I cannot explain it, but would guess he is in a remission for now.
Instead of the worst, look for the best reason.  At least he is feeling
somewhat better for now.  Purrs that he will feel better for as long as
possible.    MLB

I am so sorry about your cat, I found this link that may be helpful to your
questions about FIV.
http://www.v63.net/fivcats/pages/faq.html

Jan

"Caaagh" <nobody@spam.invalid> wrote in message
news:41cb5387$0$51389$ed2619ec@ptn-nntp-reader01.plus.n
et...

Our Smokey II was FIV and FeLV positive but lived very
comfortably for several years.  He had lost most of his
teeth by the time he wandered to us and his gums were
infected.  But our vet gave us antibiotic which helped
the gums gradually to heal.  His appetite then improved
immensely but his taste had improved also, so he would
no longer eat the (not cheap) dry food, though he could
very easily, but only the expensive canned food we
reserved for our oldest girl.  As well as tuna, chicken
liver and the occasional ground beef.  Also cream.
Very greedy for cream, but then he lived outside
always, except in the dead of winter when the wind
chill dropped to -10F and then only to come in to the
laundry room over the water heater.  He never gained
much weight that we could tell but since we couldn't
touch him, we couldn't ever weigh him to find out.  He
finally died last Spring of the accumulation of cancer,
kidney failure and some infection.  Or rather, our good
Dr Thorson came to help him when he could no longer
walk and could hardly breathe.  But he was always ready
to chat, even at the end, and eager for his food,
though his body couldn't process it.

I seem to have wandered.  I meant to say, your friend
may last longer than you think.  FIV is kind of like
human AIDs, makes the cat susceptible to other
infections.  If you can fight those -- as we did with
Smokey, battling ulcerated abscesses worse than the
pictures that showed up here a while ago -- then he may
be healthy and happy for years more.

Gum disease, which often accompanies FIV, puts cats off
their feed and they go down fast.  But correct the
problem and they can get better fast too.  Our Alice
had recurring gum inflammation that deep cleaning,
antibiotics and steroids could not eradicate.  She
would eat only canned food and chopped meat and
eventually little of that.  The carnassials and
premolars were drawn.  She was down for 3 days, then
perked up.  She began eating heavily and steadily --
mostly dry food, the expensive kind, of course -- and
has gained about 2-1/2 pounds since November a year
ago.

I wish you and your friend luck.