Moving Forward- Breeding for Resistance to Marek's Disease

[seminolewind]

How can you breed for resistance when the virus changes all the time?

 

[Nambroth]

If my girl did have it, then I think my flock may be one for the veterinary journals, one of the rarest cases on the planet. Makes no sense. No paralysis, no pale comb/wattles, no young birds showing any symptoms of any kind. Where is a head shaking smiley?

I strongly suspect that you aren't experiencing Marek's in your birds; or, if you are, it is latent and you have a good strong flock with a lot of natural immunity. But that is just a gut feeling. I don't know your flock-- only you do.

In my opinion, a sight test for Marek's is no more than a guess. That isn't good enough for me.

Bingo. A lot of necropsy work is just a guess. Sometimes it is a more educated guess than others. Not to belittle necropsies... they are very useful tools in learning what is going on. But they are only one part of the puzzle. You need many parts in order to see the whole picture. And sometimes we never do get to see the whole darn thing.
When sending a bird for necropsy, if you suspect Marek's, it might be good to request that tissue samples be taken from suspect organs for further testing (this day it is mostly going to be PCR). Organ tissues and lymph tissues are going to be the key areas to look for the virus. Thymus, heart, sometimes liver, etc. Some places will charge extra for this. I am sorry that some folks have had a less than stellar experience with Perdue. That is unfortunate. CA seems to have a really good state program in place....

Yes, I was very surprised by the cocci both times since they were past the "danger age". The last one I did not necropsy and it might not have actually been cocci. We had a 35 degree temperature drop which is why i thought she was all puffed up (although at the time I thought it might have been cocci because all the other birds were acting normal). Sure enough she was dead the next morning. I think it would have been too late to treat it anyway. We have had a very wet year, so maybe it was just genetic weakness combined with more parasites from the wet earth. Or maybe it is Mareks or another underlying disease.

Forgive me if you mentioned, was the cocci detected via the necropsy, or did you diagnose (because of obvious infection/bloody stool/etc)? It's worth mentioning that many necropsy reports will find at least some cocci in the intestinal tract, since most adult birds will have small amounts as part of their natural 'fauna'. Like you mentioned, it is opportunistic and will turn into a full blown event if the chicken is weakened or gets a secondary problem (or the cocci is the secondary problem..!).

An easy to clean and disinfect pen for raising chicks with a hen, vacuuming dander from that area with a dedicated vacuum and following your plans for keeping age groups together will go a long way to reducing risks from what I've read.

Hmmm, @Nambroth ? I wonder if an ultraviolet light on the pens would help with disinfection. Probably expensive but there are residential UV units now. Add a vacuum and air filter and you'd remove a large part of your infective viral load. The vacuum and filter would have to be cleaned after each use but if it keeps less birds from getting sick, a little extra work would be worth it. It would be easier for the smaller backyard flock owner of course.

Edited to add: UV Light would be for empty pens or coops, ie coops during the day when all residents are locked out, etc.

There might be merit to the UV idea... many viruses break down when exposed to sunlight. Herpesviruses are particularly resilient when in the environment because of the way they fully encapsulate themselves (darn them). I can't find any studies done on Marek's in particular (maybe you can!) but I have found studies done on other species of herpesvirus. They are not... terribly helpful to our application, I'm afraid. Unless I misunderstand them....

This one suggests that UV exposure seems to trigger a flare up of symptoms in humans that have Herpes simplex. It is unclear if the UV does something to the virus to help it, or if the UV does something damaging to the host (or host's cells) to cause the virus to take advantage of it. Some studies suggest that disturbances such as a wound, stress (we know this) or sun exposure reactivates the latent virus... http://www.progressivehealth.com/herpes-sun.htm

Quote: http://www.nature.com/nrneurol/journal/v3/n2/full/ncpneuro0401.html

Of note; this is suggesting that UV exposure benefits human herpes simplex virus when it has already infected a host. This is different than 'free virus' in the environment. I am unclear on if the virus, loose in the environment (not in a host) is adversely affected by UV radiation or not.

This is interesting. Not totally related, but it is insightful for those that might wonder why we can't kill the virus in an infected (human/animal). It is an older article but still interesting. http://www.reuters.com/article/2008/07/02/us-herpes-treatment-idUSN0229815620080702

It is also very important to note that UV light usually used for sterilization tends to be much more potent (has a higher energy level) than environmental UV light. This higher energy UV light is damaging to humans and animals alike, so one would need to use care to only do it when no birds were present (as you mentioned).

