Feline coronavirus: more than just gastroenteritis
What is feline coronavirus?
Feline coronavirus is an RNA virus that commonly affects cats. There are two different types:
- Feline enteric coronavirus (FECV), which invades the digestive tract; and
- Feline infectious peritonitis virus (FIPV), which is a typically chronic condition that involves infection of the intestinal epithelial cells.
Feline coronavirus (FCoV) is transmitted by the faecal–oral route. The virus is excreted in the faeces of healthy carrier animals, representing the main vehicle of infection. Some cats are resistant to FCoV and do not develop any infection, while others will become FECV carriers for some time. They may recover spontaneously, but acquired immunity is brief, then they are reinfected after a few weeks, if they live in a group with other excretors (healthy carriers).
Clinical significance: one of the main characteristics of feline coronavirus is its ability to mutate, giving rise to another disease known as feline infectious peritonitis (FIP).FECV can transform into FIPV because of mutations in the coronavirus when inside intestinal epithelial cells.
It is estimated that between 25 and 40% of domestic house cats are infected. The prevalence rises to 80–100% of cats when living in large groups in homes, shelters or catteries.
Clinical manifestations of feline coronavirus
Feline enteric coronavirus produces mild but chronic gastroenteritis. Many cats are resistant and therefore only carriers, but the virus can mutate and cause feline infectious peritonitis. FIP occurs in two different forms, known as dry and wet forms.Overpopulation, and consequently the risk of mutation to FIPV, is a risk factor for the development of feline infectious peritonitis. However, FIP mainly develops in cats with weak immunity such as in kittens, older cats or due to virus-induced immunosuppression, for example in the case of retroviruses such as feline immunodeficiency virus (FIV) and/or feline leukaemia virus (FeLV).
The dry or non-effusive form of FIP affects several organs, so it produces a wide range of clinical signs.The wet or effusive form courses with the accumulation of fluids in body cavities, such as the peritoneum and the pleura. Both the forms share some common clinical signs such as fever, inappetence and lethargy.
The two forms can be briefly described as:
- 1. Wet FIP: a fluid rich in fibrin and protein accumulates in the peritoneal cavity, with the most characteristic clinical manifestation being progressive enlargement of the abdomen. The increase in vascular permeability secondary to perivasculitis leads to the accumulation of a protein-rich fluid in the peritoneal and pleural cavities, as well as other spaces. The inflammation’s spread to other organs can cause signs of liver damage, such as jaundice, vomiting and alternating periods of diarrhoea and constipation. In addition, enlarged lymph nodes become palpable and the kidneys large and irregular.
This is the most fulminant form of the disease, with a faster onset and shorter clinical course. Survival time from the onset of the disease is just 5 to 7 weeks.
- 2. Dry FIP: with pyogranulomatous lesions in parenchymal organs, the central nervous system and eyes. Its onset is insidious, involving weight loss, depression, anaemia and fever, while fluid accumulation tends to be minimal. Palpation reveals irregularities in the viscera or mesenteric lymphadenitis. Lung lesions may manifest as granulomatous pneumonia with persistent cough but no significant dyspnoea.
Ocular and nervous signs are more common in this form of feline coronavirus.
Neurological signs include posterior paresis and ataxia progressing to tetraparesis.
Ocular signs are bilateral and include anterior uveitis (iridocyclitis with miotic pupil), hypopyon, hyphaema and corneal oedema.
The clinical course is longer than in the wet form, but even so not many cats survive more than one year.
There is no specific diagnostic test for FIP. Biopsies of affected tissues can confirm the diagnosis, but this is not usually done due to the severity of the animal’s condition.
The following complementary tests can be performed:
- Analysis of effusion fluid: FIP produces a clear yellow to reddish brown, viscous fluid that is rich in fibrin and coagulates.
- Analysis (blood count, blood chemistry, etc.): absolute neutrophilic leukocytosis, with or without left shift; eosinopaenia and lymphopaenia. Some 40% of cats develop mild to moderate normocytic and normochromic anaemia. Hyperproteinaemia mainly due to polyclonal hypergammaglobulinaemia. Elevated fibrinogen levels can also be observed.
- Serology: this infection can be diagnosed by taking a smear of a few rectal cells (curettage) and detecting viral RNA by PCR.
Secondly, cats can be tested for coronavirus exposure by looking for the presence of feline coronavirus specific antibodies using ELISA and IFA. However, these results do not provide information as to whether a cat has or could develop FIP. Furthermore, published studies indicate that some cats with confirmed FIP do not have any antibodies, so this method cannot be used to exclude FIP. Therefore, it is only used to screen for carrier cats when they are brought into shelters and diagnose the disease in conjunction with clinical signs and other tests.
Feline coronavirus is incurable.Treatment is symptomatic and based on anti-inflammatories and appetite stimulants. Studies have not found any benefit from the use of antiviral agents.
Preventive treatments are recommended to prevent the disease from spreading. Vaccination is the treatment of choice to prevent feline coronavirus, coupled with hygienic measures to prevent infection between cats, including the use of several litter trays.