What actually causes a cat's upper respiratory infection?

Most feline upper respiratory infections trace back to one of two viruses: feline herpesvirus-1 (FHV-1) or feline calicivirus (FCV), which together account for roughly 80-90% of cases, with bacteria like Bordetella bronchiseptica and Chlamydia felis responsible for most of the rest (Cornell Feline Health Center, 2023). These pathogens infect the tissue lining the nose, throat, and sinuses rather than the lower lungs, which is why the illness is called an upper, not lower, respiratory disease.

Transmission happens through direct contact with nasal or eye discharge, shared food bowls, litter boxes, and grooming tools, and airborne droplets from sneezing at close range (ASPCA, 2023). Shelters, rescues, and breeding catteries see disproportionately high rates simply because dozens of cats share airspace and surfaces, and stress from transport or a new environment suppresses immune function enough to let a dormant virus reactivate.

What are the first signs a cat parent usually notices?

Sneezing is typically the first thing owners catch, sometimes accompanied by a clear or colored nasal discharge and watery eyes that progress to thicker discharge within a day or two. Cornell's feline health specialists note that congestion severe enough to block the nasal passages can cause a cat to breathe through its mouth or lose its sense of smell, which frequently leads to a drop in appetite because food no longer smells appealing (Cornell Feline Health Center, 2023).

Some cats also develop oral ulcers, especially with calicivirus, along with excessive drooling or reluctance to eat hard kibble. A fever in the 103-105°F range is common during the acute phase, and kittens or cats with weaker immune systems may seem lethargic on top of the respiratory symptoms rather than just having a runny nose (Merck Veterinary Manual, 2024).

Why do some cats get much sicker than others?

Severity depends heavily on which pathogen is involved and the cat's prior immune exposure. Feline herpesvirus tends to hit young, unvaccinated kittens hardest and can cause corneal ulcers that threaten vision if untreated, while calicivirus is more often linked to painful mouth ulcers and, in rare virulent strains, a systemic illness with high fever and swelling (Cornell Feline Health Center, 2023).

Cats that were never vaccinated, cats under a year old, and cats with concurrent illnesses like feline immunodeficiency virus (FIV) or feline leukemia virus (FeLV) generally experience more severe or prolonged disease. The AVMA notes that once a cat is infected with FHV-1, the virus establishes lifelong latency in nerve tissue and can reactivate during stressful periods throughout the cat's life, producing recurring flare-ups even years later (American Veterinary Medical Association, n.d.).

How do veterinarians confirm it's an upper respiratory infection and not something else?

Diagnosis usually starts with a physical exam and history, since the sneezing-plus-eye-discharge pattern combined with recent shelter or multi-cat exposure is highly characteristic. Vets check for oral ulcers, assess breathing effort, and look at the cornea with fluorescein stain to rule out an ulcer if the eyes are heavily affected (Merck Veterinary Manual, 2024).

For cats that aren't improving on standard supportive care, are severely ill, or live in a multi-cat facility where identifying the exact pathogen matters for management, veterinarians may run a PCR panel on nasal, oral, or conjunctival swabs to distinguish FHV-1, FCV, Chlamydia felis, and Mycoplasma species. Chest radiographs are reserved for cats showing signs the infection has moved into the lower airway, such as labored breathing or a persistent cough (Cornell Feline Health Center, 2023).

What treatments actually help a cat recover faster?

Most upper respiratory infections in otherwise healthy adult cats resolve within 7-10 days with supportive care alone, since antivirals don't cure the underlying viral infection but rather help the immune system get ahead of it (Cornell Feline Health Center, 2023). Veterinarians commonly prescribe the oral antiviral famciclovir for confirmed or suspected herpesvirus cases, particularly when eye involvement is significant, because it's better absorbed and generally better tolerated than older topical antivirals.

If a secondary bacterial infection is suspected — thick yellow-green discharge, worsening after a few days, or a persistent fever — vets often add a broad-spectrum antibiotic such as doxycycline, which also covers Chlamydia felis and Mycoplasma (Merck Veterinary Manual, 2024). L-lysine supplementation, once a routine recommendation, has fallen out of favor after controlled studies failed to show a meaningful benefit, so current guidance leans more heavily on antivirals, antibiotics when indicated, and nursing care.

What can owners do at home to help a sneezing cat feel better?

Gently wiping crusted discharge from the nose and eyes with a warm, damp cloth several times a day keeps the airway clearer and prevents the cat from having to breathe through a blocked nose. Running a humidifier or letting the cat sit in a steamy bathroom for 10-15 minutes can loosen congestion and make breathing more comfortable, a technique recommended by feline health specialists for cats with stuffy noses (Cornell Feline Health Center, 2023).

Because a blocked nose kills a cat's appetite, warming wet food slightly to release more aroma, or offering strong-smelling options like tuna in water, often coaxes a reluctant cat to eat. Keeping a sick cat separated from other household cats for the contagious period, disinfecting shared bowls and litter boxes, and reducing environmental stress all support faster recovery and limit spread (ASPCA, 2023).

Can this happen again, and is there a way to prevent it?

Because FHV-1 hides permanently in nerve tissue after the first infection, many cats become intermittent lifelong carriers who shed the virus again during stressful events like boarding, a new pet in the home, or illness, even without ever showing symptoms in between (American Veterinary Medical Association, n.d.). This is why some cats seem to get a cold every time they're stressed.

Core vaccination against FHV-1 and FCV, given as part of the standard kitten series and boosted per AAHA feline vaccination guidelines, significantly reduces the severity of disease even though it doesn't guarantee complete prevention of infection (American Animal Hospital Association, 2020). Reducing crowding, quarantining new cats for 1-2 weeks before introduction, and minimizing stress in multi-cat households are the most practical long-term prevention strategies for shelters and homes alike.