Feline herpesvirus (FHV-1): the complete treatment guide.
Feline herpesvirus affects mainly the eyes and the upper respiratory tract. The virus never leaves the body, but each flare-up can be shortened and the eyes protected. Here is how to recognise it, how it is diagnosed, what treatment exists, and how to live with the flare-ups. We ship across the Gulf.
From the first signs to managing flare-ups, in four parts.
Everything worth knowing about feline herpesvirus and its antiviral treatment, in the order you need it.
- 1
Recognise the signs
What happens in the eyes, what happens in the airways, and the signs that cannot wait.
- 2
Confirm the diagnosis
Telling it apart from calicivirus and from chlamydial or mycoplasmal conjunctivitis.
- 3
Start treatment
HerpX™, dosing by weight, and why human antivirals are never an option.
- 4
Living with flare-ups
What it means that the virus stays for life, and how to space the episodes out.
What feline herpesvirus is
Feline herpesvirus (FHV-1), also called feline viral rhinotracheitis, is extremely contagious and most cats are infected as kittens. It is characterised by ocular signs such as conjunctivitis and corneal lesions, alongside sneezing, nasal discharge and congestion.
- 1
First infection
Appears mainly in kittens and young cats. Sneezing, nasal discharge, eye discharge, conjunctivitis, fever and reduced appetite. Most stabilise within one to two weeks with supportive care.
- 2
Latency and flare-ups
When the signs settle, the virus does not leave: it stays latent in the trigeminal ganglion. Stress, another illness or a treatment that lowers immunity can reactivate it.
The virus stays, but that does not mean the signs always return.No treatment, famciclovir included, clears feline herpesvirus from the body: it remains for life. That said, flare-ups occur only in some cats, and many carriers never show signs again. A flare-up is not treatment failure, it is normal herpesvirus behaviour.
Signs of feline herpesvirus
The eyes are this virus's characteristic target. Noticing the ocular change in time, not just the sneezing, is what makes the difference.
- 1Squinting one eye
- 2Watery eye
- 3Red eye
- 4Eye discharge
- 5Cloudy or ulcerated cornea
- 6Sneezing
- 7Nasal discharge and congestion
- 8Fever
- 9Reduced appetite and lethargy
- 10Mouth ulcers (uncommon)
If the cat is squinting, if the cornea looks cloudy, or if the surface of the eye looks damaged, do not wait.Corneal ulcers caused by feline herpesvirus can progress and threaten sight. It is the one sign on this list that does not allow a wait-and-see approach.
How it is diagnosed
Not every case of conjunctivitis or sneezing in cats is herpesvirus. If the cause changes, the treatment changes.
- 1
Clinical and ocular examination
Conjunctivitis combined with sneezing points strongly to feline herpesvirus. Corneal lesions are confirmed with fluorescein stain.
- 2
PCR
Detects the virus from a conjunctival or oral swab. Vaccinated cats and cats without signs can also test positive, so it is read alongside the clinical picture.
- 3
Separating it from calicivirus
If ulcers in the mouth dominate, feline calicivirus (FCV) is more likely. If the eyes dominate, it points to herpesvirus.
- 4
Ruling out bacterial causes
Chlamydial and mycoplasmal conjunctivitis do not improve with an antiviral. They need different treatment.
If the main problem is in the mouth, this may not be the virus.When ulcers and oral inflammation are what keep returning, feline calicivirus is worth investigating. You can compare against the FCV guide.
The treatment
The goal is not to eliminate the virus but to slow its replication during a flare-up, so the episode is shorter and the eyes are protected. Being clear about the goal makes the decisions much easier.
HerpX™ 180 mg
HerpX™ contains famciclovir, the oral antiviral with the strongest clinical support for feline herpesvirus (FHV-1), in tablets formulated for cats. Famciclovir is a prodrug of penciclovir and reaches therapeutic concentrations even in tear fluid.
- Not split human tablets: a 180 mg fixed dose intended for cats.
- One tablet per 2 kg of body weight, every 12 hours, one hour before feeding.
- In ocular cases it is usually combined with the eye drops your veterinarian prescribes.
- AROUND 2 KG
1 tablet
180 mg every 12 hours.
- AROUND 4 KG
2 tablets
360 mg every 12 hours.
- AROUND 6 KG
3 tablets
540 mg every 12 hours.
