Walsh & Hoyt: Toxoplasmosis: Pathogenesis

Once tissue cysts rupture within the human gastrointestinal tract, the released tachyzoites invade, replicate within, and disrupt host cells. They then invade contiguous cells and disseminate widely via the blood stream and lymphatic system to other organs and tissues. The development of humoral and cellular immunity usually limits and eventually terminates tissue damage; however, the barrier to passage of antibody into the eye and the CNS may permit some organisms to proliferate and destroy ocular and neurologic tissue at the same time they are disappearing from other tissues and organs. Other organisms become encysted, producing little or no response but persisting in a viable latent form. In patients with congenital infection and in infected patients who are immunocompromised from disease or drugs, normal host defense mechanisms are defective, and acute toxoplasmosis may progress to death despite treatment.