The Facts About Marek’s Disease NOT Merrick’s Disease


Marek’s disease is a nasty affliction in chickens which can cause tumours to grow in one or multiple locations on the unfortunate bird. All chicken owners should have some knowledge of Marek’s disease and what to look out for, as every flock carries some risk of becoming infected. The disease is often fatal, and there is no cure, although a few chickens do make it out alive.

Four different strains of Marek’s disease exist, with two strains affecting chickens, one which doesn’t cause illness, and another which only afflicts turkeys.

It’s a virus, but more specifically, it’s a DNA virus or alphaherpesvirus. It’s also a very hardy virus, as it has been discovered that it can survive in an exposed environment, such as the floor of a coop, for up to 5 months.

Chickens cannot pass on Marek’s disease through the egg. The chick will have to hatch and then encounter the virus to contract it. However, any chickens which are exposed to Marek’s disease should be considered lifelong carriers, even if they have been vaccinated, or don’t develop any symptoms.

Signs Your Chicken May Have Marek’s Disease

A few of the signs that your chicken may have become infected with Marek’s disease are as follows:

• Paralysis in the legs or wings, and can also cause the comb to flop.
• Tumours may also develop in major organs such as the lungs and heart, muscles, and in the follicles of the feathers.
• Chickens appear listless and lethargic.
• Chickens may show signs of wasting away or appear to be in general poor health.
• The other strain of the virus may cause blindness, turn the eyes grey and distort the shape of the pupils.
• Difficulty breathing caused by brachial nerve lesions.
• A darkening of the comb due to lymphomas growing in the heart muscle and restricting blood flow.
• Bright green or loose watery stools, which is the result of a digestive system that has shut down, or the bird losing their appetite and lacking nutrients. Over time the stools become more watery and may change in colour to bright green or yellow.

Marek’s disease may manifest as a single symptom, or it may generate several symptoms at the same time. The immune system of the chicken may also become compromised, creating further risk for the chicken to contract other diseases such as diarrhoea and infections.

How Does Marek’s Disease Spread?

Airborne particles such as dander and poultry dust can carry Marek’s, which are then breathed in by other chickens in the area. Poultry dust is made up of a few different compounds found around the chicken pen such as bedding, old feathers, chicken feed, and droppings. Dander is a term used to describe the dead skin cells which have been shed by a chicken.

Marek’s disease can also be carried into the flock on clothes, shoes, wind, rodents, and wild birds. The ease with which the disease can be transported means that any nearby infected flocks can greatly increase the risk to your flock.

The gestation period for Marek’s can be anywhere from 3 weeks, up to 25 weeks, so even if you quarantine every new chicken before introducing them to the flock, Marek’s disease can still slip by unnoticed.

Unfortunately, vaccination does not remove the risk of a chicken becoming infected with Marek’s disease once they have been exposed. The immunization serves only to build up immunity and reduce the chance of the bird developing symptoms. Fortunately, meat and eggs from infected birds pose no threat to humans when consumed.

How to be Sure Your Chicken Has Marek’s Disease?

Because there are so many signs of illness associated with Marek’s disease it can be a challenging disease to diagnose due to many of the signs possessing similarities to other conditions. Before jumping to any conclusions, you should inspect your chickens to eliminate the possibility that they may be afflicted with something else.

Lice, mites, and worms can manifest as droopiness, discolouring in the combs and wattles, and a lack of appetite. Egg binding, which is a disease that inhibits the laying of eggs, has many of the same signs as Marek’s disease including wobbly legs. She may even squat because her legs are totally failing.

Lead toxicity also manifests as partial or full paralysis of the legs, and occasionally the wings. While chickens don’t go around chewing on metal objects, they can easily swallow stray BB pellets and lead paint flakes. Even tiny amounts, to the order of a single BB shot, can cause severe neurological problems in a chicken.

Poor nutrition can also create conditions in chickens that look like Marek’s disease. For instance, a deficiency in vitamin B may cause paralysis in the legs. (Chicken Feed – Step by Step Australian Beginners Guide)

In the interests of biosecurity, if your chickens are showing signs of illness like Marek’s the recommended course of action is to move forward cautiously.

How Can I Protect My Birds Against Marek’s Disease?

Unfortunately, there is no way to fully protect your birds against the disease. The MDV-3 vaccination, or the Turkey Herpesvirus, is the most used version of the three vaccinations currently available. The other two are Rispens and SB1 (MDV-2). These are attenuated chicken Marek’s virus, or in layperson speak, they are benign versions of the virus.

Vaccinations are a related virus which helps the bird’s immune system develop some resistance against Marek’s virus as the bird ages. The hope is that once the bird is exposed, their immune system will be able to react against the virus and prevent the growth of lymphomas and the development of any of the other symptoms. A bird with strong resistance to the disease will also help decrease the amount of the virus spread by their dander.

Vaccinations are not a cure, nor do they provide immunity, and should be administered while the chicks have been out of the egg for less than 36 hours, with 24 hours being highly recommended. Providing the vaccine at such an early stage of the chicken’s life will ensure their immune system has an adequate amount of time to develop the necessary resistance.

Don’t Panic

While Marek’s disease is proving to be a tough nut to crack, the fact is, most backyard chickens go through their entire life without ever encountering it. If you want the best protection, then always buy chicks which have received their vaccinations. For more tips (Sick Chickens Signs, Symptoms and Treatments)

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