Feline Infectious Peritonitis (FIP): Causes, Transmission, Diagnosis, Treatment, and Prevention

Feline Infectious Peritonitis (FIP): Causes, Diagnosis, Treatment, and Prevention

Feline Infectious Peritonitis (FIP) is a viral disease caused by the feline coronavirus (FCoV) that primarily affects cats under 3 years of age, with the highest prevalence observed in cats between 4 and 16 months old. Although it was identified in 1950, FIP is currently considered an emerging disease and accounts for approximately 1 in 200 cases diagnosed in referral hospitals. The disease poses significant challenges due to its high mortality rate, lack of definitive diagnostic techniques, and limited treatment options, which can have a profound psychological impact on cat owners who have developed a bond with their feline companions.

Aetiology and Pathogenesis

FIP is a result of mutations in the feline enteric coronavirus (FECV), a virus that typically causes mild gastrointestinal infections in cats. FECV is shed in the feces of apparently healthy cats, and transmission occurs through direct contact via the fecal-oral route or through contaminated objects. Kittens are particularly susceptible to infection, and mutation can occur when levels of FECV replication are high around nine weeks of age. However, only a small proportion of cats exposed to the mutated variant of the virus (FIPV) develop FIP, indicating the influence of various factors, including genetic susceptibility, age at exposure, type of viral mutation, and stress-related factors during infection.

The disease course and severity vary depending on the age of the cat and the form of FIP. The exudative form of FIP is characterized by immune system-mediated vasculitis, leading to fluid accumulation in the abdomen, chest, or pericardium. In contrast, the non-exudative form is marked by the formation of pyogranulomatous lesions in various organs. The clinical signs and disease progression can fluctuate, with some cats experiencing acute symptoms and a rapid decline, while others may have a more chronic response.

Diagnostic Tests for FIP

Diagnosing FIP requires a comprehensive approach, considering various parameters, including the age and origin of the cat, clinical signs, and physical examination findings. Cats aged 4 to 36 months, living in high-density multi-cat environments, presenting with remittent fever, and unresponsiveness to antibiotics are highly likely to have FIP. However, due to the lack of definitive diagnostic techniques, several indirect tests are utilized to support the diagnosis.

Indirect tests include a complete blood count to assess for characteristic changes such as chronic non-regenerative anemia, leukocytosis with increased neutrophils, and decreased lymphocyte count. Evaluation of serum protein levels, particularly albumin, globulin, and bilirubin, can provide valuable information. Cats with FIP often exhibit elevated globulin levels, decreased albumin levels, and a low albumin/globulin (A/G) ratio. Hyperbilirubinemia and hyperbilirubinuria are also common in cats with FIP, indicating increased destruction of red blood cells.

Effusion analysis plays a crucial role in diagnosing the exudative form of FIP. Analysis of peritoneal or pleural fluid reveals characteristic features such as high protein concentration, viscosity, and specific cellularity. Ultrasonography can aid in identifying the presence of fluid and obtaining samples for further analysis. Other indirect tests include the evaluation of the albumin/globulin ratio, ocular and neurological signs, antibody titers in feline coronavirus, Rivalta's test, and acute phase proteins.

Direct tests, such as immunohistochemistry and polymerase chain reaction (PCR), aim to identify the specific causative agent of FIP. Immunohistochemistry involves the detection of viral proteins in tissue or fluid samples affected by FIP. PCR techniques can detect feline coronavirus RNA, but differentiating between enteric coronavirus and FIP coronavirus has been a challenge. However, recent advancements in RT-PCR have enabled the distinction between the two viruses by evaluating specific mutations associated with FIP. These direct tests provide more definitive evidence but are often reserved for cases where clinical signs, physical examination findings, and indirect tests strongly suggest FIP.

Treatment

Treating FIP remains challenging due to the lack of a definitive cure. Various treatment approaches have been explored, aiming to inhibit viral replication, modulate the inflammatory response, and stimulate the immune system. However, the effectiveness of these treatments is limited, and some may have undesirable side effects.

Antiviral drugs, such as protease inhibitors, have shown promise in inhibiting FIP virus replication in laboratory studies. However, their clinical use is challenging due to difficulties in achieving effective drug concentrations in affected tissues and potential toxicity to the host.

Immunomodulatory drugs, including glucocorticoids and cyclosporine A, have been used to suppress the exaggerated immune response associated with FIP. These medications aim to reduce inflammation and slow disease progression. However, their effectiveness in improving clinical outcomes and prolonging survival is still uncertain.

Immunostimulant drugs, such as feline interferon ω, have been investigated for their potential to enhance the immune response against FIP. However, clinical studies have not provided consistent evidence of their efficacy, and their use remains controversial.

Supportive care plays a crucial role in managing FIP cases. Providing proper nutrition, maintaining hydration, and managing symptoms, such as fever and pain, are essential for improving the cat's quality of life. Palliative care focuses on maximizing comfort and minimizing distress in cats with advanced stages of the disease.

Experimental treatments, including the use of antiviral peptides and novel immunomodulators, are being investigated in research settings. However, their efficacy and safety in clinical practice are yet to be established.

Prevention

Preventing the spread of FIP is crucial, particularly in multi-cat environments. Minimizing fecal contamination through proper litter box management, controlling the number of cats in a household, and implementing serological screening for antibody status can help reduce the risk of FIP transmission. Vaccination has been explored as a preventive measure, but the current FIP vaccine has limitations. The vaccine is not completely protective, and its effectiveness varies depending on the cat's age, exposure status, and individual immune response.

Feline Infectious Peritonitis (FIP) poses significant challenges in diagnosis and treatment. A thorough evaluation of clinical signs, physical examination findings, and results from both indirect and direct diagnostic tests is necessary to establish a reasonable certainty of diagnosis. While there is no definitive cure for FIP, providing supportive care and maintaining a good quality of life for affected cats remain essential. Ongoing research and advancements in treatment options hold promise for improved outcomes in the future. Implementing preventive measures, such as minimizing viral spread in multi-cat environments, can help reduce the incidence of FIP and protect vulnerable feline populations.