FIP, feline infectious peritonitis, is a contagious disease caused by a coronavirus that causes a very high mortality rate in cats (very close to 100% of cases). The disease is transmitted through the urine and faeces of contaminated subjects who come into contact with healthy subjects. It is not contagious to humans and infects especially young cats (from 3 months to 3 years) who live in colonies or live in the open air and therefore have the possibility of being infected by sick stray cats.
Coronavirus infection is very common in cats, but in most cases it does not cause any problems, except for a possible mild diarrhea, which heals spontaneously. In rare cases the virus undergoes a mutation within the infected cat’s body, and it is this mutated form that causes FIP. The mutated virus becomes resistant to the immune defences of the cat’s body and spreads beyond the intestine invading internal organs. In an unsuccessful attempt to fight the virus, the immune system produces cells and substances that accumulate in the organs and damage them. The peculiarity of this disease is that, although the normal coronavirus is very contagious, in its mutated form, the cause of FIP, it is not: the mutated virus remains confined in the body of the sick cat and cannot be transmitted to other cats. A cat suffering from FIP is therefore unable to transmit FIP to other cats, although it is still able to spread the unmodified (benign) form of the virus; the reason why this is still unknown.
FIP is still under study because there are no valid vaccines yet and it is very difficult to make both a correct diagnosis and adequate prophylaxis. FIP can present very different clinical manifestations, but it does not have unique, i.e. specific, characteristic signs for the disease (it generally presents the same symptoms that can also be at the origin of other diseases such as IVF and FeLV). The classic form of the disease, often referred to as wet FIP, is characterized by an accumulation of yellow fluid inside the abdomen (resulting in abdominal distension) and/or chest (resulting in difficulty breathing) and fever that does not respond to antibiotics. However, the presence of this fluid alone is not diagnostic for FIP, and many cases of FIP do not occur with the presence of fluid.
Initial clinical signs are often very vague and include lethargy, loss of appetite, anaemia, vomiting and depletion. Inflammatory lesions of the eyes and nervous system may occur in some forms of the disease, causing visual disturbances, behavioural changes, staggering gait and tremors. A rarer variant is called dry FIP, a long-term disease with vague symptoms. In both cases, mortality is 100%.
Unfortunately, there is still no effective treatment for this horrible disease, the veterinarian proceeds with supportive therapies for the debilitated body, such as fluid intravenous therapy to replenish lost fluids and keep the body well hydrated. The vet can prescribe corticosteroids, cytotoxic drugs and antibiotics (for secondary bacterial infections due to the weakened immune system).