Toxoplasma

Toxoplasma gondii is a protozoan parasite that can infect almost all warm-blooded animals, including humans.
In humans, it is one of the most common parasites. Blood test show that up to a third of the world population has been or is infected with "T. gondii". Infection rates differ greatly from country to country.
Although mild, flu-like symptoms occasionally occur during the first few weeks, infection with "T. gondii" generally produces no symptoms in healthy human adults. But in infants, HIV/AIDS patients, and others with weakened immunity, infection can cause serious and occasionally fatal illness (toxoplasmosis).p77
Infection in humans and other warm-blooded animals can occur
The parasite can only sexually reproduce in the intestines of members of the cat family (felids). Felids are therefore the definitive hosts of "T. gondii", with all other hosts defined as 'intermediate hosts'.