Moving Forward- Breeding for Resistance to Marek's Disease

[seminolewind]

Ya don't have to know anything to make a buck!
Maybe it's another way of saying "my chicken's had Marek's, but it's okay now"

 

[gjensen]

I think you're right about maybe needing to send blood for a PCR as a backup. I may end up doing that too. I don't care if they can't find any tumors. Do one anyway!!! This time I filled out what asked for specific tests I wanted.

I don't understand how anyone can sell Marek's resistant flock chickens? I'd first want to see their record keeping that they've kept at least 7 years. Oh, I could say my flock is Marek's resistant because the ones that are left are the resistant ones, LOL.

That is why I am reluctant to use the term resistance. You cannot quantify it until you quantify it. It has to be proven somehow.

I do believe that some strains could be found to have a reasonable amount of resistance. I doubt that we could find a strain that is immune, less a research facility or two.

 

[seminolewind]

You mean you resist the idea of saying resistant?

 

[Nambroth]

Cynthia, lots of illnessis mimic Marek's and Marek's mimics lot of other illnesses. I think the bottom line would be on necropsy, finding gross tumors, microscopic tumors, and enlarged nerves. Tumors, to a pathologist, all have tell-tale differences. A pcr is one step further . All 3 results are taken into consideration to form their opinion.

The lead symptoms are interesting. I wonder what parts of a chicken can be tested for that? Feathers?

It is a blood test. Parrot owners are often familiar with it as parrots are prone to lead and especially zinc toxicity, as parrots have a tendency to chew on metal fixtures, such as galvanized caging, or quick links on toys, etc. It is easily done on a live bird via blood draw and sending to a lab, but it is expensive. Some smaller birds (I am looking at little, like budgies) have trouble getting the test run, because it requires quite a bit of blood (0.5 milliliters of whole blood). But that is not a problem for a chicken, even a little bantam is a dozen times the size of some small parrots.

Sometimes metal toxicity can be guessed at by a complete blood count (CBC, all vet offices should be able to do this basic count), as metal toxicity can cause anemia. Blood counts may also be off as it can cause liver disease/failure as well.

X-rays can also occasionally detect lead if it is still in the gizzard and not well ground, but not always. X-rays are generally more expensive than the blood test anyhow.

CBCs and X-rays are not diagnostics, but guesses. The blood test is diagnostic.

Quote:
In this way it causes severe neurological issues. Ataxia/paralysis, sporadic movements, organ failure, seeming wasting.

Quote: and,
Quote: Source: http://www.truth-out.org/news/item/...-it-scrambles-everything-they-need-to-survive

Quote: Source: http://www.nwhc.usgs.gov/disease_information/lead_poisoning/

Does this sound familiar?? Those of us that have had Marek's birds sure might think so.

Anyhow, I know I am way off the subject which is Marek's resistance. But, it was brought up and I felt it important to mention.

More reading, with photos (some are graphic necropsy photos): http://www.nwhc.usgs.gov/publications/field_manual/chapter_43.pdf

 

[gjensen]

You mean you resist the idea of saying resistant?

Did I say that?

 

[gjensen]

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.

I started to respond to this earlier, but decided to think about this first.

When breeders began to supply birds on a commercial level, many decided to suffer low level losses rather than sell birds that were highly susceptible birds. This position registered with me. It could be said that we should have maintained this approach.

During the same time, some resisted the idea of fortified feeds believing that we were breeding nutritionally needy birds. There was evidence at the time that some strains were more tolerant of certain deficiencies than others and the traits were hereditary. This position could be argued against, but it is worth mentioning.

I certainly agree with the position that breeders would not being doing a breed any favors by over treating.

I am mixed on the bio security position. If I bring new birds in they are certainly quarantined, and they do not get put with the rest of flock afterwards. I do not think that I can expect my flock to be resistant to everything. There is too much out there to consider. Too many possibilities. I do believe that good management (or what I would call it), has to be part of it all.

I will continue to go as I have and make whatever decision I have to make when I get there.

MG and Marek's would be the two that it would be especially nice to see more resistance to.

 

[chooks4life]

For a flock to be Marek's resistant, wouldn't you have to know they had been exposed to one or more MD-positive birds and had not come down with the debilitating symptoms?

Yes, really, can't see any way around that, if it's intended to be taken as a fact rather than an assumption. It'd be great if there were affordable tests you could use at home to distinguish between birds and strains of MD, so you could for example know that a given breeder had birds that tested positive to multiple strains of MDV. Even then, seeing them in apparent good health is no guarantee they or their offspring would remain that way, you'd need more controls in place as gjensen's been saying.

Yeah, these are resistant because they're alive! LOL. I'm not sure how they quantify that and since these "official" articles suggest buying MD-resistant stock, where would one go to find that stock? Unless the wording was just unfortunate and they actually meant buy breeds known to be more resistant.

As far as my understanding on it goes, there is no resistant breed, only strains. While admittedly my knowledge of breeds is pretty limited, I can't think of a single breed that as a collective whole has been reliably kept under the conditions necessary to ensure they're as resistant as possible. Somewhere, there is always a breeder holed up in their mountaintop fortress so to speak, lol... Resistant strains is as far as it goes.

Best wishes.

 

[PetRock]

petrock, what exactly was suggestive of Marek's? Was this the final report ? Was it a joint or a nerve you saw?
With one suggestive necropsy, and 2 more limpers, it sounds like you may want to send the next victim.

