"Once access into the digestive tract has been achieved,
H. meleagridis multiplies in the ceca and attacks the tissues of the cecal walls. As the disease progresses, a cheese-like, foul-smelling, yellow substance fills the ceca. This substance can vary in form from a hardened plug to more liquid in nature, and is composed of dead cecal cells and blood. In highly susceptible birds such as turkeys, the Blackhead protozoa then enter the bloodstream through the damaged ceca and are deposited into the liver, where they do even more damage, creating signature "bulls-eye" zones of necrosis (dead tissue). Occasionally,
H. meleagridis also enters into other organs such as the kidneys, lungs, heart, and brain.
Blackhead does not kill the infected bird, and the disease requires a secondary bacterial infection to be virulent and eventually fatal. Escherichia coli, Bacillus subtilis, and Clostridium sp. are some of the bacteria noted in the secondary infections that caused death (McDougald, 2005)."
Source:
https://attra.ncat.org/attra-pub/viewhtml.php?id=343