Veterinary Advice on FIP in Cats (Feline Infectious Peritonitis)

Feline Infectious Peritonitis (FIP in cats) is a severe, debilitating, and progressive disease. In most cases, with a fatal outcome.

Distributed worldwide, it specifically affects felines, both domestic cats (Felis catus) and wild cats (lynxes, leopards, pumas, cheetahs, etc.). Cats of all ages can become ill. But, FIP symptoms in kittens are more frequent, in ages between 2-3 months to 2-3 years.

In this article, we will discuss in depth everything you need to know about FIP. A disease that is as alarming for cat owners as it is devastating for felines.

What is FIP in cats?

The causative agent is an RNA virus of the Coronaviridae family. There are several types of Feline Coronavirus within this family. But, the most common is Feline Enteric Coronavirus (FeCV). It lives in the intestine of many healthy cats and is asymptomatic.

In certain cats and under specific environmental conditions, this virus can mutate (change). It enters the bloodstream of the cat’s body, and produces the disease (FIP).

How do Cats Get FIP?

FeCV lodges in the intestine of cats and causes a chronic infection of the digestive cells. It does not produce symptoms or generate self-limiting transient diarrhea.

Due to random errors during replication in the digestive cells, the FeCV can mutate, giving origin to a pathological and harmful viral form. This new virus can travel through the cat’s intestinal wall invading the White Blood Cells and disseminating throughout the animal’s body. This gives rise to the disease called Feline Infectious Peritonitis (FIP).

The cat’s immune system detects the virus and generates antibodies against it. But these antibodies are “non-neutralizing”. They cannot prevent viral replication. It is the cat´s own inflammatory reaction that produces the symptoms of the disease.

How is FIP Transmitted?

FeCV is very contagious. The most frequent form of transmission is the fecal-oral route. Most felines shed the virus in feces for only a few months, but a small percentage shed the virus for life.

The second, less frequent transmission route is through oro-nasal secretions (saliva and mucus).

Finally, transplacental transmission from mothers to kittens. This route still needs confirmation with further studies.

The virus is fragile in the environment and dies in approximately 24 to 36 hours outside the host’s body. But it can live for several months in cold climates that preserve its vitality.

The virus enters the body of healthy cats by ingestion or inhalation. The direct form of contagion is close contact with carrier animals. The indirect way is through objects contaminated with feces (sandboxes, feeders, bedding, etc.).

Even mothers can infect their kittens through licking.

Wet vs. Dry Feline Infectious Peritonitis

In general, when a pathogen enters the body of an animal, it produces an immune response. This immunity can be Humoral (antibodies) and Cellular (white blood cells).

In FIP, both defense barriers occur but the antibodies produced cannot kill the virus. This is what makes the disease so complex.

Cellular immune response is essential to fight this virus:

• If the cellular immune system is strong, the disease does not occur
• Dry FIP in cats develops if the cellular immune system is weak
• Wet FIP in cats appears if the cellular immune system is very suppressed

Dry Fip can develop in Wet FIP and vice versa.

What are the Causes of This Disease?

Most cats come into contact with the causative agent of FIP at a very early age. It may even be the mother herself who infects the kittens. FeCV affects most felines but this does not imply that they will develop FIP.

Compared to the number of cats infected with FeCV, felines with FIP are very few. They only develop the disease when the virus mutates. And this may never happen or happens after years, months, or weeks. So… Why does the virus mutate?

The causes of the viral mutation are still unknown. But it is evident that the mutation occurs in animals with weak or immature immune systems such as:

• Kittens between 3 months and 3 years of age
• Geriatric cats
• Cats with chronic diseases: Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV)
• Cats living in poor hygienic conditions
• Stressed cats (post surgeries, post-vaccination, etc.)
• Cats living in overcrowded catteries or shelters
• Genetic factors:
• Purebreds: Abyssinian, Bengal, Birman, Himalayan, Ragdoll, and Devon Rex
• Males over females

Symptoms of Feline Infectious Peritonitis

There are no associated pathognomonic signs of PIF in cats. At the beginning of the disease, both dry FIP and wet FIP present general symptoms, such as:

• Loss of appetite
• Weight loss
• Lethargy
• Delayed growth in kittens
• Sneezing, watery eyes, and nasal discharge
• Diarrhea
• Fever (constant sign, does not respond to antibiotics and remains until the last hours of life)
• Jaundice (constant sign)

After several days to a few weeks other symptoms begin to appear.

Wet FIP Symptoms

This is the most common form of the disease, it is the most severe and has the worst prognosis. The cat’s intense inflammatory reaction produces generalized vasculitis throughout the body. There is damage to the blood vessels causing fluid accumulation in:

• Abdominal cavity (ascites). This is the most common symptom but is not pathognomonic of wet FIP. The enlargement of the abdomen is progressive and painless.
• Thorax (pleural effusion)
• Around the heart (pericardial effusion)
• Sloping areas such as the chin and scrotum (edemas)

The animal presents a very distended abdomen, respiratory distress and heart failure.