In short-- I am unclear on this. Does it help? Hurt? Do nothing?

 

[seminolewind]

Cynthia, usually a visual gives a pathologist a good reason to examine more thoroughly. There are quite a lot of reasons for tumors, and 3 types are more difficult to differentiate without more testing: Marek's, LL, and Reticuloendotheleosis . Some study said that RE was very common but the tumors on the nerves never really affects them. I don't know why I don't hear about it more often.

Anyone know anything about RE?

 

[Nambroth]

Cynthia, usually a visual gives a pathologist a good reason to examine more thoroughly. There are quite a lot of reasons for tumors, and 3 types are more difficult to differentiate without more testing: Marek's, LL, and Reticuloendotheleosis . Some study said that RE was very common but the tumors on the nerves never really affects them. I don't know why I don't hear about it more often.

Anyone know anything about RE?

I agree. And, neoplasm (tumor) growth in different organs and locations can also be 'clues' as to the reason. For example, cancerous growths or irregularities on the lymph systems and thymus are more unlikely to be reproductive in origin than those found in clusters around the ovaries, intestines, etc. It's a clue. It is always clues; and of course a pathologist and what they do will vary from place to place. Some are more through than others. I am very fortunate that I have a caring vet that is extremely thorough and went through a lot with us to try to get the best answers we could. I paid for this though, and I appreciate that not everyone can!! Or is willing to. I am very realistic.. I know that people may love their birds, but not everyone has a budget to go through what I have. I could never have done it if I had children depending on me, financially.

Anyhow, the point I was trying to get at and rambling about is that like anything, the report is only as good as the pathologist. And this is not a knock on them. A good one is very valuable and they can 'see' things we would miss at home, even those of us that study this stuff a lot. Still, there is only so far one can chase the rabbit down the hole, so to speak. My vet was able to take samples directly from the tumors and surrounding organ tissue and send them for testing, and it was very conclusive. When birds do not present tumors or lesions, it gets much harder. And, as mentioned earlier in this thread, some places will only look at the neoplasms, and say "yes, Marek's", and move on to the next bird.

I don't know anything about RE, but it sounds like I should!!

 

[speckledhen]

Cynthia, usually a visual gives a pathologist a good reason to examine more thoroughly. There are quite a lot of reasons for tumors, and 3 types are more difficult to differentiate without more testing: Marek's, LL, and Reticuloendotheleosis . Some study said that RE was very common but the tumors on the nerves never really affects them. I don't know why I don't hear about it more often.

Anyone know anything about RE?

First I've ever heard of this one, Karen. Sounds like something easily mistaken for Marek's or LL.

 

[chooks4life]

How can you breed for resistance when the virus changes all the time?

By not protecting them via vaccines etc you're not artificially assisting the weaker ones to survive an outbreak or overdose, and they do the rest themselves. Every single viral disease they've ever been exposed to is something that the species as a whole has been 'bred for resistance' against, even to some degree in cases where they were vaccinated, simply because the weakest always die when infected and the stronger ones survive to breed. Of course there are varying levels of 'strength' though.

Given, vaccines do interfere with this natural process, and according to quite a few sources I've read vaccinating is only causing greater and accelerating problems, in fact many researchers directly blame vaccinating for the increasing virulence of the disease. Makes sense to me.

The immune system responds to changes and adapts just as the virus does. That's the only reason we still have livestock at all, to say nothing of our own species survival, and wildlife etc. Antibiotics and vaccines cannot do the work of the immune system, they just help a percentage of animals that would not have survived, survive.

Given that a few times now, it's been said 'everybody should vaccinate'... I wonder if this thread isn't wandering from purpose. Vaccinating has little to nothing to do with actually breeding for resistance. Perhaps some info in this thread better belongs in a thread devoted to attempting to preserve pets at all costs against the disease, since that subject is almost completely contradictory to breeding for resistance.

Best wishes.

 

[gjensen]

I strongly suspect that you aren't experiencing Marek's in your birds; or, if you are, it is latent and you have a good strong flock with a lot of natural immunity. But that is just a gut feeling. I don't know your flock-- only you do.



