Feline herpesvirus (FHV-1) stays in the cat for life. After the first infection it retreats into the trigeminal ganglion and reactivates whenever resistance drops, so most carriers have 1 to 3 episodes a year, each running 7 to 14 days. Long-term care cannot clear the virus. It can stretch the quiet gaps to 6 or 9 months and cut each outbreak to 3 or 4 days of obvious signs.
What latency means for daily care
The virus is not living in the nose between episodes. It sits in nerve tissue, travels back down the sensory nerves when it wakes up, and sheds in tears, nasal discharge and saliva for about 1 to 3 weeks. That has 2 practical consequences. A cat with no signs can still infect a housemate during a silent reactivation, which is why bringing in a new cat is a real risk even when both look healthy. And swabbing a symptom-free cat usually returns nothing, so a negative test never rules the virus out. Diagnosis rests on history, eye and nose signs, and response to treatment.
Triggers you can actually control
Three factors come up again and again in relapse histories: stress, a change of environment, and dry air. Humidity below 40 percent dries the nasal lining and slows the mucociliary clearance that sweeps virus and debris out of the airway, which is why outbreaks cluster in heated apartments in January and February. Boarding, a move, a new baby, renovation noise and a clinic stay all lift cortisol for 3 to 10 days. The outbreak typically appears 2 to 5 days after the event, not during it, so owners rarely connect the two. Keep a one-line log: date, event, first sneeze. After 2 or 3 entries the pattern is usually plain.
Building a low-stress baseline
What works is boring and consistent. Feed at the same 2 times a day. Keep the litter box in the same quiet corner and scoop it twice daily. Give the cat 1 vertical escape route per room it uses. Pheromone diffusers help some households and do nothing in others; test for 4 weeks before judging. When guests arrive, put the cat in a room with water, a box and a bed while guests are over. If a move is unavoidable, move the cat last and set up one room with its own bowls, box and blanket before the furniture comes in.
Humidity, temperature and air
Aim for 40 to 60 percent relative humidity and 20 to 24 Celsius. A 10 dollar hygrometer is more useful than a nebulizer you use twice. In winter, a warm-mist humidifier in the room where the cat sleeps, cleaned every 3 days, keeps the nose comfortable. Skip scented candles, plug-in fresheners and aerosol sprays; irritated mucosa is exactly where the virus does damage. During an outbreak, run a steamy bathroom for 10 to 15 minutes once or twice a day. Steam loosens crusts and helps a cat that has lost its sense of smell.
Lysine: the supplement that did not hold up
L-lysine was standard advice for 20 years, usually 250 to 500 mg twice daily, on the theory that it starves the virus of arginine. Controlled trials and later reviews did not reproduce the benefit, and some work suggested high doses could worsen signs. Most veterinary ophthalmologists now skip it, or stop it if 8 weeks bring no change. It is not dangerous at typical doses, so a cat already taking it does not need an emergency stop, but it should not be the plan. That money buys a hygrometer, a humidifier and 2 fewer stressors.
What an outbreak looks like, day by day
Day 1 to 2: squinting, clear eye discharge, 1 or 2 sneezes, the classic upper respiratory signs. Day 3 to 5: thick yellow-green nasal discharge, ulcers on the cornea or tongue, appetite down by half, temperature 39.5 to 40.5 Celsius. Day 6 to 10: crusts, congestion, open-mouth breathing if the nose blocks. Most episodes settle by day 14. Anything past 14 days, any cat that has not eaten in 24 hours, any eye held shut or looking cloudy, and any fever above 40 Celsius needs to be seen the same day. A corneal ulcer can deepen into a descemetocele in 48 hours, and that is a surgical problem.
Antivirals: what the vet chooses and why
Oral famciclovir is the usual systemic choice, commonly 40 to 90 mg per kg twice daily for 7 to 21 days depending on severity and kidney function. It is well tolerated but not cheap: a 10 day course for a 4.5 kg cat often runs 60 to 150 dollars. Topical antivirals, compounded cidofovir 0.5 percent or idoxuridine 0.1 percent, are used 4 to 6 times a day when the cornea is involved. Steroid drops are avoided while an ulcer is open because they can speed melting. Antibiotics treat secondary bacterial infection, not the virus, and are started when discharge turns thick and colored.
The recheck schedule
A stable carrier needs a physical exam every 6 to 12 months with weight, temperature and a careful look at both eyes. Once a year is enough for a cat with 1 mild episode; every 6 months for a cat with 3 or more, or any cat on repeated antivirals. Keep FVRCP current even in a known carrier: it does not prevent infection but reduces severity. Ask for a Schirmer tear test at each visit if the cat has had repeated eye episodes, because chronic herpes can scar the conjunctiva and cut tear production for good.
| Trigger | What it does | Prevention action |
|---|---|---|
| Humidity under 40 percent | Dries the nasal lining, slows clearance | Humidifier to 40-60 percent, cleaned every 3 days |
| New cat in the house | Silent shedding from the newcomer | Separate room, separate bowls, 10 to 14 days before face-to-face |
| Move or renovation | Cortisol spike for 3 to 10 days | One safe room set up first, cat moved last, no workers in that room |
| Boarding or clinic stay | Crowding, unfamiliar smells | Ask for a quiet kennel, bring the cat's own blanket |
| Cold snap, drafty floor | Chilled cat, poor air quality | Warm bed 30 cm off the floor, no door drafts |
| Dental pain | Drops grooming and eating | Oral check every 6 months, dental cleaning when advised |
Five things to do this week
- Put a hygrometer in the cat's main room and log morning and evening readings for 7 days.
- Write the last 3 outbreak dates and the event that came 2 to 5 days before each one.
- Add 1 box if you have 2 cats; the rule is 1 per cat plus 1.
- Book the 6 or 12 month exam and ask for a Schirmer test and a weight trend.
- Stop buying lysine at the next order and put that money toward a humidifier.
Frequently asked
Can a cat with FHV-1 live with other cats?
Yes, with management. Keep the carrier's stress low, add 1 litter box per cat plus 1, and quarantine any new cat in a separate room with its own bowls for 10 to 14 days before introductions. Assume every carrier sheds silently now and then, so do not share food bowls, and wash hands after handling eye or nose discharge during an outbreak.
Should I give lysine every day?
Most veterinary ophthalmologists no longer recommend routine lysine, because controlled trials did not show fewer or milder outbreaks at the usual 250 to 500 mg twice daily. If your cat is already on it and stable, there is no need to stop abruptly, but do not expect it to prevent relapses. Spend that budget on humidity control and stress reduction instead.
When does an outbreak need a same-day vet visit?
Go the same day if the cat has not eaten for 24 hours, holds one eye shut or the eye looks cloudy, has a fever above 40 Celsius, breathes through an open mouth, or is still unwell after 14 days. Corneal ulcers can deepen within 48 hours, and a cat that stops eating for 2 days is at risk of hepatic lipidosis.