Moving Forward- Breeding for Resistance to Marek's Disease

[speckledhen]

Do you have a link?

I had suspected something months ago, a very hard enlarged abdomen and then it went away. Her abdomen is large now but soft. There is a lump I can feel that is the size of a large grape. I agree I think it's related to something that I may not have had any control of.

Yup right here: https://www.backyardchickens.com/t/...emoved-660-cc-of-nasty-yellow-fluid-photo-and



That lump could be anything, from a mass of cheesy solid infection mixed with cooked yolk or a tumor or who knows? My Hope has done the "bloat up, dissipate, bloat up again, go down again" cycle for 2 years. I can't believe she's still alive, strongest hen I've had. And I didn't ever drain her before this last time and I only gave her penicillin the first time and never again. Her body seems to take care of it, but she's only laid a handful of eggs in her entire life, between 30 and 40 weeks old.

 

[chooks4life]

About Marek's disease being spread vertically, officially there is not concrete proof it isn't; the research results say it's 'unimportant' or 'at best, very rare' --- whereas all the layperson's sites state 'it is NOT vertically transmitted'. Bit of a discrepancy there.

The best research I've ever read on Marek's is full of ambiguities and admissions of the disease not being completely 'mapped out' or comprehensively known, but the lower-information sources all make absolute claims, somehow purportedly based on the exact sources that refuse to commit to stating such absolutes.

There's plenty of contradiction, but the only real absolute seems to be that it's not reliable in most ways. It can be asymptomatic, infect in the first few weeks of life, and we know strains of disease change as do their methods of transmission, and according to current research MDV is rapidly changing and outstripping whatever control methods are being used against it. (Some research papers I've read are talking of 'co-existence' with it rather than continuing to attempt eradication since it's contributing to its virulence and rapid adaption rate).

Most diagnoses of Marek's seem to rely on generalizations as though they were absolutes. Until we know the concrete facts of Marek's, such as they are at the moment anyway, which we won't know until 'science' does, it's probably better to retain sight of the fact that all our knowledge on it is based on some pretty variable information, so there will be exceptions to the 'rules'. We have the general outline but not the full picture yet.

PubMed has studies for and against everything, of course, but it's one source most people here respect. From PubMed:
Quote: Source: http://www.ncbi.nlm.nih.gov/pubmed/766959
That's the 'official line' on whether or not it is able to be transmitted vertically. Not 100% a 'no', obviously.

Even more interesting, Marek's vaccines have been found to be contaminated with Avian Leukosis Virus, which of course DOES transmit vertically:
Quote: The ALVs isolated were characterized by examination of their interactions with cells of two phenotypes (C/E and C/A,E), subgroup-specific polymerase chain reaction (PCR), virus neutralization, envelope gene sequencing, and phylogenetic analysis. All four ALVs are exogenous, belong to subgroup A, and appear to be virtually identical to each other based on PCR and envelope gene nucleotide sequences. We describe herein the characterization of the contaminant viruses in vivo by means of experimental infection in chickens.

The contaminant viruses established transient viremia in specified pathogen-free (SPF) Leghorn chickens and elicited a robust and lasting antibody response detectable by enzyme-linked immunosorbent assay.

None of the contaminant ALVs induced tumors up to 31 wk of age, and mortality was insignificant.

Despite a strong antibody response against the contaminant ALVs, vertical (congenital) transmission to the progeny of experimentally infected SPF chickens took place, albeit at a very low rate (< or = 1.6%).

Experimental infection in meat-type chicken embryos resulted in viremia at hatch, suggesting that some meat-type chickens are susceptible to infection and support virus replication.

Source: http://www.ncbi.nlm.nih.gov/pubmed/16863073
(Yes, I know this doesn't mean that the Marek's can necessarily transmit vertically just because it's been accidentally paired with ALV, but there's a rich history of vaccines having unexpected results and of course 'bloopers' happening where individuals are infected by badly prepared vaccines or where the vaccine did not act as expected. So while it's probably very unlikely, I wouldn't completely dismiss the possibility.)

