Herpes and Calicivirus
As many as 90% of URIs in cats are caused by these viruses. In adult cats the "flu" is usually mild, however the virus may linger in the cat's body and flare up again repeatedly over a period of years. Cats affected this way become "carrier cats" and shed the virus intermittedly to other cats they contact.
Vaccinations are available for these viruses, and although not 100% effective in preventing disease, the vaccine can reduce the severity of the "flu" and make it less likely to be passed on to other cats. All kittens need a foundation series of vaccinations, followed by a booster one year later. Vaccines are given by injection or intranasal drops and protection starts within four days to two weeks, depending on the method. The AAFP recommends 3-year boosters, however your own veterinarian may choose a different schedule if your cat is at high risk.
Treatment of Herpes/calicivirus may include antibiotics to ward off secondary bacterial infections. Some veterinarians have found success with Interferon, which helps to boost the immune system. Positive results have also been found with the administration of l-lysine in a dosage of 250-500 mg/day. Special attention should be paid to nutrition with URI-infected cats. Because of nasal stuffiness, they may not be able to smell their food, and refuse to eat. Sometimes warming the food a bit will pep up the odor and entice the cat to eat. Dehydration can be a real problem, so moist foods may be best for the cat under treatment, as well as water given by eye-dropper, if necessary.
Chlamydia was isolated and identified in the U.S. in 1942, and in the U.K. in the 1970s. It was first called "feline pneumonitis agent" as it was isolated from the lung of a cat with pneumonia, and the condition was formerly called "feline pneumonitis". This term may still be used in some areas.
Chlamydia is most often seen in kittens and manifests by early "flu" symptoms, such as sneezing, runny nose and eyes, but more often results in conjunctivitis, commonly called "pinkeye," which may be seen in one or both eyes. The eyes develop a marked discharge, reddened and swollen conjuncivae, and lesions may develop on the eye. The conjunctivitis may or may not become chronic, and the conjunctivitis may also involve the herpes virus, which sometimes manifests in the same manner. Available tests are the polymerase chain reaction (PCR) test for herpes and a culture test for Chlamydia, if your veterinarian feels it necessary to isolate the cause.
Chlamydia is bacterial, and responds to some antibacterial agents, such as Tetracycline or other antibiotic, administered as an ointment to the eyes and/or orally. Vaccines are available for chlamydia, however the AAFP has recommended chlamydia vaccines only be given to "at risk" cats, because of the potential for greater side effects of the vaccine.
As a side note, it has been thought that conjunctivitis caused by chlamydia can also be spread to humans. It is however, not the same chlamydia that causes the more well-known STD in humans. In any case, it would be wise to practice careful hygiene when treating or handling a sick cat, and definitely to keep fingers away from your eyes. If you do contract conjunctivitis after treating a cat with chlamydia, you need to mention that fact to your opthamologist.
In closing, let me give the usual disclaimer that I am not a veterinarian, and have no veterinary training. The information presented here is to give readers a general understanding of the diseases covered and is not intended as either a diagnosis or treatment plan. Only your own veterinarian is qualified to do that, after a thorough examination of your cat.