FIP

Question 1

Etiology & pathophysiology
- type of virus, where found
- signs
- transmission
- replication
- how does FIP arise?? key to pathogenesis?

Answer 1

• Feline coronavirus (FCoV) ubiquitous in Felidae family. Especially in multi-cat settings. FCoVs are enveloped RNA viruses with ‘spikes’ on the surface.
• Cats generally show no clinical signs with FCoV (occ. mild diarrhoea +/- vomiting). Transmission via faecal-oral route.
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• FCoV will naturally replicate in enterocytes. Mutation may take place in spike protein of virus. Mutated virus taken up by macrophages and distributed through body. A second mutation generally also needed for efficient replication of virus in macrophages.
• Replication of mutated FCoV in macrophages is key to pathogenesis of FIP.
• Mutated virus in macrophages initiates body’s immune- mediated response to virus.
• That immune-mediated response leads to formation of granulomatous lesions in CNS, eyes & body organs. Also causes vasculitis which leads to fluid accumulation in body cavities.
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  Terminology: Non mutated harmless biotype = feline enteric coronavirus (FECV). Mutated virulent biotype = feline infections peritonitis virus (FIPV). Both are FCoVs…one mutated, the other is not.

Question 2

Risk factors & transmission

Answer 2

• Any cat can develop FIP. Peak age 3 months – 2 years, but any age cat can be affected. No (consistent) sex predilection.
• More common in pure bred cats. In environments that already has a high load of FCoV. Appears to affect certain family lineages of cats.
• Multi-cat dwelling (e.g. catteries, shelters, boarding), stress (e.g. rehoming, elective sx, vaccinations), immunosuppression (e.g. FIV, FeLV, infection), mingling of different age groups, frequent intro of cats, overcrowding are all known risk factors.
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• FCoV transmitted mainly via faecal-oral route. FCoV readily inactivated by heat & most disinfectants/detergents outside the cat.
• Ability of FCoV to mutate & replicate inside the individual cat will determine if FCoV remains harmless or develops into FIP.
• Cat to cat transmission of FIP /the mutated virus does not occur under natural settings.

Question 3

Diagnosis
- radiograph
- U/S
- biochem
- CBC / bloodwork

Answer 3

• Thoracic & abdominal radiographs: pleural effusion & ascites
• Serum biochem: normal or +/- hyperglobulinemia+ elevated bilirubin often with normal liver enzymes
• Abdominal ultrasound: abdo masses, lymphadenopathy, ascites
• CBC: normal or +/- stress leukogram (lymphopenia, neutrophilia w/out left shift), mild non-regen anemia of chronic inflammation
• Serum protein electrophoresis (hyperproteinemia) will show a polyclonal gammopathy
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• Evidence of fluid in a body cavity? Collect it!

Question 4

Diagnosis - fluid analysis

Answer 4

• fluid analysis (ascites or pleural fluid): clear, viscous, straw coloured fluid. Analysis will usually show a non-septic exudate with high protein and low cell count
• can submit effusion sample for Rivalta test: Sn 91% and Sp 65%
  > If (-), FIP not likely, if (+), FIP still likely
  > high sensitivity means few false negatives

Question 5

Diagnosis - first best test? second best test? test more specific for mutation?

Answer 5

• First best test: histology and immunostaining (IHC) staining of FCoV antigen in macrophages of tissue with lesions. Needs histopathology of tissue sample from laparotomy, laparoscopy, or post-mortem
• Second best test: Positive FCoV RNA RT-PCR on fluids (effusions, CSF) or FNAs (lymph nodes, liver). Not useful for blood.
• Mutation PCR test (if available): PCR detects specific mutations in spike protein that leads to FIP. Fpr effusion fluid only, not useful for blood.

Question 6

Treatment & management considerations

Answer 6

• Antiviral drugs: promising results in trials with cats but availability an issue. Watch this space…GS-441524 & remdesivir both showing very promising results…
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• Immunosuppressive drugs: cats with effusion, dexamethasone intraperitoneally or intrathoracically after effusion is removed, prednisolone orally when cat is stable
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• Immunomodulating drugs: limited control studies…nothing to write home about just yet
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  Supportive care: e.g. topical steroids (Maxidex) for uveitis, broad spectrum antibiotics to control secondary bacterial infections
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  FIP vaccine?: lack of efficacy in the few field trials that have been conducted. Generally not recommended.