Not sure what this next bit of info is worth but sooner or later I'll get around to checking the studies cited... Just some random info on MDV:
Quote:
Best wishes.

 

[tridentk9]

Tridentk9, it's important for people to contribute articles.  Please know that I'm not criticizing you, just the fact that there is very little out there that is current. 

This is the type of article I question because of the dates of the material cited.  17 out of 24 resources here were from the 70's, 80's, and 90's.  Although this article was written in 2011.  The other thing is that all the cited resources state found in "Google Scholar" and the link is a dead end.

I also question what is written about 1 week old chicks when most common with Marek's is taking 4-6+ weeks to become symptomatic, which makes it seem to me that there would not be much found in a week old chick that was positive for Marek's.

Maternal antibodies I think, is more of a theory.  I don't see how it matters with most chickens that need more than 2 weeks of protection from mom to build enough of an immune system against Marek's symptoms.

My 3 hatched from resistant parents and hatched by a resistant silkie , only one lived.  The other 2 got paralysis and wasting and were euthanized.

But the biggest problem with articles found on line is that most are not current.  And many are not dated.  It's hard to get findings that are less than 5-10 years old.

I tend to give more credence to peer reviewed articles. This mag is for the American College of Veterinary Pathologists. At least three boarded ACVP members had to find it worthwhile and the resources credible to allow it to be published. It does give it a bit more cachet.

Inhaled MDV "spores" can be found in the body within a few days. With the chick's immature immune system plus it's rapidly replicating body, the disease will affect it much sooner and harder than in an adult. As the article states, finding MDV in week old "field" (non-lab) chicks is rare, extremely rare. This is the only verified case they knew about. The other theory would be vertical transmission, let's hope it's a case of quickly replicating environmental/horizontal infection.

Dr Karel Schat, Cornell's MDV specialist, believes in maternal antibodies in chickens. IgG. It's mentioned as a known in other, peer reviewed, articles. Until shown otherwise, I'll go with that they can occur in chicks. I would guess that some individuals don't hold onto those antibodies as well as the norm though.

 

[speckledhen]

Quote: Dear Lord, that is not what anyone wants to hear, that the vaccine that is supposed to help could give them another horrible virus.

I wasn't convinced to vaccinate my birds and now, I'm even further from being convinced.

 

[chooks4life]

Dear Lord, that is not what anyone wants to hear, that the vaccine that is supposed to help could give them another horrible virus.

I wasn't convinced to vaccinate my birds and now, I'm even further from being convinced.

That's alright, it's only four lots of vaccines from two manufacturers. Which, I admit, makes me wonder... Who knows how many others they missed?

But no medicine is perfect. It's more concerning to me when they mix things and alter their normal actions because of course there is always room for unexpected and unintended consequences.

Best wishes.

 

[speckledhen]

That's alright, it's only four lots of vaccines from two manufacturers. Which, I admit, makes me wonder... Who knows how many others they missed?

But no medicine is perfect. It's more concerning to me when they mix things and alter their normal actions because of course there is always room for unexpected and unintended consequences.

Best wishes.

Exactly what I have to wonder myself.

I've been so stressed, losing sleep over stuff lately, my hens who died unexpectedly, my friend's hens (found it was something else odd, but not Marek's), thinking about rearranging the birds and downsizing/simplifying, etc, I feel like I need to sleep for a week. If there is Marek's in my soil, then my birds must be generally very resistant because I've had no symptoms in any birds so, as my pal Karen said, with my management habits and nothing else to point to it being here, I need to just relax and not borrow trouble. With that, I'm going to bed early and try not to dream about disease and other horrible stuff. G'nite, all.

 

[seminolewind]

Quote:
I'm a bit unhappy about the amount of current valid information available to all of us. This disease was recognized over 100 years ago, and it just doesn't seem like we've learned all that much since. The only real big step was the development of the vaccine, the importance of disinfecting, and not mixing ages (I would say to us that means stop adding chickens to a flock )

My major or sometimes only resource for Marek's information is from "Diseases of Poultry", Chief Editor Y. M. Saif. That book has hundreds of research scientists contributing and I feel that book has the most valid information. My other sources are from members I know here who have researched Marek's as obsessively as I have, and I seem to be meeting more and more members like that!

