Moving Forward- Breeding for Resistance to Marek's Disease

[Hamiam]

I’m very uneducated about Mareks. I recently bought chicks from Greenfire Farm that have been vaccinated. Is the vaccine a live vaccine? Can the vaccine cause the chicks to develop the disease? Have I put my unvaccinated flock at risk now?

 

[rebrascora]

Gosh, sorry I killed the thread

No, I don't think you did, but I do find some of your posts are not entirely clear as regards what you are getting at. My experience is however similar to yours as regards broody reared chicks possibly being less susceptible and having fewer casualties to Marek's as years goes by. I think there may be a number of reasons for this..... gradual exposure from a young age, stronger immune systems and no integration stress, assuming chicks are raised in the flock. And if they are raised from birds within the flock that have already been exposed and not succumbed then there may be the resistance element.
I disagree regarding introducing new adult birds from swaps/auctions etc because I do think they pose an additional threat. Firstly because they may introduce a different strain of the virus which your exisiting birds have no resistance to and secondly, the stress of integration can trigger an outbreak, not just in the new bird but also in the exisiting flock members. Keeping stress levels low is key to keeping Marek's outbreaks low. New birds can also introduce other viruses or diseases which can pass to the flock and weaken their immune system enough for Marek's to break out in birds that are carrying the dormant virus.

I'm trying a new approach this year by broody rearing hatching eggs from an outside (but local) source.... so it will be interesting to see how they fare. The broody herself had an outbreak of Marek's 7 months ago but made a full recovery from it, so I know she is carrying the virus. Unfortunately she is a big clumsy bird (will not be using her again) and only 4 chicks made it from 9 viable eggs. They were 2 weeks yesterday and doing well so far within the flock but it is still too early for Marek's to potentially make an appearance. I know it will be important to remove any young males before they reach adolescence to prevent the flock from that stress.

 

[rebrascora]

@Hamiam

Hi

The vaccination does not pose a risk to your existing flock in itself. What it does do is enable the virus to live within an infected bird, so if those chicks were infected with the virus they could still become symptomatic and shed the virus but would not necessarily die from it, like most birds that get the virus and are not vaccinated. If you got the chicks as day olds, I don't believe they pose any risk to your existing flock. If they were exposed to the virus during the first few weeks of life after vaccination, then they may carry the virus but there is no obvious way of knowing. The most likely way of introducing Marek's to your flock is by bringing in started birds.... so young pullets and cockerels or grown birds from auctions/swaps/breeders. Hatcheries usually have quite strict biosecurity within their units to prevent or significantly reduce the risk of transmission to newly hatched chicks.

 

[Hamiam]

@Hamiam

Hi

The vaccination does not pose a risk to your existing flock in itself. What it does do is enable the virus to live within an infected bird, so if those chicks were infected with the virus they could still become symptomatic and shed the virus but would not necessarily die from it, like most birds that get the virus and are not vaccinated. If you got the chicks as day olds, I don't believe they pose any risk to your existing flock. If they were exposed to the virus during the first few weeks of life after vaccination, then they may carry the virus but there is no obvious way of knowing. The most likely way of introducing Marek's to your flock is by bringing in started birds.... so young pullets and cockerels or grown birds from auctions/swaps/breeders. Hatcheries usually have quite strict biosecurity within their units to prevent or significantly reduce the risk of transmission to newly hatched chicks.

Thank you! Yes, I received them as day old chicks.

 

[Nambroth]

I’m very uneducated about Mareks. I recently bought chicks from Greenfire Farm that have been vaccinated. Is the vaccine a live vaccine? Can the vaccine cause the chicks to develop the disease? Have I put my unvaccinated flock at risk now?

Hello! I also received chicks from Greenfire this year. Marek's vaccines do not use live MDV-1 Marek's virus (of chickens). Most vaccines use a related (and harmless to chickens) virus of turkeys. Because I have had Marek's in my flock in the past 10 years, I inquired as to the exact vaccine they use at Greenfire, and (as of writing) they use the F-1-1 Marek's vaccine (Marek's MD-Vac). This is the Serotype 3 (HVT), live virus (of turkeys) Marek's virus vaccine, which is the standard Marek's vaccine. This vaccine can not cause your chickens to get or shed the chicken type of Marek's disease.

 

[rebrascora]

@Nambroth

Can I also confirm with you that this vaccine will not 100% prevent them from becoming infected with Marek's from an external source either. And if you keep turkeys with these chickens, would this vaccine pose any risk to the turkeys?

 

[Nambroth]

@Nambroth

Can I also confirm with you that this vaccine will not 100% prevent them from becoming infected with Marek's from an external source either. And if you keep turkeys with these chickens, would this vaccine pose any risk to the turkeys?

No existing Marek's vaccine will prevent a chicken from becoming infected with Marek's disease if the chicken is exposed to the virus. The vaccine is intended to help a chick build an immunity to MDV1 (Marek's Disease Virus of chickens) so that if the bird is later infected, its immune system is more "prepared" to fight the virus and there is a much higher liklihood of the chicken not developing the fatal visceral symptoms of the disease (tumors, nerve lesions, etc). Essentially, it is very directly exposing the chicken to the related, but not infectious (to the chicken) turkey virus, in the case of using the HVT-derived (Herpes Virus of Turkeys) vaccine.

There are other vaccines now in use (MDV2 vaccines), but they are not available to consumers or to small time operations in the USA (only a few of the big, commercial, high volume hatcheries use them, mostly for the commercial production of egg layers and sometimes meat birds). In essence, at least here in the US, most suppliers to backyard chicken keepers are going to be using the HVT-derived vaccine.

I am not an expert in turkey disease (in fact I know next to nothing about turkey disease!!), but based on my research and understanding of this specific disease (Marek's), HVT causes no apparent disease or symptoms in turkeys themselves. It is cited as being universal in both wild and domestic turkeys and is not known to be pathogenic in any species. Here are a few things I have bookmarked, in case they help. https://www.merckvetmanual.com/poultry/neoplasms/marek’s-disease-in-poultry https://medical-dictionary.thefreedictionary.com/turkey+herpesvirus

(edited for typos)

 

[rebrascora]

@Nambroth
Many thanks for clarifying and linking those items.

 

[Nambroth]

I hope it's helpful. This virus and the vaccines can be very confusing to learn about.

 

[rebrascora]

Yes, I knew that the most effective vaccines were not available to the general public and my personal approach is not to use the one available because it is "leaky", but then as you may be aware from my other posts, I have one of the milder strains of the disease. It is useful to have as much information on the disease and vaccine as possible so that people can make up their own mind what is the best course of action in their situation.