Hi, there. I have just read through this thread, and I can relate. One time before I had Bengals, I did a foolish thing: I babysat for three baby Bengals. Didn't realize they all had diarrhea. I ran out and got them a separate litter box from my cats (4 resident cats at the time). Turned out, several days after the kittens left the house, I noticed my gray girl kitty bleeding from her behind. She got liquid diarrhea, which she had never had before, so I was sure she caught whatever the kittens had. Next was my ex's Melanistic that I was hosting at my house. She started bleeding from her behind. Let me say here, I have had experience with my cats catching parasites, including TF, from cattery cats, but nothing is as bloody as Coccidia. That is what the Bengal kittens had that spread to my cats. I took my gray girl in for testing and the vet said she was "swimming" with it.
I too, was told the medication I was given for all four cats would not kill the Coccidia ~ just stop reproduction, and the immune system would take over from there.
It did. We went through the regimen, and eventually everything cleared up. There were no lasting ill effects.
Try not to worry. These things are so very common in catteries, so you are not alone. Thousands of people have been through the same thing with their cats.
Okay .... now to address the "medication and trust" part of your post .... When I finally got myself a couple of Bengal kids (from the same cattery the Coccidia kittens came from), I was assured their poo was "picture perfect".
Just to be safe, the breeder brought me a pair of labeled poos in zip lock baggies so I could run to the vet with them and have the new kids checked out, and their poos tested for the "usual suspects". The results came back negative. Yay! I co-mingled the kittens with my two cats (bad idea) ~ the ex's two cats were now gone. Next thing I knew, the kittens were squirting liquid diarrhea.
(Not sure where those picture perfect poos in the zip lock came from I was given Science Diet Hairball Light to feed them, when right on the bag it said not to give it to cats under a year. I was very upset. I took them back to the vet, who gave me prescription food, but long story short, we ended up testing for TF, and that was what the problem was. By this time, one of my resident cats also had the liquid diarrhea.
It is very upsetting when we are not told these things, but I agree with Junglerose, that its better not to act worried or emotional around cats, because they pick up on it. I'll say here, that most of what we worry about doesn't happen anyway, so ...
I had to pill all of my cats with Ronidazole. I have to admit, I was freaked out. My girl Bengal, Bianca, was a nightmare to pill. She fought tooth and nail. I went through just what you are going through. After the pilling ordeal for the day, I'd find a pill on the floor and not know who spit theirs out. My new kittens seemed to be hating me. Then I came up with an idea.
I called the vet and asked if they could do the pilling for me. So ... each day, I made a 10 mile trip to the vet with two Bengals in tow. I let them be the "bad guys". It saved my reputation with my new kids.
If it's impossible to make a daily vet trip, then neonyellowclover's suggestions are great. There came a day in our regimen that I could not go to the vet, (Thanksgiving holiday). On that day, and the following Sunday, I confined them to one small room: the bathroom, got each one in the corner, and used scruffing. I was alone, but somehow managed.
Here we are, almost 6 years later, and my Bengals love me. They are both lap cats. Don't worry. Bite the bullet. Do what you have to do. Jasper will love you. Look what you are doing for him. You are giving him a new lease on life. Sorry for what he has been through. There are better days ahead.