Sometimes I feel like if I ask a question a bunch of different ways, it will finally be answered , LOL. Interesting, I never thought of the part that says "herpes virus" which means it can have dormant copies. Sometimes I think that we all have important facts but like me, I get tunnel vision and and need a good slap on the head!
So Marek's can lay dormant, awake, and not necessarily grow tumors, but affect a chicken in different ways, like wasting?
Marek's is Herpesvirus of chickens. HVT is Turkey Marek's-- Herpesvirus of Turkeys.
Herpesviruses are DNA viruses, which essentially (again this is oversimplified) inject themselves into the very DNA of the host's cells, in order to trick the cell into making many copies of the virus DNA instead of the cell's own DNA. When it is latent-- dormant-- it sits there, with its copies in the cell(s), just chilling out until it becomes active again or the host dies.
If you want to rip your hair out you can learn more about herpesviridae and latency here: http://en.wikipedia.org/wiki/Herpesvirus (I know, it's Wikipedia, but it's helpful for a layperson to get a basic idea!)
I am unclear on exactly when, how, and if Marek's becomes reactivated, and what symptoms we see. I sort of suspect that reactivation of the virus (versus the initial infection) is when we see the more long-term slow advance of problems, such as general wasting, immunosupression, sometimes eye problems. This is, at best, a layman's guess based on what I have read.
When you think of reactivation of the virus, think of it like Human Herpes (Herpes Simplex, the STD) and Chicken Pox. Both can go into latency (remission, whatever you want to call it) and then pop back up later in life. Herpes has cyclical reemergence in humans, usually when the person is under stress or is sick with a secondary issue (sound familiar?) whereas chicken pox comes back as Shingles, but it is still the same virus. It has just taken a different symptom when it reactivates later in the host's life.
Good explanation. Oversimplification is a good thing; helps more people understand what's happening!