FCoV (Feline Coronavirus) is a cat’s coronavirus widespread among domesticated cats and wild cats. Following serological tests, it has been found that around 20–60% of domestic cats are infected with the FCoV. In the brood or cats living in other groups, it reaches even 100%. There are two biological types of the FCoV: FIPV (or Feline Infectious Peritonitis Virus) and FECV (or Feline Enteric Coronavirus). There is a common theory that the FIPV forms as a result of the FECV mutation in the alimentary tract of an infected cat, spreads in the body and causes infectious peritonitis FIP (or Feline Infectious Peritonitis). Another hypothesis suggests that there are virulent and non-virulent strains circulating in the population of cats, and the disease develops in cats with compromised immune systems, exposed to the contact with the virulent strain.

Although both FIPV and FECV can cause viremia, but FIPV only can replicate in macrophages and leads to the disease. Furthermore, it is indicated that some pedigree cats can exhibit genetic tendencies to get the disease. Caused by the FECV, the infections usually progress without any symptoms or very mildly. Young kittens often show diarrhoea for a few days; in addition, the upper chest infection and a higher body temperature can occur. FIPV variant causes infectious peritonitis (sometimes named coronavirus enteritis). First symptoms of the disease include a recurring fever, glumness and lack of appetite resulting in the weight loss.

Disease can take two forms, effusive (wet) FIP and non-effusive (dry) FIP. The wet FIP involves the accumulation of fluid within the abdomen and pleural cavity, effusion in the chest and pericardium, vasculitis and ascites. This leads to circulatory problems and dyspnoea. The dry FIP includes the formation of granulomatous lesions in internal organs such as a spleen and a liver; lymph nodes become enlarged; kidneys become irregularly shaped; continuous diarrhoea occurs. In addition, neurological symptoms and lesions in eyeballs occur (iritis, the presence of corneal precipitates and retinal detachment). Life span from the occurrence of the clinical symptoms in the effusive FIP is from a few days to a few weeks and in the dry FIP from a few weeks to a few months