FIP – Feline Infectious Peritonitis: Everything You Need to Know

FIP is a serious viral disease in cats caused by a mutated variant of the cat’s coronavirus.

The feline coronavirus (a virus other than that which causes covid-19 in humans) infects the gastrointestinal tract and is excreted in the feces of infected cats. Cats can be infected by the virus when they come in contact with the feces, for example if they share a litter box with an infected cat.

The virus can survive for several weeks in the environment and is highly contagious.

Many cats become infected with coronavirus, especially cats that live in multi-cat households, in catteries, etc.

However, this does not mean that all cats develop FIP. In the vast majority of cases, the infection progresses asymptomatically or with symptoms from the gastrointestinal tract in the form of mild diarrhea. The disease is in the absolute majority of cases self-healing.

For FIP to develop, the coronavirus needs to have mutated, ie. changed.

Thus, it is not the mutated form that is transmitted between cats, but the mutation occurs in the infected cat.


FIP usually affects very young or very old cats, or cats that for some reason have a weakened immune system. Half of all cats that develop FIP are younger than two years.

There is no approved drug in my home country of Sweden that can be used in the treatment of FIP and the disease almost always leads to death. The disease comes in a “dry” and a “wet” form, and mixed forms of these two are common.

Depending on the form in question and the organ affected, the symptoms can vary, but common to infected cats is that they lose weight or grow poorly, have a reduced general condition and fever peaks.

In the dry form, the course of the disease is more prolonged (weeks to months) and the cat may have problems with eyes, central nervous system (brain, spinal cord), kidneys and more. In the wet form, which has a faster course (days to weeks), the cat gets fluid in the abdominal cavity (ascites) and / or the chest cavity (hydrothorax). In these cases, the cat gets swollen around the stomach or has difficulty breathing.


It is difficult to diagnose FIP clinically, because virus samples from feces can not distinguish between the intestinal form of the coronavirus and the FIP variant. Similarly, antibody tests in blood samples can not determine if the cat is ill with FIP, only that it has been exposed to coronavirus. The veterinarian can take the help of, for example, blood samples, X-rays and ultrasounds to make a so-called probability diagnosis.

To get as close to an established diagnosis as possible, tissue samples from affected organs, samples from spinal fluid or abdominal fluid are required. The more samples that indicate FIP, the greater the probability of a correct diagnosis.


There is currently no approved drug treatment for FIP in Sweden and the disease almost always leads to death without treatment.

When should you contact a veterinarian?

If the cat is ill, it is recommended that you contact a veterinarian.

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