Most sneezing, runny eyes and mouth ulcers in cats come from two viruses: feline herpesvirus (FHV-1) and feline calicivirus (FCV). Neither has an antiviral that reliably clears it, and antibiotics do nothing to either. What decides whether a cat recovers in 7 to 10 days or ends up dehydrated and tube-fed is nursing care: fluids, a nose that works well enough to smell food, and pain control for the mouth. Two common beliefs are wrong and cost money: lysine does not help, and vaccination does not prevent infection.
Two viruses, two different patterns
FHV-1 prefers the eyes and the upper airway. Expect sneezing, conjunctivitis, squinting, a serous discharge that turns thick, and fever for 3 to 5 days. It also causes dendritic corneal ulcers, which is why any cat with a red, painful eye needs a fluorescein stain before any steroid drop goes near it. A steroid on a herpes ulcer can melt the cornea.
FCV prefers the mouth. Look for ulcers on the tongue, the hard palate and the gingiva, heavy salivation, and reluctance to eat. Some strains cause chronic gingivostomatitis, and the virulent systemic strains, rare but serious, add fever, limb edema, jaundice and skin crusts. A cat that is limping with oral ulcers and a fever is a recognized FCV presentation, not a separate orthopedic problem.
FHV stays for life
After the acute phase, FHV-1 retreats into the trigeminal ganglion and stays there. Roughly 80 percent of recovered cats become carriers, and most shed virus again within a year, classically after a stress event: a new cat, boarding, moving house, surgery, or a course of steroids. Reactivation is usually milder than the first episode, often just one watery eye and a few sneezes for a week, but the cat is infectious to others while it sheds, typically 1 to 2 weeks. This is why a "recovered" cat can start sneezing the week you bring home a kitten, and why the kitten gets blamed unfairly.
FCV survives on surfaces far longer than people expect
FHV-1 is fragile and dies on dry surfaces within hours. FCV is the opposite: it can stay infectious on hard surfaces, bowls, bedding, carriers and hands for up to a month. That changes the cleaning protocol after a case.
- Bleach at 1:32 dilution (about 4 tablespoons per liter), 10 minutes of contact time, then rinse and dry.
- Wash bowls and litter boxes daily; discard porous toys and cardboard scratchers.
- Change clothes and wash hands between cats; use separate carriers for vet visits.
- Isolate a new or recovering cat for 3 to 4 weeks, and check its vaccination status before mixing.
Vaccination reduces severity but does not stop a cat from carrying or shedding FCV, so a vaccinated cat in a multi-cat home is not a guarantee.
Why lysine is not the answer
The reasoning seemed clean: herpes needs arginine, and lysine competes with it. Controlled trials in cats did not support it. Supplemented cats showed no reduction in shedding, no faster healing and no fewer recurrences, and at least one trial found longer shedding and worse signs in the treated group. Typical doses used in those studies were around 250 to 500 mg twice daily. It is harmless enough, but it is not treatment, and money is better spent on pain relief and food.
Supportive care is the actual treatment
Four things carry most of the recovery. Hydration, because a cat with a blocked nose and a sore mouth will not drink enough: offer water in several places, add water to food, and let the vet give subcutaneous fluids if the cat is dehydrated. Airway comfort, because dry air thickens discharge: a 10 minute session in a steamy bathroom, or saline nebulization, loosens it, but never use human decongestants, which are toxic to cats. Pain control, because oral ulcers hurt: buprenorphine or meloxicam under veterinary direction makes eating possible. Nutrition, because 3 days without adequate intake triggers hepatic lipidosis in an overweight cat.
| Problem | What helps | What to avoid |
|---|---|---|
| Blocked nose | Steam, saline drops, warm food | Human decongestants, eucalyptus oil |
| Mouth ulcers | Soft food, analgesia, room-temperature food | Dry kibble, acidic treats |
| Eye discharge | Saline wipe, vet-checked drops, fluorescein stain | Steroid drops without a stain |
| Not eating 24 hours | Syringe feeding, then a feeding tube | Waiting another day |
A blocked nose is a feeding problem, not a comfort problem
Cats choose food by smell before taste. With anosmia, a cat will sit at the bowl and walk away, and owners read that as fussiness. Three fixes work: warm the food to body temperature, which volatilizes aroma; use a strong-smelling wet food or a liquid recovery diet; and offer whisker-thin strips of food on a flat plate so the cat does not have to put its nose into a bowl. If intake is still under half of normal for 24 hours, start syringe feeding small amounts every 4 to 6 hours, aiming for roughly 40 to 60 kcal per kilogram per day, and ask about a nasoesophageal tube if the cat fights it.
Antibiotics only for secondary infection
Both viruses are viral, so amoxicillin does nothing on day 2. Antibiotics become reasonable when the discharge turns thick and yellow-green, when fever persists beyond 3 to 5 days, or when the cat worsens after initial improvement. Doxycycline is the usual choice when Mycoplasma or Chlamydia is suspected, and it also has some anti-inflammatory effect. The cost of unnecessary courses is real: resistance, diarrhea, and a false sense that the cat has been treated.
Vaccines reduce severity, they do not block infection
FVRCP is a core vaccine and every cat should have it, but its protection is against disease, not against colonization. Vaccinated cats can still be infected and still shed. Kittens need a series starting at 6 to 8 weeks with doses every 3 to 4 weeks until 16 weeks, because maternal antibodies fade at different times. Adults get a booster at 1 year, then every 1 to 3 years depending on lifestyle. Intranasal vaccines can be useful in a shelter outbreak because they act locally within days.
Signs that mean the clinic today
- Open-mouth breathing, or a resting respiratory rate above 40.
- No food for 24 hours, or no water for 12 hours.
- A red, cloudy or painful eye, or a cornea that looks blue or rough.
- Fever above 40 degrees Celsius, or lethargy that deepens over a day.
- Limping with oral ulcers, or skin crusts on the face and paws.
Most cats with FHV or FCV improve within 7 to 10 days with nursing care alone, and the ones that do not are usually the ones that stopped eating early. Weigh the cat on day 1, count calories, and treat appetite as a clinical sign rather than a preference.
Frequently asked
Does lysine help a cat with herpesvirus?
Controlled trials have not shown a benefit. Supplemented cats did not shed less virus, heal faster or relapse less often, and one trial found longer shedding and worse signs in the treated group at doses around 250 to 500 mg twice daily. Lysine is not toxic, but it is not treatment, and the money is better spent on analgesia and nutrition.
Can my other cats catch it if my cat sneezes?
Yes, both viruses spread easily. FHV-1 passes in droplets and on hands and bowls, and stays latent for life, so most recovered cats become carriers that shed again under stress. FCV survives on hard surfaces for up to a month. Isolate the sick cat for 3 to 4 weeks, wash hands and bowls, and use bleach at 1:32.
Do I need antibiotics for a cat with a runny nose?
Usually not on day one, because both FHV-1 and FCV are viral. Antibiotics are reasonable when discharge turns thick and yellow-green, when fever lasts beyond 3 to 5 days, or when the cat improves and then worsens. Doxycycline is the common choice when Mycoplasma or Chlamydia is suspected.