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Feline Herpes virus or Feline Rhinotracheitis virus (FHV/FVR) is a very common viral infection affecting cats. Infection usually occurs in kittens (stressed and/or immunocompromised individuals) that have contact with carrier adults. Once infected, a cat can be a carrier for weeks to years. This is because the FHV, as with all herpes viruses, lies dormant in the body, avoiding the immune system. Infection in kittens most often results in a self-limiting upper respiratory and/or eye infection (conjunctivitis). Usually the virus sets the stage for damage to the mucosa of the upper respiratory tract, conjunctiva and oral cavity, and then bacteria secondarily infect the tissues, causing clinical signs. A carrier animal can experience flare-ups with stress or other illness later in life. Occasionally, adult cats with chronic nasal passage infection or chronic oral cavity ulceration are seen.

The most common clinical signs in kittens and stressed older cats include: ocular and/or nasal discharge, sneezing, ulceration of the oral cavity and associated hypersalivation, lethargy, decreased to complete loss of appetite, fever, red and swollen conjunctiva of the eyes, and/or coughing. The diagnosis is mainly presumptive given the clinical signs, age, history of stress or other illness and how common the infection is in cats. Cats in multi-cat households, breeding facilities, rescues and outdoor cats are more likely to obtain the infection. Most commercial feline distemper vaccines protect against the herpes virus, but often individuals are infected before ever receiving the vaccine. Routine blood work may suggest infection, but is non-specific (i.e. increased white blood cells on a complete blood cell count/CBC).

Underlying disease must be ruled out in affected cats, particularly older individuals. Immunosuppression due to infection with the Feline Leukemia and/or Feline Immunodeficiency virus(es) is perhaps the #1 rule out. Non-infectious, systemic diseases like Diabetes Mellitus and cancers must also be considered. Concurrent infection with Feline Calicivirus and/or a couple unusual bacteria may produce a particularly severe bout, taking longer for the cat’s immune system to overcome.

Because there is no definitive treatment for viral infections, therapy is primarily supportive and symptomatic. Antibiotics are used to treat secondary bacterial infections, but until the body gets the virus under control, the bacteria will just continue to come back. IV fluids and supplements are used to keep the cat well hydrated and keep normal electrolyte balance if the cat is not eating or drinking. The fever is often also responsive to fluid therapy and antibiotics. Appetite stimulants may be necessary if appetite loss is prolonged. The unfortunate cat can develop pneumonia associated with herpes viral infection and treatment in this case is usually much more involved.

In the run-of-the-mill cases, the prognosis is good. The virus is usually gotten under control by the body and future flare-up events are often quite mild. As mentioned above, chronically infected cats are occasionally seen and have a less favorable prognosis, but still not generally poor. Chronic nasal passage changes and oral cavity ulceration can be very uncomfortable for the cats (and for their owners to witness). Long-term palliative treatments can be effective, but some cats require procedures such as full mouth extractions for severe disease.

Herpes viral infection should not be ignored by the owner. Although it is the less common scenario (the self-limiting infection involving only the upper respiratory tract is more common), infection of the lower respiratory tract and pneumonia can occur and may require emergency attention. Again, the pneumonia is caused by secondary bacterial invaders and so antibiotic therapy can usually help the body get control, but intensive therapy (such as oxygen supplementation) may be needed in the interim. Prompt veterinary attention when signs begin to arise can help prevent this situation from occurring.