What is Feline Calicivirus?

Feline Calicivirus (FCV) is a highly contagious virus and one of the primary causes of upper respiratory infections and oral disease in cats. It is an RNA virus with many different strains, which makes it particularly challenging — the virus mutates readily, and different strains can cause varying degrees of illness, from mild sneezing to life-threatening systemic disease.

FCV is found worldwide and is especially prevalent in shelters, catteries, and multi-cat households where it can spread rapidly.

Symptoms

FCV infection can range from mild to severe, depending on the strain:

Common Signs

  • Sneezing and nasal discharge
  • Eye discharge and conjunctivitis
  • Oral ulcers (tongue, gums, palate, nose)
  • Drooling due to mouth pain
  • Loss of appetite
  • Mild fever
  • Lethargy

Limping Syndrome

Some FCV strains cause a transient lameness (limping calicivirus), typically in kittens. Joints become inflamed and painful, but the condition usually resolves within a few days.

Virulent Systemic FCV (VS-FCV)

Rare but extremely dangerous, VS-FCV strains cause a severe systemic infection with:

  • High fever
  • Facial and limb swelling (edema)
  • Skin ulcers
  • Jaundice (liver involvement)
  • Bleeding disorders
  • Multi-organ failure

The mortality rate for VS-FCV can reach 60% even with aggressive treatment.

Transmission

FCV spreads through:

  • Direct contact with infected cats
  • Airborne droplets from sneezing (up to 1–2 meters)
  • Contaminated objects (bowls, cages, clothing, hands)
  • Carrier cats shedding the virus without symptoms

The virus can survive in the environment for up to a month under favorable conditions, longer than FHV-1.

The Carrier State

After recovery from acute infection, many cats become chronic carriers, continuously shedding the virus from the oral cavity for weeks, months, or even years. Some carriers shed virus for life. This makes FCV particularly difficult to control in multi-cat settings.

Why Vaccination Matters

The FCV vaccine is a core vaccine, part of the FVRCP combination. Due to the diversity of FCV strains, the vaccine may not prevent infection with every strain, but it significantly reduces the severity of disease. Some modern vaccines include multiple FCV strains for broader protection.

Vaccination Schedule

  • Kittens: Part of FVRCP starting at 6–8 weeks, boosters every 3–4 weeks until 16 weeks
  • Adult cats: Two doses 3–4 weeks apart if unvaccinated
  • Boosters: Every 1–3 years

Treatment

There is no specific antiviral treatment for FCV. Supportive care includes:

  • Fluid therapy for dehydration
  • Soft, palatable food (warmed to enhance aroma for cats with congestion)
  • Pain management for oral ulcers
  • Antibiotics if secondary bacterial infections develop
  • Nutritional support via syringe feeding or feeding tubes if necessary

Most healthy cats recover within 1–3 weeks with appropriate care.

Prevention

  • Vaccination is the primary tool
  • Strict hygiene in multi-cat environments
  • Isolation of symptomatic cats
  • Disinfection with accelerated hydrogen peroxide or diluted bleach
  • Quarantine new arrivals for at least 2 weeks
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