Does every flock of chickens have merak's?


9 Years
Jun 10, 2010
I have had the sad life of owning a flock that had the merak's disease. I killed off my flock and waited a few years and then got some more chickens. The merak's is still hear but I don't want to kill my flock again. I did some research on this mega merak's sight and it said that all chickens have it, its just some chickens are more vulnerable to it. My flock is vaccinated but still have it. What can I believe, and do people really know what they say about merak's? Thank you!

I'm no expert, but I've had it explained to me this way:

If you have air in your coop, you have meraks...
Some birds will be immune and some will not.

It's frustrating and heart-breaking
Marek's is prevalent in the environment. Fact.

Many if not most birds have been exposed to Marek's in their lifetime. Fact.

Marek's is a herpes virus that causes tumors to develop. It depends on the strain of Marek's as to what kind and where the tumors develop. Neural tumors create the classic paralysis (one leg forward, the other back) and unsteady gait. Skin and follicle tumors create odd lumps and bumps and cause grey looking eyes. Internal tumors can be a silent killer that affect internal organs causing a bird to slowly waste away.

Certain lines and breeds are simply more resistant to the tumors that develop. Many birds keep the tumors at bay until some stressor lowers their immune system. It is similar to the "cold sore" appearing when a human's immune system is lowered. The virus always lives in the body, but only appears at opportunistic times.

Vaccination does not prevent "catching" Marek's only the prevention or lessening of the tumor formation.

Marek's is morphing and becoming more resistant to the strains of vaccine given, so many in the industry believe it is better to breed for resistance rather than vaccinate to avoid the "super strains" which can wipe out whole flocks and whole industries.

I would not destroy my flock again unless I had a Marek's vulnerable flock. If you have a few birds that survive with vigor, breed from them!

Keeping your flock as stress free as possible with strong immune systems is the best defense. Use good husbandry (clean litter, water, feed), no crowding, high quality feed, regular parasite management (internal and external), boosters to keep the gut flora healthy (ACV and probiotics such as yogurt or kefer).

Supposedly St. John's Wort has some evidence of helping Marek's tumors, but I've not seen enough evidence to warrant giving it to the birds on a regular basis.

What I have gleaned in my own research.

Thank you so much, a whole ton of stress and confusion has just bin lifted off my shoulders.
You are welcome.

You can lessen the chances of impact by Marek's by keeping chickens from different lines and breeds and having some that are vaccinated (it won't pass it to the others). I've even made a point to keep a turkey or two or purchase birds where turkeys are raised as they often (but not always) carry the lesser virulent form of turkey Marek's which many of the vaccines are based off of (similar to cow pox used for vaccinating against small pox).

In other words, diversify to lower your chances of your whole flock being eliminated from one strain. Then practice good husbandry and biosecurity against other poultry and wild birds.


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