Feline infectious peritonitis (FIP) is a viral disease in cats which carries a high mortality due to its characteristic aggressiveness and nonresponsiveness to fever, along with other complications. This disease is comparatively high in multi-cat households as compared to those with a single cat. It is difficult to diagnose, control, and prevent, and in cases of outbreaks within breeding catteries and kennels, can result in a high number of deaths. It is most often spread through inhalation of airborne contaminants and infected feces, but the virus can also be transmitted by humans who have come into contact with the virus, or can stay active on surfaces that have been contaminated.
This disease exploits weakened and immature immune systems, spreading by way of the white blood cells as they move throughout the body. The highest incidence is found in kittens three months to three years of age, with incidence decreasing sharply after cats reach three years of age, when the immune system is stronger. Likewise, older cats with weakened immune systems are also more likely to acquire this disease.
Symptoms and Types
Symptoms of FIP vary depending upon the strain of virus involved, the status of the cat's immune system, and the organs affected. There are two forms reported, including wet (effusive form), which targets the body cavities, and dry (noneffusive form), which targets the various organs. The wet form tends to progress more rapidly than the dry form, In either case, the body condition suffers, with the hair coat becoming rough and dull, and the cat becoming increasingly lethargic and depressed.
- Persistent and unresponsive fever
- Lack of appetite
- Weight loss (gradual)
- Poor appetite
- Gradual swelling of abdomen (potbellied appearance)
- Accumulation of fluid in the chest cavity
- Difficulty breathing
- Sneezing, runny nose
- Poor growth in kittens
- Inflammation of various parts of eye
- Neurological symptoms (e.g., loss of ability to coordinate movements, loss of vision)
FIP generally follows infection of a feline coronavirus, which typically does not cause any outward symptoms. It is assumed that there are some types of coronaviruses that mutate into the feline infectious peritonitis, either on their own or as the result of a defect in the cat's immune response. Also complicating the matter is that a coronavirus can lie dormant in a cat's body over months before mutating into FIP. The FIP virus then infects the white blood cells, using them as transportation to invade the entire body.
This disease is historically difficult to diagnose because FIP can mimic other diseases. This is especially true of the dry form. There is no single laboratory test available that can point decisively to FIP, but your veterinarian may be able to make a presumptive diagnosis based on laboratory findings. A complete blood count may show changes in the number of white blood cells (WBCs), and this will indicate that an infection is present, but it may not be clear what infection is present. While an ELISA or IFA test will show the presence of coronavirus antibodies, it cannot distinguish the type of coronavirus, or even whether it is the cause of your cats' condition, only that your cat has been in contact with the virus and has developed antibodies to it. The level of antibodies is not a predictor for your cat's susceptibility for developing the disease.
There are also few changes seen in a biochemistry profile testing. More specific testing may be used by your cat's veterinarian, including a polymerase chain reaction (PCR) test, which may differentiate the unique DNA of the FIP virus, but again, this often only shows that the virus is a coronavirus, not what type it is.
Your pet’s veterinarian may take sample of fluid from abdominal or thoracic cavity for further evaluation. In some difficult to diagnose cases, abdominal surgery may be required for diagnosis. For the most part, veterinarians base their conclusions on a process of differential diagnosis, by which the veterinarian is guided by a deeper inspection of the outward symptoms, ruling out all other diseases as the conditions are not met, and all symptoms point to one specific disease more than others.