Feline Upper Respiratory Infection

TL;DR. Feline Upper Respiratory Infection (URI) is a highly contagious, common illness in cats, primarily caused by Feline Herpesvirus and Feline Calicivirus, that responds well to supportive care and targeted veterinary treatments.

Feline URI commonly causes watery eyes, nasal discharge, and mild lethargy.

What is it?

Feline Upper Respiratory Infection (URI) is a common infectious disease affecting the upper airways, nose, throat, and eyes of cats. Similar to the common cold in humans, URI is highly contagious and can spread rapidly through feline populations. The disease is primarily driven by two viral pathogens: Feline Herpesvirus (FHV-1) and Feline Calicivirus (FCV). These viruses target the delicate mucosal linings of the nasal passages and the conjunctiva (the membranes lining the eyelids), triggering acute inflammation, congestion, and discharge.

While many cases present as acute, self-limiting infections, some cats can develop chronic or intermittent respiratory and ocular signs. The infection damages the local defense mechanisms of the respiratory tract, making the cat highly susceptible to secondary bacterial invaders such as Chlamydophila felis, Mycoplasma species, and Bordetella bronchiseptica. Understanding the mechanisms of this disease is crucial for cat owners, as prompt intervention not only relieves discomfort but also prevents severe complications like corneal ulcers or chronic nasal damage.

Causes & risk factors

Feline URI is primarily caused by Feline Herpesvirus (FHV) and Feline Calicivirus (FCV). Cats acquire these infections through direct contact with an actively infected cat, exposure to carrier cats, or contact with contaminated environments and objects (fomites) such as food bowls, bedding, toys, and human hands.

As noted in a leading veterinary internal medicine reference:

"Cats become infected through contact with actively infected cats, carrier cats, and fomites. Cats that are young, stressed, or immunosuppressed are most likely to develop clinical signs. Infected cats often become carriers of FHV or FCV after resolution of the clinical signs. The duration of the carrier state is not known, but it may last from weeks to years."

Once a cat is infected with Feline Herpesvirus, the virus remains dormant (latent) in the cat's nervous system for life. During periods of stress—such as rehoming, boarding, illness, or the introduction of a new pet—the virus can reactivate, causing the cat to shed the virus again and potentially show clinical signs. Feline Calicivirus carriers, on the other hand, often shed the virus continuously for weeks, months, or even years after their initial recovery.

There are no specific breed predispositions for Feline URI; any cat, regardless of breed, can contract the infection. However, risk factors heavily include high-density environments such as animal shelters, breeding catteries, and multi-cat households, where pathogens circulate easily.

Signs to watch for

Clinical signs can vary depending on the primary pathogen and whether secondary bacterial infections have taken hold. Symptoms are generally categorized by their frequency of occurrence:

Common Signs

• Sneezing: Often the first and most noticeable sign of infection.
• Nasal discharge: Starts as a clear, watery (serous) fluid and can progress to a thick, yellow-green (mucopurulent) discharge.
• Ocular discharge: Watery or thick discharge from one or both eyes.
• Conjunctivitis: Redness, swelling, and inflammation of the tissues surrounding the eye.
• Fever: A elevated body temperature, which often leads to lethargy.
• Anorexia: Loss of appetite, frequently because nasal congestion prevents the cat from smelling its food.
• Dehydration: Caused by decreased fluid intake and fluid loss from nasal and ocular secretions.
• Hypersalivation: Excessive drooling, often associated with painful oral lesions.

Occasional Signs

• Oral ulcerations: Painful open sores on the tongue, gums, or hard palate, most commonly associated with Feline Calicivirus.
• Corneal ulceration: Painful sores on the surface of the eye, highly characteristic of Feline Herpesvirus.
• Cough: Mild coughing may occur if the infection irritates the trachea.
• Mild interstitial pneumonia: A deeper lung infection that can occur in severe cases, particularly in kittens.
• Polyarthritis: Joint inflammation leading to temporary limping, occasionally seen with specific strains of Feline Calicivirus.
• Abortion and neonatal death: Can occur in pregnant queens experiencing severe acute infection.

Rare Signs

• Facial and limb edema: Swelling of the face and legs, typically associated with highly virulent, systemic strains of Feline Calicivirus.
• Focal necrosis: Localized tissue death, also linked to highly virulent systemic calicivirus infections.

Conjunctivitis is a frequent sign of upper respiratory infections, particularly those caused by herpesvirus.

How vets diagnose it

Your vet will begin with a thorough physical examination to assess your cat's overall health, hydration status, and the severity of their clinical signs. In many individual pet cats, a presumptive diagnosis of URI is made based on these clinical signs alone, and symptomatic treatment is started immediately.

However, in chronic cases, severe infections, or multi-cat environments like catteries, identifying the specific causative agent is highly beneficial. Your vet may recommend several diagnostic tests:

• Polymerase Chain Reaction (PCR): This is a highly sensitive molecular test that detects the DNA or RNA of specific pathogens (such as FHV, FCV, Chlamydophila, or Mycoplasma) from swabs taken from the eyes, nose, or throat.

• Serum antibody titers: Measuring antibody levels in the blood can help identify active infections. As noted in veterinary literature:

  "Demonstration of rising antibody titers against a specific agent over 2 to 3 weeks suggests active infection. Regardless of the method used, close coordination with the pathology laboratory on specimen collection and handling is recommended for optimal results."

