This article is long and has a lot of medical terminology, but it explains the eimeria strains of coccidia that affect chickens, and which strains are the most serious:
https://www.merckvetmanual.com/poultry/coccidiosis/overview-of-coccidiosis-in-poultry
https://www.merckvetmanual.com/poultry/coccidiosis/overview-of-coccidiosis-in-poultry
