Viruses · 15 authors, 16 centres
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Feline infectious peritonitis (FIP) is a fatal disease in cats caused by a mutated feline coronavirus, but recent antiviral treatments, particularly oral GS-441524, now cure most cases. Diagnosis relies on detecting the virus in effusions or tissue via PCR or antigen staining, with histopathology as the gold standard. These guidelines provide updated recommendations for veterinarians to diagnose and manage FIP effectively.
**Background:** Feline infectious peritonitis (FIP) is a fatal disease caused by a mutated feline coronavirus (FCoV). FCoV is a ubiquitous RNA virus transmitted faeco-orally; most infections are subclinical or cause mild enteritis, but a small proportion of infected cats develop FIP. The pathology involves perivascular phlebitis affecting any organ. Cats under two years old are most frequently affected. Clinical signs include fever, anorexia, weight loss, effusions (abdominal, pleural, pericardial), and sometimes ocular (uveitis) and/or neurological signs (ataxia, seizures). Diagnosis is complex; sampling effusions for cytology, biochemistry, and FCoV RNA or antigen detection is very useful. In the absence of effusions, fine-needle aspirates from affected organs for cytology and FCoV RNA or antigen detection are helpful. Definitive diagnosis usually requires histopathology with FCoV antigen detection. Antiviral treatments, particularly nucleoside analogues like oral GS-441524, now enable recovery in many cases, though they are not available in all countries.
**Methods:** The European Advisory Board on Cat Diseases (ABCD) conducted a comprehensive review of the literature published over the past 14 years, updating the previous 2009 FIP guidelines. The review covers agent properties (virus classification, genome structure, pathotypes and mutations), epidemiology (transmission, prevalence, risk factors for FIP), pathogenesis, immunity, clinical signs, diagnosis, treatment, and control. The guidelines are based on published research and expert consensus.
**Key Results:** FCoV infection is highly prevalent in multi-cat households (antibody prevalence 67% in purebred cats in one Japanese study). FIP occurs in less than 10% of infected cats, disproportionately affecting pedigree cats (1.3% vs 0.35% in mixed breeds) and those under 2 years old (39% of 222 cases were under 1 year in one study). Effusions are present in 78% of cases. Diagnosis: effusion analysis shows low A:G ratio (<0.4 strongly suggests FIP), elevated AGP (>1.5 mg/mL), and positive FCoV RT-PCR (72-100% sensitivity). Definitive diagnosis requires histopathology with immunostaining for FCoV antigen. The spike gene mutations M1058L and S1060A are associated with FIP but not fully specific. Treatment: Oral GS-441524 at 10-12 mg/kg/day for 84 days shows 81-100% cure rates in field studies (e.g., 18/18 cats in a prospective study). Remdesivir (prodrug) and molnupiravir also show efficacy. Without antivirals, median survival is 8-38 days. Supportive care (fluids, appetite stimulants) is important. Prognostic factors: lower bilirubin, better appetite/activity, higher temperature predict survival.
**Clinical Implications:** The availability of effective antivirals (GS-441524, remdesivir, molnupiravir) has transformed FIP from a uniformly fatal disease to a treatable one. Veterinarians should consider FIP in young cats with fever, effusions, and hyperglobulinaemia, and use effusion analysis or tissue PCR/immunostaining for diagnosis. Early diagnosis and treatment with antivirals (often 84-day courses) can achieve cure rates >80%. Supportive care during treatment is essential. Control in multi-cat households relies on hygiene, reducing stress, and possibly segregating FCoV shedders. Vaccination is not routinely recommended due to questionable efficacy.