Feline Upper Respiratory Infection: Complete Cat Flu Guide

Feline Upper Respiratory Infection: The Complete Cat Flu Guide

Medically reviewed by Dr. Sarah Mitchell, DVM — updated July 17, 2026. Dr. Mitchell is a small-animal veterinarian whose clinical focus is on feline preventive care, behavior, and household safety. This guide follows the 2020 AAFP/FelineVMA Feline Vaccination Guidelines and current standards from the Merck Veterinary Manual, with clinical information drawn from peer-reviewed veterinary literature.

Feline Upper Respiratory Infection (URI), commonly called "cat flu," is one of the most prevalent infectious diseases affecting cats worldwide. While often compared to a human cold, feline URI can be significantly more serious — particularly for kittens, senior cats, and immunocompromised individuals. This guide covers causes, symptoms, treatment, prevention, and when to seek emergency care.

"Cat flu is rarely fatal in healthy adult cats, but it's not 'just a cold.' Kittens can die from secondary bacterial pneumonia, and chronic herpesvirus carriers suffer repeated flare-ups that significantly impact quality of life. Vaccination and early intervention matter." — Dr. Sarah Mitchell, DVM

Understanding Feline URI Causes

What Is Feline URI?

Feline Upper Respiratory Infection is a syndrome — not a single disease — characterized by infections of the upper respiratory tract. It affects the nose, throat, sinuses, and eyes.

Primary areas affected:

• Nasal passages
• Sinuses
• Throat and voice box
• Conjunctiva (eye membranes)

Primary Pathogens

Viral Causes (the majority of cases):

Per the Merck Veterinary Manual, most acute feline upper respiratory infections are caused by FVR (FHV-1), with FCV common in many populations and bacteria typically acting as secondary invaders.

• Feline Herpesvirus-1 (FHV-1): The most common cause, also known as Feline Viral Rhinotracheitis. Highly contagious; once infected, cats carry the virus for life — a latency pattern documented in the ABCD FHV-1 guidelines (Thiry et al., Journal of Feline Medicine and Surgery, 2009).
• Feline Calicivirus (FCV): Often causes painful oral ulcers. Some strains can be severe; a particularly virulent systemic strain (VS-FCV) can be fatal — mortality in outbreaks has reached up to 67% (Radford et al., Veterinary Research, 2007).

Bacterial Causes:

• Chlamydophila felis: Primarily causes conjunctivitis (pink eye).
• Bordetella bronchiseptica: Can lead to pneumonia, especially in kittens and shelter cats.
• Mycoplasma: A secondary invader that complicates viral infections.

Most URI cases involve both viral and bacterial components, with viruses initiating the infection and bacteria causing secondary complications.

Recognizing Symptoms of Cat Flu

Common Clinical Signs

Nasal and ocular symptoms:

• Sneezing (mild to violent fits)
• Nasal discharge (clear to thick yellow/green)
• Congestion and noisy breathing
• Eye discharge and red, swollen eyes (conjunctivitis)
• Squinting or corneal ulcers (especially with FHV-1)

Oral and systemic symptoms:

• Excessive drooling or oral ulcers (especially with FCV)
• Lethargy and depression
• Fever and loss of appetite
• Dehydration

When to Seek Emergency Veterinary Care

Contact your veterinarian immediately if your cat shows:

• Difficulty breathing or open-mouth breathing
• Complete refusal to eat for more than 24 hours
• Severe lethargy or collapse
• Signs of dehydration (skin tenting, tacky gums)
• High fever (over 103.5°F / 39.7°C)
• Eye ulcers or sudden blindness
• Sudden severe symptoms in an otherwise healthy cat (possible VS-FCV)

Diagnosis and Veterinary Testing

For typical cases, URI is diagnosed based on clinical signs. However, your vet may recommend:

• PCR Testing: The gold standard for identifying specific viral DNA. Useful for confirming FHV-1 or FCV in chronic or recurrent cases.
• Bacterial Culture: To find the right antibiotic for secondary bacterial infections.
• Chest X-rays: If pneumonia is suspected.
• Blood work: To assess dehydration and overall health status.

