Marek's Disease: Are Your Backyard Chickens at Risk?

Poultry keepers must be aware of the risk of their flock contracting Marek’s Disease, particularly in growing and point of lay pullets.

In our guide, we’ll answer the most frequently asked questions—how it’s transmitted, what symptoms to look for and how to prevent it.

What is Marek’s Disease?

Marek's Disease is a herpes virus infection that can cause tumours in chickens, and while there's a vaccination available, there is no cure. 

Unfortunately, Marek’s Disease is prevalent worldwide. The good news is that only a small percentage of chickens infected with the virus actually become sick. 

There are four forms of Marek's Disease, caused by six different herpesviruses, that primarily affect the nerves of growing birds.

The most common form of Marek's Disease affects the chicken’s central nervous system, which causes paralysis in the wings and legs.

Tumours can grow in the heart, lungs, muscles, and feather follicles, with one strain of Marek’s causing blindness. You’ll spot the chicken’s eyes turning grey, which causes the pupils to become an irregular shape.

As Marek’s attacks their immune system, chickens that have contracted the disease become more susceptible to other illnesses, infections, diarrhoea and other problems.

Forms of Marek's Disease 

1. Neural (nerve form) – The “classic” form of Marek's Disease, displaying progressive paralysis
2. Ocular (eye form) – Grey, irregular iris
3. Visceral (internal organs) – tumours found in internal organs such as the ovary, heart and lungs
4. Cutaneous (skin form)  – enlarged feather follicles

Contracting and transmitting Marek’s Disease FAQs

How do chickens get Marek's Disease?

Marek’s is carried in feather dander (the feather follicle cells, to be precise) and transferred by dust from infected birds’ skin and feathers.

How old are chickens when they can get Marek's Disease?

Marek’s Disease symptoms are most common in chickens aged 12 to 30 weeks.

Deaths from Marek’s Disease are most common around 8-10 weeks and at 20-25 weeks. This is because their bodies go through considerable stress as they reach maturity—especially for pullets starting egg lay.

Are some breeds more susceptible than others to Marek’s?

Like all breed characteristics, it depends on the strain, or your chickens' bloodlines. Some chicken breeds (and birds of breeders) have excellent natural immunity. You may hear breeders say some types of chickens are more susceptible than others, but it’s not always true.

Gail Damerow’s Chicken Health Handbook states that Marek’s is more common in larger breeds of chickens. While this may be the case, I have had clients with Wyandotte bantams, Silkies (a “large” breed but lightweight compared to most) and Polish bantams diagnosed with Marek’s by a veterinarian and succumb to this dreadful disease.

Can roosters get Marek's Disease?

Marek’s affects pullets (females) far more frequently than cockerels (males).

What percentage of chickens can get Marek’s?

Gail Damerow’s Chicken Health Handbook states, “30 to 50 per cent in unvaccinated flocks, less than 5 per cent in vaccinated flocks”. This is a good benchmark, but there’s no definitive answer.

However, contracting Marek’s can depend on many factors:

• Husbandry
• Stress
• Exposure
• The strain of Marek’s immunity of your flock
• Bloodlines
• Whether they were hatched under a hen or incubator
• Age
• Breed

Can humans get Marek's Disease from chickens?

No. Marek's Disease only affects chickens and, to some extent, turkeys.

Are all exposed birds and survivors carriers?

Yes. But, the reality is that most flocks (if not all) of purebred birds in backyards have probably been exposed to some form of Marek’s, as wild birds can carry the dust and dander. But for the majority, it’s never a problem.

Please don’t cull all birds you think are carriers! Instead, you may be culling some of your hardiest, most disease-resistant birds, and these are the birds you should breed from.

Can Marek's Disease be passed through fertile eggs?

No. Marek's Disease cannot be passed via the yolk or on the shells of clean (disinfected) eggs.

What are the neural Marek's Disease symptoms?

Unfortunately, one of the symptoms of Marek's Disease is paralysis or death of previously healthy-looking birds.

Symptoms in chicks over three weeks old may include growing but failing to put on weight or stunted growth.

Symptoms in maturing or grower age chickens may include:

• Unusual gait and or lack of coordination
• Paralysis of wing or leg on one side
• Paralysis of both legs, or one leg forward and one leg under or back.
• Transient paralysis, lasting 1-2 days. Your bird may look to be recovering; however, often, they regress.
• An overfull crop that will not empty
• Pale skin
• Gasping or showing discomfort to breathe
• Not eating or drinking—as the condition worsens, they may go off their food. Chickens that are lame are going to have trouble reaching food and water. 
• Rapid weight loss or emaciation. 

The sad truth about Marek’s is that it’s often dehydration and starvation that will kill a chicken affected by Marek’s before the actual onset of disease.

Unfortunately, there is no cure, and for this reason, many people choose to euthanise the bird if they can see that they are suffering.

What are the ocular Marek's Disease symptoms?

In breeds with bay (red) coloured eyes, ocular Marek's Disease symptoms may include blindness or an irregular pupil that may be greyish or cloudy and/or dilated.

What could Marek’s Disease be mistaken for?

