Upper respiratory infections — commonly called cat flu or cat colds — are among the most common conditions seen in cats, particularly in young cats, shelter cats, and multi-cat households. While most cases are mild and self-limiting, URIs can become serious — particularly in kittens, senior cats, and immunocompromised animals — and some cats develop chronic or recurrent disease that requires long-term management.
If your cat has developed sneezing, nasal discharge, eye discharge, or appears unwell alongside respiratory signs, contact Walker Lake Veterinary Centre at (587) 786-6771 for an assessment.
Upper respiratory infections spread very easily between cats. If you have multiple cats and one develops URI signs, assume all have been exposed and monitor all cats closely. Isolate the affected cat from others where possible, particularly from kittens and senior cats who are most vulnerable.
What Is a Cat Upper Respiratory Infection?
A cat upper respiratory infection (URI) is an infection of the nose, sinuses, throat, and sometimes eyes — the upper portions of the respiratory tract. Unlike lower respiratory infections — which affect the trachea, bronchi, and lungs — URIs primarily cause nasal and ocular signs rather than breathing difficulties, though severe or complicated cases can extend to the lower respiratory tract.
URIs in cats are caused by a relatively small number of specific pathogens — different from the wide variety of organisms causing human colds — and the two most significant are responsible for the vast majority of cases.
Causes of Upper Respiratory Infection in Cats
Feline Herpesvirus — FHV-1
The most common cause of feline URI, responsible for approximately 50% of cases. FHV-1 causes an acute respiratory and ocular illness characterised by sneezing, nasal discharge, and conjunctivitis. The infection is typically severe in its initial presentation.
The defining characteristic of FHV-1 infection is latency — once a cat is infected, the virus establishes a lifelong latent infection in nerve tissue. The cat appears to recover but the virus is never fully eliminated. During periods of stress — rehoming, illness, other infections, surgical procedures — the latent virus reactivates and the cat sheds virus and may develop clinical signs again. This explains why some cats have recurrent bouts of respiratory and ocular disease throughout their lives.
Feline Calicivirus — FCV
The second most common cause of feline URI. FCV causes sneezing, nasal discharge, and oral ulceration — painful ulcers on the tongue, hard palate, and nasal planum — which is relatively specific to calicivirus compared to herpesvirus infection.
Unlike herpesvirus, calicivirus does not establish lifelong latency in most cases — many cats clear the infection completely. However, some cats become persistent virus carriers, continuing to shed virus and potentially infecting other cats without showing ongoing signs themselves. Carrier cats are a significant source of infection in multi-cat environments.
A distinct, highly virulent strain of calicivirus — virulent systemic calicivirus (VS-FCV) — causes severe systemic disease including facial oedema, limb oedema, skin ulceration, and high mortality rates. VS-FCV outbreaks have been reported in shelter populations and multi-cat environments. This strain is rare but important to recognise.
Bordetella bronchiseptica
The same bacterium that causes kennel cough in dogs can cause respiratory disease in cats — particularly in stressed, young, or immunocompromised individuals. Bordetella causes acute sneezing, nasal discharge, and sometimes pneumonia in severe cases. It is more commonly encountered in multi-species households and shelter environments.
Chlamydia felis
An obligate intracellular bacterial pathogen primarily causing conjunctivitis in cats — often severe, persistent, and affecting both eyes. Chlamydial conjunctivitis causes chemosis (conjunctival swelling), marked ocular discharge, and blepharospasm (squinting). Chlamydia typically causes milder respiratory signs than herpesvirus or calicivirus but ocular involvement can be significant. It is zoonotic — it can cause mild conjunctivitis in humans who handle infected cats, though transmission is uncommon.
Mycoplasma
Mycoplasma species are commonly isolated from cats with URI — both as primary pathogens and as secondary opportunistic organisms complicating viral infection. They contribute to conjunctivitis, rhinitis, and sometimes lower respiratory disease.
Secondary Bacterial Infections
Viral URIs damage the respiratory epithelium and suppress local immunity, allowing opportunistic bacteria — Staphylococcus, Streptococcus, Pasteurella, and others — to establish secondary infections. Secondary bacterial infections transform mild, self-limiting viral disease into more severe, prolonged illness and are responsible for much of the purulent discharge, fever, and systemic illness seen in complicated URI cases.
