Feline Infectious Peritonitis

Also known as FIP

FIP occurs in 5-10% of cats infected with Feline Enteric Coronavirus (FECoV), which is quite common
It is therefore antigenically indistinguishable from FECoV

FECoV may cause mild respiratory symptoms and diarrhoea but is often asymptomatic
Weeks, months or years may intervene between localized primary FECoV infection and FIP development
FECoV replicates in the gut, but FIP spreads systemically in the circulation
FIP gains ability to replicate in monocytes and macrophages
Almost invariably fatal
Failure of the immune system to clear antibody-antigen complexes leads to immune-mediated disease
- Deposited complexes cause inflammation and exudation
- This leads to characteristic oedema as fibrin-rich serum escapes to intercellular spaces
- Pyogranulomas can develop in major organs as a result of the immune response and the body's failure to clear away excess neutrophils
Cats previously exposed to coronavirus (and therefore with circulating antibody) may be at greater risk as they are more susceptible to taking up virus into mononuclear cells
Cats making a biased Th-1 response are more likely to evade infection, whereas cats making a balanced response are at moderate risk and cats making a biased Th-2 response are at greater risk, as the virus is best tackled by cell mediation and not antibody
Cats compromised by immunosuppression (either iatrogenic or disease-related) are at a greater risk of developing FIP

Clinical signs:

Chronic weight loss
Anorexia
Pyrexia
Depression
Fluid in the abdomen, thorax or pericardium symptomatic of wet, or exudative FIP
Granulomatous change in the organs symptomatic of dry, or nonexudative FIP

Can be shown to cause:

FECoV is endemic worldwide, with the majority of cats showing a subclinical seroconversion
Orofecal, aerosol, and contact transmission
Particular concern for catteries and homes with multiple cats
FIP arises from a mutation of FECoV (in 5-10% of chronically infected cats) and not directly from cat to cat

Clinical signs
- FIP should be suspect in all cases of chronic weight loss or recurrent fever unresponsive to antibiotics, particularly in multiple cat situations
Simple serology is impossible as most cats will have antibody to FECoV
However, 4 indicators can be used to cross reference:
- High FECoV Ab titres
- Low albumin:globulin ratio in plasma/ascites (globulin levels rise in FIP)
- High levels of glycoprotein alpha 1-acid glycoprotein (AGP)
- Low white cell counts
FIP antigen detection by immunofluorescence in macrophages gives a definite positive diagnosis
PM: look for characteristic lesions in vascular immune complex disease and lymphoid infiltration

Conventional vaccination is counterproductive as antibody worsens infection
A non-systemic vaccine (Primucell) is available outside the UK
- Temperature-sensitive mutant
- Replication confined to nasal mucosa, providing local immunity and cell-mediated immunity
- Cannot protect cats already infected with FECoV
- Kittens must be isolated until old enough to vaccinate at 16 weeks
Antibody tests are available to certify "FECoV-free" cat houses

Granulomatous Enteritis

Wet form
- Widespread miliary, white, pinhead granulomas and fibrin deposition.
  - Including the serosa of the intestine.
- Also high-protein exudates in peritoneal cavity.
Dry form
- Larger, grey granulomatous masses causing thickening of the wall of small and large intestine.

Multifocal pyogranulomas on serosa and throughout gut wall.
- Infiltration by mononuclear cells.
  - Lymphocytes, plasma cells, macrophages.
- Fewer neutrophils.
Necrosis.
Vasculitis.

coronavirus
causes pyogranulomatous lesions on the surface of many organs including the liver