Upper Respiratory Infection in Cats — Management Guide

Practical, evidence-based guide to feline upper respiratory infections (FHV-1 vs FCV): causes, diagnosis, treatments (supportive care, antivirals, antibiotics), L‑lysine controversy, chronic carriers and prevention.

Quick Overview

• What it is: "Cat cold" or feline upper respiratory infection (URI) is a common infectious syndrome caused mainly by feline herpesvirus type 1 (FHV‑1) and feline calicivirus (FCV), often complicated by secondary bacteria. Signs include sneezing, ocular/nasal discharge, fever, anorexia and sometimes mouth ulcers, pneumonia or conjunctivitis.
• Who’s at risk: Kittens, unvaccinated cats, multicat environments (shelters, catteries), stressed cats, and elderly or immunocompromised cats.
• Prognosis: Most cats recover with supportive care in 7–21 days. FHV‑1 establishes lifetime latency with periodic flare‑ups; some cats become chronic FCV shedders. Severe disease and mortality are uncommon in vaccinated adults but possible in naive kittens or virulent FCV outbreaks.

H2: Pathophysiology — In simple terms

• FHV‑1 (feline herpesvirus 1) is a DNA virus that infects the mucosa of the upper respiratory tract and eyes. After initial infection it becomes latent in nerve ganglia (especially the trigeminal ganglion). Stress, corticosteroids or concurrent illness can reactivate viral replication and clinical signs.
• FCV (feline calicivirus) is an RNA virus that replicates in oral and respiratory epithelium. Unlike FHV‑1, FCV does not become latent in nerves in the same way; some cats can become persistent oral shedders for months to years.
• Both viruses damage mucosal defenses, allowing opportunistic bacteria (Pasteurella, Mycoplasma, Bordetella and others) to cause secondary infection, prolonging symptoms and sometimes leading to pneumonia.

• No single breed is uniquely susceptible, but purebred cats in multicat breeding facilities and show cats have higher exposure risk because of close contact and stress.
• Brachycephalic breeds (Persians, Exotic shorthairs) may have more severe or prolonged signs because of narrowed nasal passages and abnormal nasal anatomy.
• Kittens and immunocompromised breeds (e.g., cats with FIV/FeLV coinfection) show more severe disease.

• Early (1–3 days): sneezing, serous nasal and ocular discharge, conjunctivitis, mild fever, lethargy, reduced appetite.
• Peak (3–7 days): discharge becomes mucopurulent if secondary bacteria present, coughing or wheeze (if lower airway involved), oral ulcers (more typical with FCV), enlarged salivary glands (rare), fever, dehydration.
• Recovery (7–21+ days): gradual improvement; some cats still sneeze for weeks. FHV‑1 cats may have recurrent episodes with stress.

• FHV‑1: severe conjunctivitis, corneal ulcers, frequent reactivation with stress.
• FCV: oral ulcers, lameness or systemic disease in virulent systemic FCV strains; may cause more systemic signs in outbreaks.

H3: History and physical exam

• Vaccination status, onset, household cat exposure, environment (shelter, boarding), appetite, hydration, and presence of dyspnea.

• Body weight, temperature, hydration status, ocular exam (fluorescein stain for corneal ulceration), thoracic auscultation.
• Minimum database: CBC and chemistry if systemic disease suspected (fever, anorexia, high risk or prolonged illness).

• PCR panels from oropharyngeal or conjunctival swabs detect FHV‑1, FCV, Bordetella, Mycoplasma, Chlamydophila felis and others — useful in shelters/outbreaks or chronic shedders.
• Virus isolation or serology are less commonly used clinically; PCR is most sensitive.

• Thoracic radiographs if cough, tachypnea or increased respiratory effort — to assess pneumonia.
• Dental exam and skull radiographs/CT if chronic unilateral nasal discharge (to look for tooth root abscess, foreign body or sinonasal disease).
• Rhinoscopy with biopsy and culture for chronic or unusual cases; referral to an internal medicine or dental specialist if imaging shows masses, foreign bodies, or if neoplasia suspected.

