Feline Immunodeficiency Virus (FIV) in Plain Language

Feline Immunodeficiency Virus (FIV) is a virus that infects cats. Its presence in the cat causes the cat’s immune system to work much less well or not at all. A cat’s immune systems helps to protect the cat from infection. If it stops working the cat is more likely to become ill because it cannot stop infections from other viruses, bacteria and fungi (fungal infections).

The disease was first discovered in 1986 in a northern Californian cattery in the USA.

Cat With FIV - Brody

Cat With FIV – Brody. A handsome grey tabby. Photo by Rocky Mountain Feline Rescue

The Virus

The particular virus that causes FIV is part of a group of viruses called lentiviruses. The virus that causes AIDS in people (HIV) is in the same group.

However, a cat with FIV cannot give the disease to a person. Neither can a person with AIDS infect a cat with his disease.

This virus is also a “retrovirus”. This sort of virus multiplies inside the cat’s cells as part of the cell’s DNA (DNA – molecules containing chromosomes and genes).

How Common is FIV?

In the United States it is believed that 2-4% of cats “in the general population” are infected with FIV. In the UK the percentage is believed to be 6%.  Of all sick cats in the UK it is believed that 14% have FIV. These sorts of figures are probably about right for other countries.

Getting FIV

Outdoor male cats in the age range of 3-5 are most likely to get FIV because they get into fights and get bitten which is a way of passing the disease from one cat to another. If a pregnant cat gets FIV she can pass it on to her kittens. Close contact between cats is not the most common way to get FIV.

The Three Stages of FIV

Infected cats go through three stages of illness:

  1. Cat is very ill
  2. Cat shows no signs of illness
  3. Cat has multiple illnesses and dies

Initial Stage

Cat has a fever and swollen lymph nodes and may have diarrhea, skin infections and anemia. This lasts for up to about 6 weeks.

Middle or Latent Stage

This is called a “latent” period. This means the disease is present but not visible. This period can last up to about 12 years. Yes, a long time. The cat seems healthy during this time.

Terminal Stage

The cat shows signs of illness that are inline with the fact that the cat has no immune system. The illnesses are “unexplained”. This means there is no obvious reason for the illnesses that can be seen. As can be expected there are lots of health problems including:

  • mouth and gum disease
  • diarrhea
  • depressed
  • doesn’t want to eat
  • loss of weight
  • fever
  • infections that show as colds
  • ear infections
  • Infections of the urinary tract
  • dementia

Diagnosing FIV

Got to see a vet for this. It will be complicated.


No effective treatment (at 2008). The only “treatment” is to minimise the risk of infection by:

  • feeding with best quality food
  • excellent parasite control (for example fleas)
  • keeping your cat indoors
  • low stress, gentle and comforting home

Preventing FIV

Stop cats roaming and fighting, There is a vaccine but there are problems with it. A vet’s advice is needed. Cats living in groups in homes should be tested. Cats with FIV should be removed from the others. See a good veterinarian.

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Feline Immunodeficiency Virus (FIV) in Plain Language — 13 Comments

  1. Marvin goes to the vet today for the first time. It will be an adventure getting him into a crate. He is late for his rabies vaccination etc. by probably a year according to his previous caretaker. He has lived outside at the local schools his whole 9 years and has been to the vet before, but no one can tell me how that went.

    He has some kind of eye infection now that must be seen by a vet. I’m glad we had the appointment already as last night he was in a tussle with some creature I have no idea what. He has a gash on his chin and a sore body. The best thing to come out of it is he slept all night on his heated bed. On the porch of course. I tried to encourage him to sleep inside. I even set myself up to stay with him downstairs for the night. He seemed to like the idea for a while, but started to scream like crazy after a while to be let out. I was happy to find him snuggled on his bed this morning.

    He is definitely as scrapper of a cat. I’ll have him tested for FIV. If he is FIV positive, then what? He is his own cat! I won’t be imposing on him anything other than what he wants. Funny how it slowly comes around to what we both want. I like that.


    • He is great cat. He is a sort of boss cat and highly independent. And that probably leads to fights. I really, really hope he does not have FIV.

      He is what I would call a community cat who has found a human companion who cares. But can he get used to that? The chances of getting FIV are pretty small for him generally but being a fighter the chances seem to be raised. Let’s hope.

