The same migration can also occur in humans. In humans, toxoplasmosis symptoms may be flu-like, in most cases there are no symptoms. Infection is more serious in individuals with poor immune response. If such people contract toxoplasmosis for the first time it can run riot in the body with the immune system unable to keep it in check. In people who have previously been infected, the dormant tissue cysts are activated.
Stress can also activate dormant cysts.
Activated tissue cysts can produce millions of toxoplasmas which can lodge in the heart or brain and other major organs. They may show no symptoms themselves, but the foetus may suffer birth defects including blindness and brain damage. Most infected babies are born healthy, but with dormant toxoplasmosis cysts, in later life these may lead to reduced vision and loss of sight. Cats are not the main source toxoplasmosis infection in humans. The vogue for 'rare cooked' meat is part of the problem.