CONDITION
Feline Herpesvirus (FHV-1)
Feline herpesvirus type 1 is one of the primary causes of upper respiratory infection in cats, characterised by sneezing, nasal discharge, and eye problems, with most infected cats becoming lifelong carriers.
Why this matters now
Feline herpesvirus infection is extremely common, with most cats exposed during kittenhood, particularly in multi-cat environments or rescue situations. Initial infection typically causes respiratory illness, while subsequent flare-ups can occur throughout life during periods of stress or immune compromise.
Primary infection usually affects kittens, causing sneezing, nasal congestion, and eye inflammation. Acute illness usually resolves within 10 to 14 days, although eye signs can last longer where the cornea is affected. Disease is particularly severe in young kittens, and occasionally the virus causes pneumonia and widespread illness that can be fatal. Following recovery, the virus establishes latency in nerve tissue, remaining dormant but periodically reactivating. Stress, other illness, or immunosuppression can trigger recurrence, with signs typically milder than the initial infection but sometimes affecting the eyes significantly.
Signals & patterns
Early signals
Sneezing episodes
Frequent, sometimes violent sneezing is often the first sign of upper respiratory infection.
Watery eye discharge
Clear fluid from one or both eyes, sometimes with reddening of the conjunctiva.
Clear nasal discharge
Runny nose that may later become thicker and discoloured if secondary bacterial infection develops.
Mild fever
Elevated body temperature may accompany acute infection, though often subtle.
Later signals
Thick, coloured nasal discharge
Yellow or green discharge suggests secondary bacterial infection complicating the viral illness.
Mouth breathing
Cats normally breathe through the nose, so breathing with the mouth open is a sign of real difficulty. Severe nasal congestion can cause it, but so can disease in the chest, and which one is responsible cannot be judged at home.
Corneal ulcers
Herpesvirus can damage the surface of the eye, causing painful ulceration visible as cloudiness or squinting.
Reduced appetite
Loss of smell from a blocked nose, and sometimes mouth ulcers, reduce interest in food. ABCD guidance treats three days without eating as the point at which feeding by tube is indicated.
Click to read about the biological mechanisms
How this is usually investigated
Diagnosis often relies on clinical signs in conjunction with history, as testing for herpesvirus has limitations in distinguishing current infection from latent carrier status.
Clinical examination
PCR testing
Fluorescein eye stain
Schirmer tear test
Blood tests
Options & trade-offs
Management combines supportive care during active episodes with strategies to reduce recurrence frequency and address specific complications like eye disease.
Supportive nursing care
Steam inhalation, gentle nasal cleaning, and encouraging food intake
Trade-offs: Forms the basis of care in most episodes; requires owner commitment; eases signs while the virus runs its course.
Antiviral medication
Drugs like famciclovir that reduce viral replication
Trade-offs: Can shorten episodes and reduce severity; famciclovir is a human medicine with no UK veterinary authorisation, so it is prescribed under the veterinary cascade; cost is a consideration.
Topical antiviral eye drops
Medication applied directly to affected eyes for ocular disease
Trade-offs: Targets eye involvement; the antiviral eye products used in cats in the UK are human medicines prescribed under the veterinary cascade; requires frequent application; can be challenging to administer; often combined with oral treatment.
L-lysine supplementation
Amino acid supplement once proposed to suppress viral replication
Trade-offs: A nutritional supplement, not an authorised medicine; a 2015 systematic review found it does not prevent or treat herpesvirus infection, and two shelter studies found more frequent or more severe disease in cats fed lysine-supplemented diets; the ABCD guideline does not recommend it and notes it might affect kitten growth.
Antibiotics
Treatment for secondary bacterial infections complicating the viral illness
Trade-offs: Does not treat the virus itself; addresses bacterial component; important for complicated cases.
Stress reduction
Environmental modifications to reduce triggers for reactivation
Trade-offs: Addresses underlying cause of flare-ups; long-term benefit; requires understanding individual stressors.
Common misconceptions
"Cats that recover from herpesvirus are no longer infected"
Most cats become lifelong carriers after initial infection, with the virus remaining dormant in nerve tissue and periodically reactivating.
"Vaccination prevents herpesvirus infection completely"
Vaccination reduces disease severity and shedding but does not prevent infection or eliminate carrier status in previously infected cats.
"Herpesvirus can spread from cats to humans or other species"
Feline herpesvirus infects domestic cats and some wild cats, such as lions and cheetahs, and grows only in cat cells, so it does not infect people. It belongs to the same broad group as the human cold-sore virus but is a different virus.
Related conditions
Feline Calicivirus
Feline calicivirus is the other major viral cause of upper respiratory infection in cats and often co-occurs with herpesvirus, particularly in multi-cat environments. The two viruses can produce overlapping signs, though calicivirus tends to cause more prominent oral ulceration.
Pneumonia
Pneumonia can develop as a secondary complication when herpesvirus infection damages the upper respiratory tract lining, allowing bacterial organisms to establish infection deeper in the airways. This progression is more commonly seen in young kittens or immunocompromised cats.
Feline Idiopathic Cystitis
Both feline herpesvirus and feline idiopathic cystitis are stress-responsive conditions in cats where environmental or emotional triggers can precipitate flare-ups.
Cat owners recognising respiratory signs or eye problems in their pet can understand that feline herpesvirus is extremely common and usually manageable in adult cats. The exceptions are young kittens, cats that stop eating, cats breathing with the mouth open and cats with a squinting or cloudy eye, where the illness can be more serious. Awareness that stress triggers flare-ups and that supportive care forms the basis of treatment helps frame realistic expectations for living with a carrier cat.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS