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Feline Respiratory Disease Complex (Feline Herpesviral Rhinotracheitis, Feline Calicivirus)

By Ned F. Kuehn, DVM, MS, DACVIM, Section Chief, Internal Medicine, Michigan Veterinary Specialists
Neil W. Dyer, DVM, MS, DACVP, Director and Pathologist, Veterinary Diagnostic Laboratory, North Dakota State University
Joe Hauptman, DVM, MS, DACVS, Professor of Surgery, Veterinary Teaching Hospital, Michigan State University
Stuart M. Taylor, PhD, BVMS, MRCVS, DECVP,

Also see professional content regarding feline respiratory disease complex.

Feline respiratory disease complex is a set of respiratory illnesses caused by a group of organisms that can cause infection alone or together. It includes those illnesses with signs including inflammation of the nasal and sinus linings, inflammation of the eye lining (conjunctivitis), tears, salivation, and mouth sores. The principal diseases are feline herpesviral rhinotracheitis and feline calicivirus, although other diseases may also be involved (see Table: Organisms Found as Part of Feline Respiratory Disease Complex).

The majority of feline upper respiratory infections are caused by feline herpesviral rhinotracheitis, although the incidence of feline calicivirus may be higher in some populations of cats. Infection with both these viruses at once may occur. Natural transmission of these agents occurs through small droplets in the air (such as from a sneeze) and contaminated objects, which can be carried to a susceptible cat by a handler. Recovering cats may harbor the virus for many months. Stress may trigger a relapse.

Organisms Found as Part of Feline Respiratory Disease Complex

Disease Organism


Feline herpesviral rhinotracheitis (FHV-1)

Accounts for the majority of acute upper respiratory infections in cats; see text for signs

Feline calicivirus (FCV)

Often hard to distinguish from feline herpesviral rhinotra-cheitis; see text for signs

Feline pneumonitis (Chlamydophila psittaci)

Conjunctivitis, sneezing, eye discharge, fever may develop; of lesser importance than FHV-1 and FCV

Mycoplasma infections

Conjunctivitis and inflammation of the nasal lining (rhinitis); of lesser importance than FHV-1 and FCV

Feline infectious peritonitis virus

May cause signs of mild upper respiratory tract infection


Virus replicates in respiratory tract; may not always cause respiratory signs

The onset of feline herpesviral rhinotracheitis is marked by fever, frequent sneezing, inflamed eyes (conjunctivitis), rhinitis, and often salivation. Excitement or movement may cause sneezing. The fever may reach 105°F (40.5°C) but subsides and then may come and go. Initially, the disease causes a clear discharge from the nose and eyes; it soon increases in amount and contains mucus and pus. At this point, depression and loss of appetite become evident. Severely affected cats may develop mouth inflammation with sores, and inflammation of the cornea occurs in some cats.

Signs may persist for 5 to 10 days in milder cases and up to 6 weeks in severe cases. The outlook is generally good except for young kittens and older cats. When the illness is prolonged, weight loss may be marked. Bacteria often infect cats that are already ill with feline herpesviral rhinotracheitis.

There are many related strains of feline caliciviruses. Some caliciviruses cause few or no signs, while others produce fluid buildup in the lungs (pulmonary edema) and pneumonia. It is often impossible to distinguish feline herpesviral rhinotracheitis from feline calicivirus infection. Two feline calicivirus strains may produce a transient “limping syndrome” without mouth sores or pneumonia. These strains produce a short fever, leg lameness, and pain on handling of affected joints. Signs occur most often in 8- to 12-week-old kittens and usually improve without treatment. The syndrome may occur even in kittens that have been vaccinated against feline calicivirus, because no vaccine protects against both of the particular strains that produce the “limping syndrome.”

Calicivirus has also been found in cats with inflammation of the gums and mouth. The lesions heal rapidly, and the infected cat regains appetite 2 to 3 days after onset, although the course of disease may last 7 to 10 days. Fever, poor appetite, and depression are common signs. Nasal inflammation (rhinitis) and conjunctivitis also can occur.

The veterinarian’s initial diagnosis is based on the typical signs as described above. These characteristics may be difficult to sort out when more than one infection is present. A definite diagnosis is based on isolation and identification of the organism through appropriate tests and microscopic examination of samples from the oral and nasal mucous membranes, nostrils, or conjunctival sacs. However, diagnosis of feline herpesviral rhinotracheitis may be difficult because the virus is shed only periodically, and because even cats without symptoms can show presence of the virus.

Treatment and Prevention

Treatment is largely directed toward the signs of illness, but broad-spectrum antibiotics are useful if secondary bacterial infections are involved. Antihistamines may be prescribed early in the course of the disease. Nose and eye discharges should be removed frequently for the comfort of the cat. Treatment with a mist (nebulization) or saline nose drops may be recommended to help remove hard secretions. Nose drops containing a blood vessel constrictor and antibiotics are sometimes prescribed to reduce the amount of nasal secretion. Eye ointment containing antibiotics may also be prescribed to prevent corneal irritation produced by dried secretions from the eye. If corneal ulcers occur in feline herpesviral rhinotracheitis infections, eye preparations containing antiviral medication may be prescribed, in addition to other antibiotic eye preparations. If the cat has great difficulty breathing, it may be placed in an oxygen tent.

Vaccines that protect against feline her-pesviral rhinotracheitis and feline calicivirus are available. One type is injected; the other is given as drops in the eyes and nose. Cats that have received the eye/nose vaccine may sneeze frequently for a few days after vaccination; ask your veterinarian if you should expect this or any other side effect from the vaccines. Vaccines against Chlamydia are also available; these vaccines are generally used in catteries or on premises where infection has been confirmed. A combination of recommended vaccinations and control of environmental factors (such as exposure to sick cats, overcrowding, and stress) provide good protection against upper respiratory disease.

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