My last source is what I've experienced and what other members have experienced. I read what's on line but find a lot of it contradicting. Even most Avian vets do not have the wealth of knowledge that we have as a group!

I believe that most Marek's cases are from chicks that were exposed early. By about 6-8 weeks average, the virus has replicated so many times that they begin to suffer symptoms. If I have chicks that have both parents naturally resistant, and hatched by another hen who is naturally resistant, I would think that the chick has mom's antibody coverage for a few weeks. My experience with that is small, 2 became symptomatic at 8 months and euthanized, and one is still living, so maybe mom's antibodies help a chick survive longer. But probably not escape the virus any better than non vaccinated exposed chicks. And the vaccine would not be given prior to exposure since they were hatched under a hen.

So, can a chicken have maternal antibodies against viruses? Herpes virus?
How hard is it to extract enough virus or antibody from a week old chick to be able to detect it?
How can we utilize the chick's antibody coverage for a few weeks?

 

[tridentk9]

Sorry- this may seem terse but I have animals wanting attention NOW! Spoiled BRaTs Trying to get this written before a 120 pound dog leaps over my head is a race.

Saif's Diseases of Poultry sections on Marek's and the circoviruses were written by Schat. It looks like the 13th edition's Chapter 2 may answer some of your questions on maternal antibodies. Not sure how much difference the development of T-cells makes in the response to MDV's attack. At a young age T-cells are pretty much still in the thymus.

100 years really isn't that much time in investigating a disease. A human vaccine for rabies (by Pasteur) was first used 129 years ago- yet over 50,000 people a year still die from rabies world wide. Sep 28 was World Rabies Day.,

Were there any carriers, subclinical or acute infections in your flock? What percentage ended up being tested? Did you get a chance to repeat tests a few weeks later to see if any had succesfully fought off the disease. Hmmm, there's an interesting rabies report .... let me search for it.

 

[chooks4life]

I'm a bit unhappy about the amount of current valid information available to all of us. This disease was recognized over 100 years ago, and it just doesn't seem like we've learned all that much since. The only real big step was the development of the vaccine, the importance of disinfecting, and not mixing ages (I would say to us that means stop adding chickens to a flock )

Ah, darn it, wish I'd bookmarked more links... While searching something like the terms 'Marek's disease vertical transmission' the other day, (looking for those resources I didn't bookmark during another search session which had mentioned vertical transmission is not completely ruled out), I came across many recent articles on it which covered your questions in this post.

The general pattern that all these informational resources had was that they dismissed the importance of vaccines as a solution and were speaking of co-existing and breeding for resistance, and they also expressed fears over the rapid adaption of the disease to whatever control measures were being used and basically it was openly admitted that we're making it far more virulent and dangerous at a rapid rate by being so heavy handed in trying to eradicate it, and eradication is no longer the answer it was thought to be decades ago.

Vaccines gave great hope and success rates initially but that's no longer the case, from what I've read, though most modern publications are still adhering to that suggestion and practice for want of knowledge of a better alternative. Plenty of commercial outfits are breeding for resistance in America too.

My major or sometimes only resource for Marek's information is from "Diseases of Poultry", Chief Editor Y. M. Saif. That book has hundreds of research scientists contributing and I feel that book has the most valid information. My other sources are from members I know here who have researched Marek's as obsessively as I have, and I seem to be meeting more and more members like that!

My last source is what I've experienced and what other members have experienced. I read what's on line but find a lot of it contradicting. Even most Avian vets do not have the wealth of knowledge that we have as a group!

It sure is extremely contradictory and variable.

I believe that most Marek's cases are from chicks that were exposed early. By about 6-8 weeks average, the virus has replicated so many times that they begin to suffer symptoms. If I have chicks that have both parents naturally resistant, and hatched by another hen who is naturally resistant, I would think that the chick has mom's antibody coverage for a few weeks.

From what I've read this is all correct.