Do not reduce the dose.Cats convert famciclovir to penciclovir less efficiently than people do, so the required dose is far higher than the human reference. The most common error is under-dosing by reasoning down from a human dose. Even as the cat improves, do not reduce or stop without veterinary direction.
Never use human antivirals
If there is one thing to take away from this page, it is this.
- 1
Aciclovir and valaciclovir
The antivirals used for herpes in people have documented toxicity in cats: they can cause bone marrow suppression and kidney damage. They are not given to cats. Similar names do not make them interchangeable.
- 2
Famciclovir is different
At appropriate doses it is considered systemically safe in cats, and its use in the species is supported by published studies. HerpX™ is that famciclovir, formulated for cats.
It is supported by published feline studies.Famciclovir use in cats rests on pharmacokinetic studies, dose-optimisation modelling and a clinical series of 59 cases with ocular, respiratory and cutaneous lesions. That is where the widely used guidance of approximately 90 mg/kg every 12 hours comes from.
When it is not used, and when it is used with care
Before starting, tell your veterinarian every medication your cat is receiving.
- 1
Not given to
Cats with allergy to famciclovir or penciclovir, with acute renal failure, or with severe liver disease. In pregnant or lactating queens, only where your veterinarian judges the benefit to clearly outweigh the risk.
- 2
Used with care in
Cats with reduced renal function, kittens under 8 weeks, and cats on long-term immunosuppressive treatment. Corticosteroids can reactivate the latent virus, so it is worth weighing that with your veterinarian.
Some interactions are worth keeping in mind.Probenecid raises penciclovir concentrations. Nephrotoxic drugs such as aminoglycosides and NSAIDs can have additive effects on the kidney. Some antifungals, rifampicin and chloramphenicol can alter famciclovir conversion.
Living with flare-ups
Famciclovir does not stop flare-ups happening. What it does is make each episode milder and shorter.
- 1
Reduce stress
Moving home, boarding, a new cat, visitors. Most reactivations follow a change in the environment. What cannot be avoided can at least be spaced out.
- 2
Eye care
Clean discharge gently with clean gauze. If eye drops are prescribed, follow exactly what your veterinarian directed. Do not use over-the-counter drops on your own initiative.
- 3
Catch it early
If sneezing, eye discharge or lethargy return, get advice promptly. The earlier treatment starts, the shorter the episode.
- 4
Other cats in the home
A cat with signs sheds virus when it sneezes. Separate bowls and clean frequently. Most are already infected, but there is no reason to add viral load.
A flare-up does not mean the treatment failed.With the virus housed in nerve tissue, reactivation at some point is expected. Even cats that flare often live completely normal lives when each episode is treated promptly.
About feline herpesvirus
Can the virus be cleared from the body?+
No. Feline herpesvirus stays latent in nerve tissue for life. That said, signs reappear only in some cats, and many carriers never show them again. The aim of treatment is to shorten each flare-up and protect the eyes.
Can I give human aciclovir?+
No. Aciclovir and valaciclovir have documented toxicity in cats and can cause bone marrow suppression and kidney damage. Cats are given famciclovir. Similar names do not mean similar safety.
Is HerpX™ an antibiotic?+
No. It is a direct-acting antiviral. Antibiotics act on bacteria and do nothing against a virus. Your veterinarian may prescribe one separately if a secondary bacterial infection appears.
How quickly is it noticeable?+
It depends on the severity of the flare-up, but most cats show a change in eye discharge and sneezing within a few days. Even so, continue treatment until your veterinarian advises otherwise.
Does vaccination prevent it?+
Core vaccines reduce the severity of illness and viral shedding, but they do not prevent infection or flare-ups in a cat that already carries the virus latently. They are still worth keeping current.
Will it spread to my other cats?+
Yes, through sneeze droplets, eye and nasal discharge, and shared bowls. In multi-cat homes most are already infected, but it is worth separating bowls and cleaning frequently while signs are present.
Can I catch it?+
No. Feline herpesvirus (FHV-1) is specific to cats: it does not infect people or dogs, and it is unrelated to human herpesviruses.
Do I need a vet visit if the cat is only squinting?+
Yes. Squinting, a cloudy cornea or an eye surface that looks damaged can indicate a corneal ulcer, and that threatens sight if it progresses. It is the sign not to monitor from home.
If your question is not here, see the FAQ.
If something is wrong with your cat's eyes
A squinting eye, watering, discharge that will not clear, or sneezing that keeps returning. See your veterinarian first, then talk to us about treatment. We ship across the Gulf.