Dry FIP Symptoms

This is the least common and most chronic form of FIP. Pyogranulomatous infiltrates develop around the blood vessels of the most irrigated organs. These are whitish plaques measuring 10 to 20 mm that occur as a consequence of the individual immune reaction. The most affected organs are kidneys, liver, spleen, pancreas, brain, and eyes. And they will produce variable clinical signs such as:

• Liver failure
• Kidney disease
• Diabetes due to pancreatic dysfunction
• Central nervous system. Neurological disorders in cats like behavioral changes, nystagmus, ataxia, tremors, seizures, paralysis
• Ocular signs. Some cats with Dry FIP may only have this symptom. PIF in cats eye symptoms are bilateral blindness due to:

1. 1. Bilateral anterior uveitis
   2. Pyogranulomatous chorioretinitis
   3. Hyphema
   4. Hypopyon
   5. Keratin precipitates
   6. Retinal detachment
   7. Conjunctivitis

How to Test for FIP in Cats?

FIP is one of the most challenging diagnoses for veterinarians. This is because the disease is complex and the current tests have limitations.

That is why, sometimes, FIP is a diagnosis by exclusion. Meaning that the vet eliminates from the list all the diseases that mimic PIF.

Blood Tests (Hematology and Biochemical)

These are non-specific findings of the disease. They will not confirm a diagnosis of FIP but may be useful in suspecting the presence of the disease.

X-rays

To detect free fluid in the abdomen and thorax

Analyses of Effusion Fluid

Approximately 75% of cats with FIP (both wet and dry but in minimal amounts in the latter case) have effusions in the thorax and abdomen. Analysis of the effusion fluid is of great diagnostic value. With an echo-guided puncture, we obtain a sample of the fluid. It has the following characteristics:

• Reddish-yellowish color
• Viscous – sticky and, in contact with oxygen, it coagulates
• High protein content
• Very few cells
• No bacteria

The identification of such fluid is supportive of FIP but not pathognomonic for it.

Rivalta Test

Practical, quick, and simple evaluation performed in the consultation room. It requires a drop of thoracic or abdominal effusion fluid. It is an excellent test to rule out FIP as it has a 93% reliability in negative cases. But only 58% in positive cases. False positives can occur in the case of cats with:

• Lymphoma
• Bacterial peritonitis
• Bacterial pleuritis

Coronavirus Antibodies

The number of cats exposed, thus, antibody-positive to FeCV is high. Approximately 30% of domestic cats and 80% of strays or those cats living in overcrowded conditions are positive. However, the proportion of positive cats that develop FIP is very low.

Measurement of antibody titers does not differentiate antibodies produced against FeCV and the mutated coronavirus that causes FIP. So:

• A positive antibody titer only indicates prior exposure to Coronavirus
• A healthy cat with elevated titers does not mean that it will develop the disease in the future. It only indicates that his body has had contact with a Coronavirus
• Cats with suppressed immune systems due to other causes may have low antibody counts. Their body is not able to produce them. But this does not mean that they have not had contact with this virus or that they do not have FIP. E.g.: FIV positive – ViLeF positive – final stages of FIP

Antigen (detects the presence of the virus itself)

• Immunoperoxidase test: Can detect viral proteins in virus-infected white blood cells in tissue. It would be best to do a biopsy of affected tissue. But many times, anesthetizing these unhealthy patients is not possible
• Immunofluorescence test: Can detect viral proteins in virus-infected white blood cells in tissue or body fluids. This is a good option to diagnose wet FIP. The sampling of the fluid is very simple and does not need anesthesia
• PCR: Can detect virus genetic material in tissues and fluids. The disadvantage is that there is no unique gene sequence associated with the FIP virus

Histopathology

This is the only certain diagnosis to reach a positive result for FIP. The pathologist will analyze the affected tissue by performing a biopsy or necropsy.

How is FIP in Cats Treated?

Symptomatic Treatment

The purpose is to improve the patient’s quality of life.

• Protein-rich food
• Administration of proteolytic enzymes
• Vitamin complexes (A, B, C, E)
• Drainage of pleural effusions if breading is difficult
• IV fluid therapy
• High-dosages of steroidal anti-inflammatory drugs to diminish the effects of the immune response
• Broad-spectrum antibiotics
• Immunosuppressive drugs such as Cyclophosphamide. They depress the cellular immune system
• Feline recombinant omega interferon (FelFN-w) as an enhancer of the cellular immune response

Anti-viral Treatment

In recent years, the hope of finding a cure for this disease has increased.

