Calci Virus Carrier Question

Hello! My parents have about 17 feral/semi-feral cats outdoors that they feed and pet. Most tolerate a couple of pats, but one tiny little girl, Scout, is extremely affectionate. She'll climb on your lap and just snuggle for a long time, purring away. My parents have 3 indoor cats, and all the cats spend all day sitting together on opposite sides of the screen door, rubbing up against each other. The outdoor cats have all been trapped and fixed and my parents would love to bring Scout indoors. Not long ago, she snuck inside, grabbed a bite from the cats's food bowl and then snuggled up on the couch for about 15 minutes before anyone even noticed. 

Just one problem - Scout (1.5 yrs old) got the calici virus badly last year and spent a few days at the vet getting $2k worth of treatment and medicine. She had bad ulcers in her mouth and got really dehydrated. A few other younger outdoor cats got sick, but none as badly as Scout.  The indoor cats got boosters for calici at this time and no one, indoors or out, has shown any symptoms in the last10 months.

The vet down there advised that she never live inside as a single cat or with my parents, as she will be a carrier forever, but is this virus really as bad as she made it seem? Don't people take in strays frequently without knowing if the cat is a carrier?  Or is it only a problem if the cat is actively showing symptoms?

I am staying at my parents' for the summer with my own cat (a former feral who was taken in). Inevitably the cats will brush faces at the screen door - do I also need to worry about my cat getting sick? 

Thanks for your help!

This is tricky. The calicivirus is contagious even when symptoms are not present, so if they adopt this cat there's a good chance the other cats will get it if they haven't already. The vaccine does not prevent transmission of the virus, but it does do a good job at lessening the severity. And the virus is usually not dangerous for adult cats with a healthy immune system. Symptoms will flare up during times of stress, so lessening stressful scenarios helps a lot.

Lots of cats carry the virus without ever show signs, which is partly why it's spread so easily. I think vets tend to err on the side of caution, partly because they only see the cats that are sick enough to be taken to the vet, and they see a lot of scenarios that could have been prevented if people hadn't taken in strays, for example. I don't think the other cats are going to be exposed to unnecessary dangers if Scout comes to live with them. There's actually a fairly good chance they already have it, because this virus is not killed easily and can be passed as easily as a common cold is for humans. But the vet is not entirely off with her warnings, either.

Scout would most definitely be healthier and happier as an indoor kitty, and keeping the others up to date with their shots, keeping everyone on a healthy diet, and keeping stress to a minimum would be what I would do, quite honestly. But I'm very pro bringing cats indoors in almost all situations where it's remotely possible. Still, I wouldn't bring a calicivirus kitty home with my FIV positive cat, because I think that would be too much of a risk for me to be comfortable.

For your kitty, make sure he's up to date on his boosters, and he could get the virus from facial contact through a screen door, so keeping that from happening might be prudent. Of course if you wanted to make sure he never got anything, he would have to be quarantined from all other cats forever, and there's only so much you can do within reason. But traveling is a stressor and does weaken the immune system (in some cats more than others), so keeping him alone or just keeping an eye on him for the first few days until he settles in is an option.

Thank you so much for such a very detailed answer. I really appreciate it! I think my parents definitely have a lot of factors to consider before making a final decision!!