The correct option is B Histomonas
Blackhead, also referred to as histomoniasis, is a disease caused by the protozoan Histomonas meleagridis. This disease initially affects the intestinal ceca and liver, causing tissue destruction. This disease primarily affects turkeys, but other poultry species can be infected as well. Clinical signs of blackhead include yellow droppings and reddening of the skin and muscles. The disease derives its name from the dark red skin of infected birds. Hence, option B is correct.