Top Ten Worst Cat Illnesses (diseases)

This is a list of the ten worst cat diseases or illnesses together with some detail and links to more information. It is my list because there is no official list. You may well disagree with it and you may wish to add to it or change the list around, which is fine. I have listed them in order of nastiness so the top disease is the worst of the worst and the bottom listed disease or illness is the least worst of the worst.

cat with fip

Two useful tags. Click either to see the articles: Toxic to cats | Dangers to cats


This disease is caused by a virus. This, of course, is not strictly a feline disease because it occurs in nearly all warm-blooded animals. Rabies is a fatal disease. Not only is it fatal the symptoms are nasty and the disease stigmatises the cat because when the cat has this disease he or she is a danger to people. The disease damages the cat’s image in the eyes of people and provides people who do not like the domestic cat with ammunition to criticise it. Another reason why rabies is particularly horrible is that when a cat is suspected of having rabies for whatever vague reason then it is liable to be killed and a post-mortem carried out on the brain. So if a cat is provoked and then attacks aggressively, the cat is liable to be branded rabid, which is very unfortunate. This bundle of factors is the reason why heads the latest. You can read more about the symptoms of this nasty disease on this page.

Feline Infectious Peritonitis (FIP)

This disease is caused by a virus and is common in wild and domestic cats. The disease is spread from cat to cat. Less than 1% of infected cats develop the secondary fatal disease. Many cats have a mild infection but become carriers. It is estimated that in catteries 80% and 90% of cats are positive for antibodies to the virus meaning that at some stage the cat had the virus. Once a cat develops a secondary form of this disease he will die. So this disease is common, is contagious and is fatal when fully developed. These are the reasons why it is ranked high in this list. You can read about this disease on this page.

Feline Leukemia Virus (FeLV)

The feline leukaemia virus accounts for about half of all internal cancers most of which are lymphomas, which is cancer of the lymph system which is part of the immune system.

This virus is also associated with other serious cat diseases including anaemia, feline infectious peritonitis, spinal cord cancers and toxoplasmosis. The feline leukaemia virus depresses the immune system which contributes to a higher incidence of secondary diseases. This virus can cause many health problems both indirectly and directly. It is associated with cancer of the blood, which is leukaemia and leukaemia of the lymph system. Read more about this disease (written in plain language)

Feline Panleukopenia

This disease is also called feline distemper and is caused by a virus. The word “distemper” is misleading because it has no relationship to distemper in dogs. The virus that causes the disease attacks white blood cells. A white blood cell count confirms diagnosis. There is a 90% mortality rate for kittens infected with this virus. Secondary infections develop which can also kill the cat. Most cats are exposed to panleukopenia during their lifetime. Read more here and here (first hand experience).

Feline Lower Urinary Tract Disease (FLUTD) and kidney disease (I will bundle the two together because they are linked).

This includes urinary tract infections. This disease is caused by a bacterial infection. Cystitis, which is inflammation of the bladder, is another term commonly used. Lower urinary tract problems are by far the major health concern of a cat owner. There is a high level of recurrence as well. It can occur in domestic cats of all ages.

Kidney failure occurs when the kidneys are unable to remove waste products from the blood. Kidney failure can be acute, meaning happening quickly and severely, or it can be chronic meaning on-going and gradually over a long period of time which is typical in older cats. Chronic renal failure is a major cause of death in the domestic cat.

Because urinary tract diseases and kidney disease is commonplace amongst the domestic cat population and because many domestic cats die of kidney failure, I have rated this feline illness as one of the worst. You can read more on this page. More.

Feline Immunodeficiency Virus (FIV)

This is caused by a virus. The virus is related to the same virus that causes AIDS in people. However, each virus is specific to the species. It affects 2% to 4% of cats in the USA in the general population, it is believed. Cats with chronic FIV suffer from a variety of illnesses some serious. For an example, about half have chronic mouth conditions. There is no effective treatment. The virus is shed in saliva. Therefore the incidence of this disease is highest amongst outdoor cats. Read more and please use the search box above this post.

