I think my cat has FIP

I found this forum while browsing for my cat's symptoms earlier this year. I adopted 2 beautiful nebelung brothers from my vet 2 years ago. One of them, Wendell, was sick for over a year and a half that we had him. He was fine-looking most of the time and after several vet visits telling us that he had hairballs, a virus, etc etc, and after spending hundreds of dollars on him we decided we couldn't spend any more money. He had just "off" days once in a month or so and we still couldn't explain it. After about a year of this going on, the timespans between his "off" days began to get closer and closer in until he was sick pretty much everyday. Once that started we noticed he began losing weight rapidly and after a few days wouldn't eat at all. That's when I came here and someone suggested FIP. The next day we brought him to a completely different vet and he said yes, unfortunately that was what he had and it was far progressed. So we had him put to sleep. I balled for a week.
Fortunately, his brother Clark has always been a robust and healthy cat and was always in contrast to Wendell with how healthy he looks. He has never had ANY health problems and always had a good appetite (he was even a little pudgy) When we had Wendell put to sleep I made sure and ask the vet if my other cat was at risk for developing this and he said it's hard to know but that since Wendell had obviously had it for a while and it progressed slowly in him that Clark was probably fine.
It's been I would say at least 4 or 5 months since Wendell has been gone and Clark has been his usual happy, healthy self with no change. Until this week.
Just in the past I would say 3 days I have noticed a 180 degree change in him. Friday was when I really noticed it and unfortunately our vet was closed today so here I sit. I am so devasted because I see the same symptoms beginning in him and I'm wondering HOW??????? Unlike Wendell developing it slow, it seems like his symptoms are deteriorating very fast.
His fur has always been very fluffy, whereas Wendells was more like a silvery sheen so you could see his body outline. So when I noticed Clark acting strange yesterday and seeing his eyes looking weird (like Wendells ALWAYS did) and seeing that he didn't want to do much of anything but sleep the past few days, I picked him up and really examined him closer and I can tell he has lost weight. It's not a huge amount but he's always been chunky and now he is lean. I just couldn't see through his hair I guess before to tell it. Good news, he's still eating but I can tell that his appetite isn't what it was. My question is this, once one of our cats was infected with the corona virus (wendell) then I'm assuming Clark would've came in contact with it also and so I'm assuming that even after Wendell died, Clark would still have the corona virus and it could mutuate to FIP just like Wendell's??? I just am dumbfounded because I thought for sure he would live a long and healthy life and now he is looking more and more like Wendell did just before he died, IN A MATTER OF DAYS. What do I do??? The vet told me FIP is a fatal disease, and hard to diagnose because there is no one "test" for it. I don't want him to get to the point that Wendell did because he was suffering. What would you do?

First of all, I'm just so sorry about Wendell.

How did the 2nd vet diagnose FIP? Was blood work done?

FIP is a disease diagnosed by elimination. The corona virus is the same thing that causes a cold - so a cat having some titre count for the corona virus doesn't mean anything, really. One of our cats had some rather mysterious symptoms that appeared to us to come on rather quickly. Our regular vet was on vacation. Another vet at the practice scared us half to death saying they thought it might be FIP. They put him in quarantine, and told us to bring in ALL of our other cats for testing. We brought the other five in, they were put in quarantine, and EVERYONE tested positive for corona virus - at varying titre counts.

FORTUNATELY our regular vet came back, and the blood work in the original cat didn't look like FIP to him - and he explained about exposure to corona virus.

The ONLY way FIP can actually be diagnosed is after they're dead, quite frankly. (Sorry to be morbid).

If you have an emergency vet near you, you may want to get your kitty there. Is he eating? He may need fluids and/or to be force fed. And he definitely needs blood work done.

I can't venture to say whether or not he also has FIP - assuming that is what happened to Wendell. I don't know enough about it. I do know there is a wet form and a dry form. One claims them very quickly, the other doesn't.

This site has a basic explanation for people - and detailed info for vets, but it may help you, especially when talking to a vet: http://www.dr-addie.com/WhatIsFIP.htm One thing this site makes very clear - it is difficult to diagnose, and the same symptoms can be indicative of many things, so treatment for whatever those other things might be is important to ensure it ISN'T something else being overlooked because of an assumption it is FIP.

Many vibes for Clark (and for you!)

When Wendell was at his worst and we brought him to the new vet, he told me that FIP was difficult to diagnose. He was a very intelligent and experienced vet (not saying he couldn't misdiagnose) and he did bloodwork along with urine tests and other tests and I can't remember specifics now but going by his condition (which at the time was very sick), his distended belly, his siezures, his eyes being dilated differently, his hair was greasy, and he was going into kidney failure, he said that is very indicative of FIP. He told me that he could only 100% say it is after he is dead because that is when they test for it but that he was very confident in saying that he had it. He had all the symptoms for the dry FIP, up until about the week that we put him sleep he never showed any signs of mucousy or cold like symptoms like the wet FIP.
Clark has also not shown any signs of wet FIP and he IS still eating at this time. I'm just starting to see signs like I did in Wendell and they seem to be progressing faster in him.

I am so sorry to hear of your situation. I lost two cats to FIP a couple of years ago. If a susceptible cat is exposed to it, then it is more likely that the virus will mutate, and obviously two brothers have a similar genetic make-up so could both have the same type of immune system and could be more likely to fall ill. Blood work will help you be more sure, as although up to 80% of cats do test positive for the virus, in the case of actual FIP the titre level usually soars above the norm, and combined with symptoms, the vets can give an informed opinion. But nothing is certain with FIP. It is so horrible.

Not saying he has or doesn't, but I wouldn't assume he does yet because he brother had it... There is trauma involved on your part (rightly so), and the thing is, there are so many possibilities, try to remain positive until you go to the vet... Make sure he eats and keep a very close eye on him- even a diary would be good now. Really monitor his food intake, litterbox and behavior, weight, etc.