FIP affects both pure- and random-bred cats. However, the disease usually starts in young kittens so it is closely linked with cat breeding and sheltering. The disease is also enhanced by improper husbandry, especially resulting from overcrowding (shelters, large multiple cat households). We also know that genetic susceptibility may account for 50% or more of the risk of developing FIP in one pure breed that was studied.
Although FIP occurs in all breeds, there is no doubt that certain bloodlines, and therefore certain matings, are more apt to produce kittens that eventually die from FIP. These genetic factors are most likely a result of the inbreeding that goes into breed development. Therefore, catteries are at the highest risk because they are subject to a high level of all three risk factors (kitten production, dense housing, genetic susceptibility). The likelihood that any given cattery will suffer at least one outbreak of FIP over a five year period is very high, and mortality in catteries can be several times higher than it is in the general population.
Shelters have the second highest risk of FIP, and the greatest incidence is among kittens adopted during periods of overcrowding and prolonged stays. Most shelter kittens are random bred, with many coming from the feral cat pool. Random bred kittens are more genetically diverse in general, so husbandry factors are more important in causing FIP in this population than genetic factors. Husbandry factors are greatly influenced by the seasonal influx of kittens.