Lecture 3 -- Feline Coronaviruses and Feline Infectious Peritonitis

These flashcards cover key concepts about Feline coronaviruses, particularly FIP, as outlined in the lecture notes.

What are the two types of Feline coronavirus biotypes?

• Feline enteric coronavirus (FECoV)

  • Mild or subclinical

  • Only infect enterocytes

• Feline infectious peritonitis virus (FIPV)

  • Mutated form of FECoV

  • Infect enterocytes and macrophages → Case systemic disease

What virus FECoV and FIP caused by?

An feline coronavirus, alpha coronavirus

• NO direct link to human COVID-19, which is caused by beta coronavirus

What are key structural features of feline coronaviruses?

• Obligate intracellular parasites: Require a host cell to replicate

• Enveloped RNA virus:

  • RNA genome: Prone to mutations

    • RNA polymerase has no proofreading

    • Unlike retrovirues, it does not make provirus (DNA copy) in the host genome

  • Lipid envelope

    • Susceptible to soap and alcohol-based disinfectants → Fragile and short-lived in the environment

  • Surface proteins

    • Give the virus a crown like appearance (hence the name coronavirus)

What are the key differences between retroviruses and coronaviruses, given that both are RNA viruses?

Retroviruses:

• Single-stranded RNA

• Use reverse transcriptase to covert their RNA genome into DNA (= Provirus)

• Envelope with glycoproteins for entering the host cell (BUT not crown-like)

Coronaviruses:

• Single-stranded RNA

• RNA genome remains RNA

  • Use RNA polymerase for replication

  • NO Provirus (DNA)

• Large spike glycoproteins, forming a crown-like appearance

Which groups of cats are at highest risk for FIP?

• Young kittens (immature immune system)

• Cats kept in groups e.g. rescue shelters

How is FCoV transmitted?

• Mainly via faeco-oral route

  • Shed in faeces and saliva → Infected by ingestion of virus

• Trans-placental spread is possible

• NOT respiratory transmission like COVID-19

Can FIP itself be transmitted between cats?

No FIP is not directly contagious.

Controlling FIP requires preventing FeCoV infection, not FIP itself.

Are FIP or FECoV zoonotic?

No

What is the pathogenesis of FCoV (How does FIP develop from FCoV) ?

1. Cats infected with FECoV shed the virus in their faeces

2. Other cats get infected via faeco-oral route → High prevalence of endemic FECoV → Mutation of FECoV to FIP

3. Antibody binds to FIP antigen → Opsonisation → Enhance uptake by macrophages

4. Instead of acting as a phagocyte, macrophages are the main host of FIP = Macrophages facilitate FIV replication and systemic spread

5. FIV enter the systemic circulation

6. Outcome depends on immune response:

   • Good cell-mediated immunity: Recovery

   • Partial cell-mediated immunity: Dry FIP

   • Poor cell-mediated immunity: Wet FIP

What are the major clinical signs of FIP?

1. Wet FIP

   • Virus antigen antibody complement complexes deposit in walls of small blood vessels → Vasculitis → Makes blood vessels leaky → Fluid accumulates in body cavities

   • Symptoms depends on which body cavity is affected

     • Dyspnea

     • Ascites

     • Muffling of heart sounds

   • Other clinical signs:

     • Fluctuating fever

     • Inappetence + Weight loss

     • Jaundice

2. Dry FIP

• Immune-mediated lesions in organs

• Signs dependant on organ involved

  • Eyes: Ocular changes e.g. iritis, uveitis

  • Abdominal organs: Jaundice

  • CNS: Paresis (Muscle weakness), Ataxia (Inability to control muscle movement), behavioural changes

What is the gold standard for definitive FIP diagnosis?

• Histopathology of granulomatous lesions associated with vasculitis.

• Obtained via exploratory laparotomy or tissue biopsy

What is the stepwise approach to diagnosing FIP in cats?

Step 1: Clinical signs and history evaluation

• Young cats?

• In muticat environments e.g. shelter?

