Feline Infectious Peritonitis (FIP)

Though it is fatal, it is not a disease that is particularly contagious (it only becomes very contagious in its mutated form, and even then it is mainly communicable through feces).  The virus that is responsible for this disease is called the coronavirus. It can be found in numerous cats and usually only provokes occasional diarrhea in 10% of infected animals.

The virus travels through the blood vessels in the intestines, thus provoking serious inflammation. Peritonitis is the membrane that covers abdominal muscles, and once the blood vessels there become inflamed due to infection, treatment becomes very difficult and often futile given the terminal nature of the disease.

FIP comes in two forms:

Effusive (wet) FIP is the most common form.

The attack is often very fast. Within 24 hours, a cat can become lethargic, feverish, lose appetite, lose weight, vomit and suffer diarrhea. Their fur will become dull, but the most apparent symptom is a huge swollen belly full of fluid, which will cause respiratory difficulty. 

Non-effusive (dry) FIP

This is the less common form and the one that is the easiest to misdiagnose. Signs are similar to the wet FIP, however, in the final stages, a cat can become disoriented and develop blindness due to ocular hemorrhages, followed by convulsions. The virus is transmitted through saliva and excrement.