I didn't have the petting bug but I did go into a household with four cats and the newest cat, who was adopted as a stray, was suddenly non-stop violently ill, passing out, and loaded with fleas. My Sim happened to be a top level veterinarian so she brought the cat to the hospital to be treated. But when she brought the cat back home, it bugged again and started throwing up in a loop, even though the game registered the cat as not being sick. My Sim was just cleaning up after the cat and couldn't focus on anything else so I adopted out the cat. I couldn't even give her a wellness treat, it was grayed out.
So, yeah. Something in Seasons bugged the pets.
