Respiratory

Diseases affecting the respiratory system can be complex in nature and sometimes frustrating to treat. In addition, diagnois may be difficult because signs of sneezing, coughing, and nasal discharge are characteristic of several respiratory diseases.

Originally, all infectious feline respiratory diseases were thought to be "pneumohnitis" caused by Chlamydia psittace. Extensive research in several countries has shown that Chlamydia psittaci is not the main cause of infectious reapiratory disease of cats, but that in fact there are numerous agents that produce clinical diseases and they may be difficult to distinguish from one another. Feline Viral rhinotrachitis
and feline calicivirus infection are approximately and feline calicivirus
infection are approximately equal in incidence and account for the majority of feline respiratory diseases. It is important to realize that multiple infections can occur in the sam ecat, and an agent that normally does not porduce clinical disease can exacerbate an infection caused by another agent of respiratory disease.

FVR, feline viral rhinotracheitis, is an acute respiratory disease of cats caused by feline herpesirus type 1 (FHV-1), a DNA (deoxyribonucleic acid) virus that is quite labile (unstable or easily deactivated), being sensitive to acid, heat, and most disinfectants. FHV-1 was thought to survive only eighteen to twenty-four hours at room temperature. Recent studies how, however, that it can survive for much longer periods of time, at least five days in some instance. All isolates of FHV-1 that have been studied belong to a single serotype (a taxonomic subdivision).

FCV infection is an acute respiratory infection of cats caused by one of number of strains of calicivirus. This virus is an RNA (ribonucleic acid) virus similar to human cold viruses.. The calicivirus is probably more resistant than the herpesvirus, surviving for one or two weeks at room temperature.

Also called pneumonitis, this acute respiratory disease is caused by
chlamydia psittaci. This is a labile bacterium, being sensitive to heat, most disinfectants, and broad-spectrum antibiotics. Although this agent is capable of causing both upper and lower respiratory tract disease, most commonly it causes conjunctivitis.

The feline reovirus is similar to reoviruses of many oter species. The prefix reo stands for respiratory enteric orphan, indicating that this virus replicates in the respiratory and enteric tracts of various animals, often without producing disease. The virus is a resistant RNA virus, and more than one serotype may exist.

Chronic, mild upper respiratory infection (URI) has become a relatively common problem, especially in catteries. Although some of these infections have been shown to be caused by herpesvirus or calicivirus, the cause of many outbreaks remains unknown. Some of these chronic infections may be part of the feline immunodeficiency syndrome caused by feline immunodeficiency virus (FIV). However, in most instances, secondary bacterial invaders are responsible, having taken advantage of damage to the upper respiratory tract tissues caused by viral agents. Chronic bacterial URIs can be extrememly frustrating to treat, and often cannot be cured.

FIP is a severe, usually fatal, generalized disease of cats caused by a coronavirus. In the initial infection, the virus may enter through and replicate in the respiratory system. Although FIP and feline leukemia are not normally included in the respiratory disease complex, one should be aware that these viruses may affect the respiratory system.

Mycoplasma (a genus of microorganism) can frequently be isolated from cats with respiratory disease, It is uncertain if the organism is capable of causing disease by itself, but it probably plays an important roly as a secondary invader. These are labile orgaism, susceptible to antibiotics.

Numerous bacteria may be involved as secondary invaders in respiratory diseases. The role of bacteria in feline respiratory disease has not been fully determined, but Bordetella bronchiseptica appears to cause severe bronchopneumonia (lung inflammation that begins in bronchioles) as a concurrent infection with some of the viruses mentioned. In some situations, it may be a primary invader, especially in young kittens. Haemophilus felis also appears to cause chronic lover respiratory tract disease. It is not known whether any of the numerous other bacteria that are common secondary invaders can produce respiratory disease without initial infection by a virus.

A severe respiratory disease (pneumonic plague) may occur in cats infected with Yersinia pestis acquired from rodents in endemic areas in the western United States. This is a rapidly fatal disease for the cat, and it is extremely contagious to humans, resulting in sever and often fatal disease. Outdoor cats with severe respiratory disease from
Yersinia endemic areas should be handled with great caution and immediately taken to a veterinarian.

Inflammation of the nasal sinuses usually develops subsequent to direct injury, allergy, cancer, or ascending (moving up into the sinuses) fungal, or, more commonly, viral and/or bacterial infections. Cats with sinusitis usually have a concurrent rhinitis (inflammation of the nasal passages) and experience intermittent bouts of sneezing, with evidence of a mily-white or thick, yellowish nasal discharge. Sometimes, the discharge is streaked with bolld. The cat's appetite remains normal, because its sense of smell is unaffected.

Radiographs (x-rays) are required to confirm a diagnoisis of sinusitis. Treatment is based on identifying the underlying cause. For example, antibiotics are emplyed for a bacterial infection, or antihuitamines for an allergy. However, if medical therapy is unsuccessful, surgery to drain and flush the sinus may be the only alternative.

Cryptococcosis neoformans is the most common cuase of fungal rhinitis (inflamation of the nasal cavity) in the cat. (However,
Blastomyces and Sporothrix have also been reported to cause fungal rhinitis on rare occasions.) Signs include sneezing with a thick nasal discharge. Usually the discharge is from only one nostril, unless the condition is chronic.

The route of viral infection is either oral or intranasal. The acute disease develops after an incubation period of from one to several days after infection, depending upon the severity of exposure and the virus involved. The clinical diseae lasts from one to several days or may linger for weeks in some cases, again depending upon the severity of the infection and the virus involved.

Infected cats excrete viruses or other agents in the saliva, the nasal and ocular (eye) discharges, the feces (of cats with calicivirus and reovirus infections), and the urine (of cats with calicivirus infections). Infection of susceptible cats occurs by direct contact with cages food and water dishes, or litter pans that have been contaminated with viral or other agents, and by aerosol exposure (moisture droplets drifting in the air) from infected cats. These viruses may be transmitted several feet by aerosol droplets. Hands, clothing, or shoes of persons handling and caring for infected cats frequently become contaminated and can serve as a vehicle for transmitting this respiratory-disease-producing agents to susceptible cats.

An important aspect of the spread of the respiratory diseases of cats is the presence of a carrier state. After recovery from FVR, cats continue to shed herpesvirus intermittently from the oroparynx (back of the mouth) for many months. Cats infected with calicivirus have been shown to shed virus continuously from the throat, and occasionally in the feces, for long periods of time Mother cats that had FVR or FCV infection as kittens may pass the virus to their young. Severe stress or another viral or bacterial infection may cause those animals carrying the virus to become infectious to other cats.

Oral, ocular, or intranasal (within the nose) infection results in a local infection of the epithelium (lining) of these regions, which then spreads to involve the remainder of upper respiratory epithelial cells; The infection may even spread to the lungs. The infection generally remains superficial but may spread through the boood (viremia) to produce a generalized infection. Feline viral rhinotracheitis generally does not produce a viremia (the presence of a virus in the bloodstream), but in certain instances, viremia may occur, and infection of the osteoblasts (bone-forming cells) may result. Viremia in pregnant cats may result in infection of the fetuses and abortion.

Although the clinical disease in feline calicivirus (FCV) infections is often milder than in FVR, the spread of virus is generally greater. Infection occurs not only in the respiratory mucosa (mucous membrane) but may also occur in the intestine. Severe pneumonia may occur in FCV infection, and ulcerations of the tongue and/or the hard palate are common.