Felis ISSN 2398-2950

Feline herpes virus: feline rhinotracheitis virus

Introduction

Classification

Taxonomy

• Order: Herpesvirales.
• Family: Herpesviridae.
• Subfamilies: Alphaherpesvirinae (see also Gammaherpesvirinae).
• Genus: Varicellovirus.
• Species: FHV-1.

Active Forms

Clinical Effects

Epidemiology

Transmission of FHV-1

• Transmitted by direct contact and by short-distance aerosolization through sneezing.
• Indirect transmission via contaminated food bowls, hands, etc (less important than direct transmission due to virus susceptibility to desiccation, disinfectants, etc).
• Fomite transmission is more important than aerosol in cats due to small lung tidal volume.
• Route of infection: intranasal, oral or conjunctival.
• Virus is shed in oropharyngeal, nasal and ocular secretions within 24 hours of infection and shedding of infectious virus lasts up to 3 weeks.

Pathological effects

• Virus growth occurs in the epithelium of the nasal mucosa, conjunctiva, tonsil and nasal turbinates: tissue damage is due to viral cytolysis. Clinical signs of upper respiratory tract disease due to this damage. May see severe nasal and/or ocular discharge, sneezing, anorexia, depression.
• Corneal lesions seen on days 3 and 12 of primary infection, in kittens: corneal edema Eye: corneal opacity, ulceration Ulcerative keratitis and rupture of eyeball often around 2-4 weeks of age. In older kittens and cats: dendritic keratitis, corneal sequestrum, adhesions to conjunctivae or to iris.
• May leave surviving cats with chronic or recurrent ocular discharge Eye: ocular discharge - overview, chronic sinusitis Sinusitis or rhinitis Rhinitis.
• Neutralizing antibody recognizes gp60, the viral hemagglutinin, which is essential for attachment to cells.
• Neutralizing antibody titers are low: 1:16-1:64.
• Neutralizing antibodies appear 20-30 days post-infection.
• Immunity is primarily cell-mediated.
• Infection is life-long, and latently infected cats may still have neutralizing antibodies.
• Maternally derived antibody protection is usually short lived, but may last until 6-10 weeks of age.
• Antibodies detected by immunofluorescence may decrease to low or undetectable levels within several months.

Other Host Effects

• Most infected cats become latently infected as carriers.
  Kittens may become latent carriers without ever showing signs.

Control

Control via chemotherapies

• Famciclovir is the treatment of choice for ocular FHV (corneal ulceration, keratitis, corneal sequestrum), chronic rhinosinusitis, and FHV dermatitis, at a dose of 62.5-90 mg/kg TID per os.
• Neither a single nor double dose of famciclovir administered prophylactically at shelter intake were efficacious in reducing upper respiratory disease incidence.
•  For ulcerative keratitis: 0.1% ophthalmic solution of 5-iododeoxyuridine 4-6 times daily for 3-5 days
• (Acyclovir Acyclovir, used for herpes simplex in man, is less active against FHV and is toxic to cats if given systemically).  
• For conjunctivitis: salt water bathing QID is often effective (5 g sodium chloride dissolved in 250 ml water).
• Topical feline interferon omega Interferon is useful for FHV-related ocular disease (ulceration, conjunctivitis).
• Feline interferon omega has been reported to be useful in FHV-related dermatitis.
• L-lysine is used in human herpesvirus infection because it competes with arginine in the formation of the herpesvirus capsid protein. However, it is contraindicated because it is ineffective, probably because arginine is an essential amino acid in the cat and reduction of plasma arginine is detrimental to immune function.
• Broad spectrum antibiotic cover useful against secondary bacterial infection.
• Good nursing, especially to encourage feeding, as cats will not eat what they cannot smell (use strong-smelling foods such as tuna, sardines).
• Eucalyptus oil on bedding or bandana, or steam inhalation, to aid clearing of nasal passages. Use with caution, since it is toxic to cats if ingested. 

Control via environment

• Disinfectant: Most detergents or bleach diluted 1:32 in water with washing-up liquid.
• When choosing a disinfectant for use around cats, be aware that deficiency of the enzyme UDP-glucuronosyl transferase renders the cat susceptible to the toxic effects of phenol-based disinfectants (including many essential oils). Quaternary ammonium compounds are not recommended.
• Rescue shelters should strive to have natural or positive pressure ventilation to reduce aerosol transmission of cat flu viruses.
• Reduction of environmental stress is an extremely important factor in FHV-1 control.
• Feline pheromone diffusers anecdotally are said to help reduce FHV-1 related clinical signs, but no reduction in virus shedding was demonstrable in experimental infection.

Vaccination

• Inactivated and modified-live vaccines are available for FHV-1, and protect reasonably well against disease but not infection, although viral shedding may be reduced. Therefore most vaccinated cats have latent FHV-1 infection.
• Intranasal vaccination is available in the USA, but not the UK.
• Immunity against FHV-1 is primarily cell-mediated.
• Post vaccination, the duration of FHV-1 immunity has been shown to last for at least 3 years.
• Only 22% of 109 cats of one year of age or older showed a rise in antibody titers post-vaccination.
• Purebred cats fail to develop a four-fold antibody titer increase after vaccination more often than domestic cats.

Other countermeasures

• FHV prevention in kittens:
  • Boost queen's immunity before conception.
  • Isolate queen from other cats before birth of kittens.
  • Ensure good intake of colostrum to supply maternally derived immunity.
  • Wean kittens early, at 2-3 weeks of age, and keep isolated from all other cats.
  • Vaccinate at 8 and 12 weeks of age.
  • In some kittens early vaccination is used, but is not licensed in UK.
• Avoid iatrogenic latent FHV reduction by minimizing use of glucocorticoids and estrous suppressants.
• Optimize nutrition to support the immune system by ensuring adequate arginine levels.

Diagnosis