Two drugs are showing good efficacy and safety in the treatment of FIP:

• Protease inhibitor 3C-GC376
• The nucleoside analog GS-441524 (tablets) and its relative Remdesivir (Injectable)

As these drugs are not yet approved by the FDA, they are not available in the USA.

Other countries are already using them such as the UK. Although the treatment is long (it can take more than a year) favorable results are being obtained on patients presenting wet FIP.

The outcome is not as encouraging in cats presenting dry FIP. Thus, it is still under investigation.

Preventive Treatment

There is only one licensed FIP vaccine in cats. It is available in Spain, USA and other European countries (not in UK).

This intranasal vaccine, called Primucell® contains a temperature sensitive mutated Coronavirus. It induces a local cell-mediated immune response in the nasal mucosa. There is considerable controversy about this vaccine. Different studies have shown variable results of efficacy in protection against the disease.

Only kittens as of 16 weeks old or more can use Primucell®. This is an important limitation, since most feline coronavirus infections come from the mother and occur at a very early age.

The Feline Vaccination Advisory Panel of the American Association of Feline Practitioners (AAFP) does not recommend this vaccine.

Sanitary Treatment

The only way to prevent FIP in cats is to prevent FeCV infection. This can be challenging given its ubiquitous nature. Some health recommendations are:

• Provide at least one litter box for every two cats, located in an easy to clean/disinfect area
• Cleaning with diluted bleach (1:32) is adequate to kill the virus
• Separate litter boxes, feeders and drinkers to avoid cross-contamination
• Remove feces from the litter box at least once a day. Clean the whole litter box as often as possible, in conjunction with a good disinfection
• Avoid stress factors and reduce the risk of cross-contamination within the same household. Keep the cats in small, stable groups of four or fewer individuals
• Perform appropriate vaccination and deworming schedules
• Sterilize both, males and females, (if they are not breeding animals)
• Check new individuals for FIV, VILEF, and Coronavirus before joining the existing flock
• Regular brushing of the coat reduces the risk of infection from feces and litter

FIP in Kittens

The mother is the most important source of infection for kittens. So, by isolating the pregnant cat from the group (two weeks before delivery) and maintaining strict hygienic measures, most kittens will remain coronavirus negative. If the mother has antibodies, they will pass to the kittens through colostrum and milk.

This immunity begins to wane at 5 to 6 weeks old. Separate kittens from their mother and keep them isolated until 12 to 16 weeks old. At this point, measure antibodies against Coronavirus. If they are negative, the isolation will have been successful.

Now their immune system is mature. These measures reduce the likelihood of these cats developing FIP in the future. As long as sick animals are not reintroduced and recontaminate them.

Diseases That Mimic FIP in Cats

Conditions that have similar symptoms include:

• Liver failure
• Kidney disease
• Diabetes Mellitus
• Abdominal tumors
• Toxoplasmosis
• Infection with mycobacterium
• Lymphocytic cholangitis
• Cardiomyopathies
• Tuberculosis

Is FIP Contagious to Other Cats, Other Animals, and Humans?

FeCV is quite contagious but unique to cats. Then, only members of the feline family can become infected. It is not contagious to people, dogs, or other species of animals.

It is important to note that while FeCV is quite contagious, FIPV (mutated virus) is not believed to be.

The National Academy of Science (PNAS) recently published a study referring that cats are susceptible to SARS-CoV-2 infection but are unlikely to develop clinical disease. Also, they mentioned that currently, no scientific evidence shows that cats play a significant role in human infection. Reverse zoonosis (human-to-animal infection), yet, can occur if infected owners expose their domestic pets to the virus during the acute phase of infection.

Determining the Final Stages of FIP in Cats

Conventional treatment focuses on minimizing the clinical symptoms that interfere with the cat´s quality of life. FIP is fatal without definitive treatment. Euthanasia may be the most humane and appropriate course of action. There is now new hope for a possible cure with antiviral treatments. But, there is still a long way to go.

How Common is the Disease?

25-40% of domestic indoor cats have FeCV. This percentage increases to 80-100% of cats living in streets and large groups.

The majority of cats carrying FeCV never show symptoms of this disease (90% or more).

So, How common is FIP in cats? The incidence is low (only 5 to 10% of infected cats).

FIP kills around 0.3-1.4% of cats worldwide. Besides, it is a source of threat to endangered wild felines.

The Life Expectancy of Feline Infectious Peritonitis

FIP in cats’ life expectancy is short. Most cats die within weeks or months of diagnosis. The prognosis is severe.

We hope that with the new treatments, life expectancy for felines will improve.

One Last Thing to Remember

It is better to have only one or two indoor cats to take proper care of and enjoy them to the fullest. With a large number of cats, it is difficult to carry out hygienic and preventive measures. In this way, we guarantee a harmonious coexistence with our best friends!