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PCR Quantitive)
In cat populations, quantitative PCR allows for the formation of groups of animals (animals shedding many or few pathogens or pathogen-free animals). This way, infection pressure is reduced and rehabilitation may be possible. A cat is considered free if PCR was negative in 3 tests at weekly intervals and each time pooled faecal samples from 3 days were examined. Quantification can also be requested following a qualitative PCR.
Feline Coronavirus (FCoV) and Feline Infectious Peritonitis (FIP)
Feline coronaviruses (FCoV) exist in two distinct pathotypes:
- Enteric FCoV: Weakly virulent strains that infect intestinal epithelial cells, typically causing mild diarrhoea.
- Mutated FCoV: Variants with spike protein mutations that replicate in macrophages and lead to feline infectious peritonitis (FIP), often fatal.
Transmission and Risk Factors
Cats in multi-cat households are more likely to shed the virus than those in single-cat homes. Higher infection pressure increases the chance of mutation from enteric FCoV to the pathogenic FIP-causing form. Studies estimate that 1–12% of FCoV-infected cats develop FIP.
Clinical Manifestations
FIP was previously classified into wet (exudative) and dry (granulomatous) forms. It is now believed that all cases eventually progress to the wet form. Clinical signs include:
- Pyogranulomatous inflammation of serosal surfaces and organs (especially liver, spleen, lungs)
- Severe polyserositis with viscous effusions (ascites, pleural/thoracic)
- Anaemia, icterus, emaciation, and persistent high fever
- Neurological symptoms and uveitis due to immune complex deposition
Diagnostic Indicators
A positive antibody titre indicates prior exposure to FCoV, common in adult cats. In healthy animals, high titres do not predict FIP development. Enteric FCoV shedders can be identified via PCR from faecal samples, while mutated FCoV is typically not excreted.
In FIP cases, antibody titres may be low or negative due to immune complex binding. Diagnostic support includes:
- Serum protein electrophoresis
- Albumin/globulin (A/G) ratio below 0.6
- Elevated gamma globulin fraction
- PCR testing from effusions or tissue samples
- Rivalta test or cytology for confirmation
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