New Questions About Mareks- More in depth questioning

[skylarms]

I had a chicken up and die. Thought for sure it was Mareks so white I was awaiting Necropsy, i searched and searched AND SEARCHED information about Mareks. ITS NOT Mareks (thank goodness) BUT In all my research, I came up with a few questions that I never could find an answer for and now I have to know

1) Once a bird become infected with Mareks, when does it start spreading the disease? Is it right away or only when it starts getting ill? I saw it is spread mainly through dander but what if its not the form that affects the feather follicles and only tumors forms? My concern was the pullet that died was the only one who came from an outside farm and I had her for 6 weeks. I was assuming that if she had it, she came with it.

2) How long after initial exposure do symptoms appear? Its it a matter of days, weeks, months? I know its can live anywhere for awhile but how long after initial exposure do symptoms start?

3) IF a bird becomes sick but no other birds get sick, will they still be carriers even though they were not ill?

4) what is everyones opinion on vaccinating older chicks and birds? I dont generally vaccinate, but now after all this reading I am paranoid

You can read symptoms anywhere, but I would like to dig a bit deeper

 

[skylarms]

So incubation time is six weeks, but from when? When do they start shedding the virus?

 

[Nambroth]

I had a chicken up and die. Thought for sure it was Mareks so white I was awaiting Necropsy, i searched and searched AND SEARCHED information about Mareks. ITS NOT Mareks (thank goodness) BUT In all my research, I came up with a few questions that I never could find an answer for and now I have to know

1) Once a bird become infected with Mareks, when does it start spreading the disease? Is it right away or only when it starts getting ill? I saw it is spread mainly through dander but what if its not the form that affects the feather follicles and only tumors forms? My concern was the pullet that died was the only one who came from an outside farm and I had her for 6 weeks. I was assuming that if she had it, she came with it.

It is my understanding that a bird can begin shedding the virus at any time. You do not need to have the folical form for it to spread. Marek's is a Herpes virus (not a species that can infect humans) and acts as such. It is generally shed in low volumes in any bird carrying the virus. It is shed in much greater volumes in an actively symptomatic bird. Here is some reading on the life cycle of herpes viruses. http://en.wikipedia.org/wiki/Alphaherpesvirus#Herpesvirus_life_cycle

2) How long after initial exposure do symptoms appear? Its it a matter of days, weeks, months? I know its can live anywhere for awhile but how long after initial exposure do symptoms start?

This is not very helpful, but pretty much at any time with exception to very young chicks. The problem is that it can be impossible to know when exposure occurred, since it can be brought in environmentally (such as on the wind or with wild animals like birds). So pinpointing an incubation time is very hard for most people. A chicken can carry Marek's for a long time and then once the body becomes stressed, the immune system just isn't enough and a normally healthy bird can suddenly succumb. The reason this answer is so hard to find is because it's so hard to tell when infection actually occurs in most birds.

3) IF a bird becomes sick but no other birds get sick, will they still be carriers even though they were not ill?

Yes, it is very likely that any birds that were housed with, near, or shared the same area at any point with a symptomatic Marek's bird have the virus and are carrying it and shedding it (though probably shedding much smaller amounts than an actively symptomatic bird). These birds have built up resistance, but it is possible for them to show symptoms later on, especially if they were not vaccinated against the Marek's serotype that is occurring in the flock.

4) what is everyones opinion on vaccinating older chicks and birds? I dont generally vaccinate, but now after all this reading I am paranoid

Opinions are like-- well, you know. Everyone has one and they probably all stink!! That said, here is my personal opinion. You don't have to agree: I do not see any reason not to vaccinate. The vaccine is cheap-- very cheap if you get it done on hatchery birds, and pretty cheap if you do it yourself-- can can save a lot of heartbreak. There are arguments that vaccinating is building up new strains of the virus. This is true. This, though, would occur naturally... viruses and immunities have been in an evolutionary battle for millions of years. Humans are just speeding it up. (the common Marek's vaccine is actually turkey Marek's virus) Further, as long as large scale operations vaccinate (and they will, trust me), then we already are going to have the mutations happening anyhow. So the best we can do to protect our small flocks is to consider vaccination.

You can read symptoms anywhere, but I would like to dig a bit deeper

 

[skylarms]

Thanks! So is the forms of md, viseral, ocular, etc- caused by different strains? Or will is a just a matter of how it presents clinically? Is one form more contagious than the other?

 

[skylarms]

okay- one more for you. If a young bird has mareks but is housed with older birds, are the older birds automatically carriers?

 

[skylarms]

Here are some answers I got when going over my report with the vet. I thought they may be helpful to someone else.

