Infectious respiratory disease in a group of dogs
Narayan Paul, DVM, MS, PhD, Pam Ferro, MS, PhD, and Andres de la Concha, DVM, PhD
Recently, three dogs from the same location were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for necropsy. The three dogs were mixed breed and genetically unrelated. Two of the dogs were 1.5-year-old males and the third was a 3 year-old female. Clinical history was not provided.
Necropsy findings were of the same nature in all three dogs with some variation in severity. Between 35% and 85% of the lung, involving mainly the cranioventral lobes and the cranial aspect of the caudal lobes, were dark red and severely consolidated. On cut section, fluid and foam oozed out of the cut surface. Portions of the affected areas of the lung placed in formalin sunk to the bottom of the container. Variable amounts of foam and fluid were found in the lumen of the trachea and airways. A gross diagnosis of acute, severe pneumonia was established. Portions of unfixed lung of the three dogs were submitted to the bacteriology and molecular sections for culture and identification, and for the canine respiratory disease PCR panel, respectively.
Streptococcus equi subspecies zooepidemicus and Escherichia coli were isolated from the lungs of the three dogs. In addition, canine parainfluenza virus type-2 RNA was detected by rtPCR (Ct values ranged from 24.5 to 29.5) in the lungs of the three dogs. Canine distemper virus, influenza A virus, canine adenovirus type 2, canine coronavirus, canine herpesvirus type 1 and Bordetella bronchiseptica nucleic acid were not detected by PCR in any of the dogs.
Pneumonia in dogs is part of the canine infectious respiratory disease complex (CIRDC) and is a multifactorial disease typically involving predisposing factors such as stress, comingling, poor nutrition, as well as other factors, which compromise the respiratory defense mechanisms. Viral infections further weaken the pulmonary defense mechanisms and facilitate colonization of the lung by bacteria.
Canine parainfluenza virus (CPIV) – synonyms – SV-5-like virus, parainfluenza-2 virus – is an enveloped RNA virus of the paramyxovirus group most frequently recognized as an upper respiratory pathogen and infrequently as a CNS infection of dogs. CPVI is easily transmitted within closely confined groups of dogs. The respiratory form is characterized by pyrexia, nasal discharge and cough. Microscopic lesions consist of rhinitis, interstitial pneumonia and bronchopneumonia.
Generally, CPIV infection of the respiratory tract of dogs has a mild to moderate clinical course, but concurrent infections with other viral and bacterial pathogens including canine distemper virus, canine herpesvirus, canine adenovirus-2, Bordetella bronchiseptica and, as in this case, with Streptococcus equi subspecies zooepidemicus can lead to severe disease and death.
Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) has been associated with severe, rapidly progressing hemorrhagic pneumonia in overcrowded canine environments. S. zooepidemicus is a commensal organism found on the oral cavity, tonsils, upper respiratory tract, skin and urogenital tract of horses and has been associated with respiratory tract infections in foals and young horses, but is not considered part of the normal tonsillar flora in either dogs or man.
S. zooepidemicus has caused several outbreaks of hemorrhagic pneumonia in dogs in recent years. Infection in dogs with S. zooepidemicus is highly contagious and characterized by sudden onset of fever, dyspnea and hemorrhagic nasal discharge. Necropsy lesions consist of pleural effusion and severe pneumonia. Microscopically, the infection is characterized by severe fibrino-hemorrhagic and necrotizing pneumonia. S. zooepidemicus sporadically causes zoonotic infections with potentially serious consequences.
Dogs that have died from acute respiratory disease should be submitted to TVMDL as soon as possible in order to obtain optimal test results. Full necropsy, histopathology, bacterial culture with antibiotic susceptibility testing, and the canine respiratory PCR panel are recommended tests.
Raegan KL, Sykes JE. Canine infectious respiratory disease. Vet Clin Small Anim 50:405-428, 2020.
For questions about this article, please contact Drs. Paul, Ferro or de la Concha at (979) 845-3414.