• Primary lymphoid leukosis (symptoms are very similar). Lymphoid leukosis typically affects maturing birds over 16 weeks. Common symptoms for lymphoid leukosis include diarrhoea and vent feathers spotted with white (urates), green (bile), and a vet may be able to feel enlarged kidney, cloacal bursa or nodular tumours through the skin). Lymphoid leukosis is egg borne, whereas Marek’s is not.
• Respiratory disease when Marek’s affects the lungs
• Transient botulism

Paralysis seen in neural Marek’s can look like:

• Blackhead
• Epidemic tremor
• Joint infection or injury (especially when they look like they’re sitting on their hocks)
• Newcastle disease
• Slipped tendon
• Riboflavin (B2) deficiency
• Tuberculosis
• Tick paralysis 

Virus Survival FAQs

What is the survival rate for Marek's Disease?

Unfortunately, almost 0%. Most vets and breeders say there’s no cure.

Marek's Disease recovery is exceedingly rare.

How long does it take for a chicken with Marek’s to die?

Some birds will survive for 3 to 4 weeks. Others will die in about ten days. Often dehydration or starvation will in fact be the cause of death before Marek's Disease takes them.

How long will Marek’s last?

Marek's Disease can survive in dust and litter for years to come. But it’s not the end of the world!

If you are a backyard chicken owner who’s been through the trauma of Marek’s, I recommend that you go for laying pullets or even first year hens when you’re looking to buy more chickens. At this age, they have built up a natural immunity to the common neural strain.

Marek’s Disease therapy FAQs

How do you get rid of Marek's Disease?

Just like other herpes viruses, once a chicken becomes infected, it will be infected for life. However, not all birds who are infected with Marek’s Disease will get sick.

Is there a Marek's Disease treatment?

No.

There is a feather pathology test available through your vet to test for Marek's Disease. If you suspect your chicken died from Marek’s, an autopsy (necropsy) is money well spent to find out.

The best you can do is:

• Eliminate other diseases and conditions with your vet – is it an injury? Infected bursa?
• Treat any vitamin deficiencies and assist your flock to manage stressful periods with veterinary-quality chicken supplements such as Solaminovit
• Practice excellent biosecurity by isolating birds with suspicious symptoms. I wouldn’t introduce new birds unless you knew if you do or don’t have Marek’s.

How can I prevent my chickens getting Marek's Disease?

Whether you have Marek’s or not, keeping your incubator hatched chicks away from all adult and wild birds until they are 5-6 months will significantly reduce stress and their disease risk.

Hygiene and biosecurity are critical for all poultry breeders. While my flock is very healthy and stress free, the immune system of a young chick (especially one hatched from an incubator) is still developing. For this reason I:

• Disinfect all eggs before incubating
• Thoroughly disinfect my incubator and brooder box after use
• Keep separate equipment such as feeders and drinkers just for raising chicks
• Keep my young and growing chicks away from adult birds until point of lay
• Feed my young birds first (to reduce the risk of any cross contamination from my adult birds) and even keep separate boots (well actually they're crocs!) at the door of my chick raising shed.

Yes, I take biosecurity seriously. But it's not a lot of extra effort and significantly reduces the risk of diseases spreading to my young birds, who are still building their immunity.

Even for experienced breeders, “breeding for Marek’s resistance” is easier said than done. Some breeding birds carry a resistance factor—B21—which is detected through a blood test.

Vaccination is the other route. It’s a single injection given in the nape (like the scruff of a dog or cat).

Vaccinating is not a simple solution, and it can be challenging to find the Marek's Disease vaccine for sale in Australia.

As with most things in life, prevention is better than cure. Read my blog about how to keep backyard chickens healthy with the right chook feed and supplements.

When should you vaccinate for Marek’s?

If you’re looking at vaccinating chickens for Marek’s, you must do it immediately after hatching. Chicks should be isolated from older and adult birds for 21 days for the vaccine to take effect.

Why doesn’t everyone vaccinate for Marek's Disease?

• Not all vaccines cover all six strains
• The vaccine is not easy to administer
• The vaccine doesn’t keep long
• The vaccine is difficult to obtain
• Expensive for small numbers of birds

Can you vaccinate chicks hatched under a broody hen?

No, once the chicks have come into contact with the mother hen, there’s no point in vaccinating.

Can vaccinated chickens get Marek’s?

Marek’s vaccination will not prevent chickens from becoming infected with the Marek’s virus and shedding the virus onto other chickens, but it does prevent paralysis (Damerow, 2010).

Is Marek's Disease painful?

The twisting and muscle spasms of Marek's Disease may be painful and stressful to a bird. 

If a bird has been veterinary diagnosed with Marek's, they may stop eating and drinking. Often at this point, it's only a matter of time, either days or weeks. So the kinder thing can be to have them put to sleep. 

But! As nasty as Marek’s Disease may seem, don’t let that put you off getting chickens! 

In both rural and urban environments, most backyard chickens live long, happy lives and never contract the disease.

Want your chickens to be the healthiest and happiest they can be? I offer backyard chicken workshops, online programs, phone coaching, and in-person support to families, schools, and free-range egg farmers. Visit my online shop for natural, tried-and-tested poultry supplies in Australia.

Grab my free guide, The First 8 Steps To Naturally Healthy & Happy Backyard Chickens now! 

Resources:

Poultry Signals A Practical Guide For Bird Focused Poultry Farming

Storey’s Guide to Raising Chickens

Chicken Health Handbook

https://www.msdvetmanual.com/poultry/neoplasms/marek-disease-in-poultry