How URI Spreads Between Cats
URI pathogens spread efficiently through:
- Direct contact — nose-to-nose greeting, mutual grooming
- Respiratory droplets — sneezing releases large numbers of virus particles into the surrounding environment. Herpesvirus particles can travel up to 1.2 metres during a sneeze
- Fomites — shared food and water bowls, bedding, grooming equipment, and hands of handlers can carry virus particles between cats
- Indirect contact — herpesvirus survives on surfaces for up to 24 hours in moist conditions
Cats are most infectious during active illness — when sneezing and producing discharge — but herpesvirus-infected cats may shed virus during stress-induced reactivation without obvious signs.
Which Cats Are Most at Risk?
Any cat can develop URI but certain groups are at higher risk of severe disease:
- Kittens — immature immune systems and higher likelihood of unvaccinated status
- Unvaccinated cats of any age
- Senior cats — declining immune function
- Cats in shelters, boarding facilities, or multi-cat households — higher pathogen exposure
- Immunocompromised cats — FIV-positive, FeLV-positive, or on immunosuppressive medication
- Cats with chronic herpesvirus infection — prone to stress-induced reactivation
- Flat-faced breeds — Persians, Himalayans, Exotics — abnormal nasal anatomy impairs normal mucus clearance
Signs and Symptoms of URI in Cats
Common Signs
- Sneezing — often the first and most obvious sign. May be mild and occasional or severe and paroxysmal
- Nasal discharge — initially clear and watery, progressing to thick, yellow or green and mucopurulent as secondary bacterial infection develops
- Ocular discharge — watery to mucopurulent discharge from one or both eyes
- Conjunctivitis — redness and swelling of the conjunctival tissue
- Reduced appetite — both from systemic illness and from loss of the sense of smell that cats rely on to stimulate eating
- Lethargy — variable, from mild to severe depending on the organism and the cat’s immune status
- Fever — particularly with bacterial secondary infection
Signs Specific to Individual Pathogens
Herpesvirus-Specific Signs
- Unilateral or bilateral conjunctivitis — often severe
- Corneal ulceration — dendritic (branching) corneal ulcers are pathognomonic for herpesvirus in cats
- Facial dermatitis — ulcerative skin lesions around the nose and mouth in some cats
- Chronic rhinitis — recurrent or persistent nasal discharge from chronic sinonasal damage
Calicivirus-Specific Signs
- Oral ulceration — painful ulcers on the tongue, hard palate, and nasal planum. The cat may drool, be reluctant to eat, and show oral discomfort
- Polyarthritis — lameness from joint inflammation occurs in some calicivirus infections, particularly in kittens
- Mild respiratory signs relative to the degree of oral ulceration
Chlamydia-Specific Signs
- Severe, persistent conjunctivitis — often the dominant and sometimes the only sign
- Chemosis — marked conjunctival swelling that may be dramatic in appearance
- Typically milder respiratory signs
Signs of Complicated or Severe URI
- Open-mouth breathing or obvious respiratory distress — always a veterinary emergency in cats
- Complete anorexia lasting more than 24 hours — significant risk of hepatic lipidosis
- Severe lethargy — unable to rise or maintain sternal position
- Marked dehydration — skin tenting, dry mucous membranes
- Persistent high fever above 40°C
- Corneal ulceration with progressive deepening — risk of perforation
- Neurological signs — herpesvirus can rarely affect the nervous system
⚠️ A cat with URI that stops eating completely requires same-day veterinary assessment. Anorexia in a sick cat risks hepatic lipidosis within 48 hours. Open-mouth breathing in a cat is always a respiratory emergency — call (587) 786-6771 immediately.
Diagnosing URI
Clinical Diagnosis
The majority of URI cases are diagnosed clinically — the combination of sneezing, nasal and ocular discharge, and other signs in a cat with appropriate exposure history is usually sufficient for a working diagnosis and initial treatment.
PCR Testing
When identifying the specific pathogen matters — for severe cases, shelter outbreak investigation, or research — PCR testing on oropharyngeal or nasal swabs identifies herpesvirus, calicivirus, Chlamydia, Bordetella, and Mycoplasma. PCR is highly sensitive and specific.
