http://Marek'sHI. I wanted to post all my information on Marek's. If you might have something to add, please PM me.
Most of us know the classic signs of Mareks. Age 8-20 or so weeks, paralysis, one leg forward, one leg back stance, tumors (on necropsy), wing walking, cloudy eye, disfigured pupil, etc. These are common signs and the easiest to see. But they are not all the symptoms. Other common symptoms include: wasting away with or without eating, any paralysis, including paralysis of the digestive system-the food stops moving and the chicken stops eating but acts like they want to eat, and may include open mouth breathing or panting. There could also be tumors or lumps at the feather follicles. These are not like goose bumps, they are a bit larger.
Common symptoms can also include dying without any symptoms, symptoms that come and go. It all depends on what organs and nerves are being effected, and it could be any nerves or organs, very noticeable would be the nerves to the legs or wings.
As I know it there are 6 different strains, nerves, eyes, organs-tumors, skin, transient (brain related), and a sudden death strain. Vaccinated chicks will NOT get Marek's from the vaccine. But vaccinated chicks can be exposed to the virus, and carry it and spread it. The vaccine only prevents the tumors and paralysis. NOTHING can protect a chicken from being a carrier and spreading Marek's.
Symptoms may be severe or mild depending on the virulence of the strain, the concentration of virus in the chicken's environment, the chicken's genetic resistance, the chicken's acquired resistance usually by age, and sometimes the breed of chicken. It is implied that Silkies and Polish are most vulnerable. But my older silkies and Polish seem to have very good resistance. And eggs laid by exposed hens seem to have resistant chicks, as well .
It only takes one exposed chicken to enter your flock, vaccinated or not. All my chicks were hatched here-except for one purchased pullet from a breeder. BUT, I have to say that if a breeder vaccinates ALL her chicks, the breeder will never know that they are selling chicks or chickens that carry Marek's. If all my chickens are vaccinated properly, I will never know if they are exposed and carry it, the symptoms will not be there, and can only be confirmed by an animal disease lab necropsy.
Sometimes you don't know your flock has it until you hatch chicks from purchased eggs, and after 6-8 weeks they start to die, one at a time. That's the way I found out. I had no idea that my flock had it for the last 2 years-since I bought the pullet. I now refer to her as "Typhoid Mary"
The only way to know for sure is a confirmed animal disease lab necropsy. Anything else would be an educated guess based on symptoms and a flock history including when a new chicken/chickens were added and how long afterwards did your chickens get it.
The vaccines produced have a hard time keeping up with new strains. A small amount of victims may die even tho they are vaccinated.
A pretty good guess has to include more than one similar death. A good history, tracking a chicken added to your flock a few months prior to your flock chickens dying off. If your flock is older, fewer will die, and that makes a history even harder because older chickens have some age related resistance. But the trouble usually starts a few months after adding a new chicken. Or new chicks dying off a few months after they arrive because your flock already carries it-unknown to you. These are just guidelines, the most usual scenarios, not the only scenarios. Marek's does not have any guaranteed list of symptoms. Just common ones are known. Some of these symptoms are also symptoms of other diseases or deficiencies. You can narrow it down. A runny nose and crusty eyes is probably not Marek's. Botulism or salmonella, or coccidiosis-the chicken will look very sick and probably not be eating. One symptomatic chicken and not a second or more -probably not, could be an injury. Medicated feed is a possible thiamin blocker and can causes paralysis. A leg injury should be ruled out.
Marek's will probably not go away for a long time. You can not prevent it. There is no vaccine to stop it. In the past years, it was a major problem in big hatcheries. In the past years, hatcheries have gotten the virus under control. In the mean time backyard chickens and small flocks have not been practicing prevention. Hatcheries now practice "all in and all out", no mixing of adults and chicks. Between batches, everything is disinfected. And all are vaccinated.
Backyard and small flocks do add chicks and adult birds to their flocks. There have been "experts" that do not recommend vaccinating because "it's not a problem" Well it is a problem. We all need to vaccinate. We need to breed resistant birds. We need to be careful adding chickens to your present flock. We need to clean and disinfect often to reduce the available virus in the environment. Even tho vaccinating will save the lives of thousands of our birds, it will not stop the spread of the virus. There is nothing that will eliminate the virus. The best we can do is get the virus under control as much as we can.
There is alot of mis-information floating around. I am trying to share the best and most recent information I have found.
I will continue to add information here. And I will also be adding some links to some very good up- to- date- information. If you can help me simplify material here or make the info more understandable, PM me.