Kitten with feline infectious peritonitis or FIP

LEFT: radiography taken, the intestines are not distinguished, which may suggest some abdominal fluid is present despite there are no clinical signs of bloating.

A 7 m.o. kitten presented as a transfer from his vets after having another episode of incoordination and abnormal behaviour. 

For some unclear reason the breeder did not want to keep this kitten and contacted a charity to give him. The kitten was obviously underweight, was not a good eater, with occasional inappetance and mild diarrhoea.

He had recently been seen for the same conditions, wobbly but not seizuring or collapsing. The rest of his litter seemed healthy though.

Several blood tests that had been performed were unremarkable, except for high levels of white cells, which could indicate some infection. Virus disease, gastroenteritis, meningitis were suspected. His tests for feline leukemia and aids ruled out those conditions. After a course of antibiotics and symptomatic treatment his condition improved much, until now that all the symptoms seemed to be back again.

At this stage FIP was high on the differential diagnostic list, along with some rare genetic disease. There were no fluids in the abdomen or in the chest, and the main issues were his difficulty in walking and his lack of appetite with some soft faeces. 

This time, after a couple of days on fluid therapy, another course of antibiotics and symptomatic treatment, the improvement only lasted one day. Some blood sample was sent to an external lab for FIP, which result was consistent with a FIP.

Due to the poor prognosis and no response to his treatment, the kitten was put to sleep. 

But... what is FIP?

FIP is an infection with the "feline coronavirus". This infection is very common in cats, but most of the time it does not cause any problems, except some mild self-limiting diarrhoea.

Uncommonly, the virus mutates (changes) to a strain of coronavirus which has the potential to cause disease. This mutated strain is the cause of FIP.

In an affected cat, the virus spreads throughout the body and can cause a wide range of different signs

In cats, FCoV most frequently causes gastrointestinal infections, but in unusual cases (with a mutated form of the virus) it can spread through the body and cause FIP.

25-40% of household pet cats have been infected with FCoV, but the infection rate increases to 80-100% for cats kept in multi-cat households or colonies.

In most cases, infection with FCoV will cause mild signs of enteritis or no signs at all. Diarrhoea is more likely to be seen in young cats.

The virus spreads throughout the body, and if replication is not contained by a good immune response, a cat will develop clinical signs of FIP. A strong immune response may enable the cat to control the infection and prevent signs developing.

Early signs are very vague with a fluctuating fever, lethargy and inappetence. After several days or weeks other signs are seen. Basically there are two types of FIP presentation

'Wet' or effusive FIP

The cat build fluid within the abdominal cavity (abdominal enlargement) and/or the chest cavity (breathing difficulties). The fluid causes damage to the blood vessels which results in fluid leaking from the blood into the abdomen or chest. 

'Dry' or non-effusive FIP

Te infection causes long-standing inflammatory lesions around blood vessels in many different organs and sites in the body. 

This inflammation affects the eyes in around 30% of cases and the brain in around 30% of cases, but can also affect liver, kidneys, lungs and skin. Signs like wobbly and unsteady gait or bleeding in the eyes may occur.

Clinical signs have started tend to get progressively worse over time and euthanasia is usually required within days or weeks. It is thought that non-effusive cases of FIP are where the cat has developed a partially effective immune response that helps but is not sufficient to stop disease development.

What cats are most often affected with FIP?

Around 80% of cases diagnosed are in cats less than 2 years old. FIP is also more common in cats kept in groups or colonies.

FIP is a very difficult disease to diagnose with because there are no clinical signs that are specific and no simple blood test to confirm a diagnosis. Typical changes are seen on routine blood tests may include lymphopenia , neutrophilia, anaemia, elevated globulin concentrations, liver enzymes and bilirubin (jaundice)

The abdomen or chest cavity has a high protein content and at least 50% are globulins. An X-rays or ultrasound could confirm if fluid is present so that a sample can be collected for analysis. 

Looking for the presence of antibodies against the virus in a blood sample (coronavirus serology) is of very limited value. A very large number of perfectly healthy cats are positive on this test. The best test to confirm FIP is to collect a biopsy from affected tissues. Unfortunately, a cat may be too sick for surgery.

It is generally an incurable and fatal disease. Supportive treatment may help relieve some signs and improve quality of life temporarily but in most cases euthanasia is the most humane course of action to avoid suffering. 

A commercial vaccine is available in some countries to help protect against FIP. It has some efficacy and can only be given to kittens over 16 weeks of age. The risk can be minimised by obtaining cats from a source with relatively few cats and by keeping cats in small stable groups. Good hygiene and avoiding overcrowding are essential strategies for minimising the risk of FIP.