Lecture 8 -- Feline Upper Respiratory Tract Infection - 'Cat Flu'

These flashcards cover key points from the lecture on Feline Upper Respiratory Tract Infection, its causes, clinical manifestations, diagnosis, treatment, and prevention.

What are the main viral pathogens associated with cat flu?

• Feline herpesvirus

• Feline calicivirus

• Bordetella bronchiseptica

• Chlamydophila

What type of virus is Feline herpesvirus (FeHV-1)?

• Double stranded DNA enveloped virus

  • Do NOT tend to mutate (Only one serotype at this moment)

  • Susceptible in environment as it can be dissolved in disinfectant

What is a key biological feature of herpesviruses?

• Establish latent infection

• Stress can reactivate the virus = Recurrence of disease

Can feline herpesvirus infect other species? or Is feline herpesvirus is zoonotic?

No

• Herpesviruses are species-specific = Only infect cats

What are the major clinical signs of FeHV-1 infection in cats?

Severe upper respiratory disease:

• Pyrexia (fever)

• Lethargy

• Sneezing

• Dyspnoea or coughing

• Nasal discharge

• Hypersalivation

Eye disease:

• Corneal ulceration

• Keratitis = Inflammation of the cornea

• Conjunctivitis

How is ocular disease caused by FeHV-1 treated?

Topical antiviral nucleoside analogues

• Trifluridine

• Acyclovir

What long-term complication can occur after FeHV-1 infection?

Turbinate damage → Chronic rhinitis → More prone to respiratory infections

What is the pathogenesis of FeHV-1 infection?

1. Oronasal infection

2. Incubation period (Short 2–6 days)

   • Because it is a acute respiratory disease

3. Multiplication of virus in oral/ respiratory tissue

4. Clinical signs resolve within 10–20 days

What type of virus is feline calicivirus (FCV)?

• Single stranded RNA non-enveloped virus

  • Mutate easily (Large number of different strains)

  • Survive in environment longer because it is difficult to control by disinfectant

What are the common clinical signs of feline calicivirus infection?

• Pyrexia (fever)

• Sneezing

• Nasal discharge

• Pneumonia

• Conjunctivitis

• Oral ulceration

• Chronic stomatitis

• Lameness

• Virulent systemic disease

P.S. Highlighted ones are the most classic signs

What is the “lameness syndrome” associated with FCV?

• Shifting lameness between limbs

  • The cat may be lame on the front right, then shift to the other leg later on

  • Resolve without treatment

  • No strong evidence of permanent joint damage

• Usually affects young cats

• Associated with pyrexia and respiratory signs

What is chronic stomatitis?

• Severe profound inflammation at the back of the oral cavity

• Proliferative, tumour-like → Super painful

• Difficult to treat → Cats with stomatitis often get put down

Is chronic stomatitis directly linked to Feline calicivirus?

No

• “Associated with” but NOT 100% “caused by” Feline calicivirus

• Since people tried to inject FCV in a healthy animal, they only got respiratory symptoms but not chronic stomatitis

What is virulent systemic disease in FCV?

• Usually caused by virulent 劇毒的 FCV strain

• Severe haemorrhagic syndrome, characterised by:

  • Facial and paw oedema

  • Skin necrosis and ulceration

  • Haemorrhage (nose or faeces)

  • Respiratory disease

  • Pyrexia

  • Jaundice

Can FCV vaccination protect cat against virulent systemic disease?

NO

How are FeHV-1 and FCV diagnosed?

• Clinical signs

• PCR or RT-PCR: Detects viral DNA (FeHV-1) or RNA (FCV)

• Virus isolation (Banned due to COVID)

  • Swab from oropharynx → Culture the virus in lab (may take up to 2 weeks)

• Serology

• Histopathology

  • Observe for issue changes if biopsied

Among the diagnostic tests for FeHV-1 and FCV, which is the most commonly used in practice?

PCR, together with clinical sign

How are FeHV-1 and FCV transmitted?

1. Direct contact: via infectious discharges e.g. saliva, nasal or ocular secretion

2. Indirect contact: via contaminated personnel, formites and environment

3. Droplet transmission: Sneezed macrodroplets (~1m)

4. Aerosol transmission (Less important)

   • Cats have small tidal volume, they don’t tend to create an infectious aerosol when they breath

What does it mean for a cat to be a carrier of a virus?

A cat that recovered from acute infection, appears clinically normal, but still harbors and may shed the virus.

How does FeHV-1 behave in carrier cats?

• A cat is infected with FeHV-1 and recovered → Become clinically normal + The animal is not shedding the virus → Virus becomes latent in the nervous system after acute infection

• Stress (pregnancy, steroids, illness) can reactivate virus

• Reactivation may or may not cause clinical signs BUT the animal can shed the virus during this time, potentially infecting other cats

How does FCV behave in carrier cats?

Even the infected cats have recovered and clinically normal, they still continue shedding the virus for 75days (half life ~75days)

Why can cats remain persistently infected with FCV?

• FCV is a single-stranded RNA virus → High mutation rate →The virus evolves rapidly inside the cat, constantly changing its surface proteins → The cat’s immune system cannot fully neutralize all viral variants = Persistently infected

What type of organism is Chlamydophila felis?

Gram-negative, obligate intracellular parasite

How is Chlamydophila felis transmitted?

By close contact between cat

What are the clinical signs of Chlamydophila felis?

• Mostly does NOT cause respiratory disease

• Unilateral conjunctivitis → And become bilateral later on

• Chemosis = Swelling of third eyelid and conjunctiva

How is Chlamydophila felis diagnosed?

PCR 

How is Chlamydophila felis treated?

Systemic doxycycline

Is there vaccination worked against Chlamydophila felis?

Yes

• BUT NOT recommended every cat gets it

• Might use it for cats in rescue shelter