Feline Viral Respiratory Disease Complex. This includes upper respiratory infections and I include conjunctivitis

pink eye in cats
Feline pink eye

The various diseases under this heading are highly contagious. They can be a serious illness. The disease can spread rapidly in a cattery or shelter or in a home where there is more than one cat. They are one of the most common infectious disease problems. There is a 50% mortality rate among kittens. One frequently sees pictures of stray cats who have contracted an upper respiratory infection leading to a secondary bacterial infection in the eye which ultimately destroys the eye leaving the cat blind. An acute viral respiratory infection may be mild or severe and it can be fatal. The disease is transmitted by direct contact with infected discharge from the eyes, mouth, nose and contaminated objects. Two major viral groups are responsible for this disease and one of them is the herpes virus group which includes feline viral rhinotracheitis (FVR). Almost all cats infected with FVR are carriers. A cat carrying the disease when stressed may exhibit symptoms of the disease. Read more. And about pink eye. And first hand experience. Please search as there are many more articles.

Mouth disease – gingivitis – periodontal disease – gum disease-feline gingivitis stomatitis

If you visit websites run by veterinarians you will notice that mouth diseases commonly gum disease are one of the most common health problems that they have to deal with. Gum disease is not life-threatening but it can be chronic if neglected and cause great discomfort for the cat. Veterinary treatment involves a general anaesthetic, which, on my calculation results in one in four hundred cats dying so there is an indirect life-threatening risk. Because it is so commonplace is listed here. You can read more on this page. Gingivitis picture.

Parasites-Cat Fleas and Ear Mites

The ubiquitous cat flea is extraordinarily commonplace and a constant nuisance to both cat and cat owner. The flea bite allergy is quite serious and causes blistering of the skin, acute to mild discomfort in the domestic cat and is difficult to manage. Also, the cat flea is difficult to manage and prevent. Because of its ubiquitous nature the cat flea is listed here. Ear mites are extremely uncomfortable to the cat. They often go untreated, one of the more you can move the date of their or cat owners like to treat them themselves in my opinion is unwise. There are, of course, many other parasites that are found in an on the domestic cat that I had selected these two is the worst. Fleas picture and please search as there are many pages.


I am referring to an allergic reaction to an allergen. Allergic reactions in cats are rather mysterious, I feel. This is because there are so many potentials for an allergic reaction. Their are allergens everywhere. A cat may be allergic to something in his food or something in the carpet that creates a contact allergy or indeed something in the air. There are hundreds of possible causes and diagnosis can be extremely difficult while at the same time an allergy can cause extreme discomfort in a cat. Allergies cause unpleasant physical reactions. The cat’s immune system overreacts. Allergens enter the cat’s body through the lungs (in respect of an allergen in the air), the digestive tract (something in the food), by injection (flea bite allergy or vaccinations, for example), or absorption through the skin (causing dermatitis for example). Feline allergies and please search.

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NOTE: THIS PAGE HAS BEEN REPUBLISHED ON 6TH MAY 2019. IT WAS FIRST PUBLISHED ON APRIL 12 2014 AT 15:54. Why do I do this? Because this is a blog and older posts can get lost over time. Some pages deserve to be recycled because of their value.

Please search using the search box at the top of the site. You are bound to find what you are looking for.

35 thoughts on “Top Ten Worst Cat Illnesses (diseases)”

  1. There was a time many years ago, that I was a dog person. (Believe it or not :))
    Until….I met Sandy, a Mama Cat who was FELV Positive, she had 5 kittens who were also positive.
    My mom and I decided to take Sandy in despite her illness and when the kittens were born we kept them all to live out their short lives. Trying to find homes for cats who are FELV Positive is a challenge even when they are kittens. Shelters automatically put them down. This was back before all the amazing rescue groups we have now, or at least before we had access via the internet to find these groups.
    So we kept them all. Looking at them as babies you would never know that they had a disease, they looked and acted normal which is why its a scary disease because though asymptomatic it can be spread to other cats.
    There was no way that we could give them up, it didn’t feel fair to euthanize a cat that wasn’t having any symptoms. So we opened our homes and our hearts knowing full well how it would end. Most of the time in rescue this is just the way that it is because it’s about them, not us.
    All of the kittens survived their first birthday but we lost each of before 15 months. Mama cat ended up being adopted by a neighbor who fell in love with her, Mama was a carrier and lived for many years after being adopted.
    To this day, I still have the kittens collars and their tags. Before we lost them we decided to make a mold of their paws and I still have those as well.
    Looking back, even though it broke my heart to lose each of them, I would do it again in a minute. I learned so much about life from those cats and how important it is to live while we are still alive. They were different than cats who do not have the disease. They seem more loving, more adventurous and they don’t sleep as much. It’s not been scientifically proven but after those kittens I went on to do FELV positive rescues only for many years and noticed the same thing every time with the rescues I brought in, there was a definite difference in how they lived.
    To say the least, they were an inspiration to me and the reason that I continue to be a advocate for all cats today.