Treatment and Supportive Home Care

Home Care for Mild Cases

Most mild URI cases can be managed at home with supportive care:

• Hydration: Provide fresh water and feed wet food to increase fluid intake.
• Nutritional Support: Offer strong-smelling foods (like tuna juice, baby food, or warmed wet food) to tempt cats who can't smell their food. Anorexia is dangerous in cats — even 24–48 hours without food can trigger hepatic lipidosis.
• Steam Therapy: Use a humidifier or run a hot shower to create a steamy bathroom; sit with your cat for 10–15 minutes to help clear nasal passages.
• Nursing Care: Gently wipe away discharge with a warm, damp cloth.
• Litter box hygiene: Cats with URI may avoid the litter box if they're congested; keep it immaculate.
• Eye care: Clean discharge gently and apply any prescribed eye medications.

Medical Treatment Protocols

1. Antibiotics: Used for secondary bacterial infections. Doxycycline is the most common first-line choice.
2. Antiviral Medications: Famciclovir is effective for severe FHV-1 cases — see Malik et al. (Journal of Feline Medicine and Surgery, 2009) for the clinical series that established it as a first-line systemic antiviral.
3. Eye Medications: Antibiotic or lubricating drops for ocular health; antiviral drops for herpes-related eye disease.
4. Lysine supplementation: Has fallen out of favor — a 2015 systematic review by Bol & Bunnik (BMC Veterinary Research) found no evidence it prevents or treats FHV-1, and some trials actually showed increased infection frequency and severity in cats receiving lysine.
5. Subcutaneous fluids: For dehydrated cats who aren't drinking enough.

Prevention: Protecting Your Feline Friend

Vaccination Is Critical

Core vaccines protect against FHV-1 and FCV (the FVRCP combination vaccine). While they may not prevent infection 100%, they significantly reduce disease severity. The 2020 AAFP/FelineVMA Feline Vaccination Guidelines recommend the following schedule:

Vaccination schedule summary:

• 6–8 weeks: First FVRCP
• 10–12 weeks: Second FVRCP
• 14–16 weeks: Third FVRCP + Rabies
• 1 year: Booster
• Adult: FVRCP every 3 years

Stress and Hygiene

• Reduce Stress: Use Feliway pheromone diffusers and maintain consistent routines. Stress is a major trigger for FHV-1 flare-ups in carrier cats.
• Sanitation: Clean surfaces with diluted bleach (1:32 ratio) to kill viruses. URI pathogens can survive on surfaces for days.
• Quarantine: Isolate new or sick cats from the rest of the household for at least 14 days.
• Hand washing: Wash hands thoroughly after handling a sick cat, especially before touching other cats.

Reducing Flare-Ups in Chronic Carriers

For cats with chronic FHV-1:

• Minimize household stress (predictable routines, no sudden changes).
• Maintain excellent nutrition.
• Consider L-lysine supplementation (consult vet — evidence is weak; see the Bol & Bunnik systematic review).
• Watch for early signs of flare-up (sneezing, eye discharge) and treat promptly.

Recovery and Long-Term Outlook

Most healthy adult cats recover in 7–14 days. However:

• 80% of cats with FHV-1 become lifelong carriers. The virus lies dormant in trigeminal nerve tissue and can reactivate during stress, illness, or immunosuppression — a latency pattern documented in the ABCD FHV-1 guidelines (Thiry et al., 2009).
• FCV carriers can shed virus for months to years.
• Chronic complications include chronic sinusitis, dental disease (especially with FCV), and recurrent eye issues.
• Long-term quality of life is generally good with proper management.

Cost Considerations

Note: These figures reflect typical US veterinary costs as of 2025. Actual prices vary significantly by region, clinic, and case complexity — always request a written estimate before treatment.

Frequently Asked Questions

Is feline URI contagious to humans?

No. Feline URI is caused by feline-specific pathogens (FHV-1, FCV, Bordetella) that don't infect humans. According to the Merck Veterinary Manual, FVR and caliciviruses are host-specific and pose no known human risk. Bordetella bronchiseptica has very rarely been documented in immunocompromised humans, so always wash hands after handling sick cats.

