Upper Respiratory Infections in Cats: What's Behind the Sneezing and How to Help

If you've ever lived with cats — especially kittens, rescues, or shelter cats — you've almost certainly experienced the sneezing, runny eyes, and nasal discharge of an upper respiratory infection. Feline upper respiratory infection (URI) is one of the most common conditions in cats, and while most cases are mild and self-limiting, others can become serious, particularly in very young, very old, or immunocompromised cats.

Understanding what causes URI, how to tell when it's serious, and how to support an affected cat makes a real difference in outcomes — and helps you avoid both under-treating genuinely sick cats and panicking over mild sneezes.

The Pathogens Behind Feline URI

The vast majority of feline upper respiratory infections are caused by just a handful of pathogens:

Feline Herpesvirus-1 (FHV-1): Also called feline viral rhinotracheitis (FVR), this is the most common URI pathogen and the most clinically important. FHV-1 causes the most severe acute disease — high fever, profuse nasal and ocular discharge, corneal ulcers, and significant lethargy. After initial infection, the virus establishes lifelong latency in the trigeminal nerve ganglia. Stress (moving, new pets, illness) triggers viral reactivation and recurrence. This is why some cats seem to get "colds" repeatedly — the virus is already inside them and reactivates, rather than re-infection occurring each time.

Feline Calicivirus (FCV): The second major URI pathogen. Calicivirus tends to cause milder respiratory signs but is associated with oral ulcers (ulcers on the tongue, hard palate, and lips) that can make eating extremely painful. FCV exists in dozens of strains with variable virulence. Highly virulent systemic strains (VS-FCV) are rare but cause severe, life-threatening disease with skin ulceration and hemorrhage. Standard calicivirus strains are common and generally self-limiting.

Bordetella bronchiseptica: A bacterial pathogen (the same genus as the dog kennel cough agent) that can cause primary respiratory disease in cats, particularly in shelter, cattery, and multi-cat environments. More commonly a secondary invader complicating viral URI.

Chlamydophila felis: A bacterial pathogen causing primarily conjunctivitis with mild respiratory signs. Particularly common in kittens and multi-cat households. Responds well to doxycycline.

Mycoplasma species: Secondary invaders that worsen and prolong URI, particularly associated with conjunctivitis and chronic disease.

In practice, many cats have mixed infections with multiple pathogens simultaneously, especially cats from high-density environments like shelters.

Clinical Signs: What URI Looks Like

The classic URI presentation includes some combination of:

Sneezing: The hallmark sign. Can range from occasional to explosive, repetitive sneezing fits that produce discharge.

Nasal discharge: Initially clear and watery. As secondary bacterial infection develops (which happens quickly in many cats), discharge becomes thick, yellow-green, and may crust around the nostrils.

Ocular discharge: Conjunctivitis (inflammation of the tissue lining the eyelids) produces watery to mucopurulent eye discharge. Squinting and light sensitivity suggest corneal involvement — always a concern with FHV-1.

Fever: Present in many acute cases. Cats with significant fevers (above 104°F / 40°C) are typically lethargic and anorexic.

Nasal congestion: The most clinically significant symptom in terms of welfare impact. Cats are obligate nasal breathers and rely on smell to identify food. A profoundly congested cat cannot smell food and will stop eating entirely — even when hungry. This "smell strike" is a major contributor to the downward spiral in severely affected cats.

Oral ulcers: Hallmark of calicivirus. Cats with oral ulcers are often hypersalivating, drooling, or pawing at their mouth. They will refuse hard food.

Lethargy: Variable. Mild cases may just be a little quieter than normal; severe cases involve cats that won't move, won't eat, and barely lift their heads.

When URI Becomes an Emergency

URI in a healthy adult cat is almost never life-threatening. The serious cases involve:

Kittens under 8 weeks old: Very young kittens deteriorate alarmingly fast. They have minimal nutritional reserves, immature immune systems, and can go from lethargic to dying within 12–24 hours of not eating. Any kitten with URI signs warrants immediate veterinary evaluation.

Cats that have stopped eating for 48+ hours: Cats are uniquely vulnerable to hepatic lipidosis (fatty liver disease) when anorexic. A cat that hasn't eaten in 48–72 hours needs veterinary intervention — tube feeding may be necessary.

Open-mouth breathing or respiratory distress: Cats with upper respiratory congestion should not need to breathe through their mouths at rest. Open-mouth breathing indicates either lower respiratory involvement (pneumonia) or such severe upper airway obstruction that the cat cannot get enough air through the nose. This is an emergency.

Corneal ulcers: Any cat with a painful, squinting, cloudy, or swollen eye needs same-day evaluation. FHV-1 corneal ulcers can progress rapidly and potentially threaten vision.

Treatment Approaches

Mild URI in healthy adult cats: Supportive care at home. Humidification (bathroom steam, cool-mist humidifier), gentle cleaning of nasal and ocular discharge with warm saline, and encouragement of eating (warming food, offering strong-smelling canned food) are appropriate measures. Most resolve in 7–14 days.

Antibiotics: Antibiotics don't treat the viral causes of URI (FHV-1, FCV), but they target secondary bacterial infections and pathogens like Chlamydophila. Doxycycline is the most commonly used antibiotic for URI in cats due to its broad-spectrum activity against Chlamydophila, Mycoplasma, and Bordetella. Azithromycin is an alternative. Antibiotics are indicated when there is purulent discharge, fever, or signs of secondary bacterial disease.

L-lysine: L-lysine (an amino acid) was historically recommended to suppress FHV-1 replication. Recent systematic reviews have found insufficient evidence for its efficacy in cats, and it is no longer recommended by current consensus guidelines.

Famciclovir: The antiviral drug famciclovir is active against FHV-1 and is used in moderate to severe herpesvirus cases or in cats with recurrent, debilitating disease. It requires veterinary prescription and appropriate dosing for cats.

Intranasal saline: Gentle saline drops help loosen nasal secretions and provide some relief from congestion. Pediatric saline nasal drops can be used — one drop per nostril, gently administered.

Appetite stimulants and assisted feeding: Mirtazapine (an appetite stimulant) or cyproheptadine can help cats resume eating. Esophagostomy tubes may be placed for cats with prolonged anorexia.

Prevention: Vaccination and Environment

Core feline vaccines include protection against both FHV-1 and FCV (combined in the FVRCP vaccine). Vaccination does not prevent infection but significantly reduces disease severity and duration. Vaccinated cats who contract URI typically have much milder clinical illness and recover faster.

In multi-cat households and shelters, good ventilation, isolation of new cats for 2–3 weeks, and prompt treatment of affected individuals are the most effective environmental controls. Because FHV-1 is lifelong once established, some degree of recurrent URI in previously exposed cats is likely regardless of management — the goal is minimizing the frequency and severity of outbreaks through stress reduction and good husbandry.