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Marek’s Disease in Small Flocks

17 November 2015


Christine Heinrichs is a freelance agricultural journalist based the US. She's the author of How to Raise Chickens and How to Raise Poultry, and a regular contributor to a variety of poultry publications.

This article from Christine Heinrichs explains the symptoms of Marek's Disease in poultry and how to prevent it occurring in small flocks.

The good news about Marek’s Disease is that it is rare in small flocks. Personally, I’ve never seen a case or even heard of anyone I know having a case. It’s nearly completely preventable.

The bad news is that the virus that causes it can be anywhere. It’s considered globally endemic in poultry. If your flock catches it, there isn’t any treatment for it and chickens that get infected are likely to die.

Causes, symptoms and how it spreads

Marek’s Disease is caused by one or more of three herpes viruses, in the same family that causes chicken pox and cold sores in people. Marek’s is not the same and you cannot catch it from your chickens. They can catch it from each other, though, and once it’s in the flock, it’s difficult to get rid of it. Young chickens less than five months old are more likely to catch it than older chickens.

Marek’s Disease causes tumours in chickens. The tumours may grow in the eyes, on the skin, in the nerves or the internal organs.

Usually the first sign is a chicken that goes lame. She’s paralysed by the tumours growing on her nerves. The skin form shows up as enlarged feather follicles and white bumps on the skin that turn into brown scabs. The eye form turns the eye grey and the iris becomes misshapen.

Tumours on internal organs are only diagnosed by cutting the chicken open, which is done in a necropsy to determine the cause of death. Some government offices offer free or low-cost necropsies as part of infectious disease programs.

All forms of Marek’s build up virus in the feather follicles, and it remains able to infect other chickens for months. All litter from chicken houses that have had Marek’s infection need to be completely cleaned and disinfected before vulnerable chickens move in.

The virus can be as airborne as a sneeze and it can live in the dirt chickens scratch up. You can carry it on your clothes. It isn’t carried in eggs, but chicks can be infected as soon as they hatch.

How to protect your flock

That’s where the miracle of vaccination comes in. Chicks can be immunised before they even hatch, usually on the 18th day of incubation. All the hatcheries I know of immunise all their chicks.

If you are hatching at home, you may want to immunise your chicks on their first day. Feed stores sell the vaccine and yes, you can give your chick a tiny injection. K.J. Theodore shows you how online. Follow all manufacturer’s directions and handle carefully. But of course you are always careful with all your chicks!

If your flock isn’t vaccinated and hasn’t had Marek’s, it simply may not exist in your area. That doesn’t mean it can’t come in, though.

If your entire flock has not been vaccinated, as many as 60 per cent of them could catch it, and most will die. Even those that appear to recover may have internal tumours that will eventually kill them.

Marek’s also affects the white blood cells that fight infection, so chickens that survive the initial infection are at risk of catching something else and succumbing to that.

Chicks hatched by their mothers will get some of her immunity. That will protect them for about three weeks. After that, they will need the protection of vaccination. Since it takes ten days to two weeks for the vaccine to develop antibodies in the chick, vaccinating on Day One is the safest policy.

The vaccine given to day-old chicks isn’t as effective as the one given to eggs. Vaccines are available against all strains of virus, and are sometimes given in combination.

As with many diseases, there are highly virulent forms of Marek’s that could still sicken even vaccinated chickens. If Marek’s is reported in your area, check with local poultry veterinarians and breeders to learn which kinds are occurring and vaccinate accordingly.

The best things small flock keepers can do to prevent Marek’s from infecting their chickens are:

  • Buy stock from hatcheries or breeders who vaccinate their birds. If you breed your own, vaccinate day-old chicks.
  • Keep the coop clean and well-ventilated. Even vaccinated chicks can be overwhelmed by virus-laden litter.
  • Separate a sick hen from the flock. If she has Marek’s, kill her humanely and take action to limit damage by vaccinating and observing the flock closely for others that may develop paralysis or other symptoms. It takes two weeks for the chicken to develop immunity.

Commercial producers have bred Marek’s Disease Resistant strains of chickens. I wasn’t able to determine whether any traditional breeds are resistant to Marek’s, but that trait comes from somewhere. Please contact me if you know of naturally resistant chicken breeds.

Chances are good that you, like me, will never see a case of Marek’s. Make that true for everyone by vaccinating your flock.

Christine Heinrichs

Further Reading

Find out more about Marek's Disease in our Knowledge Centre here.



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