    • Our rescue Brinkley is FIV+. He weighs 15 pounds and hasn’t been sick since we got him. He had a mild uri at time of rescue. He’s around 3 and not at all aggressive so he lives with the other cats. We keep close watch on him for signs of illness and he lives indoors.

      FIV cat Brinkley

      We had fostered another FIV cat who was aggressive. At that first growl he was sent to his own room and we cared for him until a rescue for FIV cats had a spot. It all depends on the attitude of the cat and the community cats as to whether they can live together. We’re lucky Brinkley fit right in.

      He hated the cage ride home so much that once we saw he would fit in we adopted him. Low stress makes a difference and we feel he,s got a lot of years ahead of him. Furby had a uri a few weeks ago and Brinkley didn’t catch it. None of the cats did.

      Hope this helps.

  2. It was an adventure and a half taking Marvin in this morning. His reaction to being caged was hard enough. He actually bloodied his left paw forcing it under the gate of the crate. (Note to self; padded cell for Marvin). Honestly I had no idea how he would be for the vet and the techs. His voice is so loud and screeching he had the whole clinic at high alert. I once saw a video of an experienced person at a well known cat rescue organization on YouTube take a chance with a cat who wasn’t used to humans get her face clawed in six places in less than a second. Honestly, I had no idea if Marvin was capable of the same reaction. He urniated in the crate. The first tech said politely, I’ll weigh him. I must have had a look of horror on my face because she said ” maybe you should wait in the next room”. I heard him screaming and some shuffling but within a minute, she brought him into the room wrapped in a towel, still yowling and the nice person said “oh, he was fine. He weighs 16.8 pounds. The doctor will be right in”. I was relieved and surprised that the vet was also able to do whatsoever she needed to do to examine him thoroughly. She gave him shots so fast even I didn’t notice, much less Marvin. His eye infection is something similar to a herpes virus. I am to put drops in twice a day for a while. He is also on antibiotics for the wounds and all else is good. The trip home was also traumatic even though I only live 4 miles from the office, but as soon as I took the towel off the crate and let him out in his own garden, it was as if nothing ever happened.

    As tough as the big guy is, he is a sweet as it gets. That never changed even in a stressful situation.

    There is always more to learn. Marvin is teaching me.


    • Phew, I was tense reading that 🙂 Gosh that must have been a tense vet visit. I have to congratulate you for doing it. I guess you knew it would be difficult. Pleased he is OK. His weight is interesting at almost 17 pounds. He is a big cat about twice the average. Although in America the cats are bigger! True. The average weight is probably over 10 pounds. For other visitors this is my take on visiting the veterinarian: Taking Your Cat To The Vet.

      • Yes, he is huge and tough, yet so gentle and sweet. Bigfoot only weighs 9 lbs. I’m sure Yellow cat is the same. Shadow is another big boy weighing probably 14 lbs.

        It has been a piece of cake giving Marvin his meds and eye drops. He is supposed to go back for a feline leukemia shot, but I’m going to have someone come here for that. Not worth the drama/trauma of another car trip!

        Thanks for following the adventures of Marvin. I’ll do a search on PoC regarding herpes virus.


      • Ha! Thanks for reminding me if your vet visit story above. I forgot to mention the multiple glasses of wine at the end of the ordeal!


    • I really like the sound of Marvin the more you write about him. I hope he’s doing well 🙂 He sounds like my Red used to be. He was in a cage for 2 short trips in his life and he didnt like it at all. He made a hole in my finger with his claw – I was comforting him letting him put his head against my finger which was through the cage. Poor boy didnt like it. Those were the only unhappy short moments in his short life and they leasted minutes, no longer.

      • Thanks Marc. Yes,Marvin is something special. I have no idea why someone didn’t take him home before I did. He lived at that school nine years of his life. He comes inside now and spends time. He is trying to be friends with Bigfoot, but Mr. Big is unsure. We’ve only had two cold mornings so far and I was overjoyed to find Marvin on his cushie heated bed when I came down as usual 4:30 am to feed him. He is no dummy. I hope he will be sleeping inside by winters end.


  3. You’d hate Sealy. He just lays there and let’s the vet do whatever. No meowing and no fighting. That’s why they remember him. Not for the missing ear and injury but how well he does for them.

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