Feline Infectious Peritonitis

Also known as:

FIP

Description

A progressive disease of the cat caused by feline coronavirus. Occurs in 5-10% of cats infected with Feline Enteric Coronavirus (FECoV)which is characterised by a variety of clinical signs, including weight loss, fever and vasculitis. Two forms of the disease exist the wet form and the dry form.

Signalment

Domestic and wild cats

Diagnosis

FIP should be suspected 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

Pathogenesis

• 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

History and 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:

• Uveitis
• Hydrocephalus
• Neurological symptoms, such as ataxia or seizures
• Chronic diarrhoea

Epidemiology

• 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

Granulomatous Enteritis

• Caused by feline

Pathology

Gross

• 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.

Histological

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

Hepatitis

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

Control

• 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

References

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