Mareks is a herpes virus and is often triggered by stress (adolescent social stress is the most common trigger, or injury/predator attack that freaks them out etc...). If it is Mareks many of us have had success with antiherpes meds (i.e. Valtrex, a cheap generic drug but you need a script from your vet, it is sold at regular pharmacies).
The antiherpes meds cannot just "fix" the damage but it prevents new cells from being infected so it is best used as a preventative or at the first sign of symptoms. Course there are also many different strains of Mareks therefore it also depends on how "hot" this virus is.
If these chicks are under any flock stress do whatever you can to minimize it asap.
