Feline herpesvirus type-1 (FHV-1) is a highly prevalent respiratory and ocular pathogen within the global cat population. This virus causes Feline Viral Rhinotracheitis (FVR), a common illness that infects cats of all ages, though kittens and cats in multi-cat environments are particularly susceptible. Once exposed, a cat becomes a lifelong carrier, as the virus persists in a dormant state within the nervous system.
The Nature of Feline Herpesvirus and Transmission
Feline Herpesvirus-1 is an alphaherpesvirus highly specific to felines. It primarily targets the epithelial cells lining the upper respiratory tract and the structures of the eye, leading to inflammation and cellular damage. Once the initial infection clears, the virus retreats into the trigeminal nerve ganglia, remaining in a latent phase.
Transmission occurs primarily through direct contact with infectious secretions, such as saliva, or discharge from the nose and eyes of an infected cat. A cat can spread the virus even before showing symptoms, with the active shedding period lasting about one to three weeks after infection. Indirect transmission is also possible through contaminated objects (fomites), including shared food bowls, bedding, or human hands. The FHV-1 virus is fragile outside a host, surviving for only 18 hours to two days, and is easily inactivated by common disinfectants.
Recognizing Acute and Chronic Symptoms
Acute FHV-1 infection manifests as upper respiratory illness. Initial symptoms include fever, lethargy, and a loss of appetite, often due to the cat’s inability to smell food. Affected cats experience severe sneezing fits, copious clear to thick nasal discharge, and ocular symptoms like conjunctivitis (inflammation and redness of the eye tissues).
Ocular involvement is a hallmark of acute FHV-1, frequently causing painful, watery eyes and sometimes chemosis (swelling of the conjunctiva). A specific sign of the virus is the formation of dendritic ulcers on the cornea—small, branching lesions on the eye’s clear surface. In severe primary cases, particularly in young kittens, the virus can lead to permanent damage, such as corneal scarring or chronic nasal and sinus inflammation.
Symptoms can recur throughout the cat’s life, usually triggered by stress, illness, or immunosuppression. These flare-ups are often milder than the initial infection, presenting as intermittent sneezing, mild watery eye discharge, or a recurrence of conjunctivitis. Secondary bacterial infections can complicate both acute and chronic cases, causing the initial clear discharge to become thick, yellow, or green.
Treating Active Infections and Managing Carriers
Treatment for an active FHV-1 infection centers on supportive care to manage symptoms and prevent complications, as there is no cure for the virus itself. Supportive measures ensure the cat maintains hydration and nutrition, which is often challenging when congestion impairs their sense of smell. Clearing nasal and ocular passages using warm compresses or nebulization with sterile saline helps relieve congestion and encourages the cat to eat.
Specific antiviral medications are employed to target the replicating virus, especially in severe cases or those with significant ocular involvement. Oral antivirals, such as famciclovir, may be prescribed to reduce the severity of clinical signs and decrease viral shedding. For eye infections, topical antivirals like idoxuridine or cidofovir may be used. If a secondary bacterial infection is identified, antibiotics are administered, but these do not treat the underlying viral cause.
Managing the carrier state involves strategies focused on minimizing the recurrence of symptoms. Because stress is a major trigger for viral reactivation, maintaining a stable and enriched environment is a primary long-term management technique. Supplements like the amino acid L-Lysine are commonly used, theorized to inhibit viral replication by competing with L-arginine, an amino acid needed by the virus. However, scientific evidence supporting L-Lysine’s efficacy remains controversial.
Prevention Strategies and Human Risk
Preventing severe FHV-1 disease centers on vaccination and rigorous hygiene protocols, especially in multi-cat settings. The Feline Viral Rhinotracheitis (FVR) component of the core FVRCP vaccine protects against FHV-1. While the vaccine does not prevent infection or the establishment of the latent carrier state, it significantly reduces the severity and duration of clinical signs upon exposure.
Kittens typically begin their FVRCP vaccine series around six to nine weeks of age, followed by boosters until they are about four months old, with subsequent boosters required throughout adulthood. In households with an infected cat, strict hygiene is paramount, including isolating sick cats and thoroughly disinfecting shared areas. Minimizing crowding and other environmental stressors also helps to reduce the frequency of viral shedding from carrier cats.
FHV-1 is a species-specific pathogen that poses no risk of infection to humans or other non-feline pets. While humans have their own forms of herpesviruses, the feline strain cannot cross the species barrier to cause disease in people. Standard hygiene practices, like handwashing after handling any sick animal, remain appropriate to minimize the transmission of potential secondary bacterial infections.