All You Need To Know About Marek’s Disease - The Happy Chicken Coop (2023)

Marek’s disease is an insidious disease that catches many keepers by surprise.

Its effect on your flock can be devastating.

We’ve discussedMarek’s in the past.

However, there is much misinformation, so this article will clarify matters for you and your birds.

Many keepers are lucky to go a lifetime and never see this disease, even though it is widespread.

To find out if it is endemic in your area, call your local extension office; they should be able to tell you if it is present near you.

I have written this article in a question-and-answer format as this is the easiest way to convey information about this complex disease.

I encourage you to read, read, read! There is a lot of information out there about Marek’s disease.

Concerning vaccines, it seems to be constantly changing.

Remember, if in doubt, please get in touch with your local veterinarian or extension office for help.

What is Marek’s Disease?

Marek’s disease is a viral disease of chickens caused by the herpes virus.

Current research shows thatthe virus has six mutationsthat can cause the disease.

Depending on the strain Marek’s disease caught, the virus can range from non-pathogenic (not causing disease) to highly pathogenic (causing illness and death).

It was first noted by the brilliant Hungarian veterinarianJozsef Marek in 1907. When he wrote his paper about it, it was likely that only one strain of the virus existed; however, other songs have mutated since then.

Reputable sources currently say that Marek’s is so widespread that you already have it in your flock, or your flock has been exposed-don’t panic!

Reading about the disease and understanding, it will help guide your decisions and treatment.

What Are The Signs of Marek’s Disease?

Some birds do not show any ‘symptoms’ of disease.

They may simply resist it, or the type of virus caught may benon-pathogenic(not causing disease).

It should be noted that there are four different presentations of Marek’s disease- Neurological, Visceral, Cutaneous, and Ocular.

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The type of presentation will dictate the kind of signs that you will see.

Signs for each form will vary- some birds display all signs, others not so many.


The neurological form of the disease is the most notable and disturbing in its presentation.

The symptoms are mainly caused by lesions affecting the nervous system, and several other problems usually follow.

Occasionally the affected bird willhave temporary paralysis, resolving itself spontaneously.

  • The bird shows progressive paralysis, usually in the legs or wings. Often the bird looks like it’s doing the splits.
  • Twisting of the head to one side or backward.
  • Respiratory problems such as labored breathing.
  • Darkened or purple comb (lack of oxygen).
  • Diarrhea.

All You Need To Know About Marek’s Disease - The Happy Chicken Coop (1)

Ocular (Eye)

  • Graying of the eye color.
  • Misshapen iris.
  • Blindness.
  • Non-reactive pupil of eye.

Cutaneous (Skin)

  • Lesions around the feather follicles.
  • Ulcers and/or scabs around follicles.

Visceral (Internal)

Often the only diagnosis of visceral Marek’s is, sadly, post-mortem due to internal maladies.

  • Cancerous tumors grow inside the bird on the organs.
  • Weight loss.

It’s also very likely that your chickenswill stop laying eggs during this time.

How Do Chickens Catch It?

The virus is primarily spread by infected dander (dead skin cells) from other birds.

However, it can be transported in dirty hen carriers, clothing and boots, wild birds, and darkling beetles in the henhouse.

It can survive for up to 65 weeks in ambient temperature in coops and for years in the soil.

The virus is spread horizontally- from chicken to chicken, not from the hen to the egg.

So the virus will spread quicker among hens in tight living conditions- make sureyour hens have enough room!

The primary age for disease manifestation is between 5-25 weeks, but this does not mean that older birds will not suffer from it.

It just means that younger birds are more susceptible.

How Can I Prevent It?

Vaccination of chicks will help lessen the severity of an outbreak if it should occur.

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However, the vaccinedoes not preventthe bird from getting Marek’s.

The vaccine allows the bird to build a better immunity to the disease, reducing the likelihood of severe symptoms or death and reducing the spread of disease if an outbreak occurs.

Part of the problem lies in the fact that the virus is constantly mutating, similar to the human flu virus.

Your birds may be vaccinated against one strain of Marek’s but not the one that infects them.

Another way to prevent the spread of Marek’s is to not add any additional hens to your existing flock.

Few backyard keepers do this. We are drawn to getting new birds periodically, so it is challenging to keep Marek’s out of your flock effectively.

