Many different strains of coronavirus are capable of infecting cats, but most do not produce serious disease. FIP-producing strains are distinguished by their ability to invade and grow in certain white blood cells. The infected cells transport the virus throughout the cat's body. An intense inflammatory reaction occurs in the tissues where these virus-infected cells locate. It is this interaction between the body's own immune system and the virus that is responsible for the disease.
Infected cats shed coronavirus in their saliva and feces.
Most cats become infected by inhaling or ingesting the virus, either by direct contact with an infected cat, or by contact with virus-contaminated surfaces like clothing, bedding, feeding bowls, or toys. Although the virus can survive for a number of weeks in the environment, it is rapidly inactivated by most household detergents and disinfectants. FIP and feline leukemia are caused by different viruses. Some cats that have FIP may also be infected by the feline leukemia virus, but the diseases are two separate entities. Initial exposure to the FIP virus usually results in no obvious clinical disease, although some cats may experience a mild upper respiratory disease that is characterized by sneezing, watery eyes, and watery nasal discharge.