Update on viral diseases in cats (Proceedings)
Feline herpesvirus (FHV) is a common pathogen of domestic cats. The virus is a ds DNA virus with a lipid envelope. The virus primarily targets epithelia of the upper respiratory tract and conjunctiva, and only rarely spreads beyond these regions to cause disease. As with all herpesviruses, after acute infection it enters a latent state in innervating sensory nerves. In cats, this most commonly occurs in the trigeminal ganglion. From this latent state, the virus can be reactivated leading to replication in the epithelia, virus shedding, and in a minority of cats, disease. Termed recrudescence, it can be stimulated by any stressor, including trauma, concurrent disease, parturition, boarding, or changes in social hierarchy.
The typical presentation of FHV infection is that of upper respiratory tract disease: sneezing, nasal and/or ocular discharge, depression, and decreased appetite. Conjunctivitis is not uncommon, and can progress to severe hyperemia and chemosis, with mucopurulent ocular discharge. Infection may lead to corneal ulceration. Less common manifestations of FHV are ulcerative dermatitis and stomatitis.Diagnostics for FHV infection primarily involves virus detection, as most cats are seropositive from either natural exposure or vaccination. Antigen detection using immunofluorescence is fast and inexpensive; however, sensitivity is relatively low, especially in chronic infections. Virus isolation remains the gold standard. However, in chronic infections, notably chronic conjunctivitis or other ocular disease, the virus may be neutralized by locally-produced antibody leading to false negative results. Genetic detection using polymerase chain reaction (PCR) has high sensitivity, such that subclinical, and even latent infections may be detected. Thus, positive results must be interpreted in light of other clinical information.
Advancements have been made in the treatment of FHV infection in cats. Nucleoside analogs developed for human herpesvirus infections have shown some efficacy against feline herpesvirus, at least in vitro. Toxic side effects have been reported with some, such as acyclovir, but others, such as ganciclovir may prove to be useful clinically. Topical administration of antiviral medications has been used with some success, and include trifluridine and idoxuridine. Interferon (IFN) has been used with some success, and has been shown to be efficacious in vitro (human alpha IFN – US; and feline omega IFN – Europe). L-lysine given orally inhibits viral protein synthesis and restricts virus replication. It is optimal when used early in infection, or as a means to prevent recrudescence during stress. Experimentally, lactoferrin has been shown to inhibit virus attachment and entry, and may be eventually be available as an antiviral treatment for FHV.
Protection following recovery is not long-lived, and reinfections may occur. Antigenic variation is not a significant problem with feline herpesvirus, thus, the antigenic coverage of vaccines is adequate. Non-adjuvanted modified live vaccines are recommended. Vaccines do not prevent infection, nor production of the carrier state. They do offer protection from disease, however.