From a litter box. The parasite, toxoplasma is excreted in the stool of healthy appearing house cats. It can be acquired from a task as simple as changing a litter box without washing ones hands.
Undercooked meat. Most people (and even some doctors) think it is cats. But cats are not a major reason for toxoplasmosis in this country. Undercooked meat is the most common way people acquire toxoplasmosis. Eat your meat well-done!