Page 368 - Small Animal Internal Medicine, 6th Edition

340 PART II Respiratory System Disorders

CHAPTER 22
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Disorders of the

Pulmonary Parenchyma

and Vasculature

VIRAL PNEUMONIAS bacterial pneumonia result from entry of bacteria of the
oral cavity and pharynx into the lungs via the airways,
Most respiratory viruses cause self-limiting signs of tracheo- which causes a bronchopneumonia involving primarily the
bronchitis in dogs (see Canine Infectious Respiratory Disease gravity-dependent cranial and ventral lung lobes (see Fig.
Complex, CIRDC, in Chapter 21) or upper respiratory infec- 20.5). Bacteria that enter the lung through the hematogenous
tion in cats (see Feline Upper Respiratory Infection in route usually cause pneumonia that assumes a caudal or
Chapter 15). In dogs, Bordetella bronchiseptica, canine influ- diffuse pattern and marked interstitial involvement. Bacte-
enza viruses, and canine distemper virus can directly result rial pneumonia of hematogenous origin was documented
in pneumonia. B. bronchiseptica and canine influenza are in more than half of cats with bacterial pneumonia on the
discussed primarily with CIRDC in Chapter 21; canine dis- basis of postmortem examination findings (MacDonald
temper is discussed in Chapter 94. Secondary bacterial infec- et al., 2003).
tions can complicate infections with these, or other, CIRDC Bacterial pneumonia is a common lung disease, particu-
organisms. Treatment is supportive for viral infection. The larly in dogs. Community-acquired infectious pneumonia
diagnostic approach and management of bacterial pneumo- has been described in puppies (Radhakrishnan et al., 2007),
nia is discussed in the next section. most often caused by B. bronchiseptica (49% of cases). Co-
In cats, calicivirus can cause pneumonia, but this mani- infection with complicated infectious respiratory disease
festation of infection is rare. The dry form of feline infectious complex (CIRDC) viruses was identified in 8 of 20 house-
peritonitis can affect the lungs, but cats are generally seen hold dogs with bacterial pneumonia (7 with canine parain-
because of signs of involvement of other organs. Feline infec- fluenza virus and 1 with canine respiratory corona virus)
tious peritonitis is discussed in Chapter 94. (Viitanen et al., 2015). However, consideration should also
be given to predisposing abnormalities. A predisposing
BACTERIAL PNEUMONIA abnormality often exists in adult dogs whose bacterial pneu-
monia is not associated with CIRDC. Abnormalities to con-
Etiology sider in all patients include aspiration of ingested material or
A wide variety of bacteria can infect the lungs. Common gastric contents caused by cleft palate, megaesophagus, or
bacterial isolates from dogs and cats with pulmonary infec- other conditions associated with aspiration pneumonia (dis-
tion include B. bronchiseptica, Streptococcus spp., Staphylo- cussed separately in a later section); decreased clearance
coccus spp., Escherichia coli, Pasteurella spp., Klebsiella spp., from the lungs of normally inhaled debris, particularly in
Proteus spp., and Pseudomonas spp. Anaerobic organisms animals with chronic bronchitis, ciliary dyskinesia, or bron-
can be part of mixed infections, particularly in animals with chiectasis; immunosuppression resulting from drugs, mal-
aspiration pneumonia or with lung lobe consolidation. nutrition, stress, or endocrinopathies; inhalation or migration
Mycoplasma spp. has been isolated from dogs and cats with of foreign bodies; and, rarely, neoplasia or fungal or parasitic
pneumonia, but its exact role is not known. Mycoplasma infection. Immunosuppression from infection with feline
cynos, in particular, may be pathogenic in dogs. leukemia virus or immunodeficiency virus is also a consid-
Bacteria can colonize the airways, alveoli, or interstitium. eration for cats.
The term pneumonia means inflammation of the lung, but
the term is not specific for bacterial disease. Infection that Clinical Features
clinically appears to be limited to the airways and peri- Dogs and cats with bacterial pneumonia are evaluated
bronchial tissues is called bacterial bronchitis. If all three because of respiratory signs, systemic signs, or both. Respira-
regions are involved, the disease is called either bacterial tory signs can include cough (which is often, but not always,
bronchopneumonia or bacterial pneumonia. Many cases of productive), bilateral mucopurulent nasal discharge, exercise

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