In regards to mareks and applies to any disease really ( I alsked about this a lot because I was researching and finding so many questions!)- Mareks is EVERYWHERE! Even if you get a bird from a flock that had it, its probably going to get it from somewhere else if it doesnt get it from that bird. Vaccination is the best preventative. If the birds are exposed after 4 months, its highly unlikely they will ever develop Mareks. Young exposed birds generally show signs from 8-16 weeks, although it can show up in older birds. The form of Mareks shows itself either as visceral, ocular, or in nerve tissue. These are not different strains, just different presentation of the disease. Certain breeds are MUCH more susceptible- silkies and polish especially. It is also more common in rare breeds as the gene pool isnt as diverse. Because of this, that is why some people lose one breed and not another. Cull birds at first time of symptoms. Vaccination helps prevent tumors, but not the disease. No need to cull the whole flock as it is so prevelant. Even if you cull and all traces of Mareks go away, it will still blow in from somewhere else.....

 

[Nambroth]

I will do my best! I am definitely not an expert, but I live with it so I research as much as I can. I think I'm also the first one to have a bird that died from Maerk's go through such a very through exam, down to the serotype, on the BYC forum. If I am wrong please step in and let me know! I'd love to chat...

Thanks! So is the forms of md, viseral, ocular, etc- caused by different strains? Or will is a just a matter of how it presents clinically? Is one form more contagious than the other?

If I understand correctly, it is simply the way it presents clinically. It seems that based on the trends that I have read about here, that the ocular form tends to show up in exposed birds that do not get the visceral tumors-- including in vaccinated birds that later succumb anyhow (due to being vaccinated against a different strain/serotype OR the individual bird not building a resistance with the aid of the vaccine, which at best is only 95% effective, and at worse is noneffective for mutated strains).

okay- one more for you. If a young bird has mareks but is housed with older birds, are the older birds automatically carriers?

I am not sure I understand. If any Marek's carrying bird is housed with any other chickens, one can assume that all become carriers. Is that what you mean? I don't think age comes into play. Once exposed, it lives in the bird's cells indefinitely even if they never present a symptom or have any problems their whole life.

Here are some answers I got when going over my report with the vet. I thought they may be helpful to someone else.

In regards to mareks and applies to any disease really ( I alsked about this a lot because I was researching and finding so many questions!)- Mareks is EVERYWHERE! Even if you get a bird from a flock that had it, its probably going to get it from somewhere else if it doesnt get it from that bird. Vaccination is the best preventative. If the birds are exposed after 4 months, its highly unlikely they will ever develop Mareks. Young exposed birds generally show signs from 8-16 weeks, although it can show up in older birds. The form of Mareks shows itself either as visceral, ocular, or in nerve tissue. These are not different strains, just different presentation of the disease. Certain breeds are MUCH more susceptible- silkies and polish especially. It is also more common in rare breeds as the gene pool isnt as diverse. Because of this, that is why some people lose one breed and not another. Cull birds at first time of symptoms. Vaccination helps prevent tumors, but not the disease. No need to cull the whole flock as it is so prevelant. Even if you cull and all traces of Mareks go away, it will still blow in from somewhere else.....

There are a few things in here that are true but perhaps a bit misleading.
Marek's can be anywhere-- everywhere-- yes. But it's not. Since the 70s and the large companies have started vaccinating their stock, Marek's is far lessened. It has only become a big issue more recently, with more people keeping small backyard flocks. Many countless people have Marek's free flocks. Many people have Marek's positive flocks but never know it (do you know anyone with a chicken that seemed to die without a specific known reason?). Then there are probably people with flocks that carry it but have built up fantastic immunity.
I will disagree with the exposure after four months remark, though. This really only applies if the bird has had a chance and a reason to build up resistance/immunity when it was a youngster. I and several others here on BYC have had birds that were exposed >4 months that have perished from confirmed Marek's. It's true that older birds seem less likely to succumb to the visceral form when exposed later in life, but this is hardly a rule. My poor roo was quite a bit older when he was exposed and he perished quickly from very aggressive visceral lymphatic tumors.
Yes, very much, to some breeds being susceptible-- poor silkies.

There is little reason to cull birds that show symptoms. Why?
1. As you mentioned- The flock may already be considered infected in full if a bird is showing symptoms. You may be somewhat reducing the amount of shed virus but this is sort of a moot point anyhow.
2. It may be a different illness, completely treatable and curable. If you value your bird try alternatives, first.
3. Many birds have gone on to live for months or years after showing symptoms.

Of course, if the chicken seems to be suffering, it is important to carefully evaluate the quality of life, and if necessary, make the decision to end it. But they don't always suffer depending on how it presents.