In healthy adults and children, infection may be without symptoms. In some cases, infection may present as a mild flu-like illness. The infection can cause serious health problems for anyone with suppressed or damaged immunity, for example people on immune suppressing drugs or people with AIDS (see entry HIV infection and AIDS).
Toxoplasmosis is one of a small group of infections that can transmit to the fetus (unborn baby) if caught for the first time during pregnancy. The risk of transmission and the degree of damage done depend on when in pregnancy the woman catches the infection. In the first trimester, the damage may be very severe, however it is less likely that infection is transmitted at this stage of pregnancy. Later on in pregnancy, the damage is less severe, but the infection is more likely to transmit and cause congenital infection (infection at birth).
Severe damage includes excess fluid on the brain (see entry Hydrocephalus), calcifications of the brain tissue that can lead to developmental delay (see entry Global Developmental Delay) and epilepsy, and damage to the retina (a light-sensitive film at the back of the eye) of one or both eyes known as retinochoroiditis. More severe damage to the brain is rare.
Damage in a severely affected infant will be apparent soon after birth. However, the vast majority of babies with congenital infection will appear normal at birth. Unless these babies are treated, problems especially with the eyes, will develop in childhood, the teens or even later.