Cat Flu: Upper Respiratory Infection Treatment Guide

"Cat flu" is the common name for feline upper respiratory infection. It's usually caused by feline herpesvirus (FHV-1) or calicivirus (FCV). Treatment is mostly supportive, but knowing what to do can speed recovery and save you an unnecessary vet visit.

What Causes Cat Flu?

Feline Herpesvirus (FHV-1): The most common cause. Infects 80%+ of cats. Causes lifelong latent infection — the virus hides in nerve tissue and reactivates under stress. Symptoms: sneezing, conjunctivitis, eye discharge, nasal discharge, fever.

Feline Calicivirus (FCV): Second most common. Causes oral ulcers, sneezing, nasal discharge, and sometimes limping syndrome or a more severe systemic form. Cats usually clear this virus over weeks to months.

These viruses are species-specific — you cannot catch cat flu from your cat.

Treatment at Home (Mild Cases)

Humidity Is Your Best Friend

Run a humidifier or bring your cat into a steamy bathroom for 10-15 minutes, 3 times daily. This loosens nasal mucus and makes breathing easier. This single intervention often makes the biggest difference.

Keep Them Eating

Cats won't eat what they can't smell. Warm wet food slightly to enhance aroma. Offer strong-smelling foods: tuna, sardines, warmed chicken baby food (no onion/garlic). A cat that stops eating for 48+ hours is at risk for hepatic lipidosis.

Clean Eyes and Nose

Gently wipe discharge with a warm, damp cloth. Use a separate cloth for each eye if conjunctivitis is present. Do this 2-3 times daily.

Reduce Stress

Keep the cat in a quiet, warm room. Minimize handling. Keep other pets separate to reduce stress.

When to See the Vet

Go to the Vet

Thick yellow/green discharge (possible secondary bacterial infection), not eating for more than 24 hours, open-mouth breathing (emergency), kitten under 6 months, cat with FIV or FeLV, eye ulcers visible, symptoms not improving after 5-7 days.

Veterinary Treatment

Antibiotics

Not always needed — cat flu is primarily viral. However, secondary bacterial infections are common. Doxycycline is the first-line choice — it also covers Chlamydia and Mycoplasma. Give with food and water to prevent esophageal irritation.

Antivirals

Famciclovir is an oral antiviral for severe or recurrent herpesvirus infections. Effective but expensive and requires 2-3 times daily dosing. Ophthalmic antivirals (cidofovir, idoxuridine) for herpesvirus eye disease.

Appetite Stimulants

Mirtazapine (transdermal gel applied to the ear) stimulates appetite when the cat won't eat due to congestion.

Hospitalization

For severe cases: IV fluids, nutritional support via feeding tube, nebulization with saline or medication, oxygen therapy.

L-Lysine — Does It Work?

Previous recommendation was to give L-lysine to suppress herpesvirus replication. Recent evidence shows it's probably NOT effective. Most veterinary organizations no longer recommend it.

Prevention

FVRCP vaccination (core vaccine for all cats). Reduce stress. Keep multi-cat households clean and well-ventilated. Quarantine new cats for 2 weeks.