It'd be easy to rule this out. Cats who have been indoor-only without access to rodents are unlikely to have it. This would be a good distinction to collect/analyze if wanting to add credibility to the toxoplasmosis theory and rule out other cat related factors.
That would still be hard to control for. I believe I recall reading that a T. gondii infection is something you get for life. Even if you adopt kittens from your local shelter at 8 weeks old, and then keep them indoors for the rest of their lives, they may have come in contact with rodents at some point before they made it to the shelter.
Hell, regardless of that, many homes in many places suffer rodent infestations at some point in time. Even if you get the exterminator in, it might be too late. This summer we bought a new house, and a few nights in, our (fully indoor) cat showed up to our bedroom, a (still breathing) mouse hanging from his mouth. So much for keeping him away from rodents.
The shedding of oocytes is how humans become infected. This is supposed to be stopped by the cats immune system a few weeks after initial infection. It is possible it could reoccur later if the cat's health changes as other life cycle stages exist in the cat.
I don't mean to judge, just an honest question: considering we're talking about indoor cats, how do you have plenty of rats inside your house? Is it something you can fix completely with professional services? It's what people usually do so I'm curious if it's a special case.
In my case, they lived in my neighbor’s unkempt yard and a few secluded spots from when the previous neighbor raised chickens. This summer, they moved out and the house was vacant for a month. First time in 20 years we found mice in our house. We did have them in our garage about 10 years ago until I changed some things.
