Feline Infectious Peritonitis

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VIRUSES
CORONAVIRUSES



Antigenicity

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

Hosts

  • Domestic and wild cats

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

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

Diagnosis

  • 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

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