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When Feline Coronavirus Turns Deadly


  • Feline infectious peritonitis (FIP) is an often-fatal viral disease caused by certain strains of the feline coronavirus; in 5% to 10% of cats with coronavirus, a mutation of the virus or an abnormality in the immune system allows the infection to progress to FIP

  • Any cat exposed to the feline coronavirus can develop FIP, however, kitties with compromised immune systems or FeLV, elderly cats, kittens, and some purebreds are at increased risk

  • Symptoms and disease progression depend on whether the FIP is the wet or dry form of the condition

  • Diagnosing FIP is challenging, a standard treatment doesn’t exist, and so the prognosis for most affected cats is poor

  • Prevention includes ensuring the health of pet’s immune system and feeding a nutritionally optimal, species-specific diet

Feline infectious peritonitis (FIP), is a complex viral disease that is prevalent in domestic and wild cats worldwide. FIP is caused by certain strains of the feline coronavirus (not to be confused with the current novel coronavirus known as SARS-CoV-2). Most strains, called feline enteric coronavirus, do not cause disease.

FIP was first recognized in cats in the 1950s. The disease is difficult to prevent, diagnose and treat. It’s 5 to 10 times more prevalent in shelter cats, and estimates are that 1% to 5% of that population dies from FIP.1

Any cat exposed to the feline coronavirus can develop FIP; however, cats who are immunocompromised, those already infected with the feline leukemia virus, geriatric cats, and kittens are most likely to develop the disease. Healthy littermates of a kitten with FIP are at 5 times increased risk of developing the disease within their first 9 months of life. Males are more commonly infected than females.

FIP is seen most often in indoor environments housing lots of cats, such as shelters, cat sanctuaries and catteries. Certain breeds, including Abyssinians, Bengals, Birmans, Himalayans and Ragdolls, are predisposed, which suggests genetics may play a role.

FIP Behaves Unlike Any Other Viral Disease We Know Of

Since there are documented small outbreaks of FIP in multi-cat environments, the disease may have a contagious component, however, the general consensus is that the disease is rarely transmitted from cat to cat.

Most kitties with a routine feline coronavirus infection are asymptomatic during the initial stages. Their immune systems respond by producing antiviral antibodies to kill off the infection. But in about 5% to 10% of cats initially affected with a benign gastrointestinal (GI) coronavirus (prevalent in felines worldwide), it seems either a spontaneous mutation occurs, or an abnormality in the immune system response allows the infection to progress to FIP.

There is still much to learn about what triggers one or the other of these internal processes that turns the virus from benign to deadly. The antibodies that should provide protection actually begin helping to infect white blood cells with the virus. These cells, in turn, spread the infection throughout the cat’s body. This results in a very powerful inflammatory response in tissues where the infected cells locate — frequently in the abdomen, kidneys, or brain.

It’s the interaction of the body’s immune system with the virus that results in disease. FIP behaves unlike any other viral disease we know of in either animals or people. Sadly, once the virus has involved one or more organs or body systems, the infection is quite progressed and almost always fatal.

While FIP Is Rare, Feline Coronavirus Is Not

Fortunately, FIP is relatively rare in the general cat population. However, feline coronavirus is found in large quantities in the feces and saliva of cats during the acute stage of infection when there are no symptoms. It’s also found to a lesser extent in cats that have recovered, as well as carrier cats.

The coronavirus can be transmitted from one cat to another through physical contact and through exposure to feces. Usually, transmission occurs long before clinical signs are noted. The virus can also live in the environment for several weeks.

The most common route of infection, though, is when an infected mother passes the virus to her kittens. This usually occurs when the litter is between 5 and 8 weeks of age.

There Are Two Forms of Feline Infectious Peritonitis

As I explained earlier, only a small percentage of cats exposed to the feline coronavirus go on to develop FIP, and it can be weeks, months, or even years after exposure before symptoms appear.

There are actually two forms of FIP, the effusive or wet form, and the non-effusive or dry form. Cats with the dry form tend to show signs of the illness more slowly — signs that are seen in several other feline diseases as well — including weight loss, depression, anemia, inflammation of the eye, and a stubborn fever that doesn’t respond to antibiotics.

The wet form of the disease is usually easier to diagnose due to an accumulation of fluid in the abdomen and sometimes the chest. Early on, symptoms may mimic those of the dry form of FIP. But effusive FIP progresses fairly rapidly. The cat may suddenly develop a potbelly as the result of abdominal fluid retention. In addition, there may be labored breathing due to a buildup of fluid in the chest.