Fluorescein Stain
A fluorescein dye applied to the cornea highlights corneal ulcers — essential in any cat with ocular signs to identify or rule out herpesvirus-associated corneal ulceration. This is quick, painless, and provides important information that affects treatment choice.
Complete Assessment
For severely affected cats, complete assessment includes:
- Physical examination including temperature, hydration status, and respiratory assessment
- Fluorescein stain of both eyes
- Chest auscultation — to detect lower respiratory involvement
- Bloodwork — in severely ill cats to assess organ function and inflammation
- Imaging — chest X-rays if pneumonia is suspected
Treating URI in Cats
Treatment depends on the severity of illness, the likely pathogen, and the individual cat’s health status.
Supportive Care
Nutritional Support
Maintaining food intake is a priority — anorexia in a sick cat risks hepatic lipidosis. Strategies include:
- Warming food gently — to enhance aroma and stimulate appetite in a nose-blocked cat
- Offering highly palatable foods — cooked chicken, tuna, strong-smelling wet foods
- Hand feeding if necessary
- Anti-nausea medication — maropitant (Cerenia) reduces nausea that suppresses appetite
- Appetite stimulants — mirtazapine provides effective appetite stimulation in cats
- Nasal clearing — gently wiping nasal discharge to improve the cat’s ability to smell food
- In severe cases — hospitalisation with assisted feeding via nasogastric or oesophagostomy tube
Hydration
Adequate hydration supports recovery and prevents complications. Options include:
- Encouraging water intake — multiple water stations, water fountain, broth added to water
- Subcutaneous fluids — administered at the clinic or at home by trained owners
- Intravenous fluids — for significantly dehydrated or severely ill cats requiring hospitalisation
Nasal Clearing
Accumulated nasal discharge impairs breathing and reduces the ability to smell food — further reducing appetite. Gently wiping discharge from around the nostrils with a warm, damp cloth several times daily is simple but impactful supportive care. Steam from a hot shower allowed to fill a bathroom with the cat present for 10 to 15 minutes can help loosen thick nasal discharge.
Antibiotic Treatment
Antibiotics do not treat viral infections — herpesvirus and calicivirus are not susceptible to antibiotics. However, most URI cases involve secondary bacterial infection that does require antibiotic treatment.
Appropriate antibiotic choices include:
- Doxycycline — the drug of choice for Chlamydia felis and Mycoplasma, and effective against most secondary bacterial pathogens. Given once daily for 4 weeks for Chlamydia
- Amoxicillin-clavulanate — broad-spectrum coverage for secondary bacterial infection
- Azithromycin — used as an alternative to doxycycline in some situations
Antiviral Treatment for Herpesvirus
Specific antiviral medications can reduce herpesvirus replication and speed recovery:
Famciclovir
An oral antiviral medication that reduces herpesvirus replication. It is the most effective and best-studied antiviral for FHV-1 in cats. It is particularly useful for severe acute herpesvirus infection and for managing chronic recurrent disease in carrier cats. Given two to three times daily for 2 to 3 weeks during active disease.
Topical Antiviral Eye Drops
Idoxuridine, trifluridine, and cidofovir eye drops target herpesvirus in ocular tissue — particularly useful for herpesvirus-associated corneal ulceration. Applied to the affected eye several times daily.
Managing Herpesvirus-Associated Eye Disease
Ocular herpesvirus causes significant and sometimes vision-threatening disease. Management includes:
- Fluorescein staining to identify and monitor corneal ulcers
- Topical antiviral eye drops — applied 4 to 5 times daily
- Topical antibiotics — to prevent secondary bacterial infection of ulcers
- Avoid topical steroids — absolutely contraindicated with corneal ulcers as they prevent healing and allow rapid progression
- E-collar — to prevent self-trauma to the eye
- Regular reassessment — corneal ulcers can progress rapidly without appropriate treatment
Managing Chronic and Recurrent Herpesvirus Disease
Cats with frequent stress-induced reactivation of herpesvirus benefit from long-term management strategies:
L-Lysine Supplementation
L-lysine is an amino acid that competes with arginine — an amino acid essential for herpesvirus replication. Supplementation with L-lysine has historically been recommended for cats with chronic herpesvirus disease. However, more recent research has questioned its efficacy — some studies show no benefit and a few suggest possible harm at high doses. Discuss L-lysine supplementation with your veterinarian.
