Conjunctivitis in Cats

By Susan Carastro, D.V.M.   

The conjunctiva is the mucus membrane that encircles the eyeball and lines the eyelids. Conjunctivitis is an inflammation of this tissue regardless of the cause. Cats with conjunctivitis may manifest clinical signs such as squinting, discharge from the eye (watery or mucosal), and redness or swelling of the conjunctiva. Conjunctivitis may also be accompanied by upper respiratory signs, including coughing, sneezing, or nasal discharge. The mucus membrane that lines the nasal cavity is affected by many of the diseases that affect the mucus membrane associated with the eye. Potential causes for conjunctivitis include feline herpes virus, chlamydia, mycoplasma, eosinophilic conjunctivitis, and allergic (environmental) disease. Feline herpes virus is by far the most common cause of conjunctivitis in the cat. Herpes is a virus that is very contagious from cat to cat. It may be transmitted from the mother (queen), from other kittens in the litter, or from acquaintances. Over 80 percent of the cats in our country have been infected with the herpes virus. The initial infection is characterized by an upper respiratory infection (coughing, sneezing or nasal discharge) and conjunctivitis. In severe cases, the cornea, the front clear part of the eye, may become involved, potentially resulting in permanent visual impairment. In most cats this is a self-limiting problem in that the animal's own immune system rids itself of the virus. However, in cats with a poor immune system, such as kittens, older cats or cats infected with feline immunodeficiency virus (similar to the AIDS virus in people), the infection can be debilitating, vision-threatening, and, in some cases, even life-threatening. The devastating aspect of this virus is that half of the cats infected will develop a dormant or latent form of the virus. Recurrent bouts of the infection in cats that develop the latent form of the virus are usually limited to conjunctivitis and/or corneal involvement. The recurrent episodes may be spontaneous, or brought on by environmental stress or drugs that suppress the immune system. It is a frustrating disease in that there in no cure for the dormant infection and recurrences are unpredictable. A definitive diagnosis of herpes virus is difficult as many of the tests used reveal false negative results (i.e., a negative test result when the cat is really infected with herpes). To date, the best diagnostic test available is polymerase chain reaction (PCR), which detects small amounts of viral DNA. In many cases, treatment may be instituted based on a high suspicion for herpes virus due to history and the clinical signs noted upon examination of the eyes. Treatment includes the use of topical antiviral drugs (i.e., Viroptic or idoxuridine) to aid in the resolution of clinical signs. Potential disadvantages of these drugs are the expense and a burning or stinging sensation in some eyes that may occur. Topical antibiotics are generally used to prevent secondary bacterial infection. Oral L-lysine, a nutritional amino acid supplement, has been shown to limit the severity of the infection and recurrent bouts of infection. Therefore, daily use of oral L-lysine is recommended to limit recurrences in cats with herpes infection. The resolution of clinical signs is variable in that many cats exhibit immediate improvement, while others may take weeks. Consequences of herpes infection include disfigurement of the lids and eye due to scarring, dry eye, visual impairment due to corneal scarring, and persistent discharge from the eye due to scarring of the tear duct. This virus is not contagious to people but is very contagious to other cats, especially when they are coughing and sneezing. Thus, if the upper respiratory signs are present, isolation from other cats is recommended. Chlamydia and mycoplasma are organisms that may infect the conjunctiva of the cat, causing similar clinical signs noted with herpes infection. Infection with these organisms is much less common, however. Identification of the organism in infected animals may be obtained by swabbing the conjunctiva and evaluating the sample under a microscope. Both of these organisms are sensitive to relatively inexpensive topical antibiotic therapy, including tetracycline and chloramphenical. Both of these drugs can prevent recurrences of the infection. Allergic or environmental diseases may result in the similar clinical signs (i.e., squinting, discharge or redness). Diagnosis is made by excluding all the other possibilities for conjunctivitis. The inflammation noted can generally be controlled with intermittent flushing of the eyes, and use of topical or oral antihistamines or topical anti-inflammatory agents. Many causes of conjunctivitis appear similar, thus testing to evaluate for the exact cause is recommended. Once the cause is identified, the appropriate medication may be instituted. -Susan M. Carastro, D.V.M., M.S., Diplomate, American College of Veterinary Ophthalmologist, practices at the following locations: Animal Eye Specialty Clinic, 372 S. Power Line Rd., Deerfield Beach, FL 3344,2 tel: (954) 421-5099; 3421 Forest Hill Blvd, W. Palm Beach, FL 33406, tel: (561) 967-5966; and at 2399 S. Kanner Hwy, Stuart, FL 34994, tel: (561) 220-8485.

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