Marek’s disease is an insidious disease that catches many keepers by surprise. Its effect on your flock can be devastating.
We’ve discussed Marek’s in the past, however there is much mis-information out there, so this article will clarify matters for you and your birds.
Many keepers are lucky enough to go a lifetime and never see this disease, even though it is very 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 and with regard to vaccines it seems to be constantly changing. Remember, if in doubt; please contact your local veterinarian or extension office for help.
What is Marek’s Disease?
Marek’s disease is a viral disease of chickens that is caused by a herpes virus. Current research shows that there are six mutations of the virus that can cause the disease.
The virus can range from non-pathogenic (not causing disease) to highly pathogenic (causing disease and death), and this depends on the strain of Marek’s disease caught.
It was first noted by the brilliant Hungarian veterinarian, Jozsef Marek back in 1907. When he wrote his paper about it, it was likely that only one strain of virus existed- however since then other strains have mutated.
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 to 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 be resistant to it, or the type of virus caught may be non-pathogenic (not causing disease).
It should be noted that there are four different presentations of Marek’s disease- Neurological, Visceral, Cutaneous and Ocular. The type of presentation will dictate the kind of signs that you will see.
Signs for each of these forms 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 will have a temporary paralysis which will resolve itself spontaneously.
- The bird shows signs of 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 backwards.
- Respiratory problems such as labored breathing.
- Darkened or purple comb (lack of oxygen).
- Graying of the eye color.
- Misshapen iris.
- Non-reactive pupil of eye.
- Lesions around the feather follicles.
- Ulcers and/or scabs around follicles.
Often the only diagnosis of visceral Marek’s is sadly, post mortem due to the nature of internal maladies.
- Cancerous tumors grow inside the bird on the organs.
- Weight loss.
It’s also very likely that your chickens will 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, on clothing and boots, wild birds, and by darkling beetles in the henhouse.
It can survive for up to 65 weeks in ambient temperature in coops and for years in soil.
The virus is spread horizontally- that is chicken to chicken, not from the hen to the egg. So the virus will spread quicker among hens in tight living conditions- make sure your 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 certainly help to lessen the severity of an outbreak if it should occur. However, the vaccine does not prevent the bird from getting Marek’s.
The vaccine simply allows the bird to build up a better immunity to the disease, reducing the likelihood of severe symptoms or death and and it also reduces the spread of disease if an outbreak occurs.
Part of the problem lies in the fact that the virus is constantly mutating, much as the human flu virus does, so 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 very difficult to effectively keep Marek’s out of your flock.
If you are compelled to add additional hens to your flock though, ensure that new birds come from a reputable source which practices quarantine strictly. You should know that Marek’s does not always show 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 disease.
Marek’s virus is resistant to some disinfectants such as Phenol; however many keepers recommend the use of Oxine. This kills the virus and has a 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, it is likely that all will get it. However, not all will show symptoms or experience disease. Birds that have been vaccinated have a higher immunity, but birds that have a weak immune system or some other ongoing health issue will probably succumb.
In infected birds that have a strong immunity or resistance, the virus goes into a ‘sleeper’ mode. It will insert itself into the birds RNA sequence and lie dormant. If the bird becomes immune suppressed at a later time 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 your flock to be entirely ‘organic’, or generally dislike vaccines you have to be aware that if Marek’s attacks your flock, there will likely be significant losses.
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 vaccine does not guarantee immunity.
If you show your birds, vaccination is highly recommended- as your girls will be in contact with other hens and the likelihood of them catching Marek’s is greatly 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.
Marek’s Disease FAQ’s
Q: How do I know if it’s active in my area?
A: You can start by calling your local extension office- they should have the information. Also talk to chicken people in your area; they are always a mine of information! If they have been bothered by Marek’s, ask them where did they get 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. Just make 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 got Marek’s disease?
A: The only way to know for certain is to have a laboratory test and evaluation by a veterinarian. However if their symptoms match the symptoms mentioned earlier on in this article- it’s likely they 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 is constantly mutating and so 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 experience devastating consequences when the disease emerges, but for most of us, the impact is minimal.
Keeping your flock healthy, practicing good house-keeping, strict quarantine practice will all help in the fight against this awful disease.