Stress Reduction
Minimising stress reduces the frequency of herpesvirus reactivation. Synthetic feline pheromone diffusers, maintaining a stable routine, ensuring adequate resources in multi-cat households, and limiting exposure to known stressors all help manage chronic herpesvirus disease.
Famciclovir During Stressful Events
Some cats with severe recurrent herpesvirus disease benefit from prophylactic famciclovir administered during anticipated stressful events — hospitalisation, rehoming, introduction of a new pet — to prevent reactivation.
Vaccination — Prevention
Core Vaccines
The core vaccines for cats include protection against both feline herpesvirus and feline calicivirus — the two most significant causes of URI. Vaccination does not fully prevent infection but significantly reduces the severity and duration of illness in vaccinated cats that are exposed.
Primary vaccination series begins at 8 to 9 weeks of age, with boosters at 3 to 4 week intervals until 16 weeks. Adult boosters are typically given annually or every 3 years depending on the specific vaccine and the individual cat’s risk profile.
Chlamydia Vaccine
A non-core vaccine recommended for cats in high-risk situations — multi-cat households with known Chlamydia exposure, shelter environments. Not routinely recommended for low-risk indoor cats.
Limitations of Vaccination
It is important to understand that vaccination against herpesvirus and calicivirus significantly reduces disease severity but does not provide sterilising immunity — vaccinated cats can still become infected and develop signs, but typically milder than in unvaccinated individuals. A vaccinated cat developing URI signs is not necessarily a vaccination failure — the vaccine is doing its job by limiting the severity of the illness.
If your cat is showing signs of a respiratory infection, book an appointment at Walker Lake Veterinary Centre. Call (587) 786-6771 or book online. Located at 5109 22 Avenue SW, Southwest Edmonton.
Book an Appointment at Walker Lake Veterinary Centre
Walker Lake Veterinary Centre provides respiratory assessment, ocular examination, antiviral and antibiotic treatment, and vaccination for cats across Walker Lake, Summerside, Ellerslie, Heritage Valley, and Southwest Edmonton.
Call us at (587) 786-6771 or book online. We are located at 5109 22 Avenue SW, Edmonton.
Clinic hours:
- Monday, Tuesday & Thursday: 9:00 AM – 7:00 PM
- Wednesday & Friday: 9:00 AM – 6:00 PM
- Saturday: 9:00 AM – 3:00 PM
- Sunday: Closed
Frequently Asked Questions
Is cat flu the same as human flu?
No. Cat upper respiratory infections are caused by feline-specific pathogens — primarily feline herpesvirus and calicivirus — that do not infect humans. Similarly, the human influenza virus does not cause illness in cats. The colloquial term cat flu is a misnomer — URI in cats is caused by different viruses than influenza and has different characteristics.
Can cats give their URI to humans?
Feline herpesvirus and calicivirus do not infect humans. Chlamydia felis can very occasionally cause mild conjunctivitis in humans who handle infected cats — good hygiene practices including handwashing after handling an infected cat are sensible precautions. Bordetella bronchiseptica can theoretically affect immunocompromised humans but transmission is very rare.
My cat had URI and recovered — can it get it again?
Yes. Cats infected with herpesvirus carry the virus for life in a latent state. During stressful periods, the virus can reactivate causing recurrent episodes of sneezing, nasal discharge, and ocular disease. Calicivirus does not typically establish lifelong latency in the same way, though some cats become persistent carriers.
How long does a cat URI typically last?
Uncomplicated mild URI in a healthy vaccinated adult cat typically resolves within 7 to 14 days with appropriate treatment. Severely affected cats, kittens, and immunocompromised individuals may take 3 to 4 weeks or longer to recover. Chronic herpesvirus-associated disease can persist indefinitely with periodic reactivation.
My cat has had a runny nose for months — is this still URI?
Chronic nasal discharge lasting more than 3 to 4 weeks despite appropriate treatment warrants further investigation. Chronic rhinitis — particularly following herpesvirus infection — can cause permanent damage to the nasal mucosa, turbinates, and sinuses, leading to persistent discharge that is difficult to fully resolve. Other causes of chronic nasal discharge include nasal polyps, nasal tumours, foreign bodies, and dental disease with sinus involvement.