Cat Eye Infection: Feline Herpesvirus, Chlamydia & Treatment

Cat eye infections are very common — but the causes are dramatically different from dogs. While dogs usually get plain bacterial conjunctivitis, 80% of cat eye infections involve FELINE HERPESVIRUS, and many also involve CHLAMYDIA felis — a cat-specific bacterium. Understanding what's actually causing your cat's infected eye changes how you treat it.

The 5 Main Causes of Cat Eye Infection

1. Feline Herpesvirus-1 (FHV-1) — The #1 Cause

Roughly 80-90% of cats have been exposed to feline herpesvirus at some point. Key facts:

• ✓Transmitted cat-to-cat; very common in shelters, multi-cat households, stray origins
• ✓Once infected, cats are LIFELONG CARRIERS
• ✓Virus hides dormant in nerve tissue, reactivates during STRESS (new pet, moving, illness, boarding)
• ✓Each flare-up: watery to yellow-green eye discharge + sneezing + sometimes fever
• ✓Can cause corneal ulcers specific to herpes (dendritic ulcers)
• ✓Kittens born to infected mothers almost always infected
• ✓Treatment: antiviral eye drops (cidofovir, idoxuridine) for severe cases; L-lysine supplementation (debated efficacy); antibiotic drops for secondary bacterial infection; stress reduction

Important: herpesvirus CANNOT be cured, but flares can be managed. Reduce stress, maintain vaccinations, treat flares promptly.

2. Chlamydia felis — Bacterial Cat-Specific

Chlamydia felis is a different species from human Chlamydia — doesn't spread between species. Features:

• ✓Most common in kittens (2-6 months) and multi-cat households
• ✓Causes chronic conjunctivitis that may persist weeks/months if untreated
• ✓Yellow-green discharge, sometimes mild respiratory signs
• ✓Often one eye first, spreads to both
• ✓Treatment: oral DOXYCYCLINE for 3-4 WEEKS (important — shorter courses risk relapse); plus topical antibiotic drops
• ✓Sometimes empirically prescribed when chronic conjunctivitis suspected

3. Mycoplasma felis

Small bacteria often co-infecting with herpesvirus. Similar treatment (doxycycline). Often found together in complex URI cases.

4. Calicivirus

Viral cause of cat upper respiratory infection. Primarily causes mouth ulcers and respiratory signs; eye involvement secondary. Less focused on eyes than herpesvirus but contributes.

5. Secondary Bacterial Infection

When viral disease damages the eye, normal bacterial flora (Staphylococcus, Streptococcus) can invade. Yellow-green thick discharge is usually secondary bacterial infection on top of viral cause. Antibiotic drops treat this effectively.

Recognizing Cat Eye Infection

• ✓Yellow or green discharge (bacterial; secondary to viral in most cases)
• ✓Watery clear discharge progressing to thicker colored discharge
• ✓Squinting or holding eye closed
• ✓Eye redness
• ✓Third eyelid showing (pink membrane in inner corner)
• ✓Sneezing (strong indicator of URI)
• ✓Reduced appetite (CRITICAL — if not eating for 24+ hours = urgent)
• ✓Lethargy
• ✓Sometimes mild fever
• ✓One eye first, often both within 1-2 days

How Did My Indoor Cat Get an Eye Infection?

Common pathways even for indoor cats:

• ✓FELINE HERPESVIRUS HIDING DORMANT — virus was already in your cat (probably from kittenhood); recent stress triggered a flare-up
• ✓NEW CAT in household brought virus
• ✓HUMANS carrying virus on hands/clothes from other cats
• ✓BORDERED OR SHELTER EXPOSURE during recent vet visit or boarding
• ✓STRESSFUL EVENT (moving, construction, new pet, loss of pet) triggered dormant herpesvirus reactivation

Treatment Approach

Vet Visit (Required for Moderate-Severe)

The vet will:

• ✓Examine eye + check for corneal ulcer with fluorescein stain
• ✓Assess for URI signs (temperature, nasal discharge, lung sounds)
• ✓Sometimes swab cytology to identify bacteria
• ✓Prescribe antibiotic eye drops (terramycin, tobramycin, oxytetracycline) 2-3x daily 7-14 days
• ✓Sometimes oral doxycycline if Chlamydia/Mycoplasma suspected (3-4 week course)
• ✓Antiviral drops for severe herpes flares
• ✓L-lysine supplementation for herpesvirus
• ✓Supportive care recommendations

Typical cost: $100-200 for exam + drops. More if oral antibiotics added.

Home Supportive Care

• ✓Gentle cleaning 2-3x daily with warm saline
• ✓Warm compresses 5-10 min 2-3x daily
• ✓Humidifier (eases breathing in URI)
• ✓Encourage eating with warm aromatic food (critical — cats stop eating fast)
• ✓Isolate from other cats
• ✓Reduce stressors
• ✓Complete full antibiotic course even if it looks better
• ✓E-collar if cat paws at eye

Prognosis

Most bacterial conjunctivitis: excellent with treatment, resolves in 7-14 days. Herpesvirus infection: flares resolve in 7-14 days but underlying virus persists for life; recurrent flares are possible. Chlamydia: excellent with proper 3-4 week doxycycline course; incomplete treatment = recurrence. Untreated infections: can cause corneal ulcers → vision loss; can spread to other cats; in kittens can cause permanent eye damage.

When to See the Vet URGENTLY

• ✓Kitten with any eye discharge
• ✓Cat not eating for 24+ hours with eye discharge
• ✓One eye with heavy squinting and pain
• ✓Cloudy or bluish eye appearance
• ✓Third eyelid covering a significant portion of eye
• ✓Breathing difficulty alongside eye issues
• ✓Blood from eye

Not sure if your cat has a bacterial infection, herpesvirus flare, or blocked tear duct? Upload a photo — AI identifies color and ranks likely feline-specific causes.