Don't panic. There are several different strains of Mareks that range from mild to severe. Course once it gets introduced to a flock one has to assume everyone has it but with milder strains birds can live perfectly normal and healthy lives.
My flock got infected by it 6 years ago and I have not had a bird get sick from it for 4.5 years after I made some flock management changes. It is a herpes virus and like most herpes viruses it can stay dormant for a lifetime, but can also be triggered by stress. Adolescent chicks going through flock integration stress are the most vulnerable as are adults that suffer from another injury or illness and get stressed out.
Initially I lost some adolescent birds to it. Now only introduce chicks using a broody (so they are raised with the flock from the start and do not undergo any integration stress). I also got a script for a human antiherpes med from my vet (Valtrex, it is cheap and generic) and if any of my birds gets sick or injured I dose them with a small amount as a preventative. Once symptoms appear it is very hard to reverse them so prevention is key.
I live in Georgia and the state vet in our area says most all of the flocks around here have it and most people never realize it. For future reference avoid buying birds that have been vaccinated as the Mareks vaccine can create asymptomatic carriers which can introduce very hot/deadly strains to new flocks. The vaccine doesn't give them the virus, but allows them to catch the virus and spread it to other birds.
Question of the Day - Wednesday, October 28th, 2025
Over researched and made myself anxious about coccidiosis