If you are compelled toadd additional hens to your flock, ensure that new birds come from a reputable source that strictly practices quarantine.

You should know that Marek’s does not always show up in quarantine, so even with rigorous measures, it is possible to bring Marek’s home with you.

As always,good housekeeping, biosecurity, and ventilation are essential tools in your fight against the disease.

Marek’s virus is resistant to some disinfectants such as Phenol; however, many keepers recommend using Oxine.

This kills the virus and has very low toxicity to the environment.

How Can I Treat Marek’s Disease?

Unfortunately,there is currently no treatment/cure for Marek’s disease.

Depending on the severity of the disease, some birds can be conservatively managed and do not require culling.

However, they will remain carriers of the disease for the rest of their lives.

Are all birds affected?

If one bird in your flock gets Marek’s, all will likely get it.

However, not all will show symptoms or experience disease.

Birds that have been vaccinated have higher immunity.

Still, birds that have a weak immune system or some other ongoing health issue will probably succumb.

The virus goes into a ‘sleeper’ mode in infected birds with strong immunity or resistance.

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It will insert itself into the bird’s RNA sequence and lie dormant.

If the bird becomes immune suppressed later in life, the virus may emerge at that time, causing symptoms.

Should I Vaccinate My Birds?

This is a very personal decision.

If you want an entirely ‘organic’ flock, or you generally dislike vaccines, be aware that if Marek’s attacks your flock, there will be a significant loss.

The birds that do not die from it will be carriers for the rest of their lives, so you should not sell, give or loan your birds to other flock owners.

If you choose to vaccinate, you may still have losses.

Some flock owners have had chicks vaccinated at the hatcheries only to have them die later from a different strain.

The vaccinedoes not guarantee immunity.

If you show your birds, vaccination is highly recommended.

Your girls will likely be in contact with other hens, and the likelihood of them catching Marek’s is significantly increased.

Many keepers and poultry people recommend that you do vaccinate since Marek’s seems to be very pervasive.

If it is endemic in your area, it would be prudent to vaccinate.

If you have older birds that have not been vaccinated, it is possible to vaccinate them at any time.

However,this can become an expensive prospect, and as noted before, the vaccine will not guarantee immunity.

When Do Chickens Show Signs of Marek’s Disease

Unfortunately, some chickens may never show signs of the disease, and each type of Marek’s disease can present itself differently.

For example, the neurological form typically has an incubation period from 3 to about 30 days after exposure.

Can other Birds Get Marek’s from My Chickens?

Typically, Marek’s disease is mainly a chicken disease. Still, some sources state that it can spread between different types of birds.

To be safe, rather than sorry, consider keeping birds like quail away from your chickens since they can catch other diseases.

There are plenty of other diseases that can be passed from one species to another, so erring on the side of caution is never a bad idea.

Marek’s Disease FAQs

Q: How do I know if it’s active in my area?

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A: You can start by calling your local extension office- they should have the information.

Also, talk to the chicken people in your area; they are always a mine of information!

If they have been bothered by Marek’s, ask them where they got the chicks from…

Q: Can I catch it?

A: No, Marek’s disease is not contagious to humans.

Q: Can I eat the eggs and meat from an infected bird?

A: The virus does not travel to the egg from the mother- eggs are safe.

Justmake sure to properly clean them.

Meat from an infected bird can be eaten as long as it is properly cooked- but we wouldn’t recommend it.

However, chances are you won’t be able to because infected birds should be incinerated to prevent the disease from spreading.

Q: How do I know if my hens have Marek’s disease?

A: The only way to know for sure is to have a laboratory test and evaluation by a veterinarian.

However, if their symptoms match the symptoms mentioned earlier in this article- they likely have Marek’s.


Marek’s is a pervasive disease that is widespread amongst chickens.

It is a cancer-causing virus and, as such, is being researched constantly because of the implications for human treatment.

As a virus, it constantly mutates and presents an ever-changing challenge.

The vaccinated bird is somewhat protected, but unvaccinated birds can be in danger of succumbing to a more contagious strain of the disease.

It is difficult, if not impossible, for the average backyard chicken keeper to keep Marek’s out of their flock.

Unfortunately, some devastating experience consequences when the disease emerges, but for most of us, the impact is minimal.

Keeping your flock healthy, practicing good housekeeping, and strict quarantine practices will all help in the fight against this awful disease.

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