I cannot find any information on there website or instructions indicating that Virkon will kill Coccidiosis. Virkon is effective on viruses,bacteria and fungi. Coccidiosis is parasitic,and Virkon will not kill parasites. As for claim to kill Marek's,i personally believe this is misleading and i am sceptical on this claim. Birds infected with Marek's can be carriers and shedders for life,therefore virus will always be around.As per the enclosed pamphlet it will. And will kill mereks which is why I purchased it in the first place along wil a long list of others.