Bingo. A lot of necropsy work is just a guess. Sometimes it is a more educated guess than others. Not to belittle necropsies... they are very useful tools in learning what is going on. But they are only one part of the puzzle. You need many parts in order to see the whole picture. And sometimes we never do get to see the whole darn thing.
When sending a bird for necropsy, if you suspect Marek's, it might be good to request that tissue samples be taken from suspect organs for further testing (this day it is mostly going to be PCR). Organ tissues and lymph tissues are going to be the key areas to look for the virus. Thymus, heart, sometimes liver, etc. Some places will charge extra for this. I am sorry that some folks have had a less than stellar experience with Perdue. That is unfortunate. CA seems to have a really good state program in place....


Forgive me if you mentioned, was the cocci detected via the necropsy, or did you diagnose (because of obvious infection/bloody stool/etc)? It's worth mentioning that many necropsy reports will find at least some cocci in the intestinal tract, since most adult birds will have small amounts as part of their natural 'fauna'. Like you mentioned, it is opportunistic and will turn into a full blown event if the chicken is weakened or gets a secondary problem (or the cocci is the secondary problem..!).


There might be merit to the UV idea... many viruses break down when exposed to sunlight. Herpesviruses are particularly resilient when in the environment because of the way they fully encapsulate themselves (darn them). I can't find any studies done on Marek's in particular (maybe you can!) but I have found studies done on other species of herpesvirus. They are not... terribly helpful to our application, I'm afraid. Unless I misunderstand them....

This one suggests that UV exposure seems to trigger a flare up of symptoms in humans that have Herpes simplex. It is unclear if the UV does something to the virus to help it, or if the UV does something damaging to the host (or host's cells) to cause the virus to take advantage of it. Some studies suggest that disturbances such as a wound, stress (we know this) or sun exposure reactivates the latent virus... http://www.progressivehealth.com/herpes-sun.htm

http://www.nature.com/nrneurol/journal/v3/n2/full/ncpneuro0401.html

Of note; this is suggesting that UV exposure benefits human herpes simplex virus when it has already infected a host. This is different than 'free virus' in the environment. I am unclear on if the virus, loose in the environment (not in a host) is adversely affected by UV radiation or not.

This is interesting. Not totally related, but it is insightful for those that might wonder why we can't kill the virus in an infected (human/animal). It is an older article but still interesting. http://www.reuters.com/article/2008/07/02/us-herpes-treatment-idUSN0229815620080702

It is also very important to note that UV light usually used for sterilization tends to be much more potent (has a higher energy level) than environmental UV light. This higher energy UV light is damaging to humans and animals alike, so one would need to use care to only do it when no birds were present (as you mentioned).

In short-- I am unclear on this. Does it help? Hurt? Do nothing?

My position is to use what we have. It is not harmful, and helpful. When I till a yard, I like to let the hot late summer sun on it for a time before I cover it with hydrated lime. After the rain washes the lime in, I will plant it.
I like to let the sun in the houses. I believe in it. Because of our summer heat, I try to get as much of the morning sun as I can. I do not like a dark poultry house, or a stuffy house. Of course there needs to be shade to.
It would do nothing for an active infection of any kind. It certainly would not limit Marek's. What it can do is help with bacteria etc. that can become a secondary infection, and help limit exposure. A bird may tolerate a low level of exposure but succumb at a higher level.

I believe that a house that gets sun and good air flow is a cleaner house. I realize that this is elementary, but I emphasize it.

 

[gjensen]

How can you breed for resistance when the virus changes all the time?

I would not worry about the virus changing in a home flock. It is something that you would never stop doing. I would only be concerned about introducing a more virulent strain from somewhere else. That or bringing in birds that are more susceptible than your own.

Breeding for resistance is not difficult in theory. If Marek's is already a problem in a flock, unless it wipes out more growers than you can stand, then that is what should be done. The problem is when it comes down to killing birds. Some can stomach more of it than others. That is often where the line gets drawn. Then how long it could take.

For a strain that is highly susceptible, it will be a lot of work and it will take a long time. For a strain that has pretty good resistance already, then it is not that big of a deal. Most strains would fall somewhere in between.

Breeding for resistance is a matter of percentages. Initially substantial progress could be made, but as time goes by the percentage of improvement would go down. The 100% percent resistant flock would be elusive. The numbers would work out something like grading does. There is also the possibility and tendency for infection rates to rebound, but if you stuck with it you would regain your footing.

