Toxoplasma Gondii in Cats
Toxoplasma gondii is a parasite of cats that, in the past, often had them being relinquished to shelters. This is a zoonotic parasite and is estimated to infect around 60 million people in the U.S. alone.
Most people have few to no clinical signs - these are more likely to be seen in immunocompromised people. In the past, women would be advised to get rid of their cats if they became pregnant because if the parasite crosses the placenta and infects the fetus, it can lead to abortion. However, most people get toxoplasmosis from eating undercooked meat, not from their pet cat.
There has to be fecal-oral transmission for people to get the parasite. Proper hand washing, cooking meat to the correct temperature and having someone else scoop the litterbox if a woman becomes pregnant are easy alternatives to surrendering a cat to a shelter.