My experience with that is small, 2 became symptomatic at 8 months and euthanized, and one is still living, so maybe mom's antibodies help a chick survive longer. But probably not escape the virus any better than non vaccinated exposed chicks. And the vaccine would not be given prior to exposure since they were hatched under a hen.

Vaccinated hens also pass on some maternal antibodies, from what I've read.

But as people here were theorizing, and which does appear to be correct as well judging from my bit of research the other day, time and severity of exposure does matter, very much so; it's a case of 'too much too soon' as one researcher said.

So, can a chicken have maternal antibodies against viruses? Herpes virus?

Yes, they do.

How hard is it to extract enough virus or antibody from a week old chick to be able to detect it?

For a researcher with a lab it seems very easy, it's a routine part of their studies on Marek's, but for a home operation, I don't know.

How can we utilize the chick's antibody coverage for a few weeks?

Seems that keeping the soil healthy is of great importance against Marek's, allowing them time to transfer from maternal to their own antibodies, so the chicks are not overexposed too soon. Ability for them to freerange large areas would lessen the likelihood of them entering the same dander-heavy areas regularly, though my mothers tended to brood outside the main coops but visit them for food... But, I usually did feed them separately until the chicks were a few weeks old, which may have something to do with the low rate of afflicted birds.

It's open to interpretation to some degree; some think 'healthy' coop floors are concrete or shavings or soil that's been doused or rinsed regularly in very strong and persistent chemicals to the point of being biologically zombified, lol, whereas I use the deep litter method and consider that healthy. Given that I've never had a problem with cocci and only a few random deaths to Marek's over the years, I think the deep litter composting method poses no greater risk than keeping carriers on concrete and bleaching it or whatever, since people who do that still lose them to MDV among other diseases at often quite high percentages.

Best wishes.

 

[seminolewind]

Sorry- this may seem terse but I have animals wanting attention NOW!

Spoiled BRaTs

Trying to get this written before a 120 pound dog leaps over my head is a race.

Saif's Diseases of Poultry sections on Marek's and the circoviruses were written by Schat. It looks like the 13th edition's Chapter 2 may answer some of your questions on maternal antibodies. Not sure how much difference the development of T-cells makes in the response to MDV's attack. At a young age T-cells are pretty much still in the thymus.

100 years really isn't that much time in investigating a disease. A human vaccine for rabies (by Pasteur) was first used 129 years ago- yet over 50,000 people a year still die from rabies world wide. Sep 28 was World Rabies Day.,

Were there any carriers, subclinical or acute infections in your flock? What percentage ended up being tested? Did you get a chance to repeat tests a few weeks later to see if any had succesfully fought off the disease. Hmmm, there's an interesting rabies report .... let me search for it.

I understand about the spoiled brat, LOL.

My flock was fine until I broke speckledhen's cardinal rule about a "closed flock", to us meaning only hatching our own eggs or day old chicks from a hatchery, or hatching eggs from someone else. Brought home a silkie pullet and 4 weeks later my silkie roo got all the classic symptoms; paralysis, grey eye, loss of perception, spastic paralysis of wings, loss of neck control. But still crowed almost every morning under my window. Broke my heart.

Then over a year I had quite a few waste away. A few were older than a year, most were around 8 months old. Then I had a hatch of 8 chicks that got paralysis and loss of perception and wasting, sometimes gasping, one each week until they were all gone. Never had a necropsy.

Lately, I had a necropsy on one hen , died from Aspergillosis and pcr negative for Marek's. And the most recent one , died of capillaria then enteritis, no sign of Marek's. So, I'm understanding from the big book that if a bird has tumors or enlarged nerves, most will have a positive pcr. But without symptoms or tumors, I wonder how often they have a false negative on a pcr.

Cynthia, I read that there's no real proof of Marek's passing mother to chick, and the virus would not survive on the outside of the egg due to the temperature and humidity.

I read that most chicks are born with the protective antibodies. I wonder if a chick exposed the first 2 weeks, then removed, has a good chance of surviving?

I do have to admit tho, in the Saif book that there are sections that are beyond my understanding.