What is Feline Herpesvirus-1?

Feline Herpesvirus-1 (FHV-1) is one of the most common causes of upper respiratory infections in cats, often referred to as "cat flu." It belongs to the Herpesviridae family and, like other herpesviruses, establishes a lifelong latent infection — meaning that once a cat is infected, the virus remains dormant in the body and can reactivate during periods of stress, illness, or immunosuppression.

FHV-1 is estimated to be responsible for approximately 50% of all feline upper respiratory infections, making it one of the most significant infectious diseases in cats worldwide.

Symptoms

Acute FHV-1 infection typically develops 2–5 days after exposure:

  • Frequent sneezing
  • Nasal congestion and discharge (clear to purulent)
  • Watery or mucoid eye discharge
  • Conjunctivitis (red, swollen eyes)
  • Corneal ulcers (in severe cases)
  • Fever
  • Loss of appetite
  • Lethargy
  • Drooling (from oral ulcers in some cases)

Most healthy adult cats recover within 2–3 weeks, but kittens, elderly cats, and immunocompromised cats can develop severe complications including pneumonia.

The Carrier State

One of the most challenging aspects of FHV-1 is the carrier state. After initial infection, approximately 80% of recovered cats become latent carriers. The virus retreats to nerve ganglia (typically the trigeminal ganglion) and can reactivate periodically, especially during:

  • Stressful events (boarding, moving, new pets, veterinary visits)
  • Concurrent illness
  • Corticosteroid treatment
  • Pregnancy and lactation

During reactivation, cats shed the virus and can infect others, often without showing obvious symptoms themselves.

Transmission

FHV-1 spreads through:

  • Direct contact with infected cats (nasal and ocular secretions)
  • Contaminated objects (food bowls, bedding, hands of caregivers)
  • Aerosol droplets from sneezing (within about 1–2 meters)

The virus is fragile outside the host and typically survives less than 18 hours in the environment. Standard disinfectants are effective against it.

Why Vaccination Matters

The FHV-1 vaccine is a core vaccine included in the FVRCP combination. While vaccination does not completely prevent infection, it significantly reduces the severity and duration of symptoms. Vaccinated cats that do become infected tend to have milder illness and shed less virus.

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 previously unvaccinated
  • Boosters: Every 1–3 years

Management of Chronic FHV-1

For cats with recurrent flare-ups:

  • L-lysine supplementation (though evidence is debated)
  • Antiviral eye drops (idoxuridine, cidofovir) for ocular flare-ups
  • Stress reduction strategies
  • Immune support through good nutrition
  • Famciclovir (oral antiviral) in severe cases

Prevention Beyond Vaccination

  • Minimize stress in multi-cat environments
  • Isolate new cats for 2 weeks before introducing them
  • Maintain good hygiene and ventilation in shelters and catteries
  • Keep cats in good overall health to support immune function
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