Feline coronavirus

Feline coronavirus (FCoV) is a positive-stranded RNA virus that is infectious to cats worldwide. This virus is part of the species Alphacoronavirus 1 of the genus Alphacoronavirus belonging to the virus family Coronaviridae. Alphacoronavirus 1 also includes the canine coronavirus (CCoV) and the porcine transmissible gastroenteritis coronavirus (TGEV). It has two different forms; the FECV (feline enteric coronavirus) that infects the intestines and the FIPV (feline infectious peritonitis virus) that causes the disease feline infectious peritonitis (FIP). Feline coronavirus (FCoV) is a positive-stranded RNA virus that is infectious to cats worldwide. This virus is part of the species Alphacoronavirus 1 of the genus Alphacoronavirus belonging to the virus family Coronaviridae. Alphacoronavirus 1 also includes the canine coronavirus (CCoV) and the porcine transmissible gastroenteritis coronavirus (TGEV). It has two different forms; the FECV (feline enteric coronavirus) that infects the intestines and the FIPV (feline infectious peritonitis virus) that causes the disease feline infectious peritonitis (FIP). Feline coronavirus is typically shed in feces by healthy cats and transmitted by the fecal-oral route to other cats. In environments with multiple cats, the transmission rate is much higher compared to single-cat environments. The virus is insignificant until mutations cause the virus to be transformed from FECV to FIPV. FIPV causes feline infectious peritonitis, for which there is no known cure; treatment is generally symptomatic and palliative only. Feline enteric coronavirus is responsible for an infection of the mature gastrointestinal epithelial cells (see also enterocytes, brush border, microvilli, villi). This intestinal infection has few outward signs, and is usually chronic. The virus is excreted in the feces of the healthy carrier, and can be detected by polymerase chain reaction (PCR) of feces or by PCR testing of rectal samples. Cats living in groups can infect each other with different strains of the virus during visits to a communal litter tray. Some cats are resistant to the virus and can avoid infection or even becoming carriers, while others may become FECV carriers. Carriers may heal spontaneously, but acquired immunity may be short, and they may go on to reinfect, usually within a few weeks, if they are living in a group with healthy, but persistent, excretory carriers. Some cats never heal, and the excretory phase remains permanently. The virus becomes feline infectious peritonitis virus (FIPV) when random errors occur in the virus infecting an enterocyte, causing the virus to mutate from FECV to FIPV. FIPV causes a lethal, incurable disease: feline infectious peritonitis (FIP). In one case study, a female cat diagnosed with FIP survived 26 months from the date of definitive diagnosis. In their pre-domestication natural state, cats are solitary animals and do not share space (hunting areas, rest areas, defecation sites, etc.). Domestic cats living in a group therefore have a much higher epidemiological risk of mutation. After this mutation, the FCoV acquires a tropism for macrophages (see also: immune cells, leucocyte, monocyte, dendritic cells, mononuclear cell, antigen-presenting cell) while losing intestinal tropism. In a large group of cats, n, the epidemiological risk of mutation (E) is higher and expressed theoretically as: E = n2 −n. A house hosting 2 cats therefore has risk of mutation E = 2. When 4 kittens (6 cats in total) are born into this house, the risk increases exponentially from 2 to 30 (62−6). Overcrowding increases the risk of mutation and conversion from FECV to FIPV, which constitutes a major risk factor for the development of feline infectious peritonitis (FIP) cases. FIP has been shown to develop in cats whose immunity is low; such as younger kittens, old cats, immunosuppression due to viral—FIV (feline immunodeficiency virus) and/or FeLV (feline leukemia virus) and stress, including the stress of separation and adoption. Infection of macrophages by FIPV is responsible for development of a fatal granulomatous vasculitis, or FIP (see granuloma). Development of FIP depends on two factors: virus mutation and low immunity where virus mutation depends on the rate of mutation of FECV to FIPV and the immune status depends on the age, the genetic pool and the stress level. High immune status will be more effective at slowing down the virus. Two forms of feline coronavirus are found in nature: enteric (FECV) and FIP (FIPV). There are also two different serotypes found with different antigens that produce unique antibodies. FCoV serotype I (also called type I) is the most frequent. Type I, that can be defined as 'FECV that could mutate to FIPV type I', is responsible for 80% of the infections. Typically, serotype I FCoV cultures are difficult to perform, with few resulting studies. FCoV serotype II (also called type II) is less frequent and is described as 'FECV type II that can mutate to FIPV type II.' FCoV type II is a recombinant virus type I with spike genes (S protein) replacement from FCoV by the canine enteric coronavirus (CCOV) spikes. The type II cultures are generally easier to perform, which has resulted in an imbalance of experiments performed with many studies about type II (even though it is a far less common form).