Feline infectious peritonitis (FIP) is associated with cats already infected with feline coronavirus (FCoV), which has a worldwide distribution and is found in domestic and wild cats. FCoV infection is very common but typically causes transient disease with mild or no intestinal signs. A small percentage of infected cats develop FIP. Pathogenesis of FIP is unclear but is thought to be related to virulence of some strains and host immunity. Thus, cats that are young and immunocompromised due to stressful conditions (crowded conditions), glucocorticoid therapy, or surgery, are more likely to develop FIP. Definitive diagnosis without invasive biopsies is difficult but important as the disease is fatal.
Clinical signs vary depending on the organs involved. The liver, kidneys, pancreas, CNS, and eyes may be affected. Organ damage and failure is due to vasculitis. Clinical signs may be vague and include lethargy, chronic weight loss, anorexia, jaundice, and fever of unknown origin. There are several forms of FIP; the more common, effusive form results in increases in body cavity fluid that cause associated signs. Dry forms may manifest with neurologic signs, ocular signs, and less often skin disorders. Signalment and history, along with clinical examination and laboratory findings, increase the index of suspicion. Common CBC findings include lymphopenia, neutrophilia with a left shift, and mild to moderate anemia. Common biochemistry findings include hyperglobulinemia with hypoalbuminemia, hyperbilirubinemia, and increased liver enzymes. Analysis of effusions is helpful, as they typically show increased protein concentrations with low cell counts. Serology and PCR assays for FCoV are not a reliable way to diagnose FIP. Definitive diagnosis requires biopsy of affected tissues and immunostaining can improve the likelihood for detection of FCoV antigen in the tissue. This test is confirmatory if positive but negative results do not rule FIP out. This disease continues to be a diagnostic challenge although more evidence-based information is being gathered.
See Feline Infectious Peritonitis and Peritonitis in The Veterinary Manuals.
References
Barker EM, Stranieri A, Helps CR, et al. Limitations of using feline coronavirus spike protein gene mutations to diagnose feline infectious peritonitis. BMC Vet Res. 2017, 48:60. doi 10.1186/s13567-017-0467-9.
Felton, S, Leutenegger CM, Balzer H, et al. Sensitivity and specificity of a real-time reverse transcriptase polymerase chain reaction detecting feline coronavirus mutations in effusion and serum/plasma of cats to diagnose feline infectious peritonitis. BMC Vet Res. 2017, 13:228. doi 10.1186/s12917-017-1147-8.
Tasker, S. Diagnosis of feline infectious peritonitis: Update on evidence supporting available tests. J Feline Med Surg. 2018 Mar, 20(3):228-243. doi: 10.1177/1098612X18758592.
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