FIP

Question 1

what is the pathogenesis of FIP?
(Transmission, what it does, the types)

Answer 1

• Cats are infected with feline enteric coronavirus (single stranded, enveloped RNA virus) usually via the faecal-oral route such as grooming paws contaminated with faeces from litter tray or fomites.
• Initially the virus replicates in enterocytes.
• It can then spread to the mesenteric lymph nodes followed by viraemia in the blood.
• In some cats (5-10% of those infected with feline enteric coronavirus) it mutates to a virulent form that is able to efficiently replicate in monocytes and macrophages. - a key event in FIP pathogenesis with the immune response mounted by the cat in response to FCoV infection.
• When FIP develops there is a reaction between replicating FCoV in monocytes and blood vessel walls, allowing extravasation of the monocytes, where they differentiate into macrophages.
• Breakdown of the endothelial tight junctions allows plasma to leak out of the vessels - effusion in the abdominal, thoracic and/or pericardial cavities ( ‘wet’ FIP).
• In more chronic forms of FIP fewer blood vessels are affected, but larger perivascular pyogranulomas result in affected organs such as the liver, kidneys, intestine, lungs, brain and/or eyes (‘dry’ FIP).

Question 2

Name the 2 pathotypes (or biotypes) of feline coronavirus and describe how they are different in terms of degree of illness they cause

Answer 2

1) Feline enteric coronavirus (FECV) – causes no clinical signs to mild, self-limiting diarrhoea
2) Feline infectious peritonitis virus (FIPV) – causes a serious systemic disease with a high mortality rate known as feline infectious peritonitis (FIP)

Question 3

What are the 3 main factors that influence how FIP disease manifests and develops in a cat?

Answer 3

1) Viral factors (strain and dose)
2) The cat’s immune response
3) Genetic factors

Question 4

FIP is often called a ‘sporadic’ infectious disease. Explain why this might be.

Answer 4

The pattern of disease development depends not only on transmission of the infectious agent between cats (usually indirectly via fomites), but also on whether a mutation occurs within an individual cat and on the cat’s immune response to the virus. Only 5-10% of cats infected with feline enteric coronavirus go on to develop FIP. So while the infectious agent feline enteric coronavirus may be found in multi-cat environments, it only sporadically causes the disease feline infectious peritonitis.

Question 5

What are the common signalment and history features of cats with FIP?

Answer 5

Less than 2 years of age, multi-cat environment, pedigree cat, male,
in kittens - recent stress such as early weaning, rehoming or neutering or a combination of stressors

Question 6

Give 2 reasons why FIP is more common in pedigree cats.

Answer 6

1) Increased susceptibility due to some as yet unknown genetic factor in the breed
2) The majority of pedigree cat breeding facilities are multi-cat environments

Question 7

What are the common clinical signs in cats with FIP?

Answer 7

Clinical signs depend on the distribution of vasculitis (which can lead to effusions) and/or granulomatous lesions (which can lead to masses) in the body. Although effusive and non-effusive forms of FIP are often described, there is much overlap between these forms. Clinical signs of FIP can change over time.

• 80% have an effusion, can be in multiple locations
  ◦ abdominal = most common, approximately 80%, ‘classic’ presentation of FIP
  ◦ thoracic = approximately 20%
  ◦ cardiac = occasionally
• Non-specific clinical signs are common: lethargy, anorexia and weight loss or stunted growth, fever (non-responsive to treatment), +/- jaundice, +/- lymphadenomegaly

Question 8

If a cat had neurological involvement what would the clinical signs be?
If a cat had ocular involvement what would the clinical signs be?

Answer 8

Neuro:
Ataxia, seizures, nystagmus, hyperaesthesia, changes in mentation

ocular:
Uveitis (uni-or bi-lateral), keratic precipitates, hypopyon (WBCs in anterior chamber), hyphaema (blood in anterior chamber), retinitis, iris colour change

Question 9

What approach would you use to diagnose FIP?

Answer 9

Diagnosis is not based on the result of one test, but on a combination of features of the signalment, history, clinical signs and laboratory tests.

If fluid is present, sample it and characterise it biochemically (appearance, protein and cell content) and cytologically.
Test fluid for FCoV antigen by reverse transcriptase PCR or immunocytochemistry.
If no fluid, look for abnormal organs/tissues to sample.

Ultimate confirmation is via histopathology and immunohistochemistry which often ends up being done post-mortem.
Rapid deterioration and no response to treatment also inform presumptive diagnosis.

Question 10

What test result makes it very likely that a cat has FIP?
What test is considered confirmatory for FIP?

Answer 10

Detection of high loads of feline coronavirus antigen with quantitative reverse transcriptase PCR (RT-qPCR) on samples of effusion, from FNA of an abnormal organ/tissue, CSF or aqueous humour
OR
Positive immunocytochemistry for feline coronavirus antigen on samples of effusion or from FNA of an abnormal organ/tissue

conformation:
Histopathological changes consistent with FIP and positive immunohistochemistry for feline coronavirus antigen