  2. Excellent article, Michael!

    I would like to add two to the list. 1. Feline Pancreatitis- Nasty illness- when caught early it can be treated but once cats get this condition they are at risk of getting it again.

    2. While this is fairly rare- some saying that it occurs 1 in 50,000 cases, some think it is more like 5 in 50,000 cases, but the three year adjuvented rabies vaccination can lead to feline fibrosarcoma which is almost impossible to treat. Some vets are now injecting cats in the tail since it is far less disabling and disfiguring than amputating the left leg.

    The one-year Purevax is not adjuvented (a substance used to enhance the effectiveness of the vaccine) therefore is a lot safer than the 3 year vaccines. So far there is no three year rabies vaccine that is not adjuvented.

    I lost a cat to fibrosarcoma. It took two years after the vaccination for the tumors to appear. Back then (before the new vaccine protocol came out) they were vaccinating EVERYTHING in the scruff of the neck. Awful!

  3. Hi Michael

    Great informative article 🙂

    I think you should have included the Calichi virus because in most cases the only thing that will make the cat more comfortable will be to take out all the cheek teeth. Undiagnosed and/or untreated it is painful and mouths become infected and ulcerated. Cats stop eating and become very unwell of course if they aren’t treated they may stop eating altogether and of course this would be fatal.

  4. When you look at this list of illnesses and think of all the hazards there are in life for cats, you wonder how so many survive to grow old.
    To me it shows how very resilient cats are.

    • Yes, cats are resilient but we have to remember the feral cats who we are told often live short lives and many of them will die of the diseases mentioned on this page and they will even die of a disease that can be treated quite easily. That said I do not believe that the lifespan of a feral cat is quite as short as people make it out to be.

      • Renny was a feral and the lady who caught him had him vaccinated then waited a week to turn him into the shelter. That likely saved him because we pulled him the same day as the whineybutts and the Pie kitties and Midnight was the only one to survive panleuk.

        • ThisA nice little snippet of information about the lady who caught this feral cat and then waited a week before turning him into a shelter after vaccinating him. There are some bloody nasty diseases out there awaiting the cat.

          • Remember the vaccinate on intake article I did? It suggested a program where people wanting to surrender their pet to bring it to the shelter for core vaccines then take the animal home for 2 weeks then bring it back. It could save thousands of shelter pets.

            Renny ended up at a rescue after he was caught and was so wild the rescue owner decided to turn him over. I spotted him and had to get permission from the director since he wasn’t adoption material. He lives in my bedroom. Only Lucky, Jubi and Oozy can play with him. He beats up anyone else. Jubi is in love with him and spends around 4 hours a day in my room. She’ll meow til we let her in then meow when ready to come out.

  5. Awe look at Pinky. That was made the day after we rescued him from the shelter. He was adopted after his eyes cleared up. Had to use oral antibiotics and antibiotic eyedrops. This wasn’t an infection to treat without a vet.

    • thats horrible the poor wee baby. Thats why its great to vaccinate im going to do that soon with Jasmin. Althou she looks in good health dont want to risk it.

    • I remember this one well, which is why I chose the picture. It is a shocking picture but I am sure it is very very common amongst unwanted cats.

        • Sigh… I do not know why but I feel a bit sad when I look at this gentle picture. Perhaps it is because of all the work you did to bring Pinky back to good health only then to say goodbye. It is just a reminder to me how time goes by.

      • yea really sad pooor baby. Ive seeen a bad case of a friend who no longer a friend her cats had a terrible case of cat flue it was horrible to witness. The cats got the attention they needed. It just makes u so aware esp in kittens to do the right thing.

  6. I used to always tell people that, if I thought ahead about what could inflict a child, I would have never had any.
    But, I don’t feel the same way today about kids or cats.
    It’s just the luck of the draw.
    I’ve had some cats inflicted with these conditions, ie. FIV, FIP, FeLV.
    The worse, by far, is FeLV. A litter of kits dropped here suffered from this. When I held them, they oozed blood from their skin, all over. It was a nightmare to take the whole litter of 5 in to be checked and euthanized.
    Just another one of those things that stay burned in my memory.


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