12/02/2023
𝕱𝖊𝖑𝖎𝖓𝖊 𝕴𝖓𝖋𝖊𝖈𝖙𝖎𝖔𝖚𝖘 𝕻𝖊𝖗𝖎𝖙𝖔𝖓𝖎𝖙𝖎𝖘 (𝕱𝕴𝕻)
Feline infectious peritonitis (FIP) is a viral disease of cats that occurs throughout the world. It is a complex disease to diagnose and in the last few years, significant developments have occurred in the treatment of this previously fatal condition.
𝓒𝓪𝓾𝓼𝓮𝓼
FIP is caused by infection with a virus known as feline coronavirus. Coronaviruses are a common group of viruses that often infect the upper respiratory tract (nose and throat) or gastrointestinal tract (intestines) in different animals. COVID-19 is a coronavirus but the coronavirus causing FIP is not the same and only infects cats. Coronavirus infection is extremely widespread in cats, especially where large numbers of cats are kept together.
Coronaviruses are common and found in the f***s of many cats. In most cats, infection causes no signs or just mild diarrhea that resolves without treatment. However, occasionally, the virus mutates (changes) inside a cat, and if their immune system reacts in a certain way, they could develop a disease called FIP. This is important, as finding coronavirus in a cat does not mean they have FIP, and it is not possible to consistently tell the difference between a coronavirus causing FIP and one causing no signs at all by just finding the virus itself.
In a cat that develops FIP, the virus spreads throughout the body and can cause a wide range of different signs due to the way it interacts with the cat’s immune system.
Most strains of feline coronavirus are found in the gastrointestinal tract and do not cause significant disease. These are referred to as feline enteric coronavirus (FeCV). Cats infected with FeCV usually do not show any symptoms during the initial viral infection, but may occasionally experience brief bouts of diarrhea and/or mild upper respiratory signs from which they recover spontaneously. FeCV-infected cats usually mount an immune response through which antibodies against the virus are produced within 7-10 days of infection. In approximately 10 percent of cats infected with FeCV, one or more mutations of the virus can alter its biological behavior, resulting in white blood cells becoming infected with virus and spreading it throughout the cat’s body. When this occurs, the virus is referred to as the FIPV. An intense inflammatory reaction to FIPV occurs around vessels in the tissues where these infected cells locate, often in the abdomen, kidney, or brain. It is this interaction between the body’s own immune system and the virus that is responsible for the development of FIP. Once a cat develops clinical FIP, the disease is usually progressive and almost always fatal without therapy that has recently become available, but that has yet to be approved to treat FIP in cats by the Food and Drug Administration (FDA) (see below). To our knowledge, coronaviruses cannot be passed from infected cats to humans.
𝓢𝓲𝓰𝓷𝓼
FIP can cause many different clinical signs, depending on the parts of the body affected and how the immune system reacts. Early signs of FIP are usually very vague with a fluctuating fever (high temperature), lethargy and reduced appetite being common. After a period of several days or weeks (or sometimes even many months) other signs usually develop. Classically, FIP has been divided into ‘wet (effusive)’ and ‘dry’ forms, but actually cats are likely to have both at different times, or a mixture of both presentations. One of the challenges of diagnosing FIP is that the clinical signs are often vague and not specific for FIP and can be seen with other diseases.
Cats that have been initially exposed to FeCV usually show no obvious symptoms. Some cats may show mild upper respiratory symptoms such as sneezing, watery eyes, and nasal discharge, while others may experience mild gastrointestinal signs such as diarrhea. In most cases, these mild signs are self-limiting. Only a small percentage of cats that are exposed to the FeCV develop FIP, and this can occur weeks, months, or even years after initial exposure to FeCV.
There are two major forms of FIP, an effusive, or “wet” form and a noneffusive, or “dry” form. Regardless of which form they ultimately progress to develop, cats infected with FIPV usually first develop nonspecific signs of disease such as loss of appetite, weight loss, depression, and fever. It is also important to note that cases of the effusive form of FIP can evolve into the non-effusive form and vice-versa.
Generally speaking, the signs of the noneffusive form, which may include the non-specific signs listed above as well as neurologic signs including seizures and ataxia (abnormal or uncoordinated movements) develop more slowly than those of the effusive form.
The signs of effusive form of FIP usually develop and progress relatively rapidly and include development of the above-mentioned non-specific signs combined with the accumulation of fluid in body cavities, including the abdomen and the thorax (chest cavity). Affected cats may develop a pot-bellied appearance due to fluid accumulation in the abdomen, and if the fluid accumulation is excessive, it may become difficult for a cat to breathe normally.
𝓓𝓲𝓪𝓰𝓷𝓸𝓼𝓲𝓼
FIP is a very difficult disease to deal with because there are no clinical signs that are specific for the diagnosis of FIP, and no simple blood test to confirm a diagnosis. FIP may be considered more likely when:
Cats are showing clinical signs compatible with FIP -
• Cats are in a higher risk category (e.g., younger cats, colony cats, etc.)
