Summary
Many cats, especially those who live outdoors in a community setting or are housed in highly populated catteries, commonly suffer a communicable, infectious condition referred to as viral conjunctivitis.
The disease of conjunctivitis is generally characterized by an inflammation of the delicate pink tissues that frame the eyeball just under the eyelids . When affected, these tissues (called the conjunctiva, plural conjunctivae) will become a deeper pink color, get puffy and swollen, and experience copious tear production. They may also become itchy and painful and become the target of self-trauma as a result of the inflammatory process. This entire collection of changes is referred to as conjunctivitis.
While this process may be initiated by viruses or bacteria, an allergic reaction is the most common cause of conjunctivitis among canines. Meanwhile, the most common cause of conjunctivitis among cats is a virus. Herpesvirus 1 (abbreviated as HPV-1) is the viral conjunctivitis which most commonly afflicts cats. Calicivirus is another major offender.
Symptoms and Identification
As described above, the signs of viral conjunctivitis include but are not limited to the following which may be present in one or both eyes:
Excessive lacrimation (tear production)
Redness
Pruritis (itchiness)
Swelling
Viral conjunctivitis is usually diagnosed by visual examination and a history of similar illness. However, the following tests may be undertaken while pursuing a comprehensive understanding of the diagnosis and the condition's potential complicating factors:
Visual inspection
Conjunctival smear with a sterile cotton swab for cytological evaluation
Skin scraping around the eye to rule out skin parasites, if a contributing factor
Conjunctival culture (obtained with a sterile cotton swab)
Response to treatment for possible concurrent skin disease
Response to treatment for possible concurrent viral disease
Response to treatment for possible concurrent dental disease
Evaluation for possible concurrent nasal disease
Affected Breeds
While all breeds of dogs are susceptible, those who suffer allergic skin disease at higher rates are clearly overrepresented . These include dogs predisposed to allergic otitis externa (link), flea allergies, atopy, and other forms of allergic skin disease.
While all breeds of cats are susceptible to conjunctivitis, purebred cats are more likely to originate from highly populated catteries where the transmission of infection is more commonplace. Those with chronic ocular conditions as a result of their brachycephalic conformation (flattened faces with short noses such as those seen in Persians and Himalayans, for example) may also be more susceptible.
Treatment
Viral conjunctivitis infections considered highly treatable, if frustrating to deal with, because of their typically recurrent nature and the frequent inability of cat owners to medicate their cats with sufficient regularity.
Antiviral treatments which may be effective include idoxuridine, trifluridine, cidofovir, famciclovir, and lysine. The first 3 are available as topical solutions. However, these may be difficult to administer to certain cats due to temperament issues.
Hence, systemic antivirals (oral or injectable drugs) may be needed for those who won't allow topical treatment. This approach may also be necessary for those who may suffer systemic signs related to feline viral rhinotracheitis (FHV-1). In these cases, famciclovir (Famvir(R)) is a relatively new oral antiviral medication that may be of some benefit.
Lysine is another systemic approach. This "nutraceutical" is typically administered in a cat's food but its effectiveness is considered modest at best.
Veterinary Cost
The cost of viral conjunctivitis diagnosis and treatment depends to a large extent on the severity of the individual cat's case and the frequency of the issue's recurrence.
For example, if this is an annual or semi-annual occurrence independent of any other obvious manifestations, owners may elect to treat each episode symptomatically and will not require the constant expense of recurring medical needs.
As such, the issue may be relatively inexpensive since incurred costs are then relegated to the price of simple diagnosis and treatment of episodes (typically between $100 and $200 apiece). If, however, more comprehensive diagnostic tests are recommended to rule out other ocular conditions the expenses will often rise significantly.
Treatment itself can also prove costly as some patients with more severe disease or frequent recurrences will require the antiviral and anti-inflammatory drugs described above, often with a higher price tag.
Prevention
Effective prevention feline viral conjunctivitis isn't often easily accomplished once the infection has been established. Managing the conjunctival inflammation and treating any underlying ocular diseases is crucial, however. Vaccination may also prove beneficial in some cases.
References
Fontenelle J, Powell C, Gionfriddo J, et al. Effect of topical cidofovir on experimentally induced FHV-1 conjunctivitis (abstract). Vet Ophthalmol 2005; 8:444.
Galle LE. Antiviral therapy for ocular viral disease. Vet Clin North Am Small Anim Pract 2004; 34:639-653.
Kern TJ. Antibacterial agents for ocular therapeutics. Vet Clin North Am Small Anim Pract 2004; 34:655-668.
Stiles J, Townsend WM, Rogers QR, et al. Effect of oral administration of L-lysine on conjunctivitis caused by feline herpesvirus in cats. Am J Vet Res 2002; 63:99-103.
Thomasy S, Maggs D, Lim C, et al. Safety and efficacy of famciclovir in cats infected with feline herpesvirus 1, in Proceedings. 37th Annu Conf Am Coll Vet Ophthalmol 2006; 43.