Feline Infectious Peritonitis

Also known as:

FIP

Description

A progressive disease of the cat caused by feline coronavirus. The disease is characterised by a variety of clinical signs, including weight loss, fever and vasculitis. FIP arises from a mutation of Feline Enteric Coronavirus (FECoV) in 5-10% of chronically infected cats and not directly from cat to cat. Two forms of the disease exist the wet or exudative form and the dry or non exudative 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 for diagnosis:

• High FECoV Antibody 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

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 then gains the ability to replicate in monocytes and macrophages.

Failure of the immune system to clear antibody-antigen complexes leads to immune-mediated disease and deposited complexes cause inflammation and exudation. This leads to characteristic oedema as fibrin-rich serum escapes to intercellular spaces. Pyogranulomas reactions 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

FECoV may cause mild respiratory symptoms and diarrhoea but is often asymptomatic.

Signs of FIP include, chronic weight loss, anorexia, pyrexia and depression. Fluid in the abdomen, thorax or pericardium are symptomatic of wet FIP. Granulomatous change in the organs are symptomatic of dry FIP. FIP has also been documented to cause: Uveitis, hydrocephalus, neurological symptoms, such as ataxia or seizures and chronic diarrhoea.

Pathology

Wet form

Widespread miliary, white, pinhead granulomas and fibrin deposition, particularly in the serosa of the small intestine and large intestine High-protein exudates can be found in peritoneal cavity.

Dry form

Larger, grey granulomatous masses causing thickening of the wall of the small and large intestine.

Histological

Multifocal pyogranulomas on serosa and throughout gut wall. Infiltration by mononuclear cells, lymphocytes, plasma cells, macrophages and a fewneutrophils. Necrosis and vasculitis will also be seen.

Treatment

Almost invariably fatal. Immunomodulators including interferon have been used to control the virus and Dr. Diane Addie at Glasgow vet school has found that cats do respond to this form of treatment. Immunosuppressive drugs such as prednisolone or cyclophosphamide may slow disease progression. Cats should recieve widespread antibiotics and suppotive therapy.

Control

Conventional vaccination is counterproductive as antibody worsens infection however a non-systemic vaccine (Primucell) is available outside the UK. Replication confined to nasal mucosa, providing local immunity and cell-mediated immunity and it cannot protect cats already infected with FECoV. Antibody tests are available to certify FECoV-free cat houses.

Prognosis

Very poor.

References

Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2) Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.[[