This article is published in this site with the special permission of END FIP®
The natural incubation period of feline infectious peritonitis varies greatly, from a few weeks to several years. Though it is unpredictable, cats are at an increased risk for developing FIP within the first 6 to 18 months after initial infection with FCoV. The onset of clinical signs of FIP is often deceptive. In some cases is quite sudden, especially in young kittens. Once the clinical signs developed, FIP is progressive and virtually always fatal.
There is a significant variation in the duration of clinical illness prior to death, a few weeks is typical but prolonged illness exceeding several months can occur as well as intermittent illness marked by periods of presumed remission.
In effusive FIP cases, the clinical course is usually acute (days to weeks) with the vast majority of cases presenting with inflammatory fluids in the abdominal cavity, some in the thoracic cavity and about 20% in both cavities.
In non-effusive FIP, the course is often chronic and insidious (weeks to months) presenting with multifocal pyogranulomatous inflammation and necrotizing vasculitis in several organs. Worth to note, cats presenting with only ocular symptoms sometimes survive for more than a year.
Source: https://www.endfip.com/clinical-course/
