FHV1_Icon.jpgFeline Herpes Virus Antibody Test (IFA)

Feline viral rhinotracheitis (FVR) is an upper respiratory or pulmonary infection of cats caused by feline herpes virus 1, of the family Herpesviridae. It is also known as feline influenza, feline coryza, and feline pneumonia. Viral respiratory diseases in cats can be serious, especially in catteries and kennels. Causing one-half of the respiratory diseases in cats, FVR is the most important of these diseases and is found worldwide. The other important cause of feline respiratory disease is feline calicivirus.

FVR is very contagious and can cause severe disease, including death from pneumonia in young kittens. It can cause flat-chested kitten syndrome, but most evidence for this is anecdotal. All members of the Filidae family are susceptible to FVR; in fact, FHV-1 has caused a fatal encephalitis in lions in Germany. FHV-1 was first isolated from cats in 1958 in the United States.

FVR is transmitted through direct contact only. It replicates in the nasal and nasopharyngeal tissues and the tonsils. Viremia (the presence of the virus in the blood) is rare. The virus is shed in saliva and eye and nasal secretions, and can also be spread by fomites. FVR has a two to five day incubation period. The virus is shed for one to three weeks post infection. Latently infected cats (carriers) will shed FHV-1 intermittently for life, with the virus persisting within the trigeminal ganglion. Stress and use of corticosteroids precipitate shedding. Most disinfectants, antiseptics and detergents are effective against the virus.

Diagnosis of FVR is usually by clinical signs, especially corneal ulceration. Definitive diagnosis can be done by direct immunofluorescence or virus isolation. However, many healthy cats are subclinical carriers of feline herpes virus, so a positive test for FHV-1 does not necessarily indicate that signs of an upper respiratory tract infection are due to FVR. Early in the course of the disease, histological analysis of cells from the tonsils, nasal tissue, or nictitating membrane (third eyelid) may show inclusion bodies (a collection of viral particles) within the nucleus of infected cells.

There is a vaccine for FHV-1 available (ATCvet code: QI06AA08, plus various combination vaccines), but although it limits or weakens the severity of the disease and may reduce viral shedding, it does not prevent infection with FVR. Studies have shown a duration of immunity of this vaccine to be at least three years. The use of serology to demonstrate circulating antibodies to FHV-1 has been shown to have a positive predictive value for indicating protection from this disease. Most household disinfectants will inactivate FHV-1. The virus can survive up to 18 hours in a damp environment, but less in a dry environment and only shortly as an aerosol.

Our test for feline herpes virus is an indirect fluorescent antibody (IFA) procedure that is carried out on Teflon matted glass slides with herpes virus (Black Strain 1984) infected cells fixed to their surface. This method requires the use of diluted patient serum being placed on the slide and incubated for 30-minutes at which time the slide is washed and a fluorescein conjugated anti-cat globulin is placed on the slide. If any antibodies to FVR are present in the patient serum they will combine with the FVR antigen fixed to the slide surface. The fluorescent antibody conjugate will then be bound to the FVR antibodies and the resulting antibody-conjugate complex viewed with an ultraviolet microscope are seen as bright areas of fluorescence in the infected cells. The total number of infected cells on our slides does not exceed 40% which leaves the negative cells to enhance contrast.