Can my cat get URI again after recovering?

Yes — especially with FHV-1. While the immune system keeps the virus dormant after recovery, stress or illness can trigger reactivation and flare-ups. FCV also has multiple strains, so reinfection with a different strain is possible.

How long is URI contagious?

FHV-1 and FCV are contagious during active infection and sometimes for weeks after symptoms resolve. Carrier cats may shed virus intermittently for life, especially during stress. Always isolate sick cats for at least 14 days.

Should I take my cat to the vet for URI?

Yes — always. While mild cases can be managed at home, only a vet can rule out complications (pneumonia, eye ulcers, dehydration) and prescribe appropriate treatment. URI in kittens is a particular emergency. For guidance on when respiratory infections progress to pneumonia and require hospitalization, see our Feline Respiratory Infections: A Vet's Survival Guide for URI and Pneumonia.

Can URI cause permanent damage?

In severe cases, yes. Possible long-term complications include chronic sinusitis (especially with FHV-1), corneal scarring and blindness (if eye ulcers aren't treated promptly), and chronic dental disease (with FCV).

Are URI and FVRCP the same thing?

No — but they're related. URI is the disease syndrome. FVRCP stands for Feline Viral Rhinotracheitis (FHV-1), Calicivirus (FCV), and Panleukopenia — the three core vaccines. The FVRCP vaccine protects against two of the main URI causes (FHV-1 and FCV).

Is there a cure for feline URI?

There's no cure for the viral forms (FHV-1 and FCV) — cats carry the virus for life. Treatment focuses on managing symptoms and preventing secondary bacterial infections. Most cats recover fully from acute symptoms within 1–3 weeks. For a closer look at the day-by-day recovery process, see our Cat Upper Respiratory Infection: Symptoms & Recovery Guide.

Can I treat URI at home without going to the vet?

Not recommended. While home care supports recovery, only a vet can diagnose the cause, rule out complications, and prescribe appropriate medications. Untreated URI can progress to pneumonia, especially in kittens. Always seek veterinary care.

Conclusion

Feline Upper Respiratory Infection is manageable with early intervention. Proactive vaccination, stress reduction, and dedicated home care are the best ways to ensure your cat's long-term health and minimize the impact of "cat flu" on your household. The key is recognizing symptoms early, seeking veterinary care promptly, and supporting recovery with proper nutrition, hydration, and environmental comfort. With appropriate care, most cats make a full recovery — though FHV-1 carriers may experience occasional flare-ups throughout their lives.

Sources and further reading:

• 2020 AAFP/FelineVMA Feline Vaccination Guidelines — Feline Veterinary Medical Association (formerly the AAFP).
• Thiry E, Addie D, Belák S, et al. Feline herpesvirus infection. ABCD guidelines on prevention and management. Journal of Feline Medicine and Surgery 11(7):547–55, 2009.
• Malik R, Lessels NS, Webb S, et al. Treatment of Feline Herpesvirus-1 Associated Disease in Cats with Famciclovir and Related Drugs. Journal of Feline Medicine and Surgery 11(1):40–48, 2009.
• Bol S, Bunnik EM. Lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats: a systematic review. BMC Veterinary Research 11:284, 2015.
• Radford AD, Coyne KP, Dawson S, Porter CJ, Gaskell RM. Feline calicivirus. Veterinary Research 38(2):319–35, 2007.
• Merck Veterinary Manual — Feline Respiratory Disease Complex.

Medical disclaimer: This article is for informational purposes only and does not constitute veterinary advice. Always consult a licensed veterinarian for diagnosis and treatment of any illness in your cat.

About the Author

Dr. Sarah Mitchell, DVM, is a contributing veterinarian specializing in feline preventive medicine. Her clinical work focuses on preventive care, behavior, and household safety — translating clinical protocols and peer-reviewed research into practical guidance cat owners can use daily, from vaccination planning to preparing for respiratory infection season in multi-cat homes.

For personalized advice for your cat, consult a licensed veterinarian in your area.

Feline URI is manageable with early intervention. Proactive vaccination and dedicated home care are the best ways to ensure your cat's long-term health and minimize the impact of "cat flu" on your household.