Feline Herpesvirus and Calicivirus

One of the most common illnesses seen in kittens less than one year of age is upper respiratory tract disease. While there are several agents responsible for upper respiratory disease in cats, the clinical signs of all tend to overlap. General signs include sneezing, discharge from the eyes or nose, fever, lethargy and loss of appetite. The two most common agents of upper respiratory disease in cats are the viruses, feline herpesvirus (FHV) and feline calicivirus (FCV). FHV is also called feline viral rhinotracheitis. FHV and FCV are each found in about 40% of cats with upper respiratory tract disease. Other non-viral agents may also be involved, and it is not uncommon for a cat to be infected by more than one agent at the same time.

Feline herpesvirus was first isolated in 1957. This virus is related to other herpesviruses, such as those that cause cold sores and chicken pox in humans. However, FHV infects only cats and never humans. FHV tends to produce more severe signs of disease than any other cause of upper respiratory tract disease. After incubation from 2 to 6 days, affected cats will become depressed, loss appetite, and suffer from fever and sneezing. Drooling may be seen if ulcers develop on the tongue. Severely affected kittens with inadequate immunity may die. In the acute stages of the disease, the virus may damage the turbinate bones in the nasal cavity, leading to chronic sinusitis later in life. Cats with chronic sinusitis suffer from bouts of sneezing and purulent nasal discharge for months to years.

Feline calicivirus was also first discovered in the 1950s. Along with FHV, it is a leading cause of infectious upper respiratory tract disease in cats. FCV is related to other caliciviruses that cause disease in humans and other animals, such as Norwalk virus. Like FHV, FCV does not infect humans.

FCV is usually associated with milder disease than FHV, although it can be associated with a wide spectrum of clinical signs. These can range from inapparent infections where cats have no signs at all, to fatal pneumonia, especially in kittens. In addition, some strains of FCV found in modified live vaccines seem to cause  ..... [Read complete article]

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