What is Marek’s Disease?

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So what is Marek’s disease? 

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Marek’s disease is a viral disease of poultry, primarily chickens. It can come in several “forms” and symptoms can include, but are not limited to: Partial or total paralysis of the legs, sometimes wings, and even neck; visceral lymphoma (cancerous tumors in the body), blindness, tumors or growths on the skin, general listlessness, wasting away, or poor health, to name a few. Some chickens get only one symptom, and some get more than one. Some chickens get symptoms, while some don’t show any signs. It is a very common disease, as it is spread via chicken dander (dust) and is easily spread on new chickens, the wind, your clothes and shoes, and even wild birds can transport it. It does not always show up in quarantine. It can be fatal, and there is no cure. Some chickens do survive it, and many build resistance to it. If you suspect you have Marek’s disease in your flock, do not panic, but please do educate yourself. This is a somewhat complicated disease and the very best thing you can do for yourself and your chickens is to learn about it and take an educated approach to managing Marek’s.

 

Marek’s 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.

What do we know about Marek’s? (Facts)

  • First, most importantly, THERE IS NO CURE. There is NO proof the vaccines work. Its simply a hit and miss. Chicks given the vaccines can get it and do die from Marek’s from time to time. There is no scientific data suggested that it prevents Marek’s.
  • It can’t be transmitted from Mother to Chick
  • If your chicken has been exposed it will be a carrier for life.
  • Being a herpes virus, your chicken may carry it and never have any issues. It prey’s on a weak immune system. Just like people, they have herpes and sometimes never have an outbreak.
  • No, you can’t get Marek’s or Herpes from your chicken.
  • Marek’s is spread commonly by chicken dander. (Dust, Dirty coop, feathers, etc)
  • It is VERY contagious. If its on your property, your chickens have it.
  • It is Airborne.
  • You CAN eat the meat and eggs from chickens that have Mareks.
  • To date, Chicken Marek’s disease virus (MDV) is not known to be zoonotic (contagious) to other commonly kept fowl, except rarely in quail, and in some cases enclosed commercial breeding of turkeys in Europe (said turkeys had been housed in closed quarters close to infected broiler chickens).
  • Other Diseases present themselves just like Marek’s. Do your research.

 

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Well, How can my chickens get it? 

  • Exposure to other chickens that have had in in the past, even thought they show no signs.
  • Putting healthy new chickens in an old coop. (You can’t clean your coop and get rid of it. Its in the ground, the wood, the poop, the air, etc)
  • Exposure to dander transported unwittingly from infected chickens by wild birds, the wind, rodents, and human traffic (shoes/clothes). The chance of transport of dander by wind, wild birds, and rodents increases if there is an infected flock nearby.
  • Marek’s disease virus is known to survive in an exposed environment (such as the soil where chickens are kept) for at least 5 months, and possibly for several years.

 

Does my chicken have Mareks? (Signs)

  • Paralysis of one or both legs, and sometimes wings. This can include staggering, increasing loss of motor control in one or both legs, inability to stand or balance. This may present sometimes as one leg forward and one leg back (“the splits”) or simple paralysis of the legs. This is caused by lesions to the sciatic nerve, that controls the legs movement.
  • Going off of food or inability to “connect” with food when trying to eat. Sometimes mistaken for a sour crop or other crop problems, lesions on the vagus nerve can cause dilation of the crop and/or proventriculus. The inner lining of the gizzard may also be effected.

  • Difficulty breathing, darkening comb. Caused by several factors; brachial nerve lesions can restrict respiration. Additionally, lymphomas are known to grow into the heart muscle, reducing the chicken’s ability for proper respiration. The comb may become very dark red or purple in appearance and gasping or trouble breathing may occur. Marek’s does not cause discharge, watering eyes or nose, or gurgling– however these symptoms may be the result of a secondary viral infection by a different disease.
  • Lymphomas / Neoplasms (cancerous tumors) throughout the chicken. Though these symptoms can usually only be observed after death and a necropsy is conducted, lymphomas typically grow on the thymus (located in the neck, near the crop). The tumors then move on to grow on any of the following: gonads, spleen, liver, kidneys, lungs, heart, proventriculus, adrenals, muscles, and sometimes skin (enlarged feather follicles). These lymphomas are often aggressive, fast-growing, and are usually fatal as they cause organ failure.
  • Weight loss, “wasting”, depression. Inability to eat, connect with food, or digest food because internal tumors can cause rapid weight loss in birds. They may also “waste away” more slowly with no other obvious symptoms.
  • Loose, watery, and/or bright green stool. As the digestive system shuts down, or because the bird is not eating enough, the stools become increasingly loose and consisting of very little to no solids. This may be accompanied by green, bright green, or yellowish coloration.

