(c) C* Point A marks the entry of infectious agent into the host* Point B marks the subclinical phase where symptoms and signs are not visible, but the disease agent induces tissue and physiological changes* Point C marks the Clinical horizon when symptoms and signs appear* Point D is present inside the Clinical phase after the Clinical horizon.ALSO REMEMBERNATURAL HISTORY OF DISEASE* Prepathogenesis phase* Pathogenesis phase:Begins with the entry of disease agent into the hostFinal outcome of the disease may be Recovery, Disability or DeathPathological changes are essentially below the level of Clinical horizonClinical stage begins when signs and symptoms appear