Canine Influenza Can Cause Lung Damage: Vaccination Helps

Reprinted with edits from The Pet Care Services Association newsletter "Boarderline,"  Oct. 2010

A new study in Veterinary Biology is the first to confirm that canine influenza virus (CIV) H3N8 easily spreads from infected dogs to other dogs.   It also showed that CIV can cause more serious forms of respiratory disease in dogs, such as pneumonia, that often go undetected in clinical practice.

Cyndy Crawford, DVM, Ph.D., University of Florida College of Veterinary Medicine, Clinical Assistant Professor of Shelter Medicine, and a leading expert on CIV, said, "This study is important for several reasons.  First, it provides clear evidence that CIV H3N8 is highly transmissible between dogs, confirming field observations recorded during naturally occurring canine influenza outbreaks in confined populations of dogs.  Second, the finding of subclinical pneumonia in nearly all infected dogs in the study underscores the virulence of this virus in both the upper and lower respiratory tract, predisposing many dogs to serious overt pneumonia requiring hospitalization."

In addition, researchers confirmed that the excretion of the virus (shedding) precedes the manifestation of clinical signs.  This is significant, according to the study, because it demonstrates that apparently healthy dogs can infect dogs they encounter at kennels, clinics, shelters, training settings, shows and other locations where they congregate.  Researchers also found evidence of "rolling" infection, which makes if difficult for infected kennels and shelters to eliminate the infection unless they close down, and keep new, uninfected dogs from entering, according to the researchers.  These locations can also become sources of disease with the potential to spread to other facilities.

(...) one of the authors of the study said, "We know that canine influenza, a new disease for many veterinarians, is often under- or misdiagnosed because clinical signs are often similar to other respiratory diseases.  Our research further suggests that infected dogs may have serious lung damage that goes undetected because it does not manifest as pneumonia."   Study authors concluded that many more dogs with CIV are likely to have lung damage not being detected clinically in veterinary practice, particularly compared to canine cough, which rarely leads to serious respiratory disease.
Dr. Crawford also noted, "Since clinical trials have demonstrated that canine flu H3N8 vaccine significantly reduces virus shedding, and the presence of subclinical pneumonia, the findings of this new study suggest that vaccination may greatly reduce the potential for rolling infections and pneumonia, thereby protecting facilities from full-blown outbreaks and individuals from hospitalizion

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