If the sires and dams are not proven, progress will be slow. Though it is heritable, the ability is not passed down uniformly. You do not only want to pick birds that are not symptomatic themselves, but birds from parents that have the best percentage of non symptomatic offspring. Picking non symptomatic offspring from parents with the best percentages. Some males may not have as many non symptomatic offspring. It would be ideal to insure the offspring are exposed evenly from year to year. Hatching a few eggs from a male, or mating will not tell us much. Then it amounts to nothing more than rolling the dice a few times.

It is natural to emphasize the sire, because he has the most influence overall. I would recommend maintaining emphasis on the female because she has equal influence in a pairing. The trait is not sex linked. I would not reduce myself to a single male.

It is my opinion that it should be an organized effort. My opinion is if it is not, we would play with it for a long time.

For susceptible or moderately susceptible birds, our commitment might be tested. Many people will become discouraged when it comes down to culling any qty. of birds. Each bird that becomes infected means more virus is shed on the property.

For a strain with a good degree of resistance already or a less virulent strain of virus would not be as problematic. A highly susceptible breed or strain could require an outcross or cross breeding to make any progress any time soon.

I do a lot of hatching. Frankly if I discover the problem, and the losses are low . . .I am going to cull symptomatic birds, and review how I manage them. That is all I will do. I do not know if I suffered substantial losses. I do not know where I would draw the line or if I would. I do not guess that I could know until the time came.

I realize that most would not get into all of that, but perhaps there is an idea in there or two.

 

[chooks4life]

I agree. Sounds like a collaborative effort is required with like minded people involved for best success.

Unfortunately breeding for resistance is still not widespread enough in practice for this to be really feasible for most; looks like times are changing though. Generally those doing the most 'breeding for resistance' are those who have no clue what Mareks' is, never mind most other diseases whether viral, or genetic, etc... And those aware of the disease are almost universally trying to practice biosecurity, lol. More awareness would assist there.

Perhaps it will be a multi-national project in future, that people in their respective countries can try to set up and work on. Probably not going to be allowed though, would likely have to remain within borders for security reasons.

It is likely to be a bit of a monumental task for sure, very time consuming not to mention risky and emotionally draining for those who get attached to them or also keep pet flocks.

Still, I see no other way forward (pending of course some miracle cure for MDV, which I'm not holding my breath waiting for)... And better this is done on as large a scale as possible, and soon, I reckon, than delayed as virulence continues its rapid increase (going by the projections that have been made based on past trends).

Complete biosecurity as a control method looks like it will only result in entire genepools being lost when sooner or later the disease gets into these protected flocks. The longer they go without exposure the worse for them, as far as I can see.

Best wishes.

 

[seminolewind]

Quote:

The way I see most vaccines like Marek's or the human influenza vaccine is that it's a tiny more harmless exposure that signals an immune response so the animal or human immune system has a jump start before the real thing comes along. I don't see that as artificial. Vaccines are not doing the work of the immune system. It's not the vaccine that fights off a virus, it's the immune system that does all the work-hopefully earlier or faster . in viruses like Marek's or Influenza, the viruses grow faster than the antibodies against them are produced. The vaccine gives the immune system an early edge at producing antibodies.

Marek's is not the only virus that has been around for 100 years and still requires a vaccine. The playing field is unfairly tipped towards the virus winning. Meaning the virus multiplies faster than the antibodies are formed.

Breeding for resistance would create those who don't need the early harmless exposure, or vaccine. They are capable of building those antibodies at a much faster rate. Or limiting exposure may give an immune system more time to produce enough antibodies. Limiting, not omitting.

I know a few people who have just let Marek's run it's course and kill many chickens in a flock until it stops except for a loss of a bird now and then. There's also more natural resistance as the chicken grows older.

I don't think you can clearly talk about one without the other. And talking about both sides brings out a whole lot more information.

I think breeding resistance or vaccination is a choice depending on what your goal is. At this time I want my pets to live a long time. I've hatched some eggs from resistant parents who have been with me for 5-6 years unvaccinated. And the offspring has all died, the last 3 dying at 8 months old, (paralysis and euthanization).

I fell that what might work as well as the vaccine is limiting exposure for the first eight months. Such as removing the chicks during the first 2 weeks of mom's passed on resistance for 5 weeks away, then again at 4 months for 4 weeks away. And give their antibodies a chance grow strong away from more virus concentrated areas of the property. I think I'd be willing to do that.