Feline infectious peritonitis is a serious and often fatal viral disease that affects mainly young cats from multiple-cat households.
It can occur in cats of any age, though it is more common in young cats. FIP is caused by a mutated form of a virus called feline enteric corona virus, or FECV. This virus is found in the gastrointestinal tract of cats and usually does not cause any symptoms. Some cats will show diarrhea, but the host’s body, most often, limits the virus and disease from it.
Feline enteric corona virus is far more common in areas where multiple cats are housed together, such as animal shelters, cat breeding facilities and households with large numbers of cats.
Certain geographic locations with higher populations of roaming cats can show high incidence of this virus, as it spreads from cat to cat by inhalation or ingestion. Outdoor cats are more at risk of developing FIP, especially when they live in areas with high populations of feral cats.
As I mentioned, feline infectious peritonitis, or FIP, is a mutated form of the feline enteric corona virus, which usually doesn’t cause disease. This means that FIP itself is not contagious. It mutates from another virus and then creates disease as a result. This is a very important point, especially with a FIP-infected cat in a multicat home. This situation does not mean the other cats in the household are necessarily at a higher risk of developing FIP, though there is an increased chance for contracting feline enteric corona virus.
The unique thing about the feline enteric corona virus is that it can cause the disease within two weeks after exposure or it can remain harmless for years or suddenly mutate into a deadly form. As a result, whether a cat develops FIP depends more on the ability of the feline enteric corona virus to mutate inside the cat, rather than from cat-to-cat transmission.
Lets talk about the symptoms associated with FIP. These cats will sometimes show few symptoms, though one might notice lethargy, as these cats often endure fevers that will cycle up and down. With progression, these patients develop decreased appetites, weight loss and then possibly a hallmark sign of the disease depending on which form it takes. There are two forms of FIP.
The wet form, or effusive form, is characterized by the development of a straw-colored clear fluid in the abdomen and sometimes the chest. This form usually progresses rapidly and is fatal.
The second form, the dry form, is characterized by enlarged lymph nodes that can usually be palpated in the abdomen. This form is not as rapidly progressing as the dry form but, long term, it too is invariably fatal. Definitive diagnosis of FIP is difficult in the living patient.
We can measure what are called antibody titers to FECV, and if these titers are high and the patient has the clinical signs of the disease, we can make a strong case for FIP infection. That said, definitive diagnosis usually involves necropsy.
FIP spreads within the cat’s body via the immune system and uses the immune response to worsen the disease. Essentially, the cat’s body spreads the mutated virus. We have tried to treat these patients with immune modifying medications to try to lesson the immune response and thus the symptoms associated with it. No treatments have proven effective in the long term.
There is ongoing research into therapy for FIP that has shown some promise using specific immune stimulating medication, though it is not available for general use at this time. There is a vaccine developed to prevent FIP, but because it protects against only a few strains of the feline enteric corona virus, it is not considered to be highly efficacious.