Toxoplasma is a parasitic infection humans may contract from cats, undercooked meat or poultry, or poorly sanitized water. The mode of transmission from cats may be indirect: a child may play in a sandbox contaminated with cat feces, a pregnant mother may clean out a kitty litter box, or a family dog may roll around in soil or sand contaminated with cat droppings and then bring the parasite into the house.
Toxoplasma may exist in an “active form” and in a “cyst form.” Antibiotics may kill the active form but do not always kill the cysts. If a human is infected, the cyst form may persist in the retina within a small retinal scar and cause occasional episodes of inflammation inside the eye (retinochoroiditis), which must be recognized and treated appropriately. Toxoplasma retinochoroiditis can be vision threatening.
European uveitis patient group: article on ocular toxoplasmosis (caution: this file is large and may take time to download).