Feline Infectious Peritonitis, also known as feline FIP, is a deadly disease that affects a very small number of cats. It is most prevalent in environments with multiple cats, where litter box sharing occurs. While there is a vaccine available, it is not known to be particularly effective, and stories of cats dying from FIP weeks after receiving the vaccine are not unusual.
Feline Infectious Peritonitis
FIP is a viral disease caused by certain strains of feline coronavirus. Most strains are avirulent, and cats carrying them will not show any symptoms. However, a small number infected with a coronavirus will experience a mutation in the strain, which will cause the virus to progress to feline infectious peritonitis virus.
Once in the infectious state, FIP is characterized by a severe inflammation of blood vessels and any organs in which the virus may be found. This is often the brain, kidneys and intestines. This happens when the immune response is hijacked, the virus takes control of white blood cells and is spread throughout the body, causing the disease.
Symptoms are often very non-specific and can include general signs such as sneezing, diarrhea, depression and weight loss. In the more advanced stages, FIP cats will sometimes display a fever that doesn't respond to antibiotic treatment.
As cats have the ability to hide disease and display no symptoms, it can sometimes be weeks, months or even years until the first symptom shows. At this point, however, the cat has usually reached a critical stage and very little can be done for it. FIP is, with very few exceptions, fatal.
There is no simple diagnostic test to determine if a cat has FIP. The only definitive method is through biopsy, or through a necropsy after death.
Vaccination
Only one vaccination is currently available, and it has shown to have very minimal effectiveness at preventing FIP. The vaccine is essentially a strand of mutated coronavirus, and is taken intranasally. It is temperature-sensitive, and cannot withstand the cat's internal temperature. Thus the vaccine remains in the sinuses and throat, where the localized immune response is supposed to prevent a coronavirus infection. This is how most coronaviruses enter the feline body, and it is believed that having the antibodies ready in the most locally susceptible area will help to prevent an infection altogether.
The vaccine, Primucell FIP, is considered generally safe for use in cats over sixteen weeks of age. It has no recorded side effects, though there are reports of cats dying from FIP weeks after receiving the vaccination, sending its effectiveness into question. Along with this, most veterinarians and shelters do not stock the vaccine for two additional reasons: first, cats are generally not at risk for developing FIP, and second, the cats that are at risk are simply too young to be administered this vaccine.
Currently, the only instance where a four month old cat may need a vaccine would be when moving from an environment where they are alone to an environment where there are other cats and litter box sharing will occur. This would apply mostly to feral and rescued cats being placed in the shelter.
The American Association of Feline Practitioners Feline Vaccine Advisory Panel generally does not advocate the vaccine's use.