Cat Upper Respiratory Infections (URI): What Causes Them, How Long They Last, and When to Worry

You adopted a kitten from a shelter and three days later she's sneezing constantly with gooey eyes and a stuffy nose. This is so common it has an informal name: "shelter sniffles." The stress of shelter life, combined with exposure to many other cats, creates ideal conditions for respiratory viruses to spread and activate. Most cases look scary and resolve uneventfully. Some require intervention. Knowing which is which matters.

FHV-1 vs. Calicivirus: The Two Main Culprits

Feline herpesvirus-1 causes classic URI signs: sneezing, nasal discharge (initially clear, becoming yellow-green if secondary bacterial infection develops), and eye discharge (conjunctivitis, sometimes with corneal ulcers). Once infected, cats carry FHV-1 for life -- it becomes latent in nerve ganglia and reactivates during stress (moving, new pets, illness, anesthesia), causing recurrent flares. An estimated 80% of cats exposed to FHV-1 become lifelong carriers.

Feline calicivirus causes similar signs but is distinguished by oral ulcers -- small, painful lesions on the tongue, gums, or roof of the mouth -- and sometimes causes limping due to joint inflammation (lameness syndrome). FCV also mutates rapidly; more virulent strains (virulent systemic FCV, VS-FCV) can cause severe, potentially fatal systemic disease with facial and limb edema, but these outbreaks are uncommon. Multiple FCV strains exist; vaccination protects against severe disease but doesn't prevent infection with all strains.

When It's Just a Cold vs. When You Need a Vet

Most adult cats with mild URI (sneezing, clear nasal discharge, mild eye discharge, eating and drinking normally) can be managed at home with supportive care: keep the cat warm, use a humidifier near their sleeping area, gently wipe discharge from nose and eyes with a warm damp cloth, ensure they're eating (cats with stuffed noses may not smell food -- warming food enhances the aroma). Anorexia for more than 24-48 hours, thick green/yellow discharge, difficulty breathing, lethargy that won't resolve, or eye cloudiness or squinting warrants veterinary evaluation.

Veterinary care can include: lysine supplementation (evidence is mixed but commonly used for FHV-1 management), famciclovir (antiviral effective against FHV-1, especially for severe cases or corneal involvement), topical ophthalmic antivirals for corneal ulcers, and antibiotics for secondary bacterial infection. Antibiotics don't treat the viral infection itself -- they treat Bordetella, Mycoplasma, or Chlamydophila that frequently complicate primary viral URIs.

Prevention: Vaccination and Stress Reduction

The FVRCP (feline viral rhinotracheitis, calicivirus, panleukopenia) core vaccine protects against FHV-1 and FCV. Vaccination doesn't prevent infection but significantly reduces severity and duration of illness. Kittens receive a series starting at 6-8 weeks, every 3-4 weeks until 16 weeks old, then a booster at 1 year, then every 1-3 years depending on risk. FHV-1 reactivation in carrier cats can be reduced by minimizing stress, maintaining stable routines, and addressing stress with environmental modification or anti-anxiety treatments.

In multi-cat homes, an ill cat should be isolated to prevent spread. FHV-1 and FCV spread via respiratory secretions (sneezing, eye and nose discharge) and are relatively fragile outside the host -- most common disinfectants inactivate them. Good hygiene (handwashing between cats, separate food bowls, daily litter box cleaning) meaningfully reduces transmission.