How does stress play a role in FIP occurrences?

Anything that stresses cats can depress immunity and also increase the likelihood that FIPV will establish itself in the body. Stress may also allow an FIPV that is being successfully contained to become active. The effect is even more powerful if the stress occurs at or shortly after the time the cat is exposed to the virus. Stressors can include overcrowding, weaning, spaying or neutering, other infections, being placed in a new and strange household, adding new cats to a household, shipping cats to new owners or other catteries, or stresses of pregnancy, parturition and lactation. Disease caused by feline herpes virus and other common upper respiratory pathogens are good indicators of cattery or shelter stresses.

If a cattery or shelter is having a lot of problems with these upper respiratory infections, it is likely that they will also have problems with FIP (especially if the genetics are unfavourable as well). For instance, one shelter had a huge FIP problem in the kittens they were adopting out. It was kitten season and the facility was overcrowded with cats and they had to stay for longer periods awaiting adoption. There was also a lot of upper respiratory disease. After researchers at UC Davis recommended limiting their intake of cats, overcrowding was eliminated and cats were adopted after shorter stays. The FIP problem decreased as did the respiratory infections.