Feline Herpesvirus

Feline herpesvirus, also known as viral rhinobronchitis, is widely present worldwide and only one serotype has been confirmed, but its virulence varies among different virus strains. The feline herpesvirus replicates and proliferates in the epithelial cells of the conjunctiva and upper respiratory tract, as well as in neuronal cells. Infection with a neural pathogen can lead to lifelong latent infection. Although feline herpesvirus is antigen related to canine herpesvirus, it is not yet known whether they can be transmitted to each other. Feline herpesvirus 1 (FHV-1) is a large virus with a envelope and double stranded DNA. It proliferates in the nucleus and forms nuclear inclusions. The feline herpesvirus is extremely unstable under acidic conditions and is highly sensitive to heat, ether, chloroform, formalin, and phenol. It can survive in dry environments for no more than 12 hours, making it quite fragile in the environment. Conventional disinfectants can effectively disinfect it. The infected object FHV-1 only infects feline animals and has also been isolated from dogs, but its importance is still unclear.

Figure 1. Feline Herpesvirus Infections. (Sykes J E, 2022)

Introductions

Chronic latent infection is a typical result of acute infection with feline herpesvirus, which intermittently reactivates and releases the virus into oral, nasal, and conjunctival secretions. Unless kept in a cat house, environmental pollution is not the main source of infection. The main sources of infection are cats in the acute infection phase and cats in the chronic latent infection phase that have been reactivated and detoxified. The possibility of placental infection has not been confirmed, but chronic latent infection in female cats is considered an urgent state during delivery and lactation, which can lead to virus reactivation and emission. Therefore, young cats may be exposed to the virus at a very early stage. But the outcome of its infection depends on the amount of maternal transitional antibodies. When there are sufficient transitional antibodies, some cats will be protected by them, resulting in asymptomatic infection and latent infection. If there is insufficient transitional antibodies, clinical symptoms may occur. In healthy small populations, the incidence of virus emissions may be less than 1%, while in symptomatic large populations, the incidence of virus emissions may reach 20%.

Etiology

The virus enters the cat's body through the mouth, nose, conjunctiva, and other pathways, causing lytic infection of the nasal mucosal epithelial cells and spreading to the conjunctiva, throat, trachea, bronchi, and bronchioles. The lesions are local multiple necrotic (neutrophil infiltration) and inflammatory lesions, and there have been reports that transient viremia may occur, especially in newborns or low-temperature kittens, because feline herpesvirus likes to replicate at lower temperatures. After 24 hours of infection, the virus begins to be released and lasts for 1-3 weeks. Acute symptoms will be relieved within 10-14 days, while some may develop chronic lesions in the upper respiratory tract and eyes. The virus spreads along the sensory nerves and reaches the neurons, especially in the trigeminal ganglion, which is the main site of latent infection. Almost all infected cats become lifelong carriers of the virus. At present, there is no simple testing method to detect this latent state, as the virus's genes exist in the nucleus of infected neurons and do not replicate.

Anti-FHV Antibody

Feline Herpesvirus Antigen