So Patches fever had disappeared by early afternoon, I went visiting him and he was really happy to see me, curious and playful. The usual Patch. The vet called again around 9 pm to tell us that he was still without a fever and doing well. The problem is that they don't know what brings these fevers. They feel it's unlikely to be FIP because cats normally don't go in an out of it, symptoms get worse and that's it. One possibility is that he may have a herpes virus (not contagious to humans) which is affecting the respiratory tract. Due to the nature of the virus he is not really getting rid of it and stress can cause it to replicate and the fever spikes (to prevent the virus to replicate further). It's a bit of a pain, like a cold sore, but manageable. They want to retest him in a month time for FIV and FeLV in case what they have seen so far are false negatives due to maternal antibodies masking the results (not sure this is really a possibility though). The strange fact is that The Dude is in perfect health. You'd think a virus would spread to him too.
This morning Patches was still without fever and eating "like a horse" as the vet said so we'll bring him home later today!
And this morning I also brought The Dude to be neutered so hopefully everything will go well and we'll pick him up tomorrow morning. Patches will have a quiet house for a day at least, and hopefully it'll be little longer before he has another episode...I'm dreading the time when we'll go on holiday and board the two of them...but the cattery we selected seems great, they even use our same vet, so hopefully everything will go well.