Cats with the dry form also have localized growths on various organs. Both forms can lead to severe neurological disease.

Kitties whose coronavirus progresses to FIP often seem to their owners to develop symptoms very suddenly. This is probably due to the ability of cats to mask illness until they’re very sick, along with the non-specific nature of the initial symptoms.

Diagnosis of FIP Is Challenging

Diagnosing feline infectious peritonitis can be difficult because many of the symptoms are common in several other diseases. In addition, there’s no simple diagnostic test for the condition. As Morris Animal Foundation describes the issue:

“Available testing is cumbersome and invasive; results sometimes cannot distinguish between the FIP virus and the related and less aggressive coronavirus. There also is no test to prospectively predict which cats are more likely to develop the disease.”2

Several tests can detect the presence of feline coronavirus antibodies, but they can’t determine what strains are involved. A positive result on an ELISA, IFA, or a virus neutralization test simply means the cat has had exposure to the coronavirus, but not necessarily a strain of the virus that causes FIP.

There is an immunoperoxidase test that can find the presence of viral infected cells in the tissues; however, it must be followed by a biopsy to evaluate the affected tissue.

Routine blood tests, including a complete blood count and serum biochemistry profile, can show elevated liver enzymes, anemia, and abnormal blood protein levels, which are typical of cats with FIP. Chest and abdominal X-rays may show an abnormal accumulation of fluid.

Blood samples from cats with very high blood protein levels can be submitted for serum protein electrophoresis testing. Cerebral spinal fluid samples can also be analyzed for protein content, which is typically elevated in FIP cats. But the only way to definitively diagnose FIP is by a surgical biopsy of an affected organ (often the intestines) or examination of tissues during an autopsy.

Veterinarians often rely on a presumptive diagnosis, which can be made with a high degree of confidence based on the cat’s history, symptoms, examination of fluids, and a high coronavirus antibody titer.

Treatment of FIP

Unfortunately, there is no cure at the present time for FIP. Once a kitty develops clinical signs of the disease, either the dry or wet form, the prognosis is very poor.

I’ve had some success helping cats overcome FIP with supportive care and homeopathic nosodes, cytokine therapy, and intravenous (IV) vitamin C therapy, in addition to immune-modulating nutraceuticals and hyperbaric oxygen.3 Sadly, I’ve also tried to help many kitties who ended up succumbing to the disease. It’s a devastating situation for both the pet parent and the veterinarian.

Many cats with the wet form of FIP live only a month or two after diagnosis. Cats diagnosed with the dry form may have another year or so with a good quality of life. Unfortunately, the dry form can progress to the wet form if the cat lives long enough.

Supportive care for FIP patients includes good nutritional and environmental maintenance, alleviating the inflammatory response of the disease, fluid therapy, draining fluid accumulation, and blood transfusions.

The Morris Animal Foundation has conducted a clinical trial treating FIP-affected cats with a novel antiviral drug. The sample size was small (a few dozen cats), but kitties in the early stages of the disease reportedly responded well to the drug, which means the conventional veterinary community has finally been able to document survivable cases of the disease.

Apparently, further development of the drug therapy will be challenging, but at least there’s a glimmer of hope that someday we’ll be able to save cats from dying from FIP.

Preventing FIP in Your Own Cat

The best way to prevent FIP is to ensure the health of your kitty’s immune system. This includes feeding a nutritionally optimal, species-specific diet, titering after kitten vaccines, providing a stress-free enriched environment for your cat, arranging regular wellness exams with your veterinarian, and keeping kitty indoors while also providing a safe outdoor enclosure or supervised walks with a harness and leash.

Especially in multi-cat households, it’s important to keep litter boxes clean and located in areas away from food and water bowls. Litter should be scooped at least once daily, removing all feces, and dumped weekly or every two weeks, at which time the box should be completely and thoroughly disinfected with mild soap (nothing harsher) and water.

New cats to the household and certainly any cat that might be infected should be kept separate from other cats for a quarantine period.

There is a vaccine available for FIP; however, I don’t recommend it. It has little to no effectiveness in preventing the disease and is not recommended by the American Association of Feline Practitioners’ Feline Vaccine Advisory Panel. This vaccine can cause substantial immune system damage and, in my opinion, should absolutely not be used.  

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