Treating feline URI is mostly supportive. Specific interventions depend on severity, suspected pathogen and complications.

H3: Supportive care (cornerstone)

• Hydration: Offer palatable wet food, subcutaneous fluids at home for mild dehydration, or IV fluids if moderate–severe dehydration. Monitor body weight and urine output.
• Nutrition: Warm, strong‑smelling foods; syringe feeding if anorexic >24–48 hours. Appetite stimulants (mirtazapine 1.88–3.75 mg per cat q48–72h or 0.5–1 mg/kg PO) can be used under vet guidance.
• Airway comfort: Humidification (steam or veterinary nebulizer) several times daily for 10–15 minutes can loosen nasal secretions. Saline drops (0.9% NaCl) into each nostril can help clear crusts.
• Eye care: Clean discharge with saline; topical ophthalmic antivirals for corneal ulcers (e.g., trifluridine 1% ophthalmic solution, typically q6–8h) and topical antibiotics to prevent secondary infection; refer to ophthalmologist for severe corneal disease.

• Famciclovir is commonly used off‑label for symptomatic FHV‑1 disease. Dosing reported in studies varies; common clinical dosing is 40–90 mg/kg PO divided every 8–12 hours (frequently 40–90 mg/kg q8–12h) for 7–21 days depending on severity. Famciclovir is generally well tolerated.
• Topical ophthalmic antivirals (trifluridine 1% q6–8h) are used for corneal involvement. Cidofovir ophthalmic drops may be considered (less irritation, longer dosing interval).
• Note: Acyclovir and valacyclovir are ineffective or toxic in cats and should be avoided.

• Antibiotics are indicated only when there is evidence of bacterial secondary infection (mucopurulent discharge, fever lasting >48–72 hours, radiographic signs of pneumonia, or positive bacterial culture).
• Common empiric choices (adjust after culture/sensitivity):

• Duration: typically 7–14 days, longer if radiographic pneumonia or chronic infection; reassess every 3–5 days.

• Interferons (e.g., recombinant feline interferon omega) have been used in some countries for FHV/FCV with mixed evidence. Consider as adjunctive therapy in refractory cases under specialist guidance.
• L‑lysine (an over‑the‑counter amino acid supplement) has been widely used historically to suppress FHV‑1. However, multiple controlled studies and recent reviews show no clear clinical benefit and some evidence of harm (increased FCV replication in some studies). Major feline infectious disease experts and guidelines no longer recommend routine L‑lysine use for feline URI (see evidence discussion below).

• Nasopharyngeal polyp removal (common in young cats with inspiratory stertor); dental extractions for tooth root abscess causing sinusitis.
• Rhinosurgery for chronic obstructions or neoplasia — referral to a veterinary surgeon or specialist recommended.

• Rationale: L‑lysine was proposed to antagonize arginine, an amino acid needed for herpesvirus replication, thereby reducing FHV‑1 replication.
• Evidence: Randomized controlled trials and systematic reviews have failed to demonstrate consistent clinical benefit (reduced signs, duration, or viral shedding). Some studies reported no effect; a few showed potential for increased FCV shedding or worse clinical scores. Because of the inconsistent or negative evidence, many specialty guidelines (veterinary infectious disease experts) do not recommend routine L‑lysine supplementation for prevention or treatment of feline URI.
• Bottom line: Discuss with your veterinarian before use. Routine L‑lysine is not considered standard of care and may be contraindicated in some situations.

• FHV‑1: latency in nerve ganglia means a cat can appear clinically normal but reactivate and shed virus intermittently, especially with stress, corticosteroids or illness.
• FCV: a subset of cats (estimates vary, often cited around 10–20% in some populations) can become persistent oral shedders and potentially infect other cats for months to years. Rarely, virulent systemic FCV strains cause high‑mortality outbreaks.
• Management: Minimize stress, maintain good vaccination status of household cats, avoid introducing naive cats to a population with shedders, and consult with your vet/shelter epidemiologist for outbreak control.