Ocular Marek’s (ocular lymphatosis):

  • Discoloration of the iris. The iris may turn grey or a pale blue color.
  • Deformity of the pupil. The pupil may change shape. A typical form is a “keyhole” shape but the pupil may also look as if it is “melting” or might become amoeba-like in shape.
  • Pupil with no reaction to light changes. The pupil in one or both eyes may become constricted in appearance and might not react to changes in light. This can create a ‘tiny pupil’ appearance, called Miosis.
  • Blindness.

Cutaneous Marek’s:

  • Lesions or deformities at the feather follicles. This may be minor to severe and can range from large bumpy nodules to crusty looking lesions. They may be rounded or hard.

General symptoms:

  • Immunosuppression. Birds infected with Marek’s may have a periodic or lifelong supression of the immune system. Marek’s virus is known to cause impairment of T-lymphocytes which weakens the immune system. Secondary diseases or illnesses may then present as the chicken’s ability to fight them off is reduced considerably. Marek’s infected birds with immunosupression are known to be much more susceptible to coccidiosis and viral respiratory diseases. Immunosuppression may be transient (does not last) or it may be permanent. Some birds experience full immunosuppression (they do not have any immune system left) in which case a secondary disease is usually the ultimate cause of death.

  • “Come and go symptoms” with no obvious resolution. Some birds may present some symptoms, appear to get well, and then become symptomatic again at a later point. Problems might seem to come and go without much reason (this can be very frustrating to diagnose).

 

How long after being infected will a chicken show symptoms?

A bird may never show symptoms. Generally, Classic Marek’s (with paralysis and/or lymphomas) has an incubation period of 3-25 weeks. Meaning, the ‘soonest’ that a chicken might show visceral symptoms after being infected is about three weeks… but on the other hand it may not show symptoms for up to 25 weeks.

After initial infection, (when the chicken breathes the virus in), the general timeline is as follows for classic Marek’s disease only:

  • Approximately 7 days: Virus latency (meaning the virus has now stored a ‘blueprint’ of itself in the chicken’s cells).
  • Approximately 10 days – death: Full replication of the virus is carried out and the chicken begins to “shed” the virus.
  • Approximately 7 days -3 weeks: Lymphocytes carrying latent Marek’s virus travel through the body, to visceral organs and nerves.
  • Approximately 3-4 weeks: In chickens that do not develop resistance, the lymphocites in the organs and nerves undergo a transformation and become gross lymphomas. It is only at this point that symptoms appear and, sadly death often follows shortly after.

Reference:  http://jgv.microbiologyresearch.org/content/journal/jgv/10.1099/vir.0.81299-0#tab2

This is a FANTASTIC book to have on hand if you have chickens.

It is my GO to book if I don’t have the internet. Or you’re a prepper like me.  Link >> The Chicken Health Book #1 Best Seller in Animal Medicine.

 

All in all Marek’s is a nasty disease. I’ve lost a few birds to what I believe was Marek’s. There really isnt much you can do. You’ll read stories of people feeding thier chickens some homemade concoction of eggs and oatmeal and herbs and what not and while it may help, each case is different. The fact of the matter is that most chickens that develop the symptoms will be dead in a week. The good thing is that Marek’s isn’t an epidemic. Its not rampant. You probably won’t lose a whole flock. Its just that one or two weaker chickens that get it and die. Its unfortunate but it happens.

Below are a list of links with a TON more information.

Microbiology Society

Purdue Website

OIE Terrestrial Manual

Bird Health

Science Direct

 

 

Please feel free to share.  Also share your stories with us on your experience with Marek’s.

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