Your question made me pull up the necropsy report and go over it again. It looks to me like they based the diagnosis on the case history that I supplied as well as the neoplastic lymphocytes they saw in the brain, heart, lung and skin. Here are excerpts from the report:

09/23/2014: The histopathologic findings in the brain, heart, lung and skin in addition to the clinical history are suggestive of
Marek’s disease caused by gallid herpesvirus 1. All diagnostic testing has been completed.

Histology:

Brain: The meninges, blood vessels, and adjacent neuropil are infiltrated by numerous neoplastic lymphocytes. These
cells frequently infiltrate the blood vessel walls.

Heart: Small blood vessels occasionally contain low numbers of neoplastic lymphocytes.

Lung: Blood vessels are occasionally occluded by the previously described neoplastic lymphocytes.

Skin: Within the dermis is a well demarcated, infiltrative mass composed of sheets of neoplastic lymphocytes. Portions
of the skin are ulcerated with a thick crust of necrotic debris, hemorrhage, and bacterial microcolonies on the surface.

Liver, kidney, peripheral nerves, crop, proventriculus, ventriculus, small intestine, large intestine, pancreas: No significant
histopathologic findings observed.

The two cockerels that we processed each had one enlarged joint and all their organs looked normal. One of them had a joint that bowed out and the other one had a joint that bowed in like rickets. I still have 11 cockerels in the same pen and so far none of them show signs of any problems with their joints or paralysis. If another does, I plan on culling him and sending him in for a necropsy. I am slowly reading through this thread and I appreciate so much the information that you have all shared.

 

[tridentk9]

I think you're right about maybe needing to send blood for a PCR as a backup.  I may end up doing that too.  I don't care if they can't find any tumors.  Do one anyway!!!  This time I filled out what asked for specific tests I wanted. 

I don't understand how anyone can sell Marek's resistant flock chickens?  I'd first want to see their record keeping that they've kept at least 7 years.  Oh, I could say my flock is Marek's resistant because the ones that are left are the resistant ones, LOL. 

+++++++++++Caution- technical jargon ahead ++++++++++++++

If you run a SNP, single nucleotide polymorphism, on the MHC-B, Major Histocompatibility Complex-B, you'd want B21 haplotype as it helps with MDV resistance. Conversely you wouldn't want B5, B13 or B19 haplotypes as they help with susceptibility. There were 14 haplotypes mapped that were involved with the resistance or susceptibility of various diseases.

Translation: there are tests that can help determine how resistant or susceptible an individual chicken should be.

How healthy it is otherwise, how much contact with the virus and levels of Natural Killer Cells will also make a difference. SNP tests are not available through normal labs but ADOL, the Avian Disease and Oncology Lab, may be able to advise of private companies that run the tests.

++++++++++Back to technical stuff +++++++

The chicken is perhaps the best nonmammalian vertebrate model that has been characterized in terms of the immune response, the genetics of disease resistance and vaccine response, and the genomic structure and function of the MHC. With respect to anti-tumor immunity, studies with chickens have concentrated mainly on immune responses against oncoviruses; this focus has resulted in the development of successful vaccines against tumors.

Particularly interesting is the association of certain MHC haplotypes with resistance to virus-induced malignancies. The first of such association to be described, and still among the strongest known, is the association of the MHC haplotype B with resistance to Marek’s disease . However, particular haplotypes are also associated with resistance of other oncogenic viruses including ALV and RSV. The strong association of MHC haplotypes and resistance to virus-induced malignancies is presumably related to the peculiarity of chicken MHC, which compared to the MHC of typical mammals, is much smaller and simpler, with a different genomic organization. Recombination is rare within the chicken MHC, and this property has been proposed to allow coevolution between interacting genes, such as the class I, TAP1, TAP2 and tapasin genes. A consequence of this coevolution is the expression of a single dominantly expressed MHC class I molecule due to peptide-binding specificity and cell-surface expression level, which determines the immune response to certain infectious pathogens and explain the striking associations with resistance to these pathogens. However, recent genetic studies have revealed that allelic difference of BG1 an IgSF receptor-like protein located in the MHC locus that contains an immunoreceptor tyrosine-based inhibition motif (ITIM) plays a major role in Marek disease and perhaps other oncogene-induced lymphomas. Interestingly, the association of MHC haplotypes with resistance to oncoviruses is not only due to antiviral responses but also to a better ability to control tumors growth and metastasis. Indeed, vaccination with low oncogenic RSV strains induces not only protective immunity but also results in regression of visceral tumors and erythroblastosis induced by RSV. Finally, contribution of non-MHC genes in resistance to viral replication and tumor growth is also documented.

RSV- Rous Sarcoma Virus

 

[JensChickies]

Found this online, not a common subject with chickens, but since my property is like an ammo dump with shell casings from .22's and buckshot all over the place, in addition to burnt foil (why, no idea) I was researching it and thought I post my findings:

http://naturalchickenkeeping.blogspot.com/2013/03/lead-and-zinc-hidden-dangers-to-your.html

The first list is regarding lead toxicity.

Quote:

 
....and a funny for you from that article, since we all need to laugh:
 
 

     

A list of possible sources for contamination on your property, taken from a different article:
This part is of interest to me, concerning paralysis and possibly lead toxicity mimicking Marek's symptoms:

It's interesting you brought this up. When I took my chicken to the vet, she said that this is very common. It mimics mereks and can be treated with medication.