Marek's Vaccination in Unexposed Chicks Over a Day-old

[InterestingChickens]

" By preventing death, vaccination greatly increased the infectious period of the most virulent strains.

I do not understand how it could increase the infection period longer, as chickens who are infected with Marek's disease are infectious for their whole life regardless of vaccination status.

I am sure there is some sort of variation between the Stereotype three vaccine and Rispens CV1988.

 

[LikeTurkeys]

Perhaps it increased transmission time for the most virulent strains (which would kill 100% of chickens), but note that we are talking about large farms here with multiple barns and the potential for not all barns to be infected. A small flock has a 100% chance of all birds being affected.

This study points out that the cumulative virus load was less in vaccinated birds after an outbreak than in unvaccinated, except in the case of the most virulent strains due to similar rates of secondary shedding (after the main infection). It also mentions that vaccination is particularly useful for strains of low virulence.

"When an outbreak does occur, vaccination reduces the amount of virus left at the end of the cohort duration"

"We find that the chance of an outbreak within a barn increases with the virulence of an MDV strain, and is significantly reduced when the flock is vaccinated, especially when there the contaminant strain is of low virulence. With low quantities of contaminated dust, there is nearly a 100% effectiveness of vaccines to reduce MDV outbreaks."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3863959/

As a side note, I am convinced that my flock has been infected with a very mild strain of Marek's disease, and dust can be managed. So according to this study it would be advantageous for me to vaccinate new chicks (I realize this does not apply to everyone).

 

[McChooky]

Some strains can break through the best vaccines available in the market.

https://www.mdpi.com/1999-4915/12/9/1048

https://www.chickenfans.com/mareks-disease-chickens/

 

[LikeTurkeys]

Some strains can break through the best vaccines available in the market.

https://www.mdpi.com/1999-4915/12/9/1048

https://www.chickenfans.com/mareks-disease-chickens/

The operative word here is "some" strains. And again, your chickens would still be worse off unvaccinated than vaccinated, especially with strains of high virulence.

 

[McChooky]

The operative word here is "some" strains. And again, your chickens would still be worse off unvaccinated than vaccinated, especially with strains of high virulence.

You're damned if you do or don't.

 

[Dovemaiden]

It's a little bit more complicated than that, and a PBS article doesn't cover much.

Here is my understanding (sorry if it gets a bit complicated!).

There are two different types of immune responses. A humoral or antibody-based response, are fully developed antibodies that bind to antigens (specific proteins on viruses) and prevent them from replicating. Maternal antibodies fall into this category.

A cell-mediated response are killer T-cells that destroy infected cells. This is the kind of response induced by vaccination.

After infection (or vaccination), a certain number of killer T-cells become memory T-cells. When the virus starts replicating again and are encountered by memory cells, they produce a massive number of killer T-cells to fight the infection. This is what produces long term immunity.

These two types of immunities are also commonly known as passive and active immunity.

The level of maternal antibodies varies from chick to chick, and in general active immunity provides better protection than passive immunity. You want to give the chicks time to develop memory T-cells before actual infection, which is why it's so important to keep them from being exposed for 1-2 weeks after vaccination. That way when the chick is exposed, the memory T-cells can quickly generate killer T-cells and prevent symptoms.

Unfortunately, Marek's disease has the ability to become latent, which means some virus won't be seen by killer T-cells. This is why a chicken will never stop shedding the virus, even if it's vaccinated. But vaccination does aid in preventing symptoms and reducing the amount of virus a chicken does shed.

I hope this makes sense. I'll provide sources later.

This is one of the best and most succint explanations of cells mediated vs. humoral i have read. Stellar!