• Typical changes are seen on routine blood tests – these may include
• Lymphopenia (low numbers of lymphocytes, a type of white blood cell)
• Neutrophilia (increased numbers of neutrophils, a type of white blood cell)
• Anaemia (low red blood cells)
• Elevated globulin concentrations (one of the major groups of proteins in the blood)
• Elevated liver enzymes (eg, ALT, ALP)
• Elevated bilirubin (and jaundice or yellowing of the gums and eyes)
None of these blood changes are specific for FIP, occurring with other diseases too, but if multiple changes are seen in combination with appropriate signs, a diagnosis of FIP becomes more likely. Many of these abnormalities may also not be present in the early stages of the disease but may become evident as the disease progresses. Thus, some tests that give normal results may have to be repeated later.
If fluid is present in the abdomen or chest cavity, obtaining a sample of the fluid and analyzing the cell and protein content can be extremely helpful. With FIP the fluid invariably has a high protein content and further analysis of cell types and types of protein present can be useful. Further tests on fluid can be performed to look for the virus (PCR for example). Looking for fluid is an important part of investigating a cat for FIP so Xrays, and particularly ultrasound, can be very helpful and again may need to repeated later as the disease progresses.
Other tests that can also sometimes be helpful include:
• Further analysis of proteins in the blood (e.g. measuring the protein acid-1-alpha glycoprotein [AGP])
• MRI scans of the brain
• Evaluation of a cerebrospinal fluid sample (the fluid that surround the brain and spinal cord) in cases where there are neurological signs
• Evaluation of fluid from the eye (aqueous humour) in ocular cases
• Needle samples of lesions in organs and lymph nodes
• Biopsies (tissue samples) taken at surgery
Looking for the presence of antibodies against the virus in a blood sample (coronavirus serology) is of very limited value – antibodies against FCoV develop when a cat meets coronavirus – this does not mean they have or will get FIP. A very large number of perfectly healthy cats are therefore positive on this test, and it should not be used for diagnosis.
𝓒𝓸𝓷𝓯𝓲𝓻𝓶𝓲𝓷𝓰 𝓪 𝓭𝓲𝓪𝓰𝓷𝓸𝓼𝓲𝓼 𝓸𝓯 𝓕𝓘𝓟
To confirm a diagnosis is very difficult, but in general finding the typical type of effusion or inflammation and finding the virus in the same areas can be useful. Ways to look for the presence of the virus include immunocytochemistry and immunohistochemistry (staining the virus so it can be detected) and PCR (testing for the viruses genetic material). These tests can be performed on fluids, needle samples, biopsies and other samples. Remember, it is not enough to find just the virus as cats without FIP may have coronavirus, we must put together the puzzle of clinical signs, imaging findings fluid and needle samples and virus detection tests.
𝓣𝓻𝓮𝓪𝓽𝓶𝓮𝓷𝓽, 𝓟𝓻𝓮𝓿𝓮𝓷𝓽𝓲𝓸𝓷, 𝓪𝓷𝓭 𝓒𝓸𝓷𝓽𝓻𝓸𝓵
There is no specific treatment for feline infectious peritonitis. Although recovery from signs has been reported, it is uncommon. Up to 95% of cats with feline infectious peritonitis will die from the disease. In one study, half of the affected cats died within 9 days. However, some cats may live for several months.
Treatment with drugs that reduce inflammation and suppress immune reactions, along with supportive care, can make the cat more comfortable. In some cats (probably less than 10%), treatment may extend survival time by several months. Treatment offers the most hope for cats that are still in good physical condition, still eating, have not yet developed nervous system problems, and that do not have additional disease (such as feline leukemia virus infection). If a cat shows no improvement after 3 days of treatment, it is unlikely to improve. If the cat's quality of life is poor and treatment has not helped, euthanasia is often considered.
When a cat in a household develops feline infectious peritonitis, all in-contact cats will have already been exposed to the same virus. Fortunately, in most cases, in-contact cats will not develop the disease. (Recall that most cats that are infected with coronavirus never develop feline infectious peritonitis.) However, cats with feline infectious peritonitis should not have contact with any new cats, especially kittens, that have not been exposed to the virus. In addition, if your cat died because of the disease, you should wait 2 months before obtaining another cat to be sure that the virus is no longer present in the environment.
A vaccine is available to help prevent feline infectious peritonitis. However, many adult cats will have been previously exposed to the virus, so vaccination will not prevent their infection. The vaccine is labeled for use beginning at 16 weeks of age, which may be too late to protect kittens in households where the virus is present. The American Association of Feline Practitioners lists the FIP vaccine as “not recommended.”
Vaccination alone cannot be relied on to control the disease within a cat facility. Other measures to reduce exposure include frequent removal of f***s (the primary source of coronavirus), early weaning, and isolation of cats that test positive for coronavirus antibodies. Additionally, isolation and testing of cats after shows, proper sanitation and cleaning using viral disinfectants, and vaccination against other feline viruses can reduce exposure. These control measures should be combined with an overall preventive health program. However, in households or facilities with large numbers of cats, it can be very difficult to eliminate feline coronavirus and, as such, there will be a risk for the development of feline infectious peritonitis.
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