Feline upper respiratory infection (URI) — often called “cat flu” — is one of the most common infectious diseases in cats, particularly in shelters, catteries, and multi-cat households. URIs are caused by a combination of viral and bacterial pathogens that affect the nose, throat, sinuses, and eyes. While most cases resolve with supportive care, severe infections can be life-threatening in kittens, elderly cats, and immunocompromised individuals.

Overview

Feline URI is typically caused by one or more of the following pathogens, often in combination:

  • Feline herpesvirus-1 (FHV-1) — Accounts for approximately 40-45% of feline URIs. Causes a latent (lifelong) infection with potential for recurrent flare-ups during stress or immunosuppression.
  • Feline calicivirus (FCV) — Responsible for approximately 25-30% of URIs. Multiple strains exist, some causing oral ulceration and rarely a severe systemic form (virulent systemic FCV).
  • Chlamydophila felis (Chlamydia) — A bacterial pathogen primarily causing conjunctivitis.
  • Bordetella bronchiseptica — A bacterium that can cause primary respiratory disease, particularly in kittens.
  • Mycoplasma species — Opportunistic bacteria that often complicate viral infections.

Transmission occurs through direct contact with infected cats, aerosolized droplets from sneezing, and contaminated fomites (food bowls, bedding, human hands). The incubation period is typically 2-10 days.

Causes & Risk Factors

  • Kittens and unvaccinated cats are most susceptible
  • Shelter and cattery environments with high population density
  • Stress (boarding, moving, new household members) can trigger herpesvirus reactivation
  • Immunosuppression from FIV, FeLV, or other concurrent illness
  • Flat-faced (brachycephalic) breeds may experience more severe disease due to narrowed nasal passages

Symptoms

  • Sneezing (often frequent and paroxysmal)
  • Nasal discharge (clear to mucopurulent)
  • Ocular discharge and conjunctivitis (red, swollen eyes)
  • Corneal ulcers (particularly with herpesvirus)
  • Oral ulcers on the tongue, palate, or lips (particularly with calicivirus)
  • Fever, lethargy, and reduced appetite
  • Congestion and open-mouth breathing
  • Drooling (with oral ulcers)
  • Dehydration, especially in kittens who stop eating

Kittens under 8 weeks with severe URI are at high risk for dehydration and secondary pneumonia. Seek veterinary care promptly if a kitten stops eating, becomes lethargic, or has difficulty breathing.

Diagnosis

Diagnosis is often made clinically based on characteristic signs. Specific testing may include:

  • Physical examination — Assessment of respiratory sounds, oral cavity, and eyes
  • PCR testing — Nasal or conjunctival swabs can identify FHV-1, FCV, Chlamydophila, Mycoplasma, and Bordetella
  • Fluorescein staining — To detect corneal ulcers associated with herpesvirus
  • Chest radiographs — If lower respiratory involvement (pneumonia) is suspected
  • Culture and sensitivity — For cases with severe or recurrent bacterial involvement

Treatment & Medications

Most feline URIs are managed with supportive care, with specific medications added based on severity and causative agent:

  • Supportive care — Keeping nasal passages clear (saline nebulization, steam therapy), maintaining hydration, and encouraging eating with warmed, aromatic foods. Appetite stimulants such as mirtazapine may be used.
  • Doxycycline — The antibiotic of choice for suspected Chlamydophila or Mycoplasma infection and to prevent secondary bacterial complications. Typically given for 3-4 weeks. Must be followed with water or food to prevent esophageal stricture in cats.
  • Amoxicillin-Clavulanate (Clavamox) — A broad-spectrum alternative antibiotic for secondary bacterial infection.
  • Famciclovir — An antiviral medication effective against feline herpesvirus-1. Used in moderate to severe herpesvirus infections, particularly with corneal involvement.
  • L-Lysine — Historically supplemented to reduce herpesvirus replication, though recent evidence questions its efficacy. Still commonly used but should not replace proven antiviral therapy.
  • Ophthalmic medications — Erythromycin or oxytetracycline ophthalmic ointment for conjunctivitis; antiviral eye drops (cidofovir) for herpetic keratitis.
  • Fluid therapy — Subcutaneous or intravenous fluids for dehydrated cats.
  • Nasal decongestants — Pediatric saline drops to help with congestion. Phenylephrine-based decongestants should only be used under veterinary direction.

Prognosis

  • Most adult cats with uncomplicated URI recover within 7-14 days with supportive care
  • Kittens and immunocompromised cats may have prolonged or complicated courses
  • FHV-1 establishes lifelong latent infection; approximately 80% of recovered cats become carriers, and some experience intermittent recurrences
  • Chronic rhinosinusitis can develop in cats with severe or repeated infections, causing lifelong nasal congestion and discharge
  • Vaccination significantly reduces severity of disease but does not completely prevent infection

Frequently Asked Questions

Can my cat give their URI to me or my dog? Feline herpesvirus and calicivirus do not infect humans or dogs. Bordetella bronchiseptica can rarely affect dogs and immunocompromised humans, but cross-species transmission is uncommon. Practice basic hygiene (hand washing) when caring for infected cats.

My cat keeps getting URIs. Why? Recurrent URIs in cats are most commonly caused by reactivation of latent feline herpesvirus during periods of stress. Minimizing stress, maintaining a stable environment, and discussing long-term antiviral therapy with your veterinarian can help reduce flare-ups.

Should I keep my sneezing cat away from my other cats? Yes. Isolate the affected cat if possible, use separate food bowls and litter boxes, and wash your hands and change clothing after handling the sick cat. Viral shedding is highest during active symptoms.

Are vaccines effective against URI? Core feline vaccines (FVRCP) protect against herpesvirus and calicivirus. They do not prevent infection entirely but significantly reduce the severity and duration of illness. Annual or triennial boosters are recommended based on your veterinarian’s protocol.

This information is for educational purposes only and does not replace professional veterinary advice. Always consult your veterinarian for diagnosis and treatment of your cat’s specific condition.