• Vaccination: Core vaccines for cats include FHV‑1 and FCV (combined in the FVRCP vaccine). Vaccines substantially reduce the severity and duration of clinical disease and likely decrease viral shedding during infection, but they do not guarantee sterilizing immunity — vaccinated cats can still become infected and shed virus, although typically less severely.
• Vaccine types: Modified‑live and inactivated vaccines are available (choice depends on age, pregnancy, and other factors). Follow your veterinarian’s recommended schedule (kittens series and regular adult boosters as appropriate).
• Biosecurity: Isolate infected cats, wash hands between handling cats, clean and disinfect bowls, bedding and litter boxes (enveloped virus FHV‑1 is less stable in the environment than non‑enveloped FCV — FCV can survive longer and requires more stringent disinfection with e.g., sodium hypochlorite solutions or accelerated hydrogen peroxide products).
• Shelter and cattery management: Quarantine new arrivals, vaccinate at intake, reduce overcrowding and stress, and use PCR testing during outbreaks to identify causative agents.

• Follow‑up: Recheck if signs worsen, if anorexia persists >48 hours, or if kittens are affected. Monitor body weight and hydration at home.
• Prevent flare‑ups: Avoid unnecessary corticosteroids, reduce stress (environmental enrichment, predictable routines), and maintain dental health.
• Chronic cases: Consider PCR testing and referral for rhinoscopy/CT if unilateral or chronic nasal discharge, or if suspecting neoplasia or fungal rhinitis.

• Most cats fully recover with good supportive care. Kittens and unvaccinated cats are at higher risk of severe disease and complications.
• Cats with FHV‑1 can live normal lives but may have periodic ocular or respiratory flare‑ups. Chronic FCV shedders require management to prevent spread to other cats.
• Quality of life considerations: Most infections are short‑term and manageable at home; chronic severe disease or virulent FCV outbreaks can significantly reduce quality of life and may require euthanasia in refractory severe cases.

• Keep the cat warm, quiet and stress‑free; isolate from other cats if possible.
• Use a humidifier or steam shower (briefly) to relieve congestion; saline nasal drops before feeding can improve smell and appetite.
• Increase palatability of food: warm wet food, strong‑smelling toppers.
• Clean eyes and nose gently with warm saline; use separate bowls/litter boxes and wash hands between cats.
• Administer medications exactly as prescribed; never give human antivirals like acyclovir without veterinary direction.
• Maintain vaccination schedule for other cats in the household.

Seek immediate veterinary care if your cat has any of the following:

• Difficulty breathing, open‑mouth breathing, blue or pale gums.
• Severe or persistent high fever, marked lethargy, collapse.
• Anorexia for >48 hours (especially kittens) or not drinking fluids.
• Severe ocular disease (corneal ulcers, marked squinting, marked discharge) or sudden blindness.
• Rapidly worsening signs, neurologic signs (seizures, ataxia), or evidence of severe dehydration.

• Feline URI is common and usually self‑limiting with supportive care. FHV‑1 and FCV are the primary viral causes; secondary bacteria may require antibiotics guided by clinical signs and culture.
• Famciclovir and topical antivirals are options for severe FHV‑1 disease. Avoid valacyclovir/acyclovir in cats.
• L‑lysine is not routinely recommended — evidence does not support a clinical benefit and may be harmful in some settings.
• Vaccination and good biosecurity dramatically reduce the risk of severe disease and are the cornerstone of prevention.

References and resources

• Cornell University Feline Health Center — Feline Upper Respiratory Infection (https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center)
• American Association of Feline Practitioners (AAFP) Feline Vaccination Guidelines (https://catvets.com/guidelines/practice-guidelines/vaccination-guidelines)
• ACVIM / Veterinary Infectious Disease literature and consensus reviews on feline upper respiratory disease
• Peer‑reviewed studies and reviews on L‑lysine and feline respiratory disease (see AAFP/Cornell reviews for summary of evidence)

Frequently Asked Questions