be confused with those of lymphoid leukosis without a qualified laboratory diagnosis.
Marek’s symptoms feet first
· Limping
· Toe’s may be swollen or bent
· Unable to weight bear on the foot or leg
· No loss of appetite
· No visible pain
· Just loss of mobility
· Usually affects one leg, then a wing
· Then it affects both legs, one leg will be stretched out front and the other out the back of the bird (classic position)
In breeds with reddish bay eyes:
Cloudy, grayish
Dilated
Irregular pupil ('gray eye, involved optic nerve)
Distorted or blinded eye
In all ages:
Sudden death of apparent healthy birds
Treatment:
Most people say NONE; to cull the birds
Some tumors, particularly those of the feather follicles, clear up and the bird recovers on its own
But survivors are carriers of this disease for the rest of their lives
On page 2 of this thread is a Pro Biotic Approach to treating Marek's Disease, I have never used it so do not know if it works, it is up to the person reading to decide if they would like to try it
Tumor formation from Marek's disease can be prevented through vaccination.
Salsbury MD-Vac, a vaccine of chick-embryo tissue culture, is recommended.
Vaccination at one day of age usually protects birds through their lifetime.
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These may be the first symptoms of Marek’s Disease, they usually show up in birds that are young, but this disease has attacked older birds also