• Consistent signs e.g. fluctuating fever, jaundice, ocular signs

Step 2: Blood test (CBC, biochemistry) + Rule out other diseases (Retrovirus e.g. FeLV and FIV)

• CBC:

  • Mild anemia

  • Neutrophila

  • Lymphopenia

• Biochemistry:

  • Hyperproteinaemia (because of increased globulin)

  • Low albumin to globulin ratio

  • Increased liver enzymes

  • Increase bilirubin

  • Azotemia

Step 3: Supportive diagnostic tests

• Wet FIP:

  • Imaging: X-ray or ultrasound to detect effusions or organ changes

  • Aspiration: High protein, low cellularity of FIP fluid

• Dry FIP

  • Histopathology: Granulomatous lesions with vasculitis (Gold standard)

  • Aspiration: Even dry FIP can have small amount of fluid accumulation

Step 4: Confirmatory testing

• RT-PCR to detect FCoV virus

What are typical haematology and blood biochemistry findings in FIP?

• Neutrophilia

• Lymphopaenia

• Mild non-regenerative anaemia

• Hyperproteinaemia due to raised globulins (antibodies)

• Decreased albumin/globulin ratio (because of increased globulin)

• Other parameter changes depending on the organ that is affected (FIP may affect kidney and liver): 

  • ↑ liver enzymes (ALT in dogs; GLDH in large animal), bilirubin, urea

What are characteristic features of FIP fluid?

• Viscous, straw-colored

• High protein content (IgG > IgA)

• Froths 奶泡 when shaken

• Forms clots on standing because of high protein

What is Rivalta’s test?

• Put a drop of FIP fluid into dilute vinegar, it forms a stable clot → That clot then gradually sinks through that fluid

P.S. Other fluid would just dissolve into solution

How does immunofluorescence (IF) testing for FCoV/FIP work?

Test for ANTIBODY

1. Lab cells are deliberately infected with FCoV = Contain viral antigens

2. Cat serum is added 

   • If the cat is infected with FCoV = Antibodies to FCoV are present, they bind to the viral antigens in the lab cells

3. Fluorescein-labeled anti-cat antibody is added → Binds the cat antibodies → Fluorescence is visualised under a microscope.

4. To quantify antibody levels, the serum is serially diluted → Fluorescence disappears when the antibodies are too few to bind enough viral antigen to produce a visible signal

   • Low antibody titres (Fluorescence disappears at lower dilutions)  = FECoV exposure

   • High antibody titres (Fluorescence may still exist even at high dilutions) = FIP exposure

What are the uses of immunofluorescence (IF) testing in FIP, apart from quantifying antibodies?

• FCoV antigen inside macrophages can be stained and visualised under a microscope, supporting the diagnosis of FIP

P.S. Helps support diagnosis but not definitive.

Can feline coronavirus serology e.g. IF, ELISA or PCR distinguish FIP or FECoV?

No

• Antibody positivity can only indicates they were infected with alphacoronavirus

• BUT does not distinguish whether the cat has FECoV or FIP

Is there an effective treatment for FIP?

• Historically, no effective treatment

• Interferon and steroids:

  • There was a study suggested they might be useful in treating FIP 

  • BUT discredited because at that time, there was no way of diagnosing FIP → Other researchers believed that the ones that survived in that study probably didn’t have FIP

• Remdesivir / GS-441524:

  • Nucleoside analogue

  • Developed after COVOID

  • Cure rates 80–100% if treated ≥12 week

  • Available in Australia and the UK

  • Expensive

Is there a FIP vaccine?

• Licensed in the USA, not in the UK

• Highly controversial due to antibody dependant enhancement = Vaccination can worsen the disease

75-100% of cats from breeding households seropositive. How can FIP be controlled in endemically infected households?

• Prevent kitten infection:

  • Isolate queens 1–2 weeks prepartum

  • Early weaning of kittens

  • Confirm kittens are seronegative from 10 weeks

• Hygiene: adequate litter trays, cleaning, reducing viral load

• Population management:

  • Reduce numbers of cats and kittens