FIP is a fatal disease of cats caused by a mutated version of the feline enteric coronavirus (FECV).

FIP is rarely transmitted by contact between cats; it is mainly due to a mutation of FECV.

Clinical signs are vague.

Definitive diagnosis can only be made based on examination of biopsies (before or after the cat dies)

What is Feline Infectious Peritonitis?

• Feline infectious peritonitis (FIP) is a fatal disease caused by one type of feline enteric (living in the intestines) coronavirus also called FECV. Other types of FECV are not dangerous to cats.
• Cats infected with the FIP form of the virus can develop a slowly or rapidly progressing disease in their kidneys, liver, intestines, heart, or other organs and eventually die.

How do cats get infected with FIP?

• From other cats with FIP
  
• From a mutation during FECV infection.
  
• It is very uncommon for cats to contract FIP from other cats. Most cats with FIP do not shed the FIP virus, but they can shed a benign FECV. This benign FECV sometimes develops a genetic mutation while in the gut of a healthy cat and effectively becomes an FIP virus (5% of kittens). Not all FECV mutations induce the FIP disease and cause the cat to die. Some families of cats appear to be genetically predisposed to contract the disease.

Clinical Signs

• FIP affects many body systems and may cause various clinical signs including enlarged lymph nodes, fluid accumulation in the abdomen and\or chest, neurological signs, and other vague signs (decreased activity level, decreased appetite, vomiting, diarrhea, etc.).

Diagnosis

• Diagnosing FIP is not easy and sometimes impossible before the cat dies. Additionally, many cases do not fit all of the rules.
• To suspect FIP, there must be:
1. A sick cat
2. A positive titer on a serology blood test, and usually
3. Abnormal findings in other blood tests and on the physical examination.
4. A positive titer by itself must never be used to diagnose FIP because the test detects antibody to all coronaviruses (including FECV which is benign, and FIP).
5. Polymerase chain reaction (PCR) tests are new DNA tests that can help suggest FIP but are not completely reliable to make a diagnosis because there are false-positive and false-negative results.
   
• Biopsies, obtained while the cat is alive or at time of necropsy (post-mortem examination), are the only way to confirm a diagnosis of FIP.

Treatment

• First, it is important to make sure the cat suffers from FIP; many cats are misdiagnosed based on false-positive blood tests (cross-reactivity with FECV).
• FIP is a fatal disease; every cat with biopsy-confirmed FIP dies.
• Palliative treatment with drugs to suppress the immune system such as corticosteroids can be tried to possibly slow the progression of the disease, but all cats with FIP will eventually die.
• Some veterinarians use drugs to stimulate the immune system (immunoregulin, interferon, acemannan) to treat cats with FIP but this therapy often is not effective or may make the disease worse.
• Cats with FIP should receive supportive therapy (rest, good nutrition, lack of stress, broad-spectrum antibiotics) for as long as the cat is reasonably comfortable.
• Once disease signs become debilitating and weight and appetite decline, FIP patients should be euthanized because death due to FIP appears to be painful.

Prevention

• Decrease the level of FECV infection by general cleanliness, fewer cats, and cleaning litter boxes frequently.
  
• Breeders may be able to breed genetic lines that have higher genetic resistance to FIP.
  
• Reduce the number of cats, especially kittens, in the environment. If possible, the whole house should have five or fewer cats, because below this number FECV infection eventually dies out. Above five cats, the virus maintains itself in the home by constantly infecting and re-infecting the same cats.
  
• If one of your cats suffers from FIP, do not introduce any other cats (especially kittens) into the environment.
  
• Unfortunately, FIP vaccination does not appear to offer any protection against FIP.