Feline coronavirus (FCoV or FECV) is a common viral infection which causes self-limiting intestinal (enteric) disease in cats. Most coronaviruses target the intestinal epithelia, which leads to malabsorption, maldigestion and diarrhea.
Coronaviruses are a large group of closely related enveloped RNA viruses and belong to the genus Alphacoronavirus, family Coronaviridae, within the order Nidovirales. Coronaviruses infect many animal species, including humans, cats, dogs and birds, causing enteric or respiratory disease. In humans, infection with coronavirus is associated with the common cold, SARS, MERS and COVID-19. The latter of which is currently a global pandemic.
The prevalence of feline coronavirus ranges from 36-75%, depending on the home environment (there is a higher incidence in multi-cat households and breeding catteries). Feline coronavirus is of particular importance among the cat population because infection occurs in two pathotypes;
- feline coronavirus (FCoV), also called feline enteric coronavirus (FECV) which is the widespread and self-limiting enteric type which produces mild diarrhea
- feline infectious peritonitis virus (FIPV), the virulent biotype which causes feline infectious peritonitis (FIP)
The exact pathology of FIP is not completely understood. A mutation of the feline coronavirus occurs some cats which enable the virus to infect and replicate in macrophages. It is the role of the macrophage to consume and destroy pathogenic invaders such as bacteria and viruses. Once consumed, the pathogen’s parts are displayed on the outer surface of the macrophage, which facilitates stimulation of antibody-producing lymphocytes. However, FIP develops, when macrophages are unable to destroy the virus, but instead, the infected macrophages disseminate through the body and cause a huge inflammatory response.
FCoVI and FCoVII
Feline coronavirus (FCoV) consists of two serotypes, I and II. Type I FCoV is the most common, and type II represents between 2-30% of infections. Evidence suggests that type II has arisen by the & recombination of type I and canine coronavirus (CCoV). FCoVI is the most prevalent, and one small Austrian survey found that 86% of cats with verified FIP had type I, 7% were type II positive, and 7% were positive for both type I and II.
Feline coronavirus (FCoV) and feline infectious peritonitis (FIPV) are not the same virus as COVID-19, and neither FCoV or FIPV are contagious to humans.
Several risk factors increase the chances of FIP developing. These include dense populations of cats, mixed ages of cats and kittens, shared litter trays, age of exposure to FCoV, stress (from overcrowding, early weaning and malnutrition), genetic predisposition, elective surgeries, breed, vaccinations and concurrent infections.
Eighty per cent of cats who develop FIP are under 24 months, and a compromised immune system increases a cat’s risk.
FCoV lives in the intestinal tract and is shed in the feces. Infection follows oronasal exposure to infected feces or contaminated surfaces.
A large percentage of FCoV infected cats are carriers; they shed the virus in their feces, which can infect other cats, but are asymptomatic. There is a higher incidence of infection in large cat populations such as cat breeders and multi-cat homes who are sharing litter trays. Stress may also play a role in breeding catteries and multi-cat households, as it is known to suppress the immune response.
Unlike FCoV, FIPV is not shed in the feces and is not contagious to other cats.
Cats with coronavirus are often asymptomatic, although some may display mild clinical signs including loss of appetite and brief diarrheal illness which resolves without specific therapy.
Feline infectious peritonitis
There are two forms of FIP, wet (effusive) and dry (non-effusive), clinical signs differ between types.
Wet FIP develops within weeks and affects the body cavities with a build-up of viscous yellow fluid triggered by damage and inflammation of the blood vessels (vasculitis). Vasculitis leads to a redistribution of fluid into the second spaces, including the abdomen, chest, pericardial (heart) and scrotum.
Dry FIP is a chronic (long-standing) disease which develops over a period of months. Inflammatory lesions develop around the blood vessels in different organs, particularly the nervous system and the eyes.
Some cats will develop both wet and dry FIP.
- Fever of unknown origin
- Loss of appetite
- Weight loss
- Fluctuating fever which does not respond to antibiotics
- Loss of appetite
- Ascites (build-up of fluid in the abdomen) or breathing difficulty if fluid is in the chest cavity (pleural effusion)
- Scrotal swelling in intact male cats
Symptoms can vary depending on the organ system affected, but may include:
- Fluctuating fever which does not respond to antibiotics
- Loss of appetite
- Neurological signs (wobbly gait) due to meningoencephalitis (inflammation of the brain and protective membrane)
- Jaundice (yellowing of the inside of the ears, whites of the eyes and gums)
- Kidney failure
- Liver failure
Diagnosis of feline infectious peritonitis can be a challenge as symptoms are often vague and can represent a number of diseases.
There is no definitive diagnostic test for FIP; diagnosis is based on signalment, clinical signs and diagnostic tests. Young cats from high-density environments who are unresponsive to antibiotic therapy will raise the veterinarian’s index of suspicion.
- Baseline tests: Complete blood count and biochemical profile may reveal nonregenerative anemia (decreased number of red blood cells), neutrophilia (increased number of neutrophils, a type of white blood cell), lymphopenia (low numbers of lymphocytes, a type of white blood cell), elevated serum protein associated with high globulin and low albumin (A:G ratio), elevated liver enzymes, and elevated bilirubin.
- Abdominocentesis or thoracentesis: A needle is inserted into the abdomen or thorax to remove fluid for analysis. Fluid will typically have a high protein content.
- Rivalta test: This test can be a useful tool for veterinarians. A 10ml tube is filled with distilled water with a drop of acetic acid. One drop of effusion from the cat is added to the test tube, if the drop retains its shape, the test is positive, if it dissipates the test is negative.
- Serum coronavirus antibody: Testing for antibodies to coronavirus is problematic because an antibody test cannot differentiate between cats infected with FCoV and FIPV. Therefore a cat with a positive test may have the mostly asymptomatic FCoV or the pathogenic FIPV. 10% of cats with FIP test negative.
- Histopathology and immunochemistry: Detection of coronavirus antigens in macrophages from affected tissues.
- Diagnostic imaging: Xray or ultrasound may reveal a build-up of fluid in the body cavities (predominantly the chest or abdomen)
Most cats with FCoV require no treatment as the infection is self-limiting. Cats with diarrhea may benefit from a bland diet to rest the gastrointestinal tract.
Treatment for cats with FIP is palliative only, corticosteroids can reduce inflammation and broad-spectrum antibiotics to reduce the risk of secondary bacterial infection.
Two antiviral drugs show promise in the treatment of FIP, a protease inhibitor (GC376) and a nucleoside inhibitor (EV0984). The precise mechanism is beyond the scope of this article, but information on both drugs can be found on the American Veterinary Medical Association page.
- A vaccine is available for high-risk cats although most studies indicate that the FIP vaccine is not effective. Cats vaccinated for FIP will test positive to coronavirus antibody tests.
- Reduce overcrowding
- Improve hygiene in multi-cat environments as the virus can survive for weeks in the right conditions
- Reduce fecal contamination, remove solids from litter trays at least twice a day, thoroughly empty, disinfect and replace with fresh litter once a week
- Provide an adequate number of litter trays in multi-cat homes, the rule of thumb is one tray per cat, plus one extra
- Antibody test all new cats
- Do your homework before bringing a new kitten or cat into the home, avoid animals from overcrowded conditions and always quarantine new cats who arrive in the home
COVID-19 and cats
A cat in Belgium recently tested positive for COVID-19 which has raised concerns for pet owners. The cat’s owner had tested positive for COVID-19 a week before the cat developed breathing difficulty and diarrhea. Vets at the University of Liège, Belgium then tested the cat and detected viral genome in the cat’s feces and vomit samples.
The standard COVID-19 test detects viral genome, and not live virus particles. So we do not know if the viral genome found in the cat samples could replicate. One opinion piece states that the cat could have eaten food contaminated with the virus, as we don’t know how much genetic material was detected as the results have not been published. It goes on to say that respiratory symptoms are a common clinical sign in cats and could have been due to asthma or a mild case of cat flu.
As of 3rd April 2020, global infection numbers have topped 1 million, but despite this, there is still no evidence of transmission between cats and people.
Idexx, a large veterinary diagnostic laboratory has tested thousands (the exact number wasn’t stated) of cat and dog samples and have so far found no positive results to date.
Current recommendations are to follow government guidelines which include self-isolation, particularly for people with symptoms, only leave home to purchase food, medicine, receive medical care, exercise, work or care for people in need, wash hands frequently with soap and water, for a minimum of twenty seconds.
- Coronaviruses belong to a large family of viruses which infect mammals and birds.
- Most coronaviruses infect one species only.
- Feline coronavirus is not the same as COVID-19 and cats infected with FCoV or FIPV are not infectious to humans.
- Feline coronavirus is widespread among the cat population and in most cases, infected cats remain asymptomatic or display mild clinical signs of diarrhea.
- One cat has tested positive for COVID-19 after acquiring the infection from its owner. Both cat and owner are recovering.
- There is still no evidence that cats can transmit COVID-19 to people.