Upper Respiratory Infections in Kittens: Causes, Symptoms, and Treatment

If you've ever brought home a shelter kitten with watery eyes and a runny nose within a few days, you've likely seen an upper respiratory infection, often just called "cat flu." It's extremely common in kittens, especially ones from shelters or large litters, and while it's rarely dangerous in an otherwise healthy kitten, it can turn serious fast in a very young or already weak one.

What actually causes it

According to VCA Animal Hospitals, two viruses, feline herpesvirus type-1 (also called feline viral rhinotracheitis, or FVR) and feline calicivirus (FCV), are responsible for roughly 90% of feline upper respiratory infections. Bacteria like Bordetella bronchiseptica and Chlamydophila felis cause a smaller share of cases, sometimes as a secondary infection layered on top of a viral one. Kittens are hit harder than adult cats mainly because their immune systems are still immature, especially in the gap after maternal antibodies fade but before their own vaccine series is complete.

Symptoms

• Sneezing, often frequent and sometimes with visible spray
• Nasal congestion and discharge, clear at first and often thickening as it progresses
• Watery or goopy eye discharge, sometimes with the eyes partly stuck shut
• Mouth or tongue ulcers, more specific to herpesvirus and calicivirus
• Reduced appetite and lethargy, partly because a stuffy nose makes food harder to smell
• Fever and swollen lymph nodes in more involved cases

Loss of smell from nasal congestion is a bigger deal in cats than it sounds. Cats rely heavily on smell to want to eat, so a kitten that stops eating during a bad URI needs attention quickly, not just patience.

How it spreads

Transmission happens through direct contact, shared bowls, bedding, or even a person's hands moving between cats without washing. The two main viruses don't survive equally long outside the body: FVR breaks down in under 18 hours on surfaces, while FCV can persist for up to 10 days, which is part of why calicivirus spreads so efficiently through shelters and multi-cat households. Diluted bleach reliably kills both viruses, but some bleach-free "pet-safe" disinfectants don't reliably eliminate calicivirus, worth knowing if you're disinfecting after an outbreak.

Treatment

There's no direct cure for the viral versions, so treatment is mostly supportive: keeping the kitten eating, keeping nasal passages clear, and preventing a secondary bacterial infection from taking hold. That typically looks like:

• Warm, strong-smelling canned food to encourage eating despite a blocked nose
• Gently wiping away eye and nose discharge to keep passages clear
• Time in a steamy bathroom to help loosen nasal congestion
• Broad-spectrum antibiotics if a secondary bacterial infection is suspected, particularly in kittens
• Antiviral medication like famciclovir for more severe herpesvirus cases
• Hospitalization and fluids for kittens too congested or unwell to eat or drink on their own

Most cases clear up in about 7 to 10 days. Vaccination doesn't fully prevent infection but does make the illness milder and shorter when it happens, which is one of several reasons the kitten vaccine series matters even for indoor-only cats.

When it's an emergency

Call a vet the same day, not the next morning, if a kitten stops eating or drinking entirely, becomes noticeably lethargic, or shows any labored or open-mouth breathing. A kitten that can't smell its food and stops eating for more than a day is at real risk of a separate, dangerous complication (a liver condition from not eating, not just the URI itself), so appetite loss is taken more seriously in kittens than the sneezing and discharge are on their own.

Frequently asked questions

Can my other cats catch this?
Yes, it spreads easily between cats, especially in the first days of illness. Keeping a sick kitten's bowls, bedding, and litter box separate, and washing your hands between handling cats, cuts down on spread within a household.

Will my kitten always be a carrier after this?
Often, yes, particularly with herpesvirus. Many cats that recover become latent carriers who can shed the virus again during stressful periods, without necessarily showing symptoms every time. This is normal and not usually something that requires ongoing treatment.

Is this the same as feline distemper?
No. Feline distemper (panleukopenia) is a different, more dangerous virus that mainly affects the digestive and immune systems, not the same illness as a typical upper respiratory infection, even though both are covered by the same core kitten vaccine.

Sources

• VCA Animal Hospitals, "Feline Upper Respiratory Infection"
• PetMD, "Upper Respiratory Infection in Cats: What Pet Parents Should Know"

This article is for general information and isn't a substitute for advice from your own veterinarian. A kitten that stops eating or shows labored breathing needs same-day veterinary attention.