• Virus isolation: This laboratory method grows and identifies the virus from conjunctival or oropharyngeal swabs. While highly accurate, it is less commonly used in routine practice than PCR.

• Bacterial culture: If a secondary bacterial infection is suspected, or if the cat is not responding to standard antibiotics, your vet may perform a bacterial culture and sensitivity test to identify the specific bacteria and the most effective antibiotic.

• Cytologic preparations of conjunctival smears: Your vet may gently scrape cells from the conjunctiva to examine under a microscope, looking for specific cellular changes or infectious organisms like Chlamydophila inclusion bodies.

Your vet may perform a conjunctival swab to run a PCR test and identify the specific virus or bacteria.

Treatment options

Treatment for feline URI is largely supportive and tailored to the specific symptoms your cat is displaying. Because the primary causes are viral, there is no single cure, but targeted therapies can significantly ease symptoms and prevent complications.

Antiviral Therapy

For cats with severe or recurrent Feline Herpesvirus infections, your vet may prescribe Famciclovir, a systemic antiviral medication. Famciclovir helps inhibit viral replication, reducing the severity and duration of both ocular and respiratory signs.

Ophthalmic Medications

If your cat has conjunctivitis or corneal ulcers, topical eye medications are essential.

• Chloramphenicol or Oxytetracycline ophthalmic ointments are broad-spectrum antibiotics used to treat or prevent secondary bacterial infections in the eyes.
• If corneal ulcers are present, your vet may prescribe Atropine ophthalmic drops. Atropine is an anticholinergic drug that dilates the pupil and relieves the painful spasms of the ciliary muscle inside the eye.

For specific bacterial infections like Chlamydophila, prolonged treatment is necessary:

"Chlamydophila infection should be suspected in cats with conjunctivitis as the primary problem and in cats from catteries in which the disease is endemic. Oral antibiotics are administered for a minimum of 42 days. In addition, chloramphenicol or tetracycline ophthalmic ointment should be applied at least three times daily and continued for a minimum of 14 days after signs have resolved."

Decongestants and Nasal Care

To help relieve severe nasal congestion, your vet may recommend Phenylephrine, an alpha-adrenergic agonist, used cautiously as a topical nasal decongestant to reduce swelling in the nasal passages. Additionally, keeping your cat in a humidified environment (such as a bathroom with a running hot shower) can help loosen thick nasal secretions.

Advanced or Specialized Therapies

In highly specific, severe, or atypical inflammatory cases, advanced medications like Cytarabine (an antineoplastic agent) are occasionally referenced in specialized veterinary protocols. However, this is not a standard first-line treatment for typical viral URIs and is reserved for complex, specialist-managed cases.

Supportive Care

Because congested cats cannot smell their food, they often stop eating. Offering highly palatable, warmed, strong-smelling canned food can encourage them to eat. If your cat is dehydrated, your vet will administer fluids either subcutaneously (under the skin) or intravenously.

Prognosis

The prognosis for cats with acute Feline Upper Respiratory Infection is generally excellent. Most cats make a full recovery within 7 to 14 days with appropriate supportive care. Chronic, lifelong respiratory disease does not develop in most pet cats.

However, it is important to remember that many cats will become lifelong carriers of Feline Herpesvirus. While they will remain completely healthy most of the time, they may experience mild, self-limiting flare-ups of sneezing or runny eyes during times of stress. Managing stress and maintaining a stable environment are key to keeping these flare-ups to a minimum.

Prevention

Preventing feline URI involves a combination of vaccination, hygiene, and stress management:

• Vaccination: The core FVRCP vaccine protects against Feline Viral Rhinotracheitis (Herpesvirus), Calicivirus, and Panleukopenia. While the vaccine may not completely prevent infection or the carrier state, it significantly reduces the severity of clinical signs if a cat is exposed.

• Hygiene and Sanitation: Because the viruses can survive on surfaces (fomites), regularly disinfecting food bowls, litter boxes, and bedding is crucial, especially in multi-cat environments. Handwashing after handling an ill cat prevents cross-contamination.

• Quarantine: New cats should be isolated from resident cats for at least 7 to 14 days to monitor for signs of respiratory disease before introduction.

• Cattery Management: In breeding or boarding facilities, diagnostic testing is highly recommended to manage outbreaks and guide prevention strategies. As noted in critical care literature:

  "Attempts to make a diagnosis in cases of feline respiratory viral illness are encouraged especially in catteries because knowledge of the causative organism can assist with treatment strategies. Because of the communicability and high mortality associated with virulent FCV infection, microbiologic testing is essential for cats suspected to have the systemic febrile syndrome..."

When to call your vet

While many mild cases of URI can be managed with home care and rest, you should contact your vet if you notice any of the following warning signs:

• Your cat stops eating or drinking entirely for more than 24 hours.
• Your cat is having difficulty breathing, is breathing rapidly, or is breathing with an open mouth.
• Your cat's eyes are squinted shut, cloudy, or showing signs of severe pain, which may indicate a corneal ulcer.
• Your cat becomes extremely lethargic or unresponsive.
• The nasal or ocular discharge becomes very thick, green, or yellow, suggesting a secondary bacterial infection.

Sources

• Internal Medicine 5th, pages 267, 268, 269
• Small Animal Critical Care Medicine, 2nd Edition, page 563