Mareks mostly affects chickens, although it has been reported in turkeys in some countries. Here is a good link to read about it: http://www.merckvetmanual.com/mvm/poultry/neoplasms/mareks_disease_in_poultry.html
Perhaps there is another disease affecting your pigeons since there are so many...
Amprollium is a very good drug for every strain of cocci. It's the drug of choice in the US. Baycox (toltrzuril) is also good, but not as readily available here. After any cocci treatment, give probiotics, and vitamins for several day. Personally I would not use vinegar in their water while they...
If a vet or vet college could perform a necropsy on a chicken that has died and the body refrigerated, they may be able to diagnose "possible Mareks' without the expensive testing. Here in the US, the price of Mareks testing is around $28 at some testing centers such as Texas A&M. Mareks causes...