Feline Infectious Peritonitis (FIP) is a serious viral disease in cats that, for many years, was considered a fatal diagnosis. The disease arises from a common virus that mutates into a severe, progressive form. However, recent scientific advancements have significantly changed the prognosis for cats with FIP.
The Cause and Development of FIP
FIP is caused by a mutated strain of feline coronavirus (FCoV). FCoV itself is a widespread and mild intestinal virus common in cat populations, especially in multi-cat environments. In most cats, an FCoV infection causes minor, if any, signs of illness, such as mild diarrhea.
FIP develops when the relatively harmless FCoV mutates inside a cat’s body. This mutated virus can escape the intestines, infect white blood cells, and spread throughout the body. This process triggers the severe inflammatory response characteristic of FIP, though only a small fraction of cats with FCoV will develop the disease.
Identifying Symptoms of FIP
The initial signs of FIP can be vague, including a fluctuating fever that doesn’t respond to antibiotics, loss of appetite, weight loss, and lethargy. As the disease progresses, it manifests in one of two forms: “wet” or “dry.” Some cats may present with a combination of both.
The wet, or effusive, form of FIP is characterized by the accumulation of fluid in body cavities due to damaged blood vessels. Fluid collecting in the abdomen can give the cat a pot-bellied appearance. When fluid builds up in the chest, it can cause difficulty breathing.
The dry, or non-effusive, form involves inflammatory lesions (pyogranulomas) in various organs, leading to more ambiguous symptoms. Depending on the organs affected, signs can include seizures, uncoordinated movements, or eye inflammation. Jaundice, a yellowing of the gums and eyes, can also occur if the liver is involved.
The Diagnostic Process
Diagnosing FIP is challenging because there is no single, definitive test that can confirm the disease in a living cat. Its clinical signs often overlap with many other conditions, so a veterinarian must piece together clues from various diagnostic tests to arrive at a conclusion.
The process often begins with bloodwork, which may reveal abnormalities like high protein levels, a low lymphocyte count, and anemia. For the wet form, a veterinarian can analyze a fluid sample. Fluid from an FIP case is typically yellow with a high protein content, and a Rivalta test can help support the diagnosis.
Imaging techniques like X-rays or ultrasound can help visualize fluid or the inflammatory lesions associated with the dry form. In some cases, a biopsy of affected tissue is required to look for the virus within the lesions. The final diagnosis is based on a combination of the cat’s history, clinical signs, and test results.
Treatment and Management
Previously, FIP treatment was limited to supportive care. The development of new antiviral medications has transformed this outlook, turning FIP into a manageable and often curable disease.
A primary breakthrough has been with nucleoside analogs, specifically the compound GS-441524. This drug, the active component of Remdesivir, works by interfering with the FIP virus’s replication. It is available in both injectable and oral forms, offering flexibility in administration.
The standard treatment protocol involves a course of medication lasting at least 12 weeks (84 days). The dosage is calculated based on the cat’s weight and the form of FIP. Throughout treatment, a veterinarian must monitor the cat’s response with regular blood tests and physical exams.
Success rates for these antiviral treatments are high, with studies showing that 80-90% of cats can achieve remission. Many cats show improvement within a few days of starting the medication. Compounded versions of GS-441524 are now more widely available to veterinarians in many countries.
Contagion and Prevention
A common concern for owners is the risk of transmission. It is important to distinguish between the common feline coronavirus (FCoV) and the mutated virus that causes FIP. FCoV is highly contagious and spreads easily through shared litter boxes and close contact.
The mutated FIP virus itself is not considered contagious, as the development of FIP is an internal event within a single cat. Therefore, a cat with FIP is not likely to transmit the disease directly to another. The primary risk in a multi-cat home is the spread of the underlying FCoV.
Prevention focuses on minimizing risk factors for FCoV and its potential mutation. Good litter box hygiene is necessary to reduce the spread of FCoV. Minimizing stress is also important, as it may be